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Adsorption-based atmospheric water harvesting: A review of adsorbents and systems
Abstract
Atmospheric water harvesting (AWH) has been an appealing prospect for decades to overcome water scarcity in remote areas. Adsorption-based AWH technologies have gained popularity due to their adaptability, and applicability using low-grade heat sources. This study presents up-to-date and future possibilities of adsorbents and systems for adsorption-based AWH. In this review, in-depth advancements in adsorbent materials are compartmentalized into adsorption equilibrium/isotherms, adsorption kinetics, and thermal conductivity. Various systems designs and modifications have been reviewed and classified accordingly. Liquid desiccants i.e., CaCl2 and LiCl-based AWH systems produced in between 0.63 to 1.0 kg/m/d of water. Recently, metal-organic frameworks (MOFs) are realized as effective adsorbents for AWH. Their excellent hydrophilicity, structural integrity, and tailorable structures can provide water in high and low relative humidity (RH) areas. MOF-841 and MOF-801 yielded maximum adsorption uptakes at 25 °C i.e., 0.5 and 0.3 g/g, respectively. MOF-801 showed an excellent water production of 0.2-0.3 L/kg/d at 5%-40% RH and 20-40°C. MOF-303 delivered ~0.7 L/kg/d at 10% RH and 27oC. Cr-soc-MOF-1 and MIL-101(Cr) resulted in maximum adsorption uptakes i.e., 1.9 g/g and 1.4 g/g, respectively. Future possibilities regarding these captivating and emerging adsorption technologies are discussed as concluding remarks.
... The active AWH systems required an external source of energy for producing potable water. Some common types of active AWH systems may include vapor compression (VC), thermoelectric cooling, and membrane based system [17,18]. Such systems have significant water production potential (WPP) ranging between 15 and 2000 L/day from civil to industrial scales, however facing limitation of huge EC [19]. ...
... On the other hand, passive AWH systems are solely powered by solar energy without the need of any external energy source or other high-grade power. Some common types of passive systems may include fog, dew and adsorption-based AWH technology [17]. The fog and dew systems are constrained by climate dependency, less WPP and thermal efficiency [20,21]. ...
... Once the adsorbent achieves saturation condition, desorption energy is supplied that could be achieve by solar, wind and low-grade waste heat to release the water-vapors [23,24]. The extensive details of both active and passive systems can be found from [17,25]. ...
... Despite many studies that have been carried out, the adsorption-based AWH systems are still only available for small-scale water supply after a disaster and in arid areas and far away from the large scale for water production. Many of the existing review papers on adsorption-based AWH systems were focused on the adsorbent materials only without paying attention to the system design and configuration [35][36][37] while few review studies highlighted the potential of system designs and configurations and emerging adsorption technologies [38]. ...
... Various hygroscopic salts (MgSO 4 , LiCl) are also incorporated with silica gel to improve the adsorptive capacity but the implementation of hygroscopic salts causes deliquescence and corrosion which influences their applicability in adsorption-based AWH systems [51]. From an economical perspective during adsorbent materials synthesis, it is indicated that the conventional adsorbent materials such as zeolite, silica gel, activated carbon, and salts despite their several limitations, have the merit of being abundant raw materials, cheaply cost, and requiring not-complicated preparation methods [37]. Moreover, it can be reported that zeolites can be employed for AWH systems, which operate at low humidity; however, the application of zeolites is required higher regeneration temperatures up to 300°C, unlike MOFs that can adsorb water at low regeneration temperatures [52]. ...
... From the adsorption kinetics aspect, the mass and heat transport properties of adsorption-based AWH systems govern their water uptake and thermal efficiency. The adsorbent's shape, packing density, crystal size, and porosity are among the fundamental parameters for vapor transport in the AWH system [37,63]. The adsorbent characteristics that govern the kinetics behavior of AWH's performance are highlighted in Fig. 8. Inter-crystalline and intra-crystalline vapor diffusion, energy transfer, and mass and heat transport in a packed-bed AWH system can be described by Eqs (1)-(5) as follows [63][64][65][66]; ...
The extraction of water from the air is considered one of the promising methods to supply fresh water, especially
in arid regions. Recently, the adsorption-based atmospheric water harvesting (AWH) systems are one of the most
efficient solutions for water extraction from the atmosphere due to their ability to work under low relative humidity
conditions using solar energy or other low-grade energy sources. The current work presents a literature
review of the adsorption-based AWH systems from perspectives of adsorbent materials, performance analysis,
energy requirements, and system configurations. The adsorption behaviour and selection criteria of the recent
promising adsorbents, especially metal–organic frameworks (MOFs), are discussed as well. Moreover, a generalized
performance analysis is presented to discuss and analyze the performance parameters and energy requirements
for the adsorption-based AWH systems. Finally, a critical discussion of the adsorption-based AWH systems
is conducted, and recommendations for future works are highlighted to increase water productivity and enhance
the system’s performance. The reviewed results highlighted that the adsorption-based AWH systems have
achieved water productivities of (0.10–2.80 l/kg) under different conditions. Subsequently, it can be inferred
that the obtainable freshwater production is still inadequate to supply water demand with an insufficiency of the
long-term stability and real practical utilization of large-scale AWH systems. It is also indicated that the Cr-soc-
MOF-1, (Cr) MIL-101, Co2Cl2 (BTDD), and (Cr) MIL-101(NH2) are recommended to be used as adsorbents in future
studies of solar adsorption-based AWH systems. It can be recommended that more studies should be carried
out considering the recommended suggestions for adsorbent materials and system design to overcome the challenges
and for further improvements to make these types of devices more efficient and competitive with other kinds of desalination systems
... Metal-organic frameworks (MOFs) have been considered to be efficient AWH adsorbents. They can supply water in high and low relative humidity [20]. A high-efficiency AWH system with hygroscopic PPy-Cl, a hydrophilic network of poly-NIPAM, and hydrophilicity switching based on the poly-NIPAM was developed by Zhao et al. [21] Effective water transport along the interconnecting networks of functional polymers enables these synergistic functionalities. ...
... frameworks (MOFs) have been considered to be efficient AWH adsorbents. They can supply water in high and low relative humidity [20]. A high-efficiency AWH system with hygroscopic PPy-Cl, a hydrophilic network of poly-NIPAM, and hydrophilicity switching based on the poly-NIPAM was developed by Zhao et al. [21] Effective water transport along the interconnecting networks of functional polymers enables these synergistic functionalities. ...
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.
... harvesting [223], and sorption [224] have been developed earlier to collect water from atmosphere but either they use a large amount of electrical energy or they are only suitable for some specific geographical locations having high and dense fogs. For real-field as well as household applications, the water collection system should have a sorbent material which can capture water vapors from humidity and release it only with a change in atmospheric conditions like temperature [33,34,225]. ...
... Therefore, handling and engineering design of deliquescent salts is a big obstacle in their use as a sorbent in atmospheric water harvesting. However, the composites of deliquescent salts with other materials [224,230] have been used as desiccants in which deliquescent salts were incorporated within the matrix of these materials to avoid the dissolution of salts and keep them in solid form within the matrix. ...
Freshwater scarcity is one of the world's foremost environmental stress concerns. In the last few years, with sustainable industrial growth and rapidly growing population, the problem of freshwater shortage has encouraged researchers to conduct comprehensive research for the development of advanced water harvesting and wastewater treatment techniques. Natural gums-based hydrogels have been widely used in different water purification and harvesting applications because of their environment friendly nature, high water absorption, adsorption and retention capacities. In this article, we presented an entirely conceptual and critical review of literature mainly focused on the potential of different natural gums-based hydrogel in water harvesting and wastewater treatment applications. First, different categories of natural gums-based hydrogels including stimuli responsive hydrogels, physically and chemically crosslinked hydrogels, were introduced. Then, the emphasis was given on the role of natural gums-based hydrogels in different wastewater treatment applications like adsorption, photocatalysis and flocculation. After that, the latest research progress on the use of natural gums-based hydrogels in atmospheric water harvesting and seawater desalination was discussed. Finally, different challenges and main limitations associated with the use of natural gums-hydrogels in water purification and harvesting applications were discussed to understand the research gaps and drawbacks which need improvements.
... AWH is the collection of water from the air and can be classified as (1) fog harvesting (rely on climatic conditions where relative humidity (RH) is 100%), (2) atmospheric water generators (condensation below the dew point temperature), and (3) adsorption-based process (vapor capture using desiccant materials). In adsorptionbased AWH systems, water vapor molecules adsorb onto desiccant materials; these water vapors are then released from the adsorbents by applying a temperature or pressure swing, powered by low-grade energy sources (e.g., solar thermal or waste heat) [34][35][36]. This process significantly reduces the sensible heat and the specific energy consumption for condensation under arid conditions, thus making AWH a viable strategy for generating fresh water [36]. ...
... According to the above statistics, the adsorption technology has been explored globally for AWH; however, this concept of the application is still new to the research focus of Pakistan. So far, only three journal articles have been published from Pakistan on this search criterion [34,35,51]. All these articles are related to the review category and none of them have mapped the AWH potential across Pakistan. ...
Atmospheric water harvesting (AWH) can provide clean and safe drinking water in remote areas. The present study provides a comprehensive review of adsorption-based AWH by using the scientometric approach. The publication types are mainly composed of articles and reviews, accounting for 75.37% and 11.19% of the total, respectively. Among these publications, ~95.1% were published in English and came from 154 different journals which demonstrates that researchers have shown a great interest in this field. However, much less contribution has been received thus far on this topic from Pakistan. Therefore, this study aims to explore a solar-driven adsorption-based AWH system in terms of varying relative humidity (RH), solar irradiance, and various types of adsorbent materials. Geospatial mapping and Monte Carlo simulations are carried out to integrate the operational parameters of the system and materials with Pakistan’s climatic conditions to forecast the AWH potential (L/m2/d). Probability distribution of 100,000 trials is performed by providing lower, mode, and upper values of the independent parameters. The possible outcomes of the adsorbed volume of water are determined by generating random values for the independent parameters within their specified distribution. It was found that MIL-101 (Cr) achieved the highest water-harvesting rate (WHR) of 0.64 to 3.14 (L/m2/d) across Pakistan, whereas the WHR was lowered to 0.58 to 1.59, 0.83 to 0.94, and 0.45 to 1.26 (L/m2/d) for COF-432, zeolite, and silica gel, respectively. Furthermore, parameter optimization and sensitivity analysis are performed to finalize the boundary conditions of the adsorption-based AWH system by ensuring the maximum volume values within the desired specification limits (1–4 L/m2/d).
... 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. In this review, we classify common sorbents into three categories: traditional porous adsorbents, salt-based composite adsorbents, and new nano-porous adsorbents. ...
... According to previous reports [163] , there are three main processes for the adsorption of guest molecules by adsorbent: external diffusion; intra-particle distribution; adsorption on the active sites. For vapor adsorption of adsorbent, the intercrystalline diffusion also needs to be considered. ...
Water shortage is an increasing threat to humankind. Porous sorbent assisted atmospheric water harvesting (psaAWH) has emerged as an effective technological countermeasure. In this review, we summarize the types of porous adsorbents used in psaAWH and provide an overview of their states of development. The water adsorption mechanism and the processes associated with each material are analyzed, and the application prospects of the adsorbents are evaluated. The effect of the inherent properties (pore size, functional group, etc.) of the adsorbent on the water harvesting performance is also discussed. Further, we focus on the water adsorption/desorption kinetics of the adsorbents and outline various methods to improve the kinetics. At this stage, there are many strategies for improving the kinetics of the adsorbent, which in turn influences the adsorption process and intra/inter-crystalline diffusion. However, there is still limited research on the transport of water molecules in microporous adsorbents for psaAWH. Thus, this aspect is reexamined herein from a new perspective (superfluidity) in the review. Based on the discussion, we can reasonably infer that water molecule superfluidity can exist in nanoconfined channels, thus promoting the rapid transport of water molecules. The formation of water superfluidity is a feasible strategy for improving the intracrystalline diffusion of the psaAWH adsorbent. Finally, we consider the future developments and challenges of psaAWH in detail. We think this review can serve as a guide for further research in this ever-expanding field.
... Adsorption-based AWH technologies are proven efficient compared to conventional ones. 8 The study is done on the zeolite material, among which AlPO 4 -LTA and AlPO 4 -34 are proven to perform well. ...
In comfort, air-conditioning control over the humidity is essential in applications such as pharmaceutical industries, electronic gadgets manufacturing units, the food sector, paper industries, etc. Relative humidity of nearly 50% can effectively prevent the growth and abidance of biological pollutants. There are several methods using which dehumidification can be achieved. The most common method is subcooling air up to the condensation temperature of the moisture trapped and then cooling again, and the condensate is collected. This method is time-consuming and needs to be more effective. On the other hand, desiccants’ dehumidification process is suitable for maintaining humidity in air-conditioning systems and producing dry air. Desiccants with economical materials, high moisture removal rate, low regeneration temperature, and steadiness after many years make a desiccant system more successful in its performance and cost. The effect of change in process air temperature, process air humidity ratio, and regeneration temperature on the system's performance is studied. This research focuses on the functioning of various desiccant dehumidification systems and their applications. A comparative study of the different dehumidification systems found efficiency, low maintenance cost, and high sustainability.
... Classification of the main AWH technologies (Bilal et al. 2022) harvesting capability, including efficient vapor condensation and liquid water collection, low energy consumption, less environmental and climatic limitations, good stability, scalable and robustness . ...
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.
... Such technologies include adsorption-driven heat transformation (AHT) and atmospheric water harvesting (AWH). [1][2][3][4][5][6] In water-based adsorptiondriven heat exchangers, that is adsorptiondriven chillers (ADCs) and adsorption heat pumps (AHPs), heating or cooling, for example, for air-conditioning, are achieved by reversible multicycling adsorptiondesorption of water vapor into/from a porous adsorbent. The regeneration of the material at each cycle could be realized by applying a (low temperature) renewable energy, such as solar or waste heat (see the working principle in Figure S1, Supporting Information). ...
The development of thermally driven water-sorption-based technologies relies on high-performing water vapor adsorbents. Here, polymorphism in Al-metal-organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans- or cis- μ-OH-connected corner-sharing AlO4 (OH)2 octahedra. Specifically, [Al(OH)(muc)] or MIP-211, is made of trans, trans-muconate linkers and cis-μ-OH-connected corner-sharing AlO4 (OH)2 octahedra giving a 3D network with sinusoidal channels. The polymorph MIL-53-muc had a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P0 ∼ 0.5 in MIL-53-muc, to P/P0 ∼ 0.3 in MIP-211. Solid-state NMR and Grand Canonical Monte Carlo revealed that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis-positioning in MIP-211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations showed that MIP-211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60°C, outperforming benchmarks sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP-211 is among the best adsorbents for adsorption-driven air conditioning and water harvesting from the air. This article is protected by copyright. All rights reserved.
... 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]. ...
... In Brazil, Ghisi et al. [4,5] showed that the use of rainwater could potentially result in a 92% peak saving in potable water use. Additional potential sources of harvesting potable water from different sources include atmospheric water harvesting and other sources [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Gitte and Pendke [23] studied water conservation practices, water table fluctuations, and groundwater recharge in watershed areas. ...
... Fog is formed by micro-sized water droplets suspended in the atmosphere. These droplets tend to grow in size, driven by their surface tension, until they are large enough to be separated and collected by gravity [11]. A fog trap net can be used to capture the small water droplets floating in the air by favoring the growth of the water droplets, after which the gathered water is available for utilization [12][13][14]. ...
Clean water scarcity is deteriorating because of the growing population and water pollution. New methods to harvest freshwater from non-traditional water sources are urgently required to address this global issue. The atmosphere contains abundant water resources. Harvesting fresh water from the air has become an emerging and attractive approach, among which sorption-based atmospheric water harvesting (AWH) is the most promising method, as it demonstrates high water producibility, wide applicability and low energy consumption. Metal-organic frameworks (MOF) are a class of emerging porous materials characterized by their large specific surface area, adjustable pore structures and chemistry. Recently, hydrolytically stable MOFs have been used as sorbents in AWH, and several MOF-based prototyping devices have been demonstrated with great practical potential. In this review, we briefly summarize the recent progress on the MOFs and their derived composites as AWH sorbents. Then, we introduce several most representative devices using MOFs for practical applications. Finally, the challenges and perspectives of this emerging field are discussed.
... Considering the difficulty and cost of MOF material preparation (CAU-10-H, MOF-303, and Ni 2 Cl 2 (BTDD)), CAU-10-H was first selected for the block compression operation in this study. After several preexperiments, 16 MPa was finally selected as the forming pressure to shape a block well, as shown in Figure S2a−c. Under a certain total mass of 5 g, CMC with mass contents of 0, 5, 10, 15, and 20% was added to CAU-10-H powder to enhance the structural strength of the block material, respectively. ...
Numerous adsorbents have been developed to extract water from air by sorption-based atmospheric water harvesting (SAWH). However, laboratory-level studies on the water uptake performance of adsorbents usually use materials with small mass such as microgram or milligram level. These findings may not be well adapted to scale-up applications. Moreover, other problems such as low thermal conductivity and structural instability may arise when the adsorbent is in the powder form. Herein, the effect of dosage scale-up on the water uptake performance of metal−organic framework (MOF) was studied. A compression method was proposed to shape the MOF powder into a block, and three MOFs (CAU-10-H, MOF-303, Ni2Cl2(BTDD)) were selected as test samples. The water uptake capacity, sorption kinetics, and adsorption isotherm of both powder and block materials were tested. Through qualitative and quantitative analysis, it was found that from small-scale powder materials to block materials, the step point of the water adsorption isotherm exhibited hysteresis, the water uptake capacity had diminished by about half, the time for MOFs reaching the saturation state increased by 10−20 times, and the adsorption rate coefficient was attenuated by more than 80%. These findings provide useful guidance and new insights for the future research of SAWH, which can help to bridge the gap between material science and engineering application.
... In Brazil, Ghisi et al. [4,5] showed that the use of rainwater could potentially result in a 92% peak saving in potable water use. Additional potential sources of harvesting potable water from different sources include atmospheric water harvesting and other sources [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. Gitte and Pendke [23] studied water conservation practices, water table fluctuations, and groundwater recharge in watershed areas. ...
In a water-scarce country such as Pakistan, rainfall is the third-largest source of freshwater. In most of the urban cities of the country, rainwater is mixed with sewerage and is rendered useless for managed aquifer recharge purposes. Therefore, this study investigates the rainfall potential for managed aquifer recharge in Lahore (Pakistan). The present research was designed and conducted
by the Irrigation Research Institute (IRI). Three different sites were selected for rainwater sample collection across the study area (Lahore), ranging from urban to rural areas. The rainwater samples
were collected and divided into three categories (direct capture, rooftop runoff, street runoff). For longer rainfall events, the effect of time on the quality of the collected rainwater samples was also studied. Spatiotemporal trends of turbidity, pH, electrical conductivity, total dissolved solids, carbonates, bicarbonates, chloride, calcium, magnesium, and hardness in the collected rainwater samples were investigated. In terms of TDS, results indicated that directly captured rainwater is most suitable for managed aquifer recharge (TDS < 50 ppm), followed by rooftop runoff (TDS < 100 ppm). In addition, the quality of rainwater samples collected at the rural site was comparatively better. Moreover, the quality of rainwater samples improved after the initial ten minutes. All in all, this study concludes that direct capture of rainwater is the most suitable option for managed aquifer recharge.
Metal–organic frameworks (MOFs) are superior sorbents for water adsorption‐based applications. The unique step‐like water isotherm at a MOF‐specific relative pressure allows easy loading and regeneration over a small range of temperature and pressure conditions. With good hydrothermal stability and cyclic durability, it stands out over classical sorbents used in applications for humidity control, water harvesting, and adsorption‐based heating and cooling. These are easily regenerated at moderate temperatures using “waste” heat or solar heating. The isotherm thermodynamics and adsorption mechanisms are described, and the presence of MOFs in the water–air system is explained. Based on six selection criteria ≈40 reported MOFs and one COF are identified for potential application. Trends and approaches in further synthesis optimization and production scale‐up are highlighted. No‐MOF‐fits‐all, each MOF has its own specific step location matching only with a certain application type. Most applications are technically feasible and demonstrated on the bench‐scale or small pilot. Their maturity is benchmarked by their technology readiness level. Retrofitting existing applications with MOFs replacing classical desiccants may lead to rapid demonstration. Studies on techno‐economic analysis and life cycle analysis are required for a rational evaluation of the feasibility of promising applications.
Atmospheric Water Harvesting (AWH) using porous adsorbents is emerging as a promising solution to combat water shortage. Thus, a clearer understanding of the developing trends and optimization strategies of different porous adsorbents can be extremely helpful. Therefore, in this concept, the different types of porous adsorbents and AWH devices are briefly introduced with a focus on the factors that influence the static and kinetic properties of porous adsorbents and their respective optimization strategies. In addition, the fast transport characteristics of water molecules in micropores are studied from the perspective of superfluidity as part of the analysis of the kinetic properties of porous adsorbents. Finally, the future development of porous materials for AWH and the accompanying challenges are summarized.
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.
With the decrease in fresh water resources, fog collection has become a promising way to obtain fresh water. This paper presents an efficient fog collector that combines wettability and spokes geometry. Water droplets move along a fixed route on the mist collector and can easily overcome the pinning effect at the end of the structure to detach from the surface and then be collected. Its fog collecting efficiency can be 1.82 times that of a planar zinc sheet, which provides a new idea for the design of subsequent fog collectors. In this communication, based on the lack of fresh water resources, the method of combining geometric structure with wettability to prepare a fog collector is proposed. And the high efficiency of fog collection is realized, which provides a new idea for the design of fog collector.
This article presents the thermodynamic assessment of an advanced adsorption chiller with an aim towards
entropy generation minimization through the selection of appropriate operating strategies, temperatures, and
design modifications. The present study carries out a second law analysis of a two-bed silica gel water pair-based
adsorption cooling system, with a focus on the under-explored aspects of a heat recovery strategy and auxiliary
consumption-reducing measures. A second law performance index, viz. specific irreversibility, is introduced for
effectively incorporating the entropy generation, auxiliary electricity consumption, and cooling capacity, and it
has been further verified to be an indicator of second law efficiency. The performance of the system has been
numerically evaluated under the normal and passive heat recovery strategies, where it is found that the passive
heat recovery strategy offers a lower entropy generation by 63%. The study further investigates the second law
efficiency impact of adopting a capillary-assisted evaporator for auxiliary electricity consumption reduction. It is
observed that the specific irreversibility could reduce by up to 22% over a conventional falling film design. The
analysis and results presented in this study are anticipated to increase the effectiveness of adsorption chillers for
heat recovery applications.
With the increasing demand for freshwater resources, the sustainable and effective utilization of atmospheric water has become a critical issue. Herein, an efficient and stable monolithic water-adsorbent is designed via functionalizing glass fiber paper loaded with two-linker metal-organic frameworks (CGF-mixed-MOFs(Al)). Firstly, a chitosan (CTS) polyelectrolyte layer is constructed on glass fiber paper to improve the MOFs loading capacity (306.71%) through electrostatic interaction and hydrophilic interaction. Subsequently, a series of two-linker metal-organic frameworks (mixed-MOFs(Al)) composed of MIL-160(Al) and Al-fumarate are tailor-made on CGF surface through a situ synthesis self-assembly technology. The resultant mixed-MOFs(Al) monolith exhibits better water harvesting ability and faster adsorption kinetics at low humidity owing to possessing more active adsorption sites. Different from CGF-MIL-160(Al) and CGF-Al-fumarate, the water sorption of CGF-mixed-MOFs(Al)5 at 30% RH, 25% RH and 20% RH reaches 0.37 g/g, 0.31 g/g and 0.25 g/g, respectively. The lab-scale atmospheric water harvesting device based on CGF-mixed-MOFs(Al)5 confirms the feasibility of this work-tailored product as a potential water sorbent in low-humidity environments. The cyclability results (50 times) indicate that CGF-mixed-MOFs(Al)5 maintains good water capture performance, integrity (no MOFs leakage) and crystallinity, which guarantees its working reliability and sustainable benefits. Therefore, our customized water adsorption system provides a simple, long-effective, economical and advanced strategy to capture more fresh water from atmosphere in arid climates.
Metal organic framework (MOF) dehumidifier presents vast application value to alleviate the humidity stress to improve the comfort of humans. Aluminum-fumarate based MOFs (AF-MOFs) are expected as an important class in this field since their flexibility allows the water adsorption properties to be tunable from the molecular level of the inorganic node and/or organic linkers. Here, AF-MOFs samples were prepared using aluminum salts containing different anions (SO4²⁻, Cl⁻, NO3⁻) to reveal how the anion components affect their morphology and thereby disclose the relationship between their structures and activities of water absorption. Systematic characterizations demonstrated that the anions achieved fine morphology control of AF-MOF samples without changing their basic framework, wherein the coordination effect between aluminum atoms in MOF units and atoms in anions (such as oxygen and nitrogen) induced this process. What's more, the water adsorption experiments revealed that by means of the collaborative assistance of specific surface area, hydrogen bond interaction and/or coordination effects, the SO4²⁻, Cl⁻ and NO3⁻ induced AF-MOFs reveal optimal water absorption performance at low, medium and high relative pressure, respectively. With no complex steps, extra morphology modulators and harsh temperature/pressure, this study provides an environmentally friendly new sight for regulating the morphology of AF-MOFs to optimize their dehumidification abilities.
Nowadays, atmospheric water harvesting (AWH) became very essential to provide fresh potable water. This technique is in practice since 1900 (US661944A) by Edger S. Belden. Atmospheric water is a source of freshwater with 13000 trillion liters availability of water at any time and can be utilized in overcoming water shortage, especially in arid and rural areas. It holds up the water molecules in the form of vapors and accounts for adding 10% of all freshwater present on the earth. Mainly, the two most common methods have been used for the extraction of atmospheric water. First, the ambient air is cooled below the dew point temperature, and second in which the moisture in atmospheric air is adsorbed/absorbed using desiccant materials. Conventional vapor compression, thermoelectric cooling, dew, and fog water harvesting based systems/technologies possess some limits in terms of energy requirements, less efficiency, and high cost. However, the adsorption based AWH technology is relatively cheaper, environment friendly, and can be operated by a low-grade thermal energy source. The limited availability of commercial instruments to harvest atmospheric water using adsorbents indicates a lack of fundamental studies. The fundamental research on water adsorption, adsorption kinetics, regeneration conditions, and water collecting surface designs has not gained as much interest as required in the field of atmospheric water harvesting. In this regard, this book chapter discusses and presents the progress in the field of adsorbent materials and system designs along with the future directions to accelerate the commercialization of this technology.
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.
The steep stepwise uptake of water vapor and easy release at low relative pressures and moderate temperatures together with high working capacities make metal–organic frameworks (MOFs) attractive, promising materials for energy efficient applications in adsorption devices for humidity control (evaporation and condensation processes) and heat reallocation (heating and cooling) by utilizing water as benign sorptive and low-grade renewable or waste heat. Emerging MOF-based process applications covered are desiccation, heat pumps/chillers, water harvesting, air conditioning, and desalination. Governing parameters of the intrinsic sorption properties and stability under humid conditions and cyclic operation are identified. Transport of mass and heat in MOF structures, at least as important, is still an underexposed topic. Essential engineering elements of operation and implementation are presented. An update on stability of MOFs in water vapor and liquid systems is provided, and a suite of 18 MOFs are identified for selective use in heat pumps and chillers, while several can be used for air conditioning, water harvesting, and desalination. Most applications with MOFs are still in an exploratory state. An outlook is given for further R&D to realize these applications, providing essential kinetic parameters, performing smart engineering in the design of systems, and conceptual process designs to benchmark them against existing technologies. A concerted effort bridging chemistry, materials science, and engineering is required.
A system that combines a vapor compression refrigeration system (VCRS) with a vapor absorption refrigeration system (VARS) merges the advantages of both processes, resulting in a more cost-effective system. In such a cascade system, the electrical power for VCRS and the heat energy for VARS can be significantly reduced, resulting in a coefficient of performance (COP) value higher than the value of each system operating in standalone mode. A previously developed optimization model of a series flow double-effect H2O-LiBr VARS is extended to a superstructure-based optimization model to embed several possible configurations. This model is coupled to an R134a VCRS model. The problem consists in finding the optimal configuration of the cascade system and the sizes and operating conditions of all system components that minimize the total heat transfer area of the system, while satisfying given design specifications (evaporator temperature and refrigeration capacity of −17.0 °C and 50.0 kW, respectively), and using steam at 130 °C, by applying mathematical programming methods. The obtained configuration is different from those reported for combinations of double-effect H2O-LiBr VAR and VCR systems. The obtained optimal configuration is compared to the available data. The obtained total heat transfer area is around 7.3% smaller than that of the reference case.
The passive capture of clean water from humid air without reliance on bulky equipment and high energy has been a substantial challenge and has attracted significant interest as a potential environmentally friendly alternative to traditional water harvesting methods. Metal-organic frameworks (MOFs) offer a high potential for this application due to their structural versatility which permits scalable, facile modulations of structural and functional elements. Although MOFs are promising materials for water harvesting, little research has been done to address the microstructure-adsorbing characteristics relationship with respect to the dynamic adsorption-desorption process. In this article, we present a parametric study of nine hydrolytically stable MOFs with diverse structures for unraveling fundamental material properties that govern the kinetics of water sequestration in this class of materials as well as investigating overall uptake capacity gravimetrically. The effects of temperature, relative humidity, and powder bed thickness on the adsorption-desorption process are explored for achieving optimal operational parameters. We found that Zr-MOF-808 can produce up to 8.66 LH2O kg⁻¹MOF day⁻¹, an extraordinary finding that outperforms any previously reported values for MOF-based systems. The presented findings help to deepen our understanding and guide the discovery of next-generation water harvesting materials.
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.
Sorbent-assisted water harvesting from air represents an attractive way to address water scarcity in arid climates. Hitherto, sorbents developed for this technology have exclusively been designed to perform one water harvesting cycle (WHC) per day, but the productivities attained with this approach cannot reasonably meet the rising demand for drinking water. This work shows that a microporous aluminum-based metal-organic framework, MOF-303, can perform an adsorption–desorption cycle within minutes under a mild temperature swing, which opens the way for high-productivity water harvesting through rapid, continuous WHCs. Additionally, the favorable dynamic water sorption properties of MOF-303 allow it to outperform other commercial sorbents displaying excellent steady-state characteristics under similar experimental conditions. Finally, these findings are implemented in a new water harvester capable of generating 1.3 L kgMOF–1 day–1 in an indoor arid environment (32% relative humidity, 27 °C) and 0.7 L kgMOF–1 day–1 in the Mojave Desert (in conditions as extreme as 10% RH, 27 °C), representing an improvement by 1 order of magnitude over previously reported devices. This study demonstrates that creating sorbents capable of rapid water sorption dynamics, rather than merely focusing on high water capacities, is crucial to reach water production on a scale matching human consumption.
Previous studies about water harvesting from airborne moisture, which is driven by a directional water transport principle, are based on either a 2D surface or a 1D filament. Porous membranes with a directional water transport capability are seldom used for water harvesting. Herein, a novel hydrophobic/hydrophilic directional‐wicking nanofibrous membrane is reported showing enhanced water harvesting ability. In comparison to the hydrophobic or hydrophilic membranes of the same structure and dimension, the directional wicking fibrous membranes have much higher water harvesting capacity. This fantastic water harvesting capability is originated from strong force to draw water from the hydrophobic to the superhydrophilic layer and ever permeable channels formed by the hydrophobic fibrous structure. Larger pores in the hydrophobic layer and smaller pores in the superhydrophilic layer facilitate water harvesting because of the enhanced directional wicking ability. The variation in pore dimension between the hydrophobic and the hydrophilic layers can result in 1.7 times difference in water harvesting capacity. These novel understandings may be useful for the development of advanced water harvesters for various applications. Hydrophobic/superhydrophilic directional‐wicking fibrous membranes with smaller pores in the superhydrophilic layer and larger pores in the hydrophobic layer show largely strengthened water harvesting capacity.
Water scarcity is a ubiquitous problem with its magnitude expected to rise in the near future, and efforts to seek alternative water sources are on the rise. Harvesting water from air has intrigued enormous research interest among many groups with Scientific American listing this technology as the second most impactful technology that can bring about a massive change in people's lives. Though desalination offers a huge prospect in mitigating water crisis, its practicality is limited by exorbitant energy requirement. Alternatively, the air above sea water is moisture rich, with the quantity of vapor increasing at the rate of 0.41 kg m⁻². Herein, a method to sustainably harvest water from this moisture rich zone is demonstrated by employing a nanoporous superhygroscopic hydrogel, which is capable of absorbing water from highly humid atmospheres by obver 420% (highest) of its own weight. The desorption process from the hydrogel, occurring at 55 °C (lowest), is triggered by natural sunlight (A.M 1.5) thereby ensuing an external energy‐less water harvesting approach. The hydrogel exhibits excellent stability even after 1000 absorption/desorption cycles. Through multiple absorption/desorption cycles, it is possible to harvest over 10 L water per kg of hydrogel daily.
Semiconductors are enabling technologies that drive today’s information economy by producing a broad spectrum of microelectronic consumer products including computers, flat-panel displays, sensors, storage devices, and lighting devices. Manufacturing of these semiconductor devices and products is capital and resources intensive and typically operates with either a vertically integrated manufacturing mode or with a cluster of supply-chain partnering companies in the vicinity of each other. Our research group has previously reported the water recycling and reuse efficiencies of “fabs” in the Science Parks in Taiwan (Lin et al., Res. Cons. Recycl. 2015), which exemplify this unique cluster of tech-manufacturing fabs demanding intensive supply of water and energy. We extend our discussion by summarizing the status of water consumption of major semiconductor and optomicroelectronic plants, and the industry’s collective and individual water reuse goals. Though the geographical location of fabs plays an important part of the water reuse efficiency, the industry generally displays a strong urgency to use water responsibly to maintain corporates’ competitiveness and to effectively manage the risks associated with water shortage. Additionally, the examination of water and energy expenditures of semiconductor fabs indicated a close water-energy relationship in the compartment of ultrapure water production process. The energy needed to treat, recycle and reuse spent water is secondary as compared to the energy demand for manufacturing processes. Using the industrial cluster in Taiwan as an example to illustrate the potential of improve water reuse through collaborative schemes, we conducted a survey-based study to assess how the industry perceived the proposed “inter-plants” and “inter-park” schemes designed to create a reclaimed water trading mechanism in place of the existing “in-plant” practice of water reclamation. Respondents showed an overall positive perception to such schemes on the basis of reducing water and energy demands in a cost-effective manner. The cost of water supply was a dominant factor in the perceived extent of benefits. Keywords: Water reuse, Water reclamation, Industrial water use, Semiconductors, Wafer fabrication, Fabs, Green manufacturing
The discovery of more-efficient and stable water adsorbents for adsorption-driven chillers for cooling applications remains a challenge due to the low working capacity of water sorption, high regeneration temperature, low energy efficiency under given operating conditions and the toxicity risk of harmful working fluids for the state-of-the-art sorbents. Here we report the water-sorption properties of a porous zirconium carboxylate metal–organic framework, MIP-200, which features S-shaped sorption isotherms, a high water uptake of 0.39 g g−1 below P/P0 = 0.25, facile regeneration and stable cycling, and most importantly a notably high coefficient of performance of 0.78 for refrigeration at a low driving temperature (below 70 °C). A joint computational–experimental approach supports that MIP-200 may be a practical alternative to the current commercially available adsorbents for refrigeration when its water adsorption performance is combined with advantages such as the exceptional chemical and mechanical stability and the scalable synthesis that involves simple, cheap and green chemicals.
In a conventional HDH system, a constant feed of seawater is required to run the system. As a result of extracting freshwater from the saline water, it is rejected at higher salinity, thus it cannot be recirculated as a feed again. The aim of this study is to come up with a zero-brine discharge system that eliminates the continuous need for the supply of source and sink in the conventional system. Based on the fact that earth's atmosphere holds a vast amount of water that can be considered as a reliable freshwater resource, especially in coastal areas. A water-from-air system is proposed in this study. The proposed system configuration comprises of two parts, a basic HDH system that uses a liquid desiccant solution instead of saline water and a desiccant-based air dryer. The liquid desiccant leaves the HDH part at a higher concentration due to the extraction of freshwater. It then enters the air dryer where it is diluted by absorbing water vapor from the ambient air. This diluted desiccant is directed to the HDH part to close the desiccant loop. In this study, Lithium chloride is used as the working fluid of the proposed system. Mathematical modeling of heat and mass transfer processes between the air and desiccant in the humidifier and dehumidifier is developed to predict the performance of the desalination system. The proposed system produces about 8 kg of freshwater per hour.
Energy-efficient production of water from desert air has not been developed. A proof-of-concept device for harvesting water at low relative humidity was reported; however, it used external cooling and was not desert-tested. We report a laboratory-to-desert experiment where a prototype using up to 1.2 kg of metal-organic framework (MOF)–801 was tested in the laboratory and later in the desert of Arizona, USA. It produced 100 g of water per kilogram of MOF-801 per day-and-night cycle, using only natural cooling and ambient sunlight as a source of energy. We also report an aluminum-based MOF-303, which delivers more than twice the amount of water. The desert experiment uncovered key parameters pertaining to the energy, material, and air requirements for efficient production of water from desert air, even at a subzero dew point.
The extraction of water from air is a promising way to supply fresh water, especially in remote, arid regions. This process can be supported by desiccant materials such as zeolites, metal−organic frameworks, or hygroscopic salts. Here we present a composite material that is able to absorb 660 kg of water per cubic meter of bulk material from air at 10 mbar water vapor pressure and 28 °C. The material consists of calcium chloride incorporated into an alginate-derived matrix. A simple synthesis route leads to spherical beads of the composite with a diameter of approximately 2 mm. This macroscopic structure allows for good vapor permeability through packed beds. The collected water can be released at 100 °C, potentially enabling a solar-driven application. In addition, the synthetic route uses cheap, non-toxic, and easily accessible materials allowing for widespread application. Extraction of water from air is a promising way to secure fresh water supplies in remote, arid regions. Here a composite material consisting of calcium chloride incorporated into alginate-derived beads is described, and shown to reversibly absorb 660 kg of water per cubic meter of material from the air.
Atmospheric water is abundant alternative water resource, equivalent to 6 times of water in all rivers on Earth. This work screens 14 common anhydrous and hydrated salt couples in terms of their physical and chemical stability, water vapor harvesting and release capacity under relevant application scenarios. Among the salts screened, copper chloride (CuCl2), copper sulfate (CuSO4) and magnesium sulfate (MgSO4) distinguish themselves and are further made into bi-layer water collection devices, with the top layer being photothermal layer while the bottom layer being salt-loaded fibrous membrane. The water collection devices are capable of capturing water vapor out of the air with low relative humidity (down to 15 %) and releasing water under regular and even weakened sunlight (i.e. 0.7 kW/m2). The work shines light on the potential use of anhydrous salt towards producing drinking water in water scarce regions.
Adsorption-based desalination (AD) is an emerging concept to co-generate distilled fresh water and cooling applications. The present study is aimed to provide a comprehensive review of the adsorption desalination systems and subsequent hybridization with known conventional cycles such as the multiple-effect AD (MED), solar regenerable, integrated evaporator-condenser cascaded, and ejector integrated systems. The systems are investigated for energy consumption, productivity enhancement, and performance parameters, including production cost, daily water production, and performance coefficient. Comprehensive economic aspects, future challenges, and future progress of the technologies are discussed accordingly to pave researchers' paths for technological innovation. Traditional AD systems can produce specific daily water production of 25 kg per kg of adsorbent. The solar adsorption desalination-cooling (ADC) showed a promising specific cooling power of 112 W/kg along with a COP of 0.45. Furthermore, for a hybrid MEDAD cycle, the gain output ratio (GOR) and performance ratio (PR) is found to be 40%, along with an augmented water production rate from 60% to two folds. The AD technology could manage the high salinity feed water with the production of low salinity water with a reasonable cost of US$0.2/m 3 .
Non-corrosive ionic liquids with negligible vapor pressure are potential substitutes for traditional absorbents used in absorption refrigeration chillers. In this study, we aimed to investigate the thermophysical properties and water sorption characteristics of the 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) ionic liquid and water binary systems. Density, thermal conductivity, specific heat capacity, viscosity, and surface tension were determined at various [EMIm]Ac mass fractions in the 20–100% range, as well as at various temperatures. In addition, mathematical relationships between the measured thermophysical properties and the studied variables (temperature and mass fraction) were developed. The water sorption and desorption performance were investigated for the [EMIm]Ac aqueous solution. Modified two-step sorption mechanism and linear desorption kinetics were proposed for the absorption and desorption process, respectively. These properties are helpful for the calculation and evaluation of the performance of the absorption and desorption based on the [EMIm]Ac/water working pair.
This study presents a simple, inexpensive and new method for the thermal conductivity measurement of low thermal conductivity materials using thermoelectric technology. The proposed system consists of a thermoelectric cooler, a thermoelectric generator and two heat sinks cooled with two fans. To measure the thermal conductivity, a sample is placed between a thermoelectric cooler and a thermoelectric generator. The heat generated on the hot side of the thermoelectric cooler passes through the sample and enters the thermoelectric generator makes a temperature difference between its two sides. The temperature difference produces an electrical voltage which is a function of the thermal conductivity, thickness of the sample and the power consumption of the thermoelectric cooler. As a result, a mathematical modeling was used to obtain a nonlinear function for estimation of the thermal conductivity as a function of produced electrical voltage, thickness of the sample, electrical voltage and electrical current of the thermoelectric cooler. The proposed method evaluated by testing several materials with known thermal conductivity (0.02 W.m-1. K-1 - 0.05 W.m-1. K-1) and the results showed a good agreement (maximum error of 10%) between the reference values and the experimental data. The measuring time of the system is considerably short and it only took 12 minutes. Repeatability of the measurement method for different materials showed that the rate of change is between 0.5% - 6%. A linear correlation for thermal conductivity estimation of Polystyrene with density of 8.0 Kg.m-3 to 25 Kg.m-3 has been proposed with a maximum error of 7%. Another linear correlation has been proposed for thermal conductivity estimation of other materials (0.02 W. m-1. K-1 to 0.05 W. m-1. K-1) with a maximum error of 10%.
In order to increase the performance and power output of the conventional combined cycle power plant (CCPP), a CCPP-AdCS (adsorption cooling system) with a maximum cooling capacity of 6000 kW is proposed in the present study. A model for CCPP simulation is developed, and it is validated through practical data. The thermal performance and economic analysis of the proposed CCPP-AdCS are evaluated. The results reveal that the CCPP-AdCS has the largest desorption and cooling capacity when the desorption temperature is 60 • C, and the maximum cooling degree of the inlet air is 8.73 • C. Compared to the CCPP, the power output can be significantly improved by the CCPP-AdCS. The maximum power output augmentation is 22.72 MW in July when the desorption temperature is 60 • C. By comparing to the existing literature, the CCPP-AdCS shows higher energy efficiency increment than CCPPs that integrated with absorption cooling system or mechanical cooling system. The payback time (PBT) of the CCPP-AdCS is only 2.34 years when the CCPP-AdCS is operated at a desorption temperature of 60 • C.
Atmospheric water harvesting (AWH) is a promising solution to the world’s water shortage. Meanwhile, adsorption-based atmospheric water harvesting (ABAWH) has shown a higher ability to supply water in arid areas using clean and cheap energy. Numerous modern adsorbents for this application have been introduced so far, and many prototypes have been provided. However, there is still a long way to go for widespread and practical use of this technology. Dedicated designs, operating strategies, environmental compatibility, and energy supply are issues that still need further consideration. This article has tried to summarize what has been achieved so far in ABAWH, analyze the challenges ahead, and provide solutions to continue the path.
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-based atmospheric water harvesting (AWH) technologies can enable decentralized and distributed water supplies in arid and water scarce regions with limited infrastructure. Recent advances in novel adsorbents, such as metal-organic frameworks (MOFs) and advanced zeolites, with high sorption capacity at low humidity and facile regeneration, promise the development of efficient AWH technologies. However, a comprehensive thermodynamic analysis based on fundamental material properties to predict optimal operating parameters and system-level efficiency has not been pursued. In this work, we present a generalized theoretical framework to optimize the energetic performance of thermally-driven adsorption-based AWH systems using fundamental material properties, such as adsorption isotherms. Using example characteristics of recently reported MOFs (MOF-801, MOF-303, and Ni2Cl2BTDD) with step-wise adsorption isotherms, we present AWH system-level theoretical efficiencies of each MOF based on the First and Second Law of Thermodynamics. We show the impact of heat source temperature from realistically achievable low-grade heat sources (up to 100 °C) on the overall efficiency. We also present the concept of a cascaded system which operates two adsorbent beds in series, and by capturing the condensation heat of the first bed, an increase in the overall efficiency can be achieved. At ambient conditions with relative humidities (RHs) below 40%, which is typical of arid climates, we show theoretical thermal (thermal energy to water conversion) and Second Law efficiencies of 0.33 and 0.18 with MOF-801 and MOF-303, and 0.56 and 0.19 with Ni2Cl2BTDD, respectively. For the cascaded system, a thermal efficiency of 0.7 and Second Law efficiency of 0.23 can be achieved with Ni2Cl2BTDD, over an order of magnitude greater than state-of-the-art refrigeration systems. Our framework presented can identify optimal operating parameters, and enable system-level predictions using materials properties for AWH and other related applications, including thermal energy storage, dehumidification, and desalination.
Effect of addition and hybridization of Graphene (G) and Silica (SiO2) nanoparticles on thermal conductivity of water, was experimentally studied. Initially, XRD, FTIR and FESEM tests were performed to specify phase and structural analysis and microstructural-observation of nano-materials. After that, nano-materials were dispersed and homogenized in distilled water by magnetic stirrer and ultrasonic vibrator, using the two-step method. The stability of graphene and silica nanoparticles in the base fluid at different pH values was examined. Thermal conductivity of three types of nanofluids, G/Water, SiO2/Water and G-SiO2/Water, at different volume fractions (φ) of 0.05–1% and temperature (T) range of 25-50 °C was measured. For predicting the thermal conductivity of G-SiO2/water hybrid-nanofluid, a two-variable correlation with R-Squared = 0.99 was extracted from experimental data by curve fitting method. The most and the least thermal conductivity enhancement attributed to G/water and SiO2/water mono-nanofluids respectively; while thermal conductivity enhancement between these two values and closer to the greater value associated with G-SiO2/water hybrid-nanofluid. By comparing the thermal conductivity results of the three present types of nanofluids, G-SiO2/Water hybrid-nanofluid would be a good choice as a high thermal and cost-effective nanofluid for thermal equipment.
This paper addressed the scarcity of experimental studies on the duo effect of magnetic excitation and hybrid nanofluid on the thermo-convection characteristics in enclosures. Novel Fe2O3-MWCNT (80:20)/deionized water (DIW) nanofluids with volume concentrations (φ) of 0.05–0.4 vol% were employed in a rectangular cavity exposed to magnetic excitation (4.89–21.95 mT) to examine the thermo-convection heat transfer behavior. The prepared hybrid magnetic nanofluids (HMNFs) were characterized for their stability, viscosity, thermal conductivity, and morphology. The DIW and stable HMNFs were charged into the cavity and differentially heated at ΔT of 20–35 °C under steady conditions. The results showed that without magnetic excitation, the average Nusselt number (Nuav) were observed to augment as Rayleigh number (Ra) and ΔT increased. Nuav and average heat transfer (Q̇av) were augmented for φ ≤ 0.2 vol% but they depreciated with φ > 0.2 vol% when compared with DIW. As the viscosity of HMNFs and φ increased heat transfer was noticed to depreciate. At ΔT = 35 °C, highest Nuav (11.33%) and Q̇av (11.21%) were achieved with φ = 0.05 vol%. With the magnetic excitation of 4.89–21.95 mT applied to the bottom, side (vertically and horizontally) and top (perpendicular and parallel to ΔT direction) walls of the cavity containing 0.05 vol% HMNF at ΔT = 35 °C, Q̇av was enhanced by 0.86%–1.46% and 1.72%–5.02% for the bottom and side walls when compared with the case of no magnetic excitation. Highest Q̇av (2.69%–5.02%) was recorded when the magnetic excitation was applied vertically on the side wall. Conclusively, the obtained results were observed to be strongly related to φ, ΔT, strength of magnetic excitation, use of HMNFs, position, and configuration of magnetic excitation.
Molecular dynamics (MD) simulation is one of the most common simulation methods which predict the dynamical and thermodynamical properties of atomic structures based on classical Newton's laws. In this study, the effect of copper nanoparticles on the thermal behavior of the fluid in zig-zag nanochannel was investigated using molecular dynamics simulation. In our simulations, water molecules were used to model the base fluid, and platinum atoms were used to model the nanochannel walls. To investigate the effects of copper nanoparticles on the base fluid, physical quantities such as potential energy, density, velocity, temperature profiles, and finally, the thermal conductivity has been reported. The results show that, by adding nanoparticles to the base fluid, the maximum density increases. On the other hand, the maximum velocity decreases from0.22°A/ps to 8°A/ps to. From the velocity behavior of the fluid particles, the temperature decreases from 363 K to 330 K. Furthermore, a study of the thermal conductivity of the simulated system by using the Green-Kubo method showed an increase in the thermal conductivity of water up to 0.679 W m⁻¹ K⁻¹. The increase of the nanofluid thermal conductivity is consistent with the increase in heat transfer, which can be a promising parameter in industrial applications.
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.
The advancement of additional methods for freshwater generation is imperative to effectively address the global water shortage crisis. In this regard, extraction of the ubiquitous atmospheric moisture is a powerful strategy allowing for decentralized access to potable water. The energy requirements as well as the temporal and spatial restrictions of this approach can be substantially reduced if an appropriate sorbent is integrated in the atmospheric water generator. Recently, metal–organic frameworks (MOFs) have been successfully employed as sorbents to harvest water from air, making atmospheric water generation viable even in desert environments. Herein, the latest progress in the development of MOFs capable of extracting water from air and the design of atmospheric water harvesters deploying such MOFs are reviewed. Furthermore, future directions for this emerging field, encompassing both material and device improvements, are outlined. The latest progress in the development of metal–organic frameworks and their integration in an apparatus for water harvesting are reviewed.
Atmospheric water harvesting technologies can be classified based on working principles, namely condensation technology, sorption technology and other technologies. Condensation technology utilizes various refrigeration technologies such as vapor compression cycle, thermoelectric cooling and adsorption/absorption cooling for condensing water vapor. Water harvesting processes can be operated as long as electricity is available. For other technologies, it can be further divided into innovative technologies and hybrid technologies. For innovative technologies, renewable energy powered VCC systems, solar chimney and geothermal cooling systems are used. Based on the above three categories, This paper summarizes these water harvesting technologies from perspectives of system configurations, test setups, simulation methods, performances analysis and important findings. Based on current review study, performances and research gaps of these technologies are compared and evaluated, and possible future research for atmospheric water harvesting in humid or dry climate regions are proposed.
The Supply of sustainable freshwater has turned into a fundamental problem in numerous countries. The increment in population, the industrialization of the world, and variation in global warming temperatures lead to an increase in droughts, storms, and floods around the world. Therefore, the problems of water scarcity appear worldwide. Contrary to popular belief, the largest reserves of water are available in the air. Accordingly, several technologies have been developed for the production of drinking water from humid air in the research works. But, the critical problem is the high energy consumption in this equipment. Therefore, the issues of water-energy nexus are the particular subject in the design and the construction of this equipment. The use of renewable energy (solar and wind energy) proposed as the solution for the reduction of energy costs. For example, the development of new desiccants for water harvesting by the utilization of solar energy has been reported in the literature. This paper describes an overall summarized presentational view of the various technologies for water extraction from humid air with the focusing on the water-energy nexus.
Clean water shortage has long been a challenge in remote and landlocked communities especially for the impoverished. Atmospheric water is now considered as an unconventional but accessible fresh water source and sorption-based atmospheric water generator (AWG) has been successfully demonstrated a reliable way of harvesting atmospheric water. The water vapor sorbents with high water uptake capacity and especially fast vapor sorption/desorption kinetics have become the bottleneck to a desirable clean water productivity in AWG. In this work, we developed a new nano vapor sorbent composed of a nano carbon hollow capsule with LiCl inside the void core. The sorbent can capture water vapor from ambient air as much as 100% of its own weight under RH 60% within 3 h and quickly release the sorbed water within just half hour under 1 kW/m² sunlight irradiation. A batch-mode AWG device was able to conduct 3 sorption/desorption cycles within 10 h during one day test in the outdoor condition and produced 1.6 kgwater/kgsorbent. A prototype of continuous AWG device was designed, fabricated, and successfully demonstrated, hinting a possible way of large-scale deployment of AWG for practical purposes.
This paper discusses effective ways to harvest water from air for residential use in dry climate area. An air handling process was proposed to humidify the air through multi-stage desiccant wheels before being dehumidified by the evaporator to harvest water. This approach not only increases the evaporating temperature but also increases the water harvesting rate (WHR) greatly. Two configurations of multi-stage desiccant wheels were compared, and proper desiccant wheel structure, length and number of stages were suggested. As for the energy system, two configurations of heat pump system (HPS) were compared and heat recovery is highly recommended, which can increase the system performance by around 70%. Effects of condensing temperature and outlet humidity ratio of air after water harvesting on WHR and water harvesting efficiency (WHE) were studied. When the ambient condition is 40 °C and 5 g·kg⁻¹, it is suggested to be operated under the condition that ωreg,out is 6 g·kg⁻¹ and tC is 90 °C. WHR and WHE can reach 32.5 kg·h⁻¹ and 1.26 kg·kWh⁻¹, respectively. Performances of the system, which adopts MSDW-2 and HPS-2, under different ambient conditions were studied and ωreg,out ranges with high WHE were summarized for different ranges of ωambi.
The thermodynamic balancing is a powerful tool to minimize the entropy generation in a thermal system. This tool is investigated to thermodynamically balance a novel desiccant-based humidification-dehumidification (HDH) system by extracting the recirculated air. It is carried out for a zero, single, double, triple, quadruple, quintuple, and infinity extractions. The HDH system is incorporated with a number of air dryers to produce freshwater from the humid air. An enthalpy pinch, which is described as the minimum air-to-desiccant enthalpy difference, is used as an index to approach the system thermodynamic balancing. For small values (< 20 kJ kga−1) of enthalpy pinch, the gained output ratio (GOR) is improved substantially as a function of extraction number. While for an enthalpy pinch between 20 and 47.8 kJ kga−1, more than one extraction has no further enhancement in the GOR values. Moreover, for more than 47.8 kJ kga−1 enthalpy pinch, the extraction schemes show no additional improvement in the system performance. The number of air dryers from one to twenty is used to improve condensed water production from 9.5 to 190 kg per hour, respectively.
Water scarcity is a current concern and a future problem. Air-water harvesting (AWH) is a novel proposed solution to provide enough water for human-being's needs especially in remote areas. However, the sorbent material is one of the challenging components of these systems. Generally, a proper sorbent must have a high water uptake capacity, a low regeneration temperature and an easy replacement structure, suitable to deploy in the bed. Here we synthesized three active carbon felt composites with a layer structure and analyzed their potential for being used in AWH systems. The performance of these ACFs composites concerning three different salts was investigated. Experimental results showed that the highest capacity is 2.9 g water per g sorbent at 70% of RH without any leakage. Also, pore parameters, non-equilibrium and equilibrium adsorption, regeneration temperature, recyclability and thermal diffusivity of samples were tested. The thermodynamic cycle of the system is studied, and a three-phase sorption cycle is proposed in this study. The detailed analysis reveals that the presence of the combined use of adsorption-absorption process can improve the sorption capacity extensively. The experimental and theoretical studies proved that these composites are very promising materials for water harvesting applications. To demonstrate these materials capability, a prototype is proposed which adopts these materials as its desiccant. This small prototype automatically could harvest 1.51 g of fresh water per cycle per g of sorbent at RH of 70%, without any human involvement.
Cryogenics-based energy storage (CES) is a low-carbon bulk energy storage technology without geographical constraints. CES additionally has a significantly higher exergy density, longer cycle life, low storage losses, and negligible environmental impact compared to competing technologies. This paper aims to identify the trade-offs between thermodynamic effectiveness and investment cost using the exergy-based methods. The base case system has a power of 100 MW/400 MWh, and integrated cold and heat recovery. The base case has a relatively high specific cost of installed capacity (2087 €/kW). The cost of the discharged electricity is reduced from 267 to 195 €/MWh. The cost of electricity charged to the system is revealed to have a small effect on the final product cost. Parametric and structureal measures to decrease the cost of the final product are identified and applied. The increase in compression pressure is found to improve the cost-effectiveness of the system most significantly. The iteration results of the exergoeconomic optimization are presented and compared to the base case. Cost savings amount to 40% and the optimized case enabled the system to approach the aimed range of product cost <200 €/MWh with a reduction in efficiency from 47% to 40%.
Atmospheric water harvesting (AWH) is the capture and collection of water that is present in the air either as vapor or small water droplets. AWH has been recognized as a method for decentralized water production, especially in areas where liquid water is physically scarce, or the infrastructure required to bring water from other locations is unreliable or infeasible. The main methods of AWH are fog harvesting, dewing, and utilizing sorbent materials to collect vapor from the air. In this paper, we first distinguish between the geographic/climatic operating regimes of fog harvesting, dewing, and sorbent-based approaches based on temperature and relative humidity (RH). Because utilizing sorbents has the potential to be more widely applicable to areas which are also facing water scarcity, we focus our discussion on this approach. We discuss sorbent materials which have been developed for AWH and the material properties which affect system-level performance. Much of the recent materials development has focused on a single material metric, equilibrium vapor uptake in the material (kg of water uptake per kg of dry adsorbent), as found from the adsorption isotherm. This equilibrium property alone, however, is not a good indicator of the actual performance of the AWH system. Understanding material properties which affect heat and mass transport are equally important in the development of materials and components for AWH, because resistances associated with heat and mass transport in the bulk material dramatically change the system performance. We focus our discussion on modeling a solar thermal-driven system. Performance of a solar-driven AWH system can be characterized by different metrics, including L of water per m2 device per day or L of water per kg adsorbent per day. The former metric is especially important for systems driven by low-grade heat sources because the low power density of these sources makes this technology land area intensive. In either case, it is important to include rates in the performance metric to capture the effects of heat and mass transport in the system. We discuss our previously developed modeling framework which can predict the performance of a sorbent material packed into a porous matrix. This model connects mass transport across length scales, considering diffusion both inside a single crystal as well as macroscale geometric parameters, such as the thickness of a composite adsorbent layer. For a simple solar thermal-driven adsorption-based AWH system, we show how this model can be used to optimize the system. Finally, we discuss strategies which have been used to improve heat and mass transport in the design of adsorption systems and the potential for adsorption-based AWH systems for decentralized water supplies.
The rapid increases in global population and economic growth have resulted in serious water scarcity in many countries. One of the solutions is to harvest water via dehumidification from ambient air by condensation. However, similar to the traditional air conditioning system, it takes a lot of energy in the condensation process to cool down air to the dew point temperature for dehumidification. Therefore, we propose a combined hollow fiber membrane dehumidification & humidity harvesting system in this study, which not only dehumidifies air but also harvests humidity to generate clean water simultaneously. The driving force for water vapor permeation comes from a dry sweep air combining with a small vacuum pressure of 0.17 bars. The calculation results show that the newly proposed membrane system not only produces fresh cool air but also condenses clean water with minimum energy. It produces 1 m ³ fresh cool air at merely 8.0 kJ while the traditional air conditioning system needs 10.55 kJ, which means an energy saving up to 24.3%. Moreover, it also produces by-product clean water. The calculation shows that it consumes only 687.4 kJ to produce 1 kg clean water while it needs 1125 kJ to do the same from the atmospheric air directly. Therefore, the newly proposed membrane system saves 38.9% energy on humidity harvesting.
The scarcity of water facing the world is one of the biggest challenges of this century. This challenge requires research plans in the field of water desalination that is not suitable for human use or the harvesting of water from the air. In this work, the performance of the water harvesting unit from the ambient air is studied. For this purpose, a vapor compression system is designed and built, a 372[Formula: see text]W reciprocating compressor is selected depending on the use of a small family consisting of four persons. The components of the vapor compression system are designed depending on the compressor power. The unit evaporator is modified to condensate the water vapor associated with the air instead of cooling the air. The effect of volume flow rate of air across the evaporator is studied. The range of air volume flow rate is from 224 to 244[Formula: see text]m ³ /h, as well as the operation mode of the unit which either continues to condensate or freeze the water vapor on the evaporator is also studied. The result showed that the water harvesting unit can work at a relative humidity as low as about 20%. The maximum water production for the unit is 7.9[Formula: see text]l/day with a power consumption of 1.76[Formula: see text]kW-h/l at the volume flow rate of air is 230[Formula: see text]m ³ /h. When an evaporative cooler is turned on in the test chamber, the amount of water production increases to about 13.11[Formula: see text]l/day with a power consumption of 1.068[Formula: see text]kW-h/l, for the same volume flow rate of air mentioned above.
Biomass from crop residue remains an underutilized and inexpensive energy resource around the world. Inadequate supply chain management forces farmers to resort to field burning of crop residue, resulting in environmental, health, and economic issues. In this study, we conceptualize a novel approach for biomass utilization which jointly addresses the common and often concurrent issues of energy, environment, and water. We propose to use the thermal energy from the combustion of the producer gas obtained from biomass gasification to power an off-the-grid refrigeration system which can condense moisture from air. We conduct a detailed thermodynamic analysis of vapor-adsorption cycle-based atmospheric water harvesting (AWH) system to develop an integrated modeling framework. We use the ambient weather data to report that the biomass-powered AWH can condense 800–1200 L of water per 1000 kg of biomass. Based on the local population and biomass availability, this can meet up to 10–12% of the potable water requirements in certain states of India. We also discuss the immediate challenges underlying this waste-to-value concept. Finally, we discuss that the proposition to jointly address energy, water, and the environment issues may motivate key paradigm shifts in policies required for practical implementation of this technology.
Condensation of water vapor available in atmospheric air can be considered as a solution for water scarcity problem. In this paper, a comprehensive thermodynamic analysis of water production from humid air using thermoelectric coolers (TECs) is presented. The system consists of a number of thermoelectric coolers, a fan to supply the required air flow circulation, two cold and hot air channels, heat sinks and solar cells for powering the thermoelectric coolers and fan. Effects of various design parameters are investigated and discussed. The proposed design is optimized to get the maximum effectiveness which is defined as the amount of produced water per unit of energy consumption. Sensitivity analysis is used to find the optimum number of TECs, length of the channels and performance of the system at different temperatures. The resulting system is capable of producing 26 ml of water within 1 h from the air with 75% relative humidity and the temperature of 318 K by consuming only 20 W of electrical power. In addition, the annual performance and optimization of this device in three southern cities of Iran are presented based on hourly meteorological data. Finally, comparison of the present system with other air water generators indicates that the proposed design is the most energy efficient system among similar devices especially in high relative humidity.
Even if people live in an arid desert, they know that plenty of water exists in the air they breathe. However, the reality tells us the atmospheric water cannot help to slake the world's thirst. Thus an important question occurs: what are the fundamental limits of atmospheric water harvesting that can be achieved in typical arid and semi-arid areas? Here, through a thorough review on the present advances of atmospheric water-harvesting technologies, we identify the achievements that have been acquired and evaluate the challenges and barriers that retard their applications. Lastly, we clarify our perspectives on how to search for a simple, scalable, yet cost-effective way to produce atmospheric water for the community and forecast the application of atmospheric water harvesting in evaporative cooling, such as electronic cooling, power plant cooling, and passive building cooling.
In this study, a solar ejector cooling system is theoretically analyzed to evaluate refrigerants and determine their performance characteristics and environment-friendly nature for a fixed ejector geometry under a set of standard operating conditions. The results show that the refrigerant R1234yf is the best choice for the cycle, and is an environment-friendly refrigerant with thermo-physical properties similar to that of R134a. Moreover, it has a high entrainment ratio and is cheap when compared to other refrigerants, nonflammable, and safe. The results indicate that the cooling cycle COP increases during the day hours as the generator temperature increases and reaches a maximum value of 0.59 at an optimum generator temperature of 86 \({^{\circ }}\)C in the middle of the day. The overall efficiency of the system varied in the range 38–45%. Furthermore, it was found that increasing the generator pressure by 40% reduced the COP by 58.5% and increased the critical backpressure by 27.3%.
In recent decades, many scientific works have been carried out to accomplish innovative solutions to achieve new resources for fresh water or improve the exploitation of current water resources. One of these new resources is the water vapor content of air. The objective of this study is to analyze the production of liquid water from atmospheric water vapor with assisted of a refrigeration cycle. The evaporator of this cycle will be as the cool surface and so the dehumidifier of the system that produces fresh water. In this study, a computer program was also developed to carry on a flexible thermodynamic model for a gas compression refrigeration cycle exclusively for fresh water production. The amount of water production and energy intensity under different climate conditions are analyzed. Despite most of previous studies, it has been tried to provide more real working conditions and some simplifying assumptions have been avoided. A case study is carried out based on ambient temperature and humidity intervals of system's best performance. The results show that a residential size of the system can produce 22–26 l/day fresh water while energy intensity is between 220 and 300 Wh/l. Since the proposed system can work without any brine discharging and environmentally friendly, a comparison of this method with other desalination technologies has been carried out, as well.
In this manuscript, experimental investigations have been performed in order to generate water from atmospheric air by using different composite materials under atmospheric condition of NIT, Kurukshetra, Haryana, India [29°58′ (latitude) North and 76°53′ (longitude) East]. In this analysis, three composite materials named LiCl/sand(CM-1), CaCl2/sand(CM-2) and LiBr/sand (CM-3) have been used as salt with 37% concentration and sand as a host material. The absorption and regeneration processes have been performed to generate water from atmospheric air. The absorption process has been carried out at night in the open atmosphere whereas regeneration process took place during the day time by using newly designed 1.54 m² Scheffler reflector. The maximum amount of water generated from CM-1, CM-2 and CM-3 are 90 ml/day, 115 ml/day and 73 ml/day in 330 min, 270 min and 270 min respectively and the annual cost of water generation are $0.71, $0.53 and $0.86 respectively.
Water harvesting from air in passive, adsorption‐based devices holds great potential for delivering drinking water to arid regions of the world. This technology requires adsorbents that can be tailored for a maximum working capacity, temperature response, and the relative pressure range in which reversible adsorption occurs. In this respect, metal–organic frameworks (MOFs) are promising, owing to their structural diversity and the precision of their functionalization for adjusting both pore size and hydrophilicity, thereby facilitating the rational design of their water‐sorption characteristics. Here, chemical and structural factors crucial for the design of hydrolytically stable MOFs for water adsorption are discussed. Prevalent water adsorption mechanisms in micro‐ and mesoporous MOFs alongside strategies for fine‐tuning of their adsorption behavior by means of reticular chemistry are presented. Finally, an approach for the selection of promising MOFs with respect to water harvesting from air is proposed and design concepts for next‐generation MOFs for application in passive adsorption‐based water‐harvesting devices are outlined. Metal‐organic frameworks (MOFs) hold great promise as adsorbents for water harvesting from air. Structural parameters influencing the hydrolytic stability of and mechanisms of water‐adsorption in MOFs are discussed, and methods for fine‐tuning the adsorption behavior by reticular chemistry are illustrated. The working principles for MOF‐based passive water‐harvesting devices are outlined and design aspects for next‐generation MOFs are proposed.
Fog is an important water resource, especially in arid and semi-arid zones. The usual method to collect fog water is placing a rectangular mesh perpendicular to the wind which traps fog droplets. The collector catches a fraction of the fog’s water droplets, allowing them to grow by coalescence until large enough to fall by gravity for collection. Fog events can last from minutes to hours, or even longer. This study aimed to evaluate the efficiency (η) of a standard fog collector (SFC) to gather fog water. Efficiency is defined as the ratio between the water reaching the collector’s gutter (CW) and the liquid water flux (LWF) normal to the collector’s mesh, integrated in a period of time. After a fog event begins, mesh collectors require some time to reach saturation and begin dripping; further, the system does not achieve a stationary state at field conditions. Therefore, we considered entire fog events when evaluating efficiency. The CW was measured using a rain gauge, and the LWF was calculated based on the liquid water content (LWC) obtained through a fog droplet spectrometer, and data of wind velocity registered by a meteorological station. The duration of the analyzed events ranged from 20 min to 11 h 40 min. A lag of up to one hour between the arrival of fog and the beginning of the measured water output was observed. Both processes started simultaneously when preceded by another fog event.
For the analyzed events, η ranged between 0% and 36.8%. Isolated events of up to 30 minutes resulted in zero CW measurements because the mesh requires time to become saturated before dripping. Furthermore, η was zero if the mean dew point depression (DPD) was above 0.2 °C or the mean LWC was below 0.045 g m⁻³. We found that η decreases with increasing mean volume diameter (MVD) for MVD ≳ 10 μm. Finally, η increased with wind speed for events in which the MVD > 12 μm.