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Adsorption-based atmospheric water harvesting powered by solar energy: Comprehensive review on desiccant materials and systems
Abstract
Atmospheric water harvesting has been inexorably proliferated as a potential source of freshwater, notably for remote areas that lack access to water and electricity. This technology could be significantly operated with renewable energy sources. The current study comprehensively reviews the state-of-the-art atmospheric water harvesters and their desiccant materials. Firstly, a detailed survey on desiccant materials, silica gel, metal-organic frameworks (MOFs), hydrogels, zeolite, hygroscopic salts and composite desiccant materials is illustrated. The review particularly focuses on the materials adsorption capability, kinetics, proper matching with climate conditions. Moreover, the most suitable adsorbents are thoroughly surveyed for a wide range of climate conditions, especially for water scarcity regions (i.e., arid zones) that are characterized by low relative pressures. Moreover, various designs of solar-powered atmospheric water harvesters are comparatively summarized, including fixed and portable installations. It can be concluded that MOF-801, MOF-808, MOF-841, HKUST-1, and CPO-27(Ni) have a superior potential for water harvesting in arid areas. Additionally, MIL-101(Cr) has superior water uptake and kinetic at high relative pressure (i.e., humid areas), and it is irrelevant for water harvesting at dry zones. It is found that the cost of the collected water from atmospheric water harvesting technology is about 0.062-0.86 $/kg of adsorbent. This work provides beneficial perspectives for selecting the most relevant desiccant materials beside the appropriate solar system for water harvesting applications.
... Still, they are very energyintensive and expensive technologies. Moreover, most locations without fresh water are in underdeveloped countries with limited access to intense energy, which can power the systems [6,7]. In addition, it is well recognized that potable water processes such as multi-stage flashing, multi-effect distillation, and reverse osmosis generate considerable concentrated effluent that has a negative impact on the ecosystem and marine life [8]. ...
... The simplicity of fog technology makes it a promising candidate for long-term sustainability. Nevertheless, the efficiency of the fog collecting technique is limited, making it only suitable for specialized applications [7]. ...
... Four crucial criteria of ideal desiccant material (moisture harvester) for atmospheric water harvesting applications[7]. ...
Water scarcity is one of the most challenging problems that the world has ever faced. There are numerous methods to remedy the water crises. One is using atmospheric water harvesting (AWH) to provide water. So far, there is much research on the subject of AWH. However, there is still a lack of establishing an extensive comparison between different technologies and methods used to harvest atmospheric water. In this review, we provide details on the thermodynamic performance of the AWH system. The systems are categorized into both active and passive systems. Heat pumps, membranes, thermoelectric solar systems, and adsorption systems are some atmospheric harvesting technologies that will be thoroughly discussed. Based on the comparison that had been made, it was found that TEC systems are the best for small applications. In contrast, systems such as vapour recompression can meet great demands as they can be integrated with different types of energy, such as natural gas and biogas. Solar systems as passive systems can also be coupled with active systems to boost the efficiency of vapour recompres-sion systems and reduce energy consumption. Furthermore, this review will focus on recent development for each category, the utilization of different advanced materials, and the prospect and challenges associated with AWH.
... Adsorption-based system is promising as it can be operated by renewable sources or waste heat and is not limited by relative humidity of the ambient air. Consequently, adsorption-based AWH systems have become the subject of research by reputable scientific organizations in the past few decades (Gado et al. 2022;Ejeian and Wang 2021). In this chapter, the working principles and the state of the art of each AWH technology are presented. ...
... The vapor concentration water harvesting method by adsorbent materials has attracted numerous researchers' attention in the last few decades due to its many advantages (Gado et al. 2022;Ejeian and Wang 2021). These sorption-based systems can also be used for other applications such as desalination, cooling, and heat pump (Summa et al. 2021;Alsaman et al. 2022;Moossa et al. 2022;Hassan et al. 2020aHassan et al. , b, 2021Hassan et al. , 2022b. ...
... However, some disadvantageous features hinder its use in AWH such as low adsorption capacity, mainly when used in low humidity climate conditions and unfavorable thermal properties. Recent progress in research on silica gel can be found in Gado et al. (2022), Rocky et al. (2021), Askalany et al. (2013), Wang et al. (2009). ...
Many countries worldwide, particularly those with arid climates, face a serious problem regarding freshwater scarcity. Climate change, accompanied by economic and population growth, are worsening the problem. Remote communities with no access to freshwater are suffering the most from this problem. Clouds, fog near land, and water vapor (humidity) in the surrounding air are the three most common kinds of atmospheric water found in the atmosphere. Humidity in the surrounding air represents a great and reliable source for providing fresh water, especially if it can be extracted in an affordable and efficient manner. Water extraction from the atmosphere, unlike desalination, does not have a significant impact on the hydrological cycle or on vital water sources in the vicinity. The water quality is also adequate for drinking and other residential and agricultural uses because the source of the atmospheric water is usually clean. Depending on the atmospheric water source, the AWH technologies can be categorized into artificial rain, fog water and dew water collection technologies. In arid coastal areas, fog water collection technologies can be feasible and accessible technologies to alleviate the scarcity of freshwater. Moreover, fog water is often collected in a rectangular mesh perpendicular to the wind, which traps fog droplets. In comparison, dew water collection technologies are minimally susceptible to meteorological and geographical limitations compared with fog collection methods. Dew collection technologies are considered condensation-based technologies, which fall into three primary categories: direct condensation harvesting, vapor concentration by adsorbent material, and by-product collection from an integrated system. Furthermore, the vapor concentration and water vapor condensation processes can be classified as passive or active, depending on the energy input to the system. In this chapter, the state-of-the-art of various AWH technologies will be introduced, in addition to techno-economic comparative assessment of these technologies.
... Conversely, decreasing the temperature sources would inevitably lead to maloperation of the adsorption system since a minimum regeneration temperature constrains its operation. Also, the increment in the intermediate temperature ruins the compression system's performance (Gado et al., 2022). ...
... The linear driving force (LDF) model is used to describe the adsorption/desorption rate of regular density (RD) silica gel/water as follows (Gado et al., 2022): ...
... The energy balance of the desorber bed is presented as (Gado et al., 2022): ...
In the current study, intermittent characteristics of hybrid adsorption-compression refrigeration systems are evaluated, notably for cold storerooms. This hybrid system utilizes ultra low-grade heat (65(C) and works with natural refrigerants. Herein, the dual-bed adsorption system operates with a working pair of silica gel/water (R718), while isobutane (R600a) is adopted for the compression system. Phase change material (PCM) is additionally incorporated to prolong the compressor off durations and improve the stabilization of the air temperature inside the cold storeroom. Mathematical modeling of the proposed systems is established using MATLAB/SIMULINK framework and validated with relevant literature. An examination of the temporal behavior of the hybrid system's leading indicators such as temperature profiles, cooling capacity, COP, electric power, and electricity demand based on the intermittent characteristics has been conducted and compared against the baseline system. The results demonstrate that the energy saving of the hybrid system during the intermittent operation mode (37%) outperforms the continuous operation mode (31.63%). Also, the hybrid system at the steady-state stage attains COP of ∼4 compared to ∼2.3 for the baseline system. However, incorporating PCM into the hybrid system abates the air temperature fluctuation inside the cold storeroom, diminishes the cyclic operations, and reduces the on-time ratio by 24.1% compared to the baseline system (34.8%) while slightly reducing the system COP. The utilization of hybrid refrigeration systems accompanied by PCM has significant profit over conventional compression systems in the market.
... The linear driving force model and the modified Freundlich equation for the silica gel/water pair sorption rate are defined as [34]: ...
... For validation of the adsorption model and solution, the outlet temperatures of the key elements, namely, desorber, adsorber, condenser, and evaporator, are considered. With a maximum relative error of 2.5%, the outlet temperatures of the adsorption system's components match well with the reported data in Ref. [34], as demonstrated in Fig. 5. Regarding the compression subsystem's verification, an average relative error of 4.2% in the system COP indicated has an average relative error of about 4.2% for the current reported results against the experimental data of different cooling water inlet temperatures in Ref. [36] according to Fig. 6, which shows a satisfactory consistency between the experimental and simulation results. Moreover, the validity of the compression system is examined at different evaporation temperatures as listed in Table 4. ...
... It can be seen that fall within 9%. It should be highlighted that the adapted experimental data for the adsorption cooling systems are invoked from the reported experimental work of Saha et al. [34], as listed in Table 5. Also, the types, heat conductance (UA) and heat capacitance (MC p ) of the utilized heat exchanger for the adsorption system are identical to the present system. ...
An assessment of the cascade adsorption-compression refrigeration system by adopting renewable energy for cold storage applications based on energy, exergy, exergoeconomic, and enviroeconomic perspectives is presented. The cascade cycle aims to dwindle the electric power of the compression subcycle with reduced condensation pressure. The thermodynamic modeling of the proposed system is developed at climatic conditions of Alexandria/Egypt for two scenarios of renewable systems, including (i) biomass-solar (Scenario-I) and (ii) biomass-solar-wind (Scenario-II). The results demonstrate that the COP of the cascade system is ameliorated by 41.6% compared to the conventional compression system; highlighting an energy saving of 42%. The proposed system has an annual average COP and exergetic efficiency of 0.122 and 1.78%, respectively for Scenario-I and 0.124 and 1.8%, respectively for Scenario-II. Scenario-I and Scenario-II deliver refrigeration at 0.235 $/kWh, and 0.237 $/kWh, respectively. Herein, the exergoeconomic parameter for Scenario-I and Scenario-II is 0.70 kWh/$ and 0.69 kWh/$, respectively. It is found that both scenarios alleviate about 32.75 and 5.35 tons of CO2 per annum based on environmental and exergoenvironmental standpoints, respectively. Besides, the enviroeconomic and exergoenvironmental parameters are about 474.90 $/kW and 77.60 $/kW respectively, over the project lifespan of 20 years for both scenarios.
... Then, the vapor condenses on the enclosure walls and can be collected, meanwhile, the reactivated and unsaturated desiccant will be cooled down for the next water-capture cycle [74]. One of the key units is the desiccant, which performs the cycle of water vapor adsorption and water desorption [91,92]. The desiccant not only determines the water collection rate but also is associated with energy consumption. ...
... For example, a kind of salt gel beads made of an alginate-derived matrix with calcium chloride owns a water holding capacity of 660 kg water/m 3 and can release water at a temperature of 100 • C [95]. In addition, some MOF-based desiccants were also explored and presented promising water adsorption ability [91,96]. ...
The unequivocal global warming has an explicit impact on the natural water cycle and resultantly leads to an increasing occurrence of extreme weather events which in turn bring challenges and unavoidable destruction to the urban water supply system. As such, diversifying water sources is a key solution to building the resilience of the water supply system. An atmospheric water harvesting can capture water out of the air and provide a point-of-use water source directly. Currently, a series of atmospheric water harvesting have been proposed and developed to provide water sources under various moisture content ranging from 30–80% with a maximum water collection rate of 200,000 L/day. In comparison to conventional water source alternatives, atmospheric water harvesting avoids the construction of storage and distribution grey infrastructure. However, the high price and low water generation rate make this technology unfavorable as a viable alternative to general potable water sources whereas it has advantages compared with bottled water in both cost and environmental impacts. Moreover, atmospheric water harvesting can also provide a particular solution in the agricultural sector in countries with poor irrigation infrastructure but moderate humidity. Overall, atmospheric water harvesting could provide communities and/or cities with an indiscriminate solution to enhance water supply resilience. Further research and efforts are needed to increase the water generation rate and reduce the cost, particularly via leveraging solar energy.
... Given that one of the main shortcomings of AWH systems is scalability, most of the studies mainly focused on examining water production using extremely thin layers of sorbent materials [18,34]. So far, scaling up AWH systems by using several kilograms or tons of sorbent materials is still struggling due to the vast required installation areas and synthesis of sorbent materials [37]. As an example, LaPotin et al. [24] utilized two air-gapped layers of AQSOA Z01 zeolite to develop a proper temperature gradient between the layers, in which the layer thickness is 6.4 mm. ...
This study proposed a scalable prototype of atmospheric water harvesting (AWH), which encompasses a triply periodic minimal surface (TPMS) structure and sorbent material. This is mainly targeted for boosting water productivity via ameliorating the heat transfer and intra/intercrystalline diffusivity inside the sorbent material (i. e., silica gel). In this respect, Gyroid as a TPMS structure was 3D-printed using AlSi10Mg powder, which has a superior surface area-to-volume ratio and elevated thermal conductivity. Additionally, the thermoelectric module was employed for dual periodic cooling and heating of the sorbent material, ensuring multi-cycling and continual water productivity. Three relative humidity levels (i.e., low, moderate, and high) were used to examine the daily water productivity and system efficiency for the AWH system with TPMS in comparison to pure sorbent. It was found that, under humid conditions (70 %RH), the utilization of TPMS indicated a daily water productivity and system efficiency of 136 L/kg m2 and 6.8%, respectively. By contrast, the AWH system without TPMS exhibited a daily water productivity and system efficiency of 74 L/kg m2 and 3.7%, respectively. Moreover, investigating the influence of the sorbent layer thickness indicated that decreasing the sorbent layer from 40 mm to 10 mm upgraded the water harvesting 1.9 times, achieving 391 L/kg m2. This is because of the lower vapor transport resistance of thinner sorbent layers. This research underscores the importance and proof-of-concept of incorporating TPMS-derived structures in sorbents to enhance the water productivity of AWH systems, thereby facilitating their transition to practical large-scale systems and increasing their feasibility for commercialization and real-world applications.
... Pharmaceutical, electrical, shoe, and textile manufacturers all rely on solid desiccant materials to keep their goods safe from damage caused by humid air. Molecular sieves, clays, and silica gel are the most widely used solid desiccant materials in the packaging industry; however, they have low dehumidification efficiencies at a given humidity level and a high desorption temperature, both of which necessitate a great deal of energy to regenerate the desiccants [5]. Polymeric materials were studied as a potential replacement for traditional solid desiccants. ...
The production of innovative materials with improved features applicable in many domains is a key application of nanotechnology with far-reaching implications for modern society. Nanoparticle-based polymer composites are quickly becoming one of the most promising new materials, with potential uses spanning the chemical, physical, and biological sciences as well as engineering. Application of nanoparticle-based polymer composites for indoor air quality maintenance was discussed, as were their production, hybrid functionalization, and feasible synthesis procedures (filter membrane). The batch foaming procedure has been used to create foam from the thermoplastic polymer polypropylene (PP). Foaming is a blown process, where carbon dioxide is utilised as the blowing agent. Nanoparticles of titanium oxide (nano TiO2) are also used for reinforcement. Scanning electron microscopy (SEM) was utilised to investigate the NTPMs' surface morphology, while other physio-chemical characteristics were investigated by means of various analytical methods, including Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermo-gravimetric analysis (TGA). The adsorption isotherm and kinetics of water vapours were analysed to get insight into the water vapour adsorption characteristics of the NTPMs. The kinetics of adsorption pointed to a combination of intraparticle diffusion and liquid field driving processes for the transport of water vapours. Because of their high dehumidification effectiveness, synthetic NTPMs have the potential to replace many of the currently used traditional solid desiccant materials
... The rotor structure is constructed in the shape of a beehive in order to have the largest possible area of hygroscopic material in contact with the air [69]. The hygroscopic material may be silica gel or a mixture of silica gel and zeolites [70]. ...
A review of desiccant dehumidification technologies for improving air quality is presented, mainly focusing on alternatives for air conditioning systems for minimizing Sick Building Syndrome. The principles and types of desiccant wheels, as well as the existing selection software for these types of equipment, were reviewed and comparatively evaluated. The study focused on the Brazilian context; thus, information about this country’s air conditioning systems and laws were evaluated. Possible applications of desiccant wheels, such as their integration into cooling cycles and the sensible heat wheel, were also analyzed. Finally, several examples of commercial desiccant wheel selection software that are useful in many situations were evaluated. Nevertheless, it was evidenced that the available software could not perform an operation analysis for only a specific period. Therefore, creating computational tools to select desiccant wheels is essential when considering the data from the different Brazilian regions for a year.
... The adsorbent is the core of the entire SSAWH technology, and the hygroscopic performance of the hygroscopic material itself can directly affect the final water production efficiency of SSAWH [72]. Up to now, quite a few adsorbent materials with high water sorption, low desorption energy consumption, and stable cycling performance have been explored and developed [73], and have been applied in various indoor and outdoor scenarios. ...
... The rotor structure is made in the shape of a beehive to have the largest possible area of hygroscopic material in contact with the air [69]. The hygroscopic material may be silica gel or a mixture of silica gel and zeolites [70]. ...
A review of desiccant dehumidification technologies for improving air-quality has been presented, especially focusing on alternatives for air conditioning systems for minimizing the Sick Building Syndrome. The principles and types of desiccant wheels, as well as the existing selection software for these types of equipment, were reviewed and comparatively evaluated. The study focuses on the Brazilian context, therefore, information about air condition systems and laws of this country were evaluated. Possible applications of desiccant wheels are also analyzed, such as their integration into cooling cycles and the sensible heat wheel. Finally, several commercial desiccant wheel selection software were evaluated, which are useful in many situations. Nevertheless, it was evidenced that the available softwares are not capable of performing an operation analysis for only a specific period. Therefore, it is essential to create computational tools to select desiccant wheels, considering the data from the different Brazilian regions for a year.
... Also, LiCl salt has been introduced into a HKUST-1 to create composite desiccant material that possesses the water uptake of 1.09 g/g and 0.5 g/g at 50% and 30% RH, respectively, and temperature of 25 °C Gado et al. 2022). The utilization of these sorbents can be limited by the low hydrothermal stability of HKUST-1. ...
Due to the rapidly growing population, industry, and agriculture, the potable water shortage is becoming one of the global challenges of our time. Simultaneously, the atmosphere contains 12,900 km3 of moisture available everywhere, regardless of geographical location and climatic conditions. In this context, the technology of Adsorptive Water Harvesting from the atmosphere (AWHA) is considered a promising method for decentralized water supply for domestic and sanitarian purposes in arid regions. The AWHA is based on the reversible sorption of water vapor on a desiccant and heat-powered desorption of the stored water with its subsequent condensation. The sorbent is a key element of AWHA, and its properties strongly affect the system’s performance. New opportunities for AWHA might open up with the development of novel adsorbents with advanced properties. In this chapter, first, the principle and basic technical solutions of AWHA are described and the properties of the sorbent required are outlined. Then the new classes of advanced sorbents suggested for AWHA are reviewed with a special focus on Metal–Organic Frameworks and the composite sorbents based on a hygroscopic salt embedded inside a matrix, the properties of which can be tuned according to the climatic conditions of a specific region, where the process is realized. Finally, the advantages and challenges of these adsorbents are discussed and some prospects on the adsorbents promising for continuously operating and scalable AWHA systems are provided.
... The global demand for freshwater is increasing over time. However, freshwater resources are limited, and only 3% of the water on earth is suitable for human consumption [1,2]. Meeting the growing human demand for freshwater while protecting ecosystems is one of the most difficult and important challenges of this century [3]. ...
... Moreover, the cost and maintenance of such local solutions are usually lower than long-distance transportation (Mohamed et al., 2017). These expenses can be reduced even more if the water harvesting technologies are integrated with renewable energy resources, such as solar and wind, and many researchers are currently working in that direction (Gado et al., 2022;Mohamed et al., 2017;Tu et al., 2018). The water harvesting methods are usually categorized into fog/dew collection and moisture extraction, which can be done by condensate and desiccant dehumidification techniques . ...
Drinking water scarcity is becoming an urgent problem worldwide, and it affects developing and developed countries alike. Kazakhstan is not an exception and has its primary sources of drinking water (groundwater, rivers, and lakes) continuously depleted and polluted; moreover, the country will be close to its exploitation limits within the following decades. However, modern technologies allow us to harvest drinking water from unintegrated sources, like the atmosphere. Therefore, it is crucial to research which non-conventional technologies can be used to obtain drinking water from unintegrated sources for the country, considering the cost, viability of use through the year, and local climate conditions. Thus, the present assessment was performed for the 14 demographic regions in Kazakhstan and two city-states, and a map depicting the most feasible technology for each region is presented, including their levelized cost per liter. Seven mature technologies were found to be feasible in Kazakhstani year-round climates. However, Air AW 3 technology and Artificial Glaciers (AG) were the most cost-effective for family-size and village-size solutions, respectively. The water provided via utility pipelines proved to be the most cost-effective manner , when available, to supply drinking water at a family-size scale, but found a less expensive competitor in the AG technology for village-size solutions. Moreover, the lack of utility water pipelines in some Kazakhstani regions, principally countryside rural areas, makes it vital to deploy and implement these alternative water-harvesting technologies to guarantee the future water security of these regions.
KEYWORDS
atmospheric water harvesting, drinking water, economic
performance, Kazakhstan, unintegrated sources
... Adsorption-based HAW differs from standard HAW systems in that it uses desiccant materials to absorb water vapors from the air and achieves better thermal efficiency [17]. ...
Nowadays, harvesting water from the atmosphere is becoming a new alternative for generating fresh water. To the author’s best knowledge, no mathematical model has been established to describe the process of harvesting water from the atmosphere using porous materials. This research seeks to develop a new mathematical model for water moisture absorption in porous materials to simulate and assess harvesting atmospheric water. The mathematical model consists of a set of governing partial differential equations, including mass conservation equation, momentum equation, associated parameterizations, and initial/boundary conditions. Moreover, the model represents a two-phase fluid flow that contains phase-change gas–liquid physics. A dataset has been collected from the literature containing five porous materials that have been experimentally used in water generation from the air. The five porous materials include copper chloride, copper sulfate, magnesium sulfate, manganese oxides, and crystallites of lithium bromide. A group of empirical models to relate the relative humidity and water content have been suggested and combined with the governing to close the mathematical system. The mathematical model has been solved numerically for different times, thicknesses, and other critical parameters. A comparison with experimental findings was made to demonstrate the validity of the simulation model. The results show that the proposed mathematical model precisely predicts the water content during the absorption process. In addition, the simulation results show that; during the absorption process, when the depth is smaller, the water content reaches a higher saturation point quickly and at a lower time, i.e., quick process. Finally, the highest average error of the harvesting atmospheric water model is around 1.9% compared to experimental data observed in manganese oxides.
... That is why sustainable access to freshwater has been recognized as one of the great engineering challenges of the 21st Century. Consequently, numerous research efforts and different commercial technologies have been developed over the years to obtain freshwater from unconventional sources, such as seawater desalination and atmospheric water harvesting (AWH) [7][8][9][10]. Unfortunately, most commercial desalination plants operating worldwide currently are powered by fossil fuels, and it is estimated that energy-intensive desalination technologies are consuming about 75.2 TWh annually. ...
Global warming and climate change, accompanied and assisted by rapid economic and population growth, are causing a sharp rise in cooling demands and stressing the already-limited supply of freshwater for many countries worldwide, especially those developing under hot-climate conditions. Thus, it is imperative to find solutions to meet cooling and freshwater needs without negatively affecting the environment and exacerbating the global warming problem. Solar-driven hybrid desalination/cooling technologies are a promising solution that can help in reducing greenhouse gas emissions and increasing overall efficiency and energy savings. The present study summarizes research efforts in meeting cooling and freshwater demands using the available solar resources. Various solar desalination technologies, such as multi-effect distillation (MED), single and multi-stage flash (MSF), reverse osmosis (RO), adsorption, absorption desalination, and membrane distillation (MD), and their integration with different cooling technologies, are reported. The study reported system performance indicators, such as water production rate, cooling capacity, Coefficient of Performance, and freshwater cost.
... Researchers extensively studied adsorption chillers both experimentally and theoretically to enhance their performance in terms of cooling capacity and COP, thereby reducing their size. [14][15][16] Furthermore, researchers investigated extensively different adsorbent materials and pairs to boost the adsorption chillers cooling performance and thus reduce their size. 17 Common adsorbent materials used in cooling application include metal-organic frameworks, activated carbon, silica gel, and zeolite. ...
In this study, theoretical performance investigation and economic analysis of hybrid solar system‐driven integrated reverse osmosis (RO)/adsorption multigeneration system have been performed. The system delivers the required cooling during summer operation via adsorption chiller freshwater and electricity via RO unit and photovoltaic/thermal (PVT) collectors, respectively, throughout the year for building in Alexandria, Egypt during the typical daily working hours. A hybrid solar system comprising evacuated tube collectors (ET) and PVT collectors is proposed to supply the required heat and electricity. Four configurations: Case 1 has only PVT, Case 2 has 75% PVT and 25% ET, Case 3 has 50% PVT and 50% ET, and Case 4 has 25% PVT and 75% ET. A dynamic model for the performance of the proposed multigeneration system is constructed and analyzed using MATLAB software. The results show that increasing PVT area share improves system energy and exergy efficiencies and economic performance but at the expense of produced cooling capacity. The average cooling of the adsorption chiller is 5.8, 7.6, 9.5, and 11.5 kW for Cases 1 to 4, respectively, and RO specific energy consumption is about 2.467 kWh/m3 of freshwater. Energy savings of approximately 32.95 MWh/year are achieved for Case 1, while its CO2 emissions cut is about 18.06 of equivalent tonCO2 per year. The Payback periods of the proposed system are about 10.3, 11.68, 15.85, and 24.3 years for Case 1 to Case 4, respectively, demonstrating the system economic viability.
... We have seen a preference for using low-cost chemicals and a desire to find a balance between cost and water-harvesting efficiency. 79,129 However, to date, there has been little available literature on the detailed cost analysis of water harvesting using passive AWH technologies. We call for an adequate assessment of the costs of materials, catchment devices, and support/ maintenance to fill this research gap. ...
The lack of freshwater has been threatening many people who are living in Africa, the Middle East, and Oceania, while the discovery of freshwater harvesting technology is considered a promising solution. Recent advances in structured surface materials, metal−organic frameworks, hygroscopic inorganic compounds (and derivative materials), and functional hydrogels have demonstrated their potential as platform technologies for atmospheric water (i.e., supersaturated fog and unsaturated water) harvesting due to their cheap price, zero second energy requirement, high water capture capacity, and easy installation and operation compared with traditional water harvesting methods, such as long-distance water transportation, seawater desalination, and electrical dew collection devices in rural areas or individual-scale emergent usage. In this contribution, we highlight recent developments in functional materials for “passive” atmospheric water harvesting application, focusing on the structure−property relationship (SPR) to illustrate the transport mechanism of water capture and release. We also discuss technical challenges in the practical applications of the water harvesting materials, including low adaptability in a harsh environment, low capacity under low humidity, self-desorption, and insufficient solar-thermal conversion. Finally, we provide insightful perspectives on the design and fabrication of atmospheric water harvesting materials.
... The adsorption/desorption rate of silica gel/water pair is governed by the linear driving force (LDF) model as follows [20]: ...
Hybrid vapor compression systems based on adsorption are recognized as a viable alternative to traditional energy-intensive compression systems. Solar-powered hybrid adsorption-compression refrigeration systems feature a solar-powered silica gel/water-based adsorption cooling system paired with a traditional compression system that utilizes R134a as a refrigerant. Herein, the system feasibility of a solar-operated hybrid adsorption-compression refrigeration system has been evaluated theoretically using typical climatic data of Alexandria, Egypt. Mathematical modeling is generated and compared to the most relevant experimental data. PVT collectors are exploited to drive both the adsorption and the compression units. Simulation results suggest that using a three-to-one system size ratio between the adsorption and compression subsystems might considerably raise the COP from 2.9 to 5 for the compression system. It is observed that at an ideal size ratio of 7, the proposed system can considerably deliver an energy saving of 30.8 percent, compared to the hybrid system of the size ratio of 3, which attains only energy savings of 22.1 percent. Furthermore, the utilization of PVT collectors might feed the hybrid system by 3.474 kWh and augment the electric grid by 100 kWh, at an ideal size ratio of 7. Overall, investigating hybrid adsorption-compression systems might offer unique insight on optimizing the performance of conventional counterparts.
... To estimate the adsorption kinetics of the silica gel/water pair, the Linear Driving Force model (LDF) is used as given by Eqs. (12) and (13) ( Gado et al., 2022;Zhai and Wang, 2009). ...
Energy, exergy, economic and environmental assessment is performed for an integrated hybrid solar system powering a multigeneration system. The proposed multigeneration system is integrated parallel/series configurations of organic Rankine cycle (ORC) unit and adsorption chiller under weather conditions of Alexandria-Egypt. The solar subsystem comprises photovoltaic/thermal collectors (PVT) connected in parallel arrangement with evacuated tube solar collectors (ET). The system output aims to provide annual electricity requirements via PVT collectors and the ORC unit and supply cooling requirements during summer via an adsorption chiller for a small building. The hot water output of the solar system is used to drive the ORC unit and adsorption chiller in four configurations; (Conf-1) hot water drives the adsorption chiller, then its output hot water runs the ORC unit (series), (Conf-2) it drives the ORC first, then the adsorption chiller (series), (Conf-3) hot water is divided between adsorption and ORC (parallel), and (Conf-4) hot water drives only adsorption without using ORC unit. Moreover, the impact of the area ratio of the PVT to ET collector and the ORC working fluid and its flow rate on the system performance is investigated. A complete mathematical model is developed for the system components and solved using MATLAB software. The results show that Conf-4 has the best cooling production performance with an average value of 9.6 kW during the summer months and energy efficiency with an average value of 0.3 during August. Conf-1 is the best performing configuration in cooling production of about 5.6 kW average cooling capacity compared to Conf-2 and Conf-3. In contrast, Conf-2 has the best ORC unit performance with a maximum output of 1.2 kW on a typical day in July. Increasing the PVT collector area in the solar configuration negatively affects cooling production but increases electricity production, which augments the system’s overall exergy and energy efficiencies. R600 is the best ORC working fluid compared to R290 and R134a in terms of average ORC power production of about 0.72 kW compared to 0.63 kW for R290 and 0.39 kW for R134a. Conf-1 is found to have the best energy savings of about 50.8 MWh/year and thus the best emissions of approximately 10.06 equivalent tonCO2 per year. The system Payback period is about 9.8, 9.95, 9.9, and 8.45 years for Conf-1 to Conf-4, respectively, proving the system’s economic feasibility.
... Uptake rates of the adsorption material can be estimated as below [51]: ...
This study examines the energetic and economic feasibility of a new hybrid renewable biomass-solar-wind energy system for driving both cascaded adsorption-compression refrigeration systems compared with its counterpart conventional compression system for the same input energy. Two renewable energy scenarios are proposed: biomass-solar-battery (Scenario-I) and biomass-solar-wind-battery system (Scenario-II) for autonomously driving the cascaded adsorption-compression system. Herein, biomass and thermal waste heat from photovoltaic/thermal collectors are exploited for the adsorption system's operation. By contrast, the compression unit is propelled by the electric power of the photovoltaic/thermal collectors besides wind energy. In that respect, surplus electricity beyond the battery bank's charging is converted into heat through an electric heater. These scenarios are investigated and compared using representative meteorological data of New Borg El-Arab city, Egypt. The results demonstrate that Scenario-I is more cost-effective than Scenario-II, which has a cost of refrigeration of 0.235 $ kWh − 1 compared to 0.237 $ kWh − 1 of Scenario-II. Herein, photovoltaic/thermal collectors in Scenario-I ultimately deliver 100% of the required electric load beside excess electricity of 16.6 kWh. Comparably, Scenario-II delivers surplus electricity of 15 kWh due to the designed fewer numbers of photo-voltaic/thermal collectors. Whereas biomass energy covers most of the requisite thermal demand for both scenarios. Moreover, a trade-off between the proposed cascaded adsorption-compression cycle and the renewable-based conventional compression cycle has been conducted. Herein, two proposed systems of photovoltaic-battery (Scenario-III) and photovoltaic-wind-battery (Scenario-IV) are proposed for the conventional compression cycle. The results exhibit that Scenario-III would attain a minimum annual cost of $2714 compared to $4045 for the cascaded system, notably in Scenario-I. In general, using renewable energy mix to drive cooling/refrigeration systems could pave the way towards abating ongoing energy demands and undermining global warming and climate change impacts.
The shortage of freshwater is a global problem, however, the gel that can be used for atmospheric water harvesting (AWH) in recent years studying, suffer from salt leakage, agglomeration, and slow water evaporation efficiency. Herein, a solar‐driven atmospheric water harvesting (SAWH) aerogel is prepared by UV polymerization and freeze‐drying technique, using poly(N‐isopropylacrylamide) (PNIPAm), hydroxypropyl cellulose (HPC), ethanolamine‐decorate LiCl (E‐LiCl) and polyaniline (PANI) as raw materials. The PNIPAm and HPC formed aerogel networks makes the E‐LiCl stably and efficiently loaded, improving the water adsorption‐desorption kinetics, and PANI achieves rapid water vapor evaporation. The aerogel has low density ≈0.12–0.15 g cm ⁻³ , but can sustain a weight of 1000 times of its own weight. The synergist of elements and structure gives the aerogel has 0.46–2.95 g g ⁻¹ water uptake capability at 30–90% relative humidity, and evaporation rate reaches 1.98 kg m ⁻² h ⁻¹ under 1 sun illumination. In outdoor experiments, 88% of the water is harvesting under natural light irradiation, and an average water harvesting rate of 0.80 g water g sorbent ⁻¹ day ⁻¹ . Therefore, the aerogel can be used in arid and semi‐arid areas to collect water for plants and animals.
We present a novel power-to-water (P2W) battery that can store electricity as thermal energy and discharge it as a heat source for hygroscopic solution desorption. The battery can work in two scenarios: atmospheric water harvesting (AWH) and dehumidification. The involvement of high-grade energy and sophisticated design enables better sorption kinetics and storage density. A proof-of-concept prototype verified the feasibility and achieved a record-breaking water production rate of more than 10.2 g (Ldevice h)-1. Also, the battery can achieve a round-trip efficiency of 90% for AWH and 68% for dehumidification in large-scale storage. The inexpensive storage medium contributes to a very low cost per energy (∼20 $ kWh-1) which means that P2W batteries excel in short- and long-duration storage. The long-term transient performance studies demonstrate impressive competitiveness over the traditional AWH and vapor-compression dehumidification systems. P2W provides new directions for the development of versatile, scalable, repeatable, and sustainable energy storage systems.
Throughout human history, water and energy have played pivotal roles in the expansion and progress of societies. However, the availability of fresh water on Earth is limited, constituting less than 3% of the global water resources. Moreover, the distribution of freshwater across countries is inequitable, with a considerable amount being returned to oceans and underground reservoirs. The escalating effects of global warming further disrupt the natural water cycle, posing a serious threat to numerous countries in the form of drought and famine. To meet the increasing demand for freshwater, desalination technologies have been widely employed worldwide. Nevertheless, most of the existing commercial desalination methods heavily rely on fossil fuels and contribute to significant greenhouse gas emissions, exacerbating the issue of global warming. Consequently, the integration of hybrid renewable energy sources into desalination processes emerges as a promising solution to simultaneously address the freshwater demand and combat global warming. So, utilizing hybrid renewable energy supply to drive various desalination technologies is a very promising solution to meet freshwater demands and help mitigating the global warming problem. Therefore, it is imperative to gain a comprehensive understanding of the latest advancements in hybrid renewable energy-driven desalination technologies to guide future research endeavors in this domain. The primary objective of this study is to perform a bibliometric analysis in order to identify the key sources, authors, countries, research institutions, and topics within the field of hybrid renewable energy-driven desalination technologies. By utilizing the R Bibliometrix library and the biblioshiny application, a dataset comprising 451 publications obtained from the Scopus database was analyzed. The results of the analysis reveal a substantial increase in the annual publication rate within this research field over the past five years. Notably, Iran, the United States, and China have emerged as leading contributors in terms of total publications. However, it is noteworthy that countries in the Middle East and the Mediterranean region, in addition to China and the USA, exhibit prominent involvement in various categories of research within this field.
Atmospheric water harvesting (AWH) has consistently emerged as a possible source of fresh water, especially in regions where water and energy are scarce. Harvesting water from ambient air has the potential to be largely powered by renewable energy sources. Renewable energy has demonstrated a greater potential to produce water in arid regions using adsorption-based atmospheric water harvesting (ABAWH). Adsorbent is the only component in the ABAWH process that converts ambient air or moisture to water. In this direction, metal–organic frameworks (MOFs) have recently emerged as effective AWH adsorbents. The chapter focuses on the development of MOF-based adsorbents with excellent adsorption performance. Various parameters, such as adsorption kinetics, climatic conditions, and adsorption–desorption rate, have been covered in this chapter. This chapter also looks at the current advancements in AWH technologies and achievements. It is expected that this chapter will provide the reader with challenges that have been identified that retard the potential practical application of MOFs in AWH technology.
Atmospheric water harvesting appears to be a potential way to address water scarcity, particularly in locations where liquid water is scarce. Rainwater harvesting (RWH) is a low-cost, easy approach that requires little special expertise or understanding and has numerous advantages in remote areas. The purpose of this chapter is to examine various types of sustainable atmospheric water harvesting techniques. AWH appears to be a potential methodology for decentralized water production, overcoming the difficulties of long-term conveyance and supply of fresh drinking water in remote areas. Structural designs of innovative materials enable moisture harvesters to have desirable characteristics including high water uptake, durable recyclability, and easy collection of water, accelerating the next generation development of AWH. In this chapter, we first show the sorption mechanism for moisture-harvesting materials, including absorption and adsorption, and then review essential needs and moisture harvester design concepts. The development of an atmospheric water harvester that can generate water irrespective of geographical location, humidity level, low cost, and can be manufactured using local materials is the primary goal of all methods.
Freshwater scarcity is a major problem threatening many countries worldwide, notably those with arid climate conditions that lack access to fresh water. Humidity harvesting represents a reliable source of providing fresh water, especially if it can be extracted affordably and efficiently. Sorption-based atmospheric water harvesting (AWH) has the merit of being powered economically and sustainably by utilizing waste heat or solar energy compared to other AWH techniques. The first part of this chapter comprehensively presents the working principles of the atmospheric water harvesting technology. Afterward, a detailed appraisal of state-of-the-art sorption materials, such as activated carbon fiber, zeolite, silica gel, metal–organic frameworks, calcium chloride with various host materials, and hydrogels, where its adsorption isotherms and kinetics are examined in detail. The challenges and prospects of these sorption materials are also demonstrated. Moreover, numerous designs of solar-powered atmospheric water harvesters, including fixed and movable installations, are summarized and categorized. For the sake of comparison, operation concepts, advantages, disadvantages, and freshwater production capabilities are indicated. In that regard, the viability of those systems is also exhibited under different meteorological conditions. Eventually, the obstacles and limitations that hinder their utilization and future research directions are explored. Accordingly, AWH technology is introduced as a promising solution for freshwater supply, particularly in rural areas and arid deserts where water and energy are scarce.
An energetic, exergetic, economic, and environmental multicriteria evaluation of the feasibility for an integrated system comprised of an adsorption system and proton exchange membrane electrolyzer operating via photovoltaic/thermal collectors is introduced. The present system produces concurrent green hydrogen, cooling, and hot water under the meteorological conditions of Alexandria, Egypt. The generated electricity from photovoltaic/thermal collectors drives the electrolyzer for hydrogen production. The waste heat from photovoltaic/thermal collectors drives the adsorption unit during summer for cooling purposes, while in winter, it is used for domestic hot water supply. The adopted analysis is built in Simulink and consequently justified with existing literature. The transient variation of temperature profiles, cooling capacity, heating power, COP, input and output exergies, energetic and exergetic efficiencies are investigated. Investigating the daily performance of the adsorption cooling system during the summer exhibits an average daily COP of 0.47 and a system cooling capacity of about 7 kW. The results reported that the adopted system annually yields cooling, heating, and hydrogen of 8282 kWh, 1723 kWh, and 626 kg, respectively. Moreover, it is exhibited that the present system could attain annual energetic and exergetic efficiencies of 12.3% and 10.6%, respectively. The proposed system demonstrated a substantial payback period of 0.8 years and carbon dioxide mitigation of 52.2 tons. Consequently, combining the photovoltaic/thermal collectors wth adsorption cooling systems and electrolyzers could be pronouncedly appropriate for multigeneration systems.
As an effective way to obtain freshwater resources, atmospheric water harvesting (AWH) technology has been a wide concern of researchers. Therefore, hydrogels gradually become key materials for atmospheric water harvesters due to their high specific surface area and three-dimensional porous structure. Here, we construct a core-shell hydrogel-based atmospheric water harvesting material consisting of a shell sodium polyacrylate (PAAS) hydrogel with an open pore structure and a core thermosensitive poly N-isopropylacrylamide (PNIPAAm) hydrogel with a large pore size. Theoretically, the mutual synergistic hygroscopic effect between the core layer and the shell layer accelerates the capture, transport, and storage of moisture to achieve continuous and high-capacity moisture adsorption. Simultaneously, the integration of polydopamine (PDA) with the hydrogel realizes solar-driven photothermal evaporation. Therefore, the prepared core-shell hydrogel material possesses great advantages in water adsorption capacity and water desorption capacity with an adsorption of 2.76 g g-1 (90% RH) and a desorption of 1.42 kg m-2 h-1. Additionally, the core-shell structure hydrogel collects 1.31 g g-1 day-1 of fresh water in outdoor experiments, which verifies that this core-shell hydrogel with integrated photothermal properties can capture moisture in a wide range of humidity without any external energy consumption, can further sustainably obtain fresh water in remote water-shortage areas.
Water collection from moisture in air, i.e., atmospheric water harvesting, is an urgent future need for society. It can be used for water production everywhere and anytime as an alternative water source in remote areas. However, water harvesting and collection usually relies on desalination, fog, and dewing harvesting, which are energy intensive. In this respect, metal–organic frameworks (MOFs) have broad applicability for water harvesting in water-scarce areas; therefore, the current discussion focuses on this approach. Furthermore, recent progress on MOFs for moisture harvesters is critically discussed. In addition, the design, operation, and water harvesting mechanisms of MOFs are studied. Finally, we discuss critical points for future research for the design of new MOFs as moisture harvesters for use in practical applications.
Graphical Abstract
MOF adsorbents offer excellent operating capacity in various temperature and pressure ranges. Rational water harvesters can thus be developed by adjusting structural properties such as the porosity, functionalities, and metal centers, thereby enabling new devices to produce water even in remote areas.
Efficient freshwater production techniques are urgently required to address the global water scarcity problem. In this regard, solar-driven atmospheric water harvesting (AWH) technology, which can capture water vapor from ambient air and release it under sunlight, is a sustainable and feasible strategy to obtain freshwater. Metal-organic frameworks (MOFs) have emerged as promising adsorbents for achieving solar-driven AWH, even in arid regions with relative humidity as low as 10%. During the water desorption process, excellent light absorption and photothermal conversion abilities are much important for fast kinetics and multiple cycles. However, the related photothermal performance of MOFs-based adsorbents has been rarely concerned. Herein, the latest development of MOFs-based adsorbents for efficient solar-driven AWH are reviewed, and corresponding design and modification strategies to improve its water adsorption and photothermal properties are proposed. Besides, water harvesters with different configurations are briefly introduced. Furthermore, an outlook about the key trends of solar-driven AWH is outlined.
Developing efficient water adsorbents for atmospheric water harvesting in desert regions still remains a challenge due to the lack of useful strategies to enhance low-pressure water uptakes and adsorption-desorption kinetics. Herein we demonstrate a simple and efficient polyvinylpyrrolidone (PVP) assisted self-assembly strategy for the fabrication of core-shell [email protected](Cr) (M-8010) supraparticles. The water uptake capacity of the prepared supraparticles is about 225% and 390% higher than that of pure MOF-801 and MIL-101 at 8% RH, respectively, benefiting from the synergistic effect between the preconcentration functions of shell MOF-801 and the high storage capacity of core MIL-101. Fast water capture and release kinetics of M-8010 supraparticles is also achieved. Their water collection rate is estimated to be about 0.253 Lwater/kgadsorbents per day under 10-20% RH, demonstrating that the M-8010 supraparticles are a great potential and stable adsorbent for water harvesting under extremely arid environments. This work may pave a new way to design [email protected] supraparticles for high-performance water harvesters in desert areas.
In this work, shape–stable composite phase change materials (CPCM) were prepared, which consist of lauric acid (LA)–palmitic acid (PA) eutectics, polyvinyl butyral (PVB) and carbon nanofibers (CNF). The PVB acted as supporting material, and the CNF was used as enhanced thermal conductivity additive. The Fourier transformation infrared spectroscope (FT–IR) and X–ray diffractometer (XRD) patterns indicate no chemical reactions took place among LA, PA, PVB and CNF. The SEM image shows the LA–PA eutectics and CNF were evenly distributed in the PVB. The thermogravimetric analyzer (TGA) results presents that the CPCM had no degradation at operating temperature (around 40°C) and has good thermal stability. Thermal conductivity of CPCM2, 4, 5 and 6 (CNF mass ratio is 0, 1, 3and 5 wt%) is 0.18, 0.22, 0.28 and 0.40 W/(m⋅K), respectively. Latent heat of CPCM6 is 131.20 J/g, and its melting point is 34.07°C.
The main objective of this study was the design of an efficient adsorptive process to extract water from thin air, based on MIL-100(Fe), which is a promising material in water adsorption-related processes. Indeed, equilibrium and dynamic studies were performed to evaluate the suitability of this adsorbent. CO2, N2, and O2 adsorption equilibrium isotherms were measured at three different temperatures, and CO2 was the gas that presented a higher affinity towards MIL-100(Fe). H2O adsorption equilibrium isotherms follow a Type VI isotherm, showing two steps (0.21 < P/Po < 0.30 and 0.36 < P/Po < 0.40) attributed to the presence of two different cavities (25 and 29 Å) on its structure. The obtained data were regressed against adsorption equilibrium isotherm models (Langmuir model, Dual Ising-Single Langmuir model, and Polanyi's potential theory). The H2O adsorption dynamic behavior was in agreement with the expected from the H2O vapor adsorption equilibrium isotherms. Furthermore, the dynamic adsorption behavior of water adsorption in fixed-bed experiments was well predicted by the developed model. Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) analysis revealed a high regeneration capability during the adsorption/desorption cycles. Additionally, the structure remains stable during the water vapor contact and after exposure at different temperatures. Temperature Swing Adsorption (TSA) process, with a column volume of 0.35 m³, allowed maximum H2O productivity of 86.8 l·day⁻¹ for MIL-100(Fe).
Fog is an underestimated source of water, especially in regions where conventional methods of water harvesting are impossible, ineffective, or challenging for low-cost water resources. Interestingly, many novel methods and developments for effective water harvesting are inspired by nature. Therefore, in this review, we focused on one of the most researched and developing forms of electrospun polymer fibers, which successfully imitate many fascinating natural materials for instance spider webs. We showed how fiber morphology and wetting properties can increase the fog collection rate, and also observed the influence of fog water collection parameters on testing their efficiency. This review summarizes the current state of the art on water collection by fibrous meshes and offers suggestions for the testing of new designs under laboratory conditions by classifying the parameters already reported in experimental set-ups. This is extremely important, as fog collection under laboratory conditions is the first step toward creating a new water harvesting technology. This review summarizes all the approaches taken so far to develop the most effective water collection systems based on electrospun polymer fibers.
Freshwater scarcity is a globally significant challenge threatening the development of human society. Sorption-based atmospheric water harvesting offers an appealing way to solve this challenge by extracting clean water from the air. However, the weak ability of sorbents to capture water from dry air and the low water productivity of devices are two long-standing bottlenecks for realizing efficient atmospheric water harvesting. Here, we report a vertically aligned nanocomposite sorbent, [email protected], by confining lithium chloride (LiCl) in a reduced graphene oxide (rGO) and sodium alginate (SA) matrix. The sorbent shows high water uptake, as high as thrice its weight, by integrating the chemisorption of LiCl, deliquescence of monohydrate LiCl·H2O, and absorption of LiCl aqueous solution. Moreover, [email protected] exhibits fast sorption-desorption kinetics enabled by the vertically aligned and hierarchical pores of the rGO-SA matrix as water vapor transfer channels. We further engineered a scalable solar-driven rapid-cycling continuous atmospheric water harvester with synergetic heat and mass transfer enhancement. The water harvester using [email protected] realized eight continuous water capture-collection cycles per day and ultrahigh water productivity up to 2120 mLwater kgsorbent-1 day-1 from dry air without any other energy consumption. Our demonstration of the high-performance nanocomposite sorbent and scalable atmospheric water harvester offers a low-cost and promising strategy for efficiently extracting water from the air.
Freshwater scarcity is a global threat to modern era of human society. Sorption-based atmospheric water harvesting (AWH) is prospective to provide fresh water for remote water-stressed areas lacking in water and electricity. Adsorbent material plays a vital role in such AWH systems. Here, we report a solid adsorbent synthesized by impregnating hygroscopic salt lithium chloride (LiCl) into solidified activated carbon fiber felt (ACFF modified by silica sol). Composite samples immersed with different mass concentrations of silica sol are prepared and characterized for dynamic water uptake, equilibrium water uptake, textural and thermal properties. AS5Li30 (ACFF + 5 wt% silica gel + 30 wt% LiCl) exhibits an efficient water uptake of 2.1 g/g at 25 °C and 70% relative humidity (RH). The material further demonstrates a heat storage capacity of 5456 kJ/kg. Its low regeneration temperature (< 80 °C) and good cycle stability make it feasible to be used in practical water production applications, driven by solar energy and other low-grade energy. Estimation results show that water harvesting unit can produce 1.41 g H2O /g AS5Li30 under 25 °C and 75% RH.
Access to clean water is a global challenge, and fog collectors are a promising solution. Polycarbonate (PC) fibers have been used in fog collectors but with limited efficiency. In this study, we show that controlling voltage polarity and humidity during the electrospinning of PC fibers improves their surface properties for water collection capability. We experimentally measured the effect of both the surface morphology and the chemistry of PC fiber on their surface potential and mechanical properties in relation to the water collection efficiency from fog. PC fibers produced at high humidity and with negative voltage polarity show a superior water collection rate combined with the highest tensile strength. We proved that electric potential on surface and morphology are crucial, as often designed by nature, for enhancing the water collection capabilities via the single-step production of fibers without any postprocessing needs.
This paper thoroughly reviews the integration of absorption, adsorption and desiccant cooling technologies into vapor compression cooling/refrigeration systems. Different configurations of hybrid absorption-compression cooling systems have been collectively listed and studied based on energetic, exergetic, economic and environmental analysis. Several reviewed studies revealed that such systems could diminish the electricity consumption by 45-88% in comparison with conventional compression systems. Besides, various arrangements of hybrid adsorption-compression cooling systems have been intensively investigated using cascade, partially integrated and fully integrated systems. These layouts of integrated adsorption-compression cooling systems focus on escalating the performance of vapor compression cooling systems by dwindling their condensation temperatures. Surveys showed that using adsorption cooling systems with oversized capacity could result in increasing the performance until approaching freezing limits, while downscaled adsorption cooling systems could worsen the system performance as a result of increasing the intermediate condensation temperature. The amalgamation of vapor compression systems with both solid and liquid desiccant cooling cycles has also been reported and compared with different regeneration schemes; for instance, electric energy, solar energy and heat rejected from the assisted vapor compression cooling systems. Considerable studies confirmed that using multi-stage solid desiccant cooling systems compared with single-stage solid desiccant cooling systems can be operated at lower regeneration temperatures. Also by introducing integrated liquid desiccant-vapor compression systems, cooling can be attained with a dehumidification process that cools the supply air lesser than its dew point with an energy provision of 30-80%. This work is beneficial for researchers involved in the field of multi-integrated cooling systems.
The atmosphere contains an abundance of fresh water, but this resource has yet to be harvested efficiently. To date, passive atmospheric water sorbents have required a desorption step that relies on steady solar irradiation. Since the availability and intensity of solar radiation vary, these limit on-demand desorption and hence the amount of harvestable water. Here, we report a polymer–metal-organic framework that provides simultaneous and uninterrupted sorption and release of atmospheric water. The adaptable nature of the hydro-active polymer, and its hybridization with a metal-organic framework, enables enhanced sorption kinetics, water uptake, and spontaneous water oozing. We demonstrate continuous water delivery for 1440 hours, producing 6 g of fresh water per gram of sorbent at 90% relative humidity (RH) per day without active condensation. This leads to a total liquid delivery efficiency of 95% and an autonomous liquid delivery efficiency of 71%, the record among reported atmospheric water harvesters.
In article number 2002936, Swee Ching Tan and co‐workers report the synthesis of a moisture‐hungry Cu‐complex and use it for fabricating a “Smart Farm” device that can autonomously harvest atmospheric water during the night and release water during the day under natural sunlight. Driven by solar energy, the device enables self‐sustaining irrigation, which can help to alleviate both water and food scarcity.
Drinking water resources have always been limited in the gulf region of the Middle East and other desert regions around the world. In attempt to provide viable supplement, a device that harvests clean drinking water from air is designed, built and tested. The operation of the device is based on harvesting water naturally from air using adsorption materials. The prototype of this device consists of sorbent (silica gel is used in this study) exposed to radiant flux, water sorbent unit, condenser and reflector. Experimental studies of production of fresh water from air in controlled indoor environment have been carried out using the prototype. Several experimental tests were conducted under the conditions of 22 °C ambient temperature, a range of relative humidity (RH) from 30 to 60%, a range of silica gel thickness from 25 to 35 mm, surface area to volume ratio from 0.29 to 0.4 and radiant heat flux range from 509 to 556 W/m². The prototype was able to produce up to 159 g of water per 1 kg of silica gel in a 12 h cycle when exposed to 556 W/m² radiant flux. In terms of per one day (24 h), the harvester can produce 800 mL of water with an overall efficiency of 50% for 25 mm silica layer thickness. Increasing the relative humidity speeds up the adsorption cycle and increases the water capture, release and collection rates. The system can be improved by adding multiple layers of sorbent stacked on top of each other and by using sorbents with improved adsorption and desorption properties.
This review paper enlightens the importance of renewable resources such as water and elaborates the role of textiles to enhance the efficiency of fog water collectors. Due to water scarcity, there is a dire need of harvesting water from all of its available resources. Fog is one of those water resources. Fog harvesting is generally considered as one the most economical and facile methods in arid agricultural regions where clean and pure water necessity for drinking and farming purposes is required. The yield regarding fog harvesting method is around 1-10 L m −2 day −1 as reported in the previous literature. The limitation of the available literature for this hot issue was our motivation to provide an up to date knowledge about the parameters that are capable of enhancing the water collector's efficiency through fog either practically or theoretically. Moreover, we highlighted the appropriate structures and designs beneficial for increasing the water collection efficiency and fog harvesting phenomenon.
The earth's atmosphere houses an enormous amount of water, which could be effectively exploited for a plethora of applications. While the development of materials for harnessing this abundant resource has gained impetus in recent years, limited efforts have been devoted to in‐depth research on their agricultural applications. Herein, a novel copper(II)–ethanolamine complex (Cu‐complex), which has a maximum water uptake of up to 300% and a water production rate of 2.24 g g⁻¹ h⁻¹ under natural sunlight, is reported. As a proof‐of‐concept application, using this material, a fully automated and self‐sustainable solar‐powered SmartFarm device is developed. The Cu‐complex harvests atmospheric water during the night, stores the adsorbed water within, and efficiently releases the adsorbed water during the day when the device is exposed to sunlight. The water harvesting and irrigation process can be fine‐tuned to suit different types of plants and local climates for an optimal cultivation. With the SmartFarm in operation, the demand for freshwater for irrigation could be greatly reduced and urban farming techniques such as large‐scale rooftop farming could be promoted with a view of alleviating both water and food scarcity in the near future.
Water is essential to life. It is estimated that by 2050 nearly half of the world population will live in water stressed regions, due to either arid conditions or lack of access to clean water. This Outlook, written for the general readers, outlines the parameters of this vexing societal problem and presents a solution to the global water challenge. There is plenty of water in the air that potentially can be harvested not only from the desert atmosphere where the humidity is low but also from more humid regions of the world where clean water is needed. In principle, the materials used to harvest water from air in these climates should be applicable to deployment anywhere in the world to extract atmospheric water at any time of the year. Metal–organic frameworks (MOFs) have emerged as a unique class of porous materials capable of trapping water at relative humidity levels as low as 10%, and doing so with facile uptake and release kinetics. From laboratory testing to field trials in the driest deserts, kilogram quantities of MOFs have been tested in several generations of devices. The initial results of these experiments showed that MOFs could capture water from desert climates and deliver over one liter per kilogram of MOF per day. More than an order of magnitude increase in water productivity could be achieved with members of the MOF family when employed in an electrified device operating at many cycles per day. We show that the vision of having clean water from air anywhere in the world at any time of the year is potentially realizable with MOFs and so is the idea of giving “water independence” to the citizens of the world.
Atmospheric moisture is a ubiquitous water resource available at any time and any place, making it attractive to develop materials for harvesting water from air to address the imminent water shortage crisis. In this context, we have been exploring the applicability of covalent organic frameworks (COFs) for water harvesting and report here a new porous, two-dimensional imine-linked COF with a voided square grid topology, termed COF-432. Unlike other reported COFs, COF-432 meets the requirements desired for water harvesting from air in that it exhibits an 'S'-shaped water sorption isotherm with a steep pore-filling step at low relative humidity and without hysteretic behavior - properties essential for energy efficient uptake and release of water. Further, it can be regenerated at ultra-low temperatures and displays exceptional hydrolytic stability, as demonstrated by the retention of its working capacity after 300 water adsorption-desorption cycles.
Freshwater scarcity is a global challenge threatening human survival, especially for people living in arid regions. The sorption‐based atmospheric water harvesting (AWH) is an appealing way to solve this problem. However, the state‐of‐the‐art AWH technologies have poor water harvesting performance at arid climates due to the low water sorption capacity of common sorbents under low humidity conditions. Here, we report a high‐performance composite sorbent for efficient water harvesting from arid air by confining hygroscopic salt in metal‐organic framework matrix (LiCl@MIL‐101(Cr)). The composite sorbent shows 0.77 g/g water sorption capacity at 1.2 kPa vapor pressure (30% RH at 30 °C) by integrating the multi‐step sorption processes of salt chemisorption, deliquescence, and solution absorption. We demonstrate a high‐efficient AWH prototype with LiCl@MIL‐101(Cr) enabling harvesting 0.45‐0.7 kg water per kg material under laboratory and outdoor ambient conditions powered by natural sunlight without optical concentration and additional energy input.
The huge amount of moisture in the air is an unexplored and overlooked water resource in nature, which can be useful to solve the worldwide water shortage. However, direct water condensation from natural or even hazy air is always inefficient and inevitably contaminated by numerous impurities of dust, toxic gas, and microorganisms. In this regard, a drinkable and clean water harvester from complex contaminated air with a wide humidity range based on porous sodium polyacrylate/graphene framework (PGF), which can actively sorb moisture from common or even smoggy environments, efficiently grabs impurities, and then releases clean water with a high rejection rate of impurities under solar irradiation, is proposed. This PGF shows a superhigh equilibrium uptake of 5.20 g of water per gram of PGF at a relative humidity (RH) of 100% and 0.14 g g-1 at a low RH of 15%. The rejection rate of impurities is up to 97% for the collected clean water. Moreover, a water harvesting system is established to produce over 25 L clean water per kilogram of PGF one day, enough to meet several people's drinking water demand. This work provides a new strategy for effective production of clean water from the atmosphere of practical significance.
This article aims to improve the system cooling capacity of an adsorption chiller working with a silica gel/water pair by an allocation of the optimum cycle time at different operating conditions. A mathematical model was established and validated with the literature experimental data to predict the optimum cycle time for a wide range of hot (55 °C-95 °C), cooling (25 °C-40 °C), and chilled (10 °C-22 °C) water inlet temperatures. The optimum and conventional chiller performances are compared at different operating conditions. Enhancement ratio of the system cooling capacity was tripled as the cooling water inlet temperature increased from 25 °C to 40 °C at constant hot and chilled water inlet temperatures of 85 °C and 14 °C, respectively. Applying the concept of the optimum cycle time allocation, the system cooling capacity enhancement ratio can reach 15.6% at hot, cooling, and chilled water inlet temperatures of 95 °C, 40 °C, and 10 °C, respectively.
Water scarcity is one of the greatest challenges facing human society. Because of the abundant amount of water present in the atmosphere, there are significant efforts to harvest water from air. Particularly, solar‐driven atmospheric water generators based on sequential adsorption–desorption processes are attracting much attention. However, incomplete daytime desorption is the limiting factor for final water production, as the rate of water desorption typically decreases very quickly with decreased water content in the sorbents. Hereby combining tailored interfacial solar absorbers with an ionic‐liquid‐based sorbent, an atmospheric water generator with a simultaneous adsorption–desorption process is generated. With enhanced desorption capability and stabilized water content in the sorbent, this interfacial solar‐driven atmospheric water generator enables a high rate of water production (≈0.5 L m−2 h−1) and 2.8 L m−2 d−1 for the outdoor environment. It is expected that this interfacial solar‐driven atmospheric water generator, based on the liquid sorbent with a simultaneous adsorption–desorption process opens up a promising pathway to effectively harvest water from air. A novel interfacial solar‐driven atmospheric water generator can simultaneously adsorb water and desorb water based on a liquid sorbent, 1‐ethyl‐3‐methyl‐imidazolium acetate. With enhanced desorption capability and continuous water supplement in the sorbent, this atmospheric water generator can achieve a high rate of water production (≈0.5 L m−2 h−1) and 2.8 L m−2 d−1 for the outdoor environment.
In the present study, a theoretical assessment of an adsorption-assisted cascade compression refrigeration system powered by photovoltaic/thermal collectors is performed. The proposed system is intended to produce refrigeration and electricity simultaneously. Herein, mathematical modeling of the proposed system is developed using MATLAB/SIMULINK and validated with the open literature. The impact of collector area, compressor displacement volume, cooling water temperature, and brine temperature on the system performance are quantitatively investigated and analyzed. The economic analysis of the proposed system has also been conducted. It is observed that decreasing the compressor displacement volume and cooling water temperature could substantially increase the overall coefficient of performance and energy saving. Furthermore, the results demonstrate that the system performance enhances with the increase of the collector area and the brine temperature. It is found that the proposed system can concurrently attain a daily average cooling capacity and electricity yield of 1.7 kW and 103 kWh at cooling and brine temperatures of 30 C and -20 C, respectively. Simulation results indicate that the proposed system can generate annual refrigeration production and electricity production of 34.4 kWhc m-2 and 213 kWhel m-2, respectively, with an annual average coefficient of performance of 2.38. Moreover, the economic analysis exhibited that the photovoltaic/thermal collectors-assisted cascade adsorption-compression system is economically competitive for refrigeration applications, revealing an annual energy saving of 24.8% and a payback period of 3.9 years. In this regard, cascade adsorption-compression systems could significantly extend the potential application and energy savings for cooling systems and heat pumps.
Sorption-based atmospheric water harvesting (SAWH) has emerged as an attractive way to relieve water scarcity. However, the daily water yield of currently reported SAWH devices remains low to satisfy the rising demand for drinking water. The sorption and desorption kinetics, long-term stability and especially facile scaling-fabrication of adsorbents and scaled-up device implementation have become the bottleneck to such large-scale SAWH application. To overcome these challenges, an air-cooled SAWH device was fabricated to investigate its atmospheric water harvesting (AWH) performance under real island climate and its feasibility of multicyclic operation. Under monocyclic operation, the device demonstrated the superior water productivity as much as 3.9 kg day⁻¹, or 0.39 kgwater kgadsorbent⁻¹ day⁻¹, at 31°C and 70% RH, with a thermal efficiency of 25.4% (desorption at 94°C). The SAWH device demonstrated successful water production through 2 adsorption-desorption cycles within one day, with increased thermal efficiency to as high as 32.2% and increased water harvesting performance up to 0.42 kgwater kgadsorbent⁻¹ day⁻¹ by 20–90%. This is the first demonstration in multicyclic SAWH at large scales, holding the promise of large-scale and practical water supply in island areas while opening up new applications such as indoor dehumidification.
Water vapors adsorption capacity of deliquescent salts is very high, but they dissolve in the adsorbed water by forming crystalline hydrates which restricts their use in different water vapor adsorption applications. This limitation can be overcome by incorporating deliquescent salts within a polymer matrix which will keep the salt solution in place. Furthermore, if the polymer matrix used is also capable of adsorbing water vapor, it will further improve the overall performance of desiccant systems. Therefore, in this work, we are proposing the synthesis and use of a highly effective new solid polymer desiccant material, i.e. superporous hydrogel (SPHs) of sodium acrylate and acrylic acid P(SA+AA), and subsequently its composite with deliquescent salt, i.e. calcium chloride (CaCl2), for the adsorption of water vapors from humid air without the dissolution of deliquescent salt in the adsorbed water. Synthesized SPH composite was characterized using different techniques like scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Parental P(SA+AA)-SPHs matrix alone exhibited the adsorption capacity of 1.02 gw/gads which increased to 3.35 gw/gads after incorporating CaCl2 salt in the polymer matrix. For both materials, experimental isotherm data agreed with Guggenheim, Anderson and Boer (GAB) isotherm model and exhibited type-III adsorption isotherm. The adsorption kinetics followed linear driving force model. Furthermore, adsorbents were used successively for ten cycles of adsorption and regeneration. Therefore, the proposed polymer desiccant material overcomes the problem of dissolution of deliquescent salts and purposes a new class of highly effective solid desiccant material.
The present study focuses on the synthesis and characterization of new composites comprising of RD silica gel and metal-organic framework (MOF) MIL 100(Fe) to upgrade the performance of the adsorption-based atmospheric water harvesting system. The impact of adding MIL 100(Fe) on the porous properties, thermal conductivity, and water adsorption characteristics of the composites has been experimentally investigated. Furthermore, three performance indicators are introduced to investigate the performance of the system, including net adsorbate uptake (Δq) and the efficiency estimation using two different approaches. Results showed that the maximum increment in the thermal conductivity was found in the composite having the highest concentration of MIL 100(Fe) (69 wt%). Thermodynamic cycles were drawn to show the performance of the composites with heat source temperatures of 50 °C and 70 °C. A composite of 29% RD silica gel, 69% MIL 100(Fe), and 2% PVP showed the highest value of Δq (213.8% increment over parent RD silica gel). In contrast, the efficiency of the system was enhanced up to 187% than that of the silica gel-based AWH system.
Silica sol gels have the potential to act as sealing agents to reduce leakage risks associated with long-term CO2 storage. This study considers the effects of brines of varying chemical composition on the formation of sol gels, their viscosity, and their long term stability. The gelation times of sol–gel solutions were measured for different concentrations of SiO2, Na+, K+, Ca2＋, and Mg2+ as well as pH levels. Individually, increased concentrations of SiO2, Na+, K+, Ca2＋, and Mg2+ reduced gelation time. However, the combined effects of Na+, HCl, and Ca2＋ or Mg2+ were found to delay gelation, compared to when only Ca2＋ or Mg2+ is added. Gelation times were similarly found to be a complex function of the pH of the system.
Empirical fits were obtained describing the gelation times and the precursor sol viscosities from the start of activation until gelation. Expressions are presented that relate the changes in the fitting parameters in response to variations in gel composition. There is good agreement between the experimental measurements and the models, which could be used to predict gelation rates in field-scale applications.
The durability of the gel was also investigated through experiments in which the gels were exposed to different solutions of varying salinity and pH. These results showed that silica gels were stable after 45 days of brine exposure, with the most significant change being a slight expansion of the gel. Additional experiments revealed that the gels remained thermally stable for expended periods at a temperature of 60 °C.
The present study focuses on the synthesis and characterization of new composites comprising of RD silica gel and metal-organic framework (MOF) MIL 100(Fe) to upgrade the performance of the adsorption-based atmospheric water harvesting system. The impact of adding MIL 100(Fe) on the porous properties, thermal conductivity, and water adsorption characteristics of the composites has been experimentally investigated. Furthermore, three performance indicators are introduced to investigate the performance of the system, including net adsorbate uptake (Δq) and the efficiency estimation using two different approaches. Results showed that the maximum increment in the thermal conductivity was found in the composite having the highest concentration of MIL 100(Fe) (69 wt%). Thermodynamic cycles were drawn to show the performance of the composites with heat source temperatures of 50 °C and 70 °C. A composite of 29% RD silica gel, 69% MIL 100(Fe), and 2% PVP showed the highest value of Δq (213.8% increment over parent RD silica gel). In contrast, the efficiency of the system was enhanced up to 187% than that of the silica gel-based AWH system.
This paper numerically investigated the influence of adsorbent materials’ thermal and adsorption characteristics on the overall performance of solar adsorption cooling cum desalination systems. A case study using an array of solar collectors was conducted to compare the emerging Aluminum Fumarate metal–organic framework (Al-Fum) with conventional silica gel (SG) under typical meteorological data at a selected site. Although the adsorption characteristics of Al-Fum outperforms SG at the material level, the former’s low thermal characteristics increased the cumulative heat stored and limited the integrated-system performance. The low thermal diffusivity of Al-Fum slowed down the integrated system’s response, providing that the average solar COPs of the SG-based system over different months were higher by 83%, 43%, and 22% at inlet chilled water temperatures of 15 °C, 20 °C, and 25 °C, respectively, and 1 mm fin spacing. However, the best specific cooling power of the AF-based system were higher than those of the SG-based system by − 16.6%, 16.8%, and 30.5% at these temperatures. Furthermore, the SG-based system was more negatively affected by reducing the heat storage initial temperature from 70 °C to 50 °C, but it attained COP and solar COP higher than those of the AF-based system by 14.9%–63%, respectively.
This study theoretically investigates the energetic and economic feasibility of three configurations of a solar-driven hybrid adsorption-compression cooling system using typical meteorological data of Cairo, Egypt. In Configuration-I, adsorption system is driven by solar collectors and vapor compression system is electrically powered. In Configuration-II, supplementary photovoltaic panels are used to power the vapor compression cycle, resulting in a net-zero electricity consumption scheme. For prolonged operation, Configuration-III is presented with an additional cold storage tank between adsorption and compression subsystems. Silica/gel water is utilized as a working pair in the adsorption cycle, while R410A is employed for the vapor compression system. Mathematical modeling is formulated using the MATLAB/Simulink platform and validated against experimental data from the most relevant literature. For Configuration-I, theoretical results demonstrate that the electricity consumption reduces in June from 22.37 kWh to 5.9 kWh by increasing the size ratio between the adsorption and the compression systems from 0.867 to 1.333. Configuration-I can substantially alleviate the electricity consumption by 62.5% compared to the conventional vapor compression system. It is also found that Configuration-II can save electrical energy consumption as high as 2897 kWh/year. Although Configuration-III experiences annual energy savings of 47% compared with Configuration-I that achieves 64%, it operates for prolonged durations as a redeeming feature. Moreover, economic analysis is conducted for the three examined configurations, revealing that Configuration-II is economically viable with a payback period of 9.65 years. These findings could spur designers and stakeholders into utilizing new hybrid cooling systems in preference to the predominant compression cooling systems.
Adsorption-based heat transformation systems are studied from the twentieth century; however, their performance is low to replace conventional systems. Metal-organic frameworks (MOFs) are providing a new class of micro- and nano-porous organic adsorbents. These have adjustable geometry/topology with a large surface area and pore volume. A comparison of the coefficient of performance (COP) between the MOFs and conventional adsorbents-based cooling systems is made for the years 1975–2020. Conventional adsorbents achieve COP of 0.85, whereas it is improved to 2.00 in the case of MOFs. The main bottleneck in the lower COP level is the low adsorption equilibrium amount. This study is aimed to provide comprehensive detail of water-vapor adsorption equilibrium and physicochemical properties of hydrophilic MOFs. Zn based MOFs are not stable in the presence of water-vapors, whereas MIL series, Zr, Ni, and Cu based MOFs are relatively more stable. Among the studied MOFs, MIL-101(Cr) possesses the highest adsorption uptake of 1.45 kg/kg at 25 °C (saturation condition) and outperformed for heat transformation applications. Its uptake can be increased to 1.60 kg/kg by coating with graphite oxide. For water desalination, MIL-53(Al) exhibits specific daily water production of 25.5 m³/ton.day (maximum) with a specific cooling power of 789.4 W/kg. Both MIL adsorbents are found promising which can be considered for various adsorption applications.
Adsorption technologies for Heat Conversion (AHC) and Water Harvesting (AWH) hold great potential for energy management because they can utilize renewable energy or low-grade heat resources. A keystone for the successful implementation of these technologies is the properties of the adsorbent. Metal–organic frameworks (MOFs) show tremendous promise for these applications, owing to their high adsorption capacity and the possibility of target-specific design. However, there are several challenges to be solved, namely, low hydrothermal stability of MOFs, high cost, and complicated synthesis. The further progress of these technologies depends on the inter-disciplinary research in Applied Thermal Engineering (ATE) and Materials Science (MS) and close collaboration between these two scientific societies is required. In this review, we try to bridge the gap between ATE and MS scientists. To this purpose, the principles of AHC and AWH are described, the specific features of adsorbents needed for AHC and AWH are defined, and promising MOFs are considered. MOFs fabrication strategies and long-term reliability are viewed. Finally, we provide some perspectives on advanced MOFs promising for continuously-operating and scalable AHC and AWH systems.
Adsorption-based, atmospheric water harvesting is a promising method for addressing water scarcity, which is a common issue in island areas, which often contain a large amount of fresh water in the air. Most existing adsorption-based atmospheric water harvesting systems usually require an additional cooling source, e.g., water-cooling, to cool the released humid high-temperature air below its dew point to harvest liquid water. To date, large-scale atmospheric water harvesting devices that use air cooling in such conditions have not yet been developed. Herein, we report a forced air-cooled proof-of-concept device for harvesting water from island air. Fabricated using 21 kg activated carbon fibre felt (ACFF)–silica sol–LiCl30, this device generated up to 7.7 kg of water (adsorption at 31 °C with 63% relative humidity) per day-and-night cycle, with a thermal efficiency (ratio of thermal energy to water conversion) of 0.37, using air cooling alone in laboratory-simulated island conditions. This study verifies the possibility of using air cooling to condense released humid air. It provides a flexible water generation solution for island regions with limited supplies of fresh water and power.
Solar energy powered sorption-based atmospheric water harvesting (AWH) is a novel strategy for obtaining fresh water in water-scarce regions. The major challenge is to design a cost-effective all-in-one solid bulk sorbent that can capture water from air, even when outdoor conditions are cool, dry, and with low-intensity nature sunlight. Here, we report a strategy comprising solution exchange and lyophilization for integrating a lithium chloride hygroscopic agent, a nanofibrillated cellulose hydrophilic skeleton and a graphene solar absorber, to exploit a solar-powered nanostructured biopolymer hygroscopic aerogel (NBHA) for AWH. The intrinsic porous bilayer structure with interconnected micron- and nano-scale channels of NBHA enables it readily absorb moisture (even at a low relative humidity of ~18%), has a high-water storage capacity, and requires little energy from natural sunlight for solar-driven light-to-vapor conversion. Liquid water was successfully harvested outdoors in natural sunlight of 0.10–0.56 kW m⁻² using a facile device based on the NBHA. This work provides a convenient, effective, and practical solution for AWH, even in severe environmental conditions.
Recent work has demonstrated adsorption-based solar-thermal-driven atmospheric water harvesting (AWH) in arid regions, but the daily water productivity (L/m2/day) of devices remains low. We developed and tested a dual-stage AWH device with optimized transport. By recovering the latent heat of condensation of the top stage and maintaining the required temperature difference between stages, the design enables higher daily water productivity than a single-stage device without auxiliary units for heating or vapor transport. In outdoor experiments, we demonstrated a dual-stage water harvesting device using commercial zeolite (AQSOA Z01) and regeneration under natural, unconcentrated sunlight where 0.77 L/m 2 /day of water was harvested. Our modeling showed that by further increasing top-stage temperatures via design modifications, approximately twice the daily productivity of the single-stage configuration can be achieved. This dual-stage device configuration is a promising design approach to achieve high performance, scalable, and low-cost solar-thermal AWH.
Since their discovery a few decades ago, metal–organic frameworks (MOFs) have suffered from poor hydrolytic stability. Since then, significant effort has been devoted to design robust MOFs, including their utilization for water-related applications to overcome relevant societal challenges. This short review provides guidelines on the key parameters that drive the assembly of hydrothermally stable MOFs together with the most relevant physicochemical features needed in their water-related applications. It also highlights some of the recent advances in MOF-water applications (based on water sorption or mediation and separation in the presence of water) as well as the most critical challenges to overcome.
The regulation of the balance of the sensible and latent loads remains a critical problem for built environment control. Unlike the traditional vapor compression system that features high-energy consumption and environmental-unfriendly processes, desiccants represent an alternative air-conditioning method that takes advantage of the low-grade energy, decreases the energy consumption and even employs use of water vapor. Though the desiccant-based systems can achieve spatial moisture transfer through the periodic adsorption/desorption process, however, the water-stable desiccants with high water uptake and mildly reversible adsorption are required, and the traditional desiccants cannot meet these requirements. In this respect, metal-organic frameworks (MOFs), possessing a variety of structures and precise functional ability to optimize their properties, are promising porous materials exhibiting high potential for rational design and sorption-based applications. In this review, intrinsic properties and prevalent water adsorption mechanisms of the potential micro/mesoporous MOF desiccants have been elucidated. Subsequently, the selection criteria of the promising MOF desiccants for water loading removal from air in the built environment is proposed and some currently available water-stable MOFs based on different working humidity ranges have been analyzed for the potential humidity control from the aspects of microstructure, isotherms and regeneration conditions. Finally, approaches for screening the well-suited MOFs from material and system levels is presented. Overall, the cases of actual applications in the active or passive way have confirmed that MOF-based systems can effectively regulate the humidity load within the desirable range, thus, underlining the high potential of large-scale applications in the near future.
Four different LiBr-based composite materials have been synthesized with silica gel or activated carbon as host porous matrix. High salt contents were incorporated in these composites: 37 wt% and 53 wt% for silica gel/LiBr composites; 32 wt% and 42 wt% for activated carbon/LiBr composites. The performance of these materials in conditions representative of the applications of sanitary hot water production and space heating demonstrates the very high potential of the silica gel/LiBr 53 wt% composite. It exhibits an unprecedented energy storage density of 261 kWh/m³ (adsorption temperature: 30 °C, desorption temperature: 80 °C and water vapor pressure of 12.5 mbar) and of 381 kWh/m³ when the desorption temperature reaches 120 °C. This promising material presents a good composition homogeneity, high water uptakes between 10 °C and 80 °C, and no measurable loss of sorption properties upon 10 cycles. This composite was tested in an open type laboratory set-up to complete its analysis for heat storage applications, at the scale of 200 g. The best energy storage density reached during 3 h 26 min was as high as 246 kWh/m³ (adsorption temperature: ~29 °C and water vapor pressure of ~12.5 mbar).
This investigation provides theoretical and experimental study of a solar powered foldable apparatus used for water extraction from air in arid regions. The experiments were performed under the climate conditions of Mansoura city, Egypt (31.04N latitude and 31.3785E longitude). The main components of the apparatus are absorber, which is a layer of black cotton cloth impregnated with Calcium Chloride (CaCl2) solution. It was designed to resemble an accordion shape, transparent polyvinyl chloride (PVC) cover, to enable the solar rays to transmit energy of solar radiation to the black absorber for raising its temperature. During night time, the absorber was placed in atmospheric air by unfolding and putting it on a telescopic stick for absorption process. The absorber collects moisture because of partial water vapor pressure difference between solution and air. During day time, the cover was mounted to isolate the absorber from the surroundings. The sun rays raised the absorber temperature, evaporation occurred, and the evaporated water condensed on the internal surface of the transparent cover. Water was finally collected in a graduated flask. Ambient temperature, temperature of cover, solar radiation and accumulated condensate were recorded during experiments. The accumulated water reached 750 g/day.
Tillandsia‐inspired hygroscopic photothermal organogel (POG) is developed to realize atmospheric water harvesting. The combination of designable hydrophilic co‐polymeric skeleton, hygroscopic liquid medium, and photothermic component endows POG continuous, high‐efficient moisture sorption and effective solar‐heating water releasing.
Abstract
Tillandsia species with degenerated roots have evolved into hygroscopic leaves that absorb moisture from air. This interesting biological adaptability has inspired us to develop an integrated hygroscopic photothermal organogel (POG) to achieve a solar‐powered atmospheric water harvesting (AWH). The well‐designed hydrophilic co‐polymeric skeleton is fabricated to accommodate hygroscopic glycerin medium, which enables the POG self‐contained property, mechanically flexibility and synergistic enhancement of moisture sorption. The integration of interpenetrated photothermal component of poly‐pyrrole‐dopamine (P‐Py‐DA) can endow the POG an efficient solar‐to‐thermal property for controllable solar‐driven interfacial water releasing. The integrated POG has an equilibrium moisture sorption of 16.01 kg m⁻² at the RH of 90 %, and daily water production as high as 2.43 kg m⁻² day⁻¹ is achieved in actual outdoor experiments.
As the global water shortage problems become more serious, vigorously developing water extraction from atmospheric air is significant and broad prospects. In order to improve water vapor uptake, a new type of composite material was fabricated by impregnating porous HKUST-1 with the aqueous solution of hygroscopic salt LiCl. The effect of impregnation salt concentration on hygroscopicity of HKUST-1/LiCl was discussed. The crystalline phase and morphology of the composites were characterized by Scanning Electron Microscopy and X-ray diffraction. The experimental results indicated that the composites obtained by dipping HKUST-1 with the solution of 20% LiCl, exhibited excellent adsorption capacities and fast adsorption rates. Its amount adsorbed at 25 ℃ and 50% RH reached 1.09 g/g, which were much higher than the pristine HKUST-1. Additionally, the composite material with a high water uptakes at low relative humidity (25 ℃, 30% RH, 0.50 g/g) suggested that the composite had excellent adsorption properties. All the results indicated that the novel composite material HKUST-1/LiCl are expected to be a promising candidate for water generation from atmospheric air by natural sunlight.
In this study, the performance of solar still incorporated with thermal energy storage (TES) unit of phase change material (PCM) is evaluated based on energy and exergy methodologies. Energy payback time for solar still with and without PCM is quantified and compared. Furthermore, the performance of both configurations is also evaluated from exergoeconomic and exergoenvironmental points of view. Experiments for solar still with and without PCM are conducted in summer and winter seasons subjected to the weather conditions of Alexandria, Egypt. The findings showed that the addition of a PCM storage unit to solar still system increased the annual energy and exergy savings by 10% and 3%, respectively. The results indicated that the incorporation of PCM in solar still was found ineffective compared to traditional still based on energy payback time. Based on the exergy approach, the integration of PCM in the solar still system is not effective where the conventional still (without PCM) achieved more than 400% more CO2 mitigations compared to PCM-based solar still system. Also, the exergoeconomic and exergoenvironmental parameters of the modified system were very poor related to those of traditional still. Therefore, for PCM-based solar stills systems to become competitive from global energy and environmental approaches, attempts should be performed by industrialists and engineers to find storage materials with low embodied energy and with low cost in conjunction with its evaluation from energy and exergy outputs to get a complete picture about the effectiveness of the system. In this case, the potential of thermal energy storage techniques for low-temperature solar-powered desalination systems will be thermodynamically, economically, and environmentally effective.
Atmospheric water harvesting (AWH) emerges as a promising means to overcome the water scarcity of arid regions, especially for inland areas lacking liquid water sources. Beyond conventional system engineering that improves the water yield, the novel moisture harvesting materials provide new aspects to fundamentally promote the AWH technology benefiting from their high tunability and processability. Innovative material and structural designs enable the moisture harvesters with desirable features such as high water uptake, facile water collection and long-term recyclability, boosting the rapid development of next-generation AWH. In this perspective, we first illustrate the sorption mechanism, including absorption and adsorption for moisture harvesting materials and summarize fundamental requirements as well as design principles of moisture harvesters. Recent progress on material and structural designs of moisture harvesters for AWH is critically discussed. We conclude with prospective directions for next-generation moisture harvesters to promote AWH from scientific research to practical application.
Air humidity, as a source of water, is more or less available everywhere. The sorption capacity of water is a significant factor for the efficiency of atmospheric water harvesting (AWH) systems, which are based on the adsorption phenomenon. Lithium chloride has a high water-uptake rate, but has a very low delinquency relative humidity (DRH). Therefore, a host is required to make a stable composite. Composite of activated carbon fiber (ACF) and lithium chloride can keep the adsorbent immobile even after the occurrence of deliquescence, which also causes the three-phase sorption. However, the amount of salt inside the composite is limited by the prevention of leakage. In this paper, a binary salt composite is produced by a new method in order to enhance the water sorption capacity in terms of volume, and mass and the prevention the leakage. The effect of adding MgSO4 to the composite has been experimentally investigated for at different levels of relative humidity. The results showed that sorption capacity per unit volume and mass can be improved by the two-stage addition of MgSO4 without leaking in the adsorbent, reaching 0.78 g water/cm³ and 2.29 gwater/gadsorbent. The prototype made by the selected composite showed that AWH energy intensity was lower at higher relative humidity. The device was tested successfully in an arid climate and produced 0.92 gwater/gadsorbent when maximum RH reached 35% during the adsorption process.
We report an in‐situ polymerization strategy to incorporate a thermo‐responsive polymer, poly(N‐isopropylacrylamide) (PNIPAM), with controlled loadings into the cavity of a mesoporous metal‐organic framework (MOF), viz. MIL‐101(Cr). The resultant MOF/polymer composites exhibit an unprecedented temperature‐triggered water capture and release behavior originating from the thermo‐responsive phase transition of the PNIPAM component. This result sheds light on the development of stimuli‐responsive porous adsorbent materials for water capture and heat transfer applications under relatively mild operating conditions.
Atmospheric water harvesting (AWH) is considered to be a promising technology to address the global water shortage. However, researchers are still searching for optimized desiccants with all the desired features such as high water sorption capacity, low desorption temperature, wide light spectrum absorption, ease to scale up and low cost. Here, we modified sodium alginate (SA) by occupying both G-blocks and M-blocks with more hydrophilic cations, i.e., Li and Ca. Functionalized carbon nanotube (FCNT) is embedded in the hydrogel structure to increase solar spectrum absorption. In summary, these features enable binary composite to adsorb about 5.6 g of water per gram of desiccant. For the first time, the idea of rational combination of a binary hydrophilic polymeric salt was embodied. We believe that this binary/FCNT sorbent is a promising material for application in water sorption-based technologies.
The article presents the synthesis of composite adsorbents by impregnating zeolite 13X with binary salts (LICl + CaCl2). The phase composition and element content of the composite adsorbent were characterized by X-ray diffraction (XRD) and Inductively coupled plasma (ICP). And its pore structure was discussed through N2 adsorption-desorption analysis. The results show that the formation of the solid solution changes the pore structure of the composite adsorbent which affects its adsorption performance. At the temperature of 25 °C and the relative humidity of 80%, CS6 exhibits the maximum adsorption capacity of 1.1 g/g compared with other adsorbents. The recycling test of CS6 shows that the adsorption capacity is 91.8% of the first time after 12 cycles. Finally, the dynamic adsorption curve and sorption isotherm were fitted by the LDF model and Polanyi Potential Adsorption Theory. It is shown that the simulation curve has good consistency with the measured data.
The present study proposed a new system of atmospheric water harvesting from extreme low humid regions under climatic conditions of Hail city (27.64 oN, 41.75 oE), Saudi Arabia. The concept of the proposed system was to activate the tubular solar still by a parabolic solar concentrator. This concept would increase TSS ability to evaporate water from strong desiccant of calcium chloride under extreme low humid conditions. The TSS was opened and exposed to atmospheric air during night hours starting the absorption process. At the beginning of the sunrise, the TSS was closed and placed at the focal line of the parabolic concentrator starting the regeneration process. The proposed system was able to produce 0.51 L/kg of calcium chloride. The system thermal efficiency and water production cost were 24.61% and $0.15 respectively. The proposed device increased the productivity and the efficiency of the TSS by 292.4% and 82.3%, while reduced the water production cost by 25%. The proposed system was compact, small and portable that could be operated easily in a desert, remote and isolated areas without any need for water resource or infrastructure. The proposed new system could be lifesaving in urgent situations especially in the desert areas.