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Investigation of adsorption performance deterioration in silica gel–water adsorption refrigeration
Abstract
Silica gel acts as a key role in adsorption refrigeration systems. The adsorption deterioration must greatly impact the performance of the silica gel–water adsorption refrigeration system. In order to investigate the adsorption deterioration of silica gel, many different silica gel samples were prepared according to the application surroundings of silica gel in adsorption refrigeration systems after the likely factors to cause such deterioration were analyzed. The specific surface area, silanol content, adsorption capacity and pore size distribution of those samples were tested and the corresponding adsorption isotherms were achieved. In terms of the experimental data comparisons, it could be found that there are many factors to affect the adsorption performance of silica gel, but the pollution was the primary one to decline the adsorption capacity. In addition, the adsorption performance of the deteriorated samples after being processed by acid solution was explored in order to find the possible methods to restore its adsorption performance.
... This study was extended in 2008 to investigate the dynamic characteristics of the system integrated with a solar-powered hot-water supply [24]. Furthermore, in 2012, they experimentally investigated the performance deterioration of a silica gel-water adsorption chilling system and determined that pollutants were the main cause [25]. Solmus et al. ...
... The refrigeration exergy, E eva , was calculated in a manner similar to that of previous studies [69,70], as given in Eq. (25). ...
Energy usage for space cooling and air conditioning has been rapidly growing in recent years and is expected to increase further owing to global warming and climate change. Adsorption chillers can provide an eco-friendly solution to space cooling because they utilize low-grade thermal energy such as waste hot water produced by the primary power-generation unit. In this study, dynamic analysis of a fuel-cell-system-driven adsorption refrigeration system was performed to expedite the optimal multibed configuration and its operating conditions. The scope of the study was extended to investigate maximizing the waste heat utilization achieved via exergy analysis of multibed configurations. The adsorption-to-desorption time ratio was integrated into the physical configuration of the adsorption chiller, and a new variable was introduced as a "time constant" that controls the cycle time and, under ideal conditions, equates the heating requirements of different bed configurations. Dynamic simulations for different bed configurations were conducted to evaluate the performance, specific cooling capacity, and unutilized exergy in the outlet waste stream. Under the operating conditions of 25 • C and 80 • C cold water and hot water temperatures, respectively, the five-bed configuration with a time ratio of 0.25 proved to be optimal, resulting in increases of 45.8%, 10.2%, and 15.1% in the specific cooling capacity, performance, and exergy efficiency, respectively, compared with those of the conventional two-bed configuration. The four-bed configuration yields very similar results, but with a slightly lower specific cooling capacity.
... Silica gel is one example of sorbent that is currently employed for dehumidification applications but suffers from high temperature recovery requirements (more than 100°C) and degradation of stability over adsorption−desorption cycles. 15 Recent research has focused on metal−organic frameworks (MOFs), a network of coordinated metal ions and organic ligands in materials with highly controlled properties. 16 Such sorbents can offer narrow pore size distributions targeted toward pore sizes favorable for water adsorption, while preventing undesirable hysteresis between the adsorption and desorption cycles. ...
... This degradation is caused by the dehydroxylation of the silica surface. 15 Cr-MIL-101 had the highest open porosity and highest water uptake with nanometric particle size. This high open porosity led to the fastest kinetics at larger layer thicknesses. ...
... It has also been proven that soaking in an acidic solution and washing with distilled water constitute an effective method of restoring the adsorption capacity of silica gel. 70,71 Micropore sintering, which occurs due to the long-term use of a chemical adsorbent, was examined by Yuan, who experimentally determined that with increased numbers of CaCl 2 /silica gel cycles, the adsorption capacity of the composite adsorbent decreased rapidly. For 40 cycles, the adsorption capacity is 15.3% of the initial value; after 70 uses, the adsorbent had no further capacity. ...
... (a) Schematic diagram of the adsorption capacity test system and (b) adsorption isotherm of samples 1, 3, and 4 (at 55 ± 1 ○ C).70,71 ...
This paper reviews recent research on adsorption refrigeration systems. Common and new-type adsorbent–adsorbate working pairs for adsorption refrigeration are summarized and classified. The performance evaluating parameters such as the coefficient of performance and specific cooling power are analyzed for an adsorption refrigeration system, and the influential factors of adsorption refrigeration system performance are investigated from the adsorbent and adsorption bed, respectively. The factors from the adsorbent include the following: the adsorbent particle size, size of micropores inside the adsorbent, total porosity of the adsorbent, and adsorbent stability. Optimization methods for improving adsorbents’ stability are proposed, and four preparation methods for composite adsorbents are summarized. Methods for improving the performance of an adsorption refrigeration system from the adsorption bed are illustrated by examples, including increasing the heat exchange area, improving the surface coating technology, utilizing the heat pipe technology, and designing the multiple adsorption bed system. Among these factors, the working pairs of adsorption refrigeration play the most important role for the system performance, and developing the new type of composite adsorbent to improve the performance and stability is the effective strategy to optimize the system performance. This article also provides suggestions on recent progress and the innovation directions for an adsorption refrigeration system.
... Les adsorbants hydrophobes tels que les charbons actifs, les silicates, sont ceux qui ont l'affinité avec les composés non-polaires comme les huiles. En plus des propriétés hydrophiles d'absorbant, la présence de micropores dans la structure influence considérément la cinétique et la capacité d'adsorption des matériaux [34][35][36]. ...
... Le gel de silice est connu pour être utilisé comme un agent dessiccateur, pour la séparation des gaz et liquides ainsi que pour des systèmes de refroidissement et de stockage de chaleur [36,38,40]. Le frein principale d'utilisation de gel de silice pour le stockage d'énergie thermique vient du fait que la grande capacité d'adsorption est possible à haute pression de vapeur d'eau [31] et donc l'utilisation d'un réservoir spécial pour l'eau est nécessaire. ...
L’épuisement des combustibles fossiles et l’augmentation de la demande d’énergie, entrainent l’intérêt croissant du développement des énergies renouvelables et des systèmes efficaces énergétiquement. Néanmoins, le décalage entre le besoin en énergie et la fourniture de celle-ci par les énergies renouvelables rend nécessaire l’utilisation d’un système de stockage. Parmi les différentes technologies de stockage d’énergie thermique, les composites formés d’une matrice poreuse et d’un sel hygroscopique, permettent de profiter à la fois des capacités d’adsorption/désorption de la matrice et des réactions chimiques du sel. La difficulté principale du développement d’un tel système est la compréhension incomplète des phénomènes physico-chimiques mis en jeu.Le premier objectif de cette thèse est d’étudier les réactions d’hydratation et de déshydratation du sel MgSO4. La caractérisation physico-chimique des solides ainsi que des expériences de thermogravimétrie isotherme et isobare ont été réalisées. Il a été montré que le système est divariant et que les hydrates obtenus sont non-stœchiométriques. Un modèle thermodynamique a été développé et appliqué aux données expérimentales. Les études cinétiques des réactions de déshydratation et d’hydratation ont été réalisées ce qui a permis de définir les étapes limitantes ainsi que d’écrire deux modèles et d’appliquer aux résultats expérimentaux. Enfin différents matériaux composites zéolite/ MgSO4 ont été synthétisés. Ces matériaux ont été caractérisés et leur capacité de sorption a été mesurée. Les résultats mettent en évidence une augmentation de la capacité de sorption, mais uniquement pour des pressions de vapeur d’eau importantes.
... Wang et al. [25], investigated the adsorption performance deterioration in silica gel/water adsorption refrigeration. It could be found that there are many factors to affect the adsorption performance of silica gel, but the pollution was the primary one to decline the adsorption capacity. ...
... Physical adsorbent AC/ammonia [10][11][12][13][14][15] 0.61 2000 À 5 100 AC/methanol [16][17][18] 0.78 16 15 90 AC/ethanol [19][20][21] 0.8 N.A 3 80 Silica gel/water [22][23][24][25] 0.61 208 12 82 Zeolite/water [26][27][28] 0.4 600 6.5 350 ...
... Wang et al. [25], investigated the adsorption performance deterioration in silica gel/water adsorption refrigeration. It could be found that there are many factors to affect the adsorption performance of silica gel, but the pollution was the primary one to decline the adsorption capacity. ...
... Physical adsorbent AC/ammonia [10][11][12][13][14][15] 0.61 2000 À 5 100 AC/methanol [16][17][18] 0.78 16 15 90 AC/ethanol [19][20][21] 0.8 N.A 3 80 Silica gel/water [22][23][24][25] 0.61 208 12 82 Zeolite/water [26][27][28] 0.4 600 6.5 350 ...
... The other disadvantage is that environmental temperature will have a great influence on the refrigeration performance. Refrigeration performance for solar energy application will decrease greatly when cooling temperature is higher than 35-40°C in summer time [4]. Compared with typical adsorption refrigeration, resorption refrigeration has flexibility to adapt different heat source temperature by employing different alkali metal halides [5]. ...
... The bulk adsorption molar quantity of 3, 4, 5 and 6 of MnCl 2 and 5, 6, 7 and 8 of CaCl 2 are similar to the procedures above. For NH 4 Cl, the bulk adsorption molar quantity start from 0, 1, 2 and 3. ...
... Activated carbon is cheaper than zeolite and Silica-gel. Also Silica-gel may not be available in most countries, besides its deterioration phenomenon of the adsorption capacity and aging [11]. Activated carbon has another advantage such as it can be produced with properties to suit particular applications by varying the activation time and temperature. ...
... The experimental results showed that the system can produce 4-5 kg of ice with a surface area of 0.75 m 2 and COP of the system varied between 0.12 and 0.147 when the energy received by the collector varied from 14 MJ to 16 MJ, while the system can produce 7-10 kg of ice with a surface area of 1.5 m 2 and COP of the system varied between 0.125 and 0.14 when the energy received by the collector varied between 28 MJ and 30 MJ. Fig.9. Schematic of the solar solid-adsorption ice maker: (1) adsorbent bed; (2) glass cover; (3) damper; (4) insulated material; (5,15) pressure gauges; (6,23,24) temperature gauges; (7,9,10,12) connecting flanges; (8,11,17,20,25) valves; (13) evaporator; (14) bracket; (16) condenser; (18) refrigerant input pipe; (19) reservoir; (22) ice box. [16] Buchter et al. [33] tested a refrigerator with a 2 m 2 solar collector area, and used a ventilation dampers to increase night cooling of the adsorbent bed (Fig.10). ...
In recent years, the adsorption processes have become a good alternative for traditional vapor compression refrigeration systems. Since, their using saves energy and less cost in most applications of air conditioning and refrigeration systems. The present paper has been focused on the ice making system from point of view of experimental and modeling methods.
... The presence of silanol groups with high porosity is responsible for the good adsorption properties and dehumidification performances. Wang et al. have experimentally investigated the causes of performance degradation of silica gel in adsorption systems with these conclusions (Wang et al., 2012(Wang et al., , 2014: ...
... Despite desiccant wheels that are directly exposed to atmospheric air, adsorption chiller applications are characterized by better resistance to degradation (Wang et al., 2012). Thermal stresses in silica gel in desiccant wheels are lower both in terms of frequencies and regeneration temperature. ...
Desiccant rotors are commonly used in large scale solar cooling open cycle applications. As is well known, adsorption heat sensibly reduces the dehumidification capacity of the desiccant material and results in lower system performance. The aim of this work is to describe an innovative solution that permits simultaneous mass and heat transfer. In particular, two components working with silica gel fixed beds were studied and compared. The first component is a simple packed bed containing silica gel grains. The second component is a fin and tube heat exchanger commonly used in several air conditioning applications wherein the spaces between the fins are filled with silica gel grains. In this case, the adsorption material is cooled through a recooling loop. For both solutions, results are presented in terms of dehumidification performances versus operation time, storage of adsorption capacity and energy required for the regeneration of the desiccant. © 2015 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
... refrigerators face challenges such as larger equipment requirements due to the need for a substantial amount of adsorbent (Inaba, 2001), performance degradation from adsorbent crushing (Kumida, 2006), and degradation of adsorption characteristics (Wang et al., 2012). ...
Heat-driven thermoacoustic coolers (HDTACs) are promising technologies for reusing waste heat. Although numerous studies have been conducted on HDTACs, they have predominantly focused on small units at the laboratory scale, with limited work on larger units for factory installations. This study explored a loop-type HDTAC with multiple thermoacoustic cores connected in series with the cold side of the cooler adjacent to the ambient side of the engine using linear thermoacoustic theory. For a large 1000-core diameter HDTAC designed for factory installations and a small 40-core diameter HDTAC designed for laboratory use, the cold heat exchanger temperature (TC), number of engine and cooler core pairs (n = 3-5), and flow path diameter of the regenerator were varied. The engine hot heat exchanger temperature (TH) relative to the cooler cold heat exchanger temperature and the Carnot-specific efficiency coefficient of performance (COP/COPCarnot) of the entire device are calculated, then design parameters of the device to achieve low temperature operation and high efficiency were indicated. The results show that, for small HDTACs, both low-TH operation and high-COP/COPCarnot were achieved at n = 5 (e.g., the maximum value of COP/COPCarnot for TC = −50°C was 0.31 at TH = 248°C). For large HDTACs, the maximum COP/COPCarnot was achieved with n = 3 (e.g., the maximum value of COP/COPCarnot for TC = −50°C was 0.49 at TH = 178°C).
... In repeated cycles, the desiccant performs effectively; however, the desiccant surface is lost. Similar work by Wang et al. (2012) used various samples to study the deteriorating silica gel adsorption capacity. It concluded that contamination could not be evaded and the reduction of adsorption capacity, silanol content, and surface area due to desiccant pollution with impurity ions and solid matter. ...
The present article regards a systematic review of adsorption cooling systems assisted by solar, ultrasound, and microwave energy sources. Numerical and experimental studies are included in this work, while the emphasis is given to the presentation of the mathematical formulation techniques. Due to the exceptional capability of utilizing low-grade energy, the adsorption cooling system attracted researchers amid increasing demand for cooling applications, decreasing the consumption of rapidly lasting fossil fuels. A significant quantity of energy is available as waste heat from industry, power stations, solar radiation, etc. The critical review is done on adsorption cooling systems to enhance the existing system's efficiency, which contributes to the reduction of pollution and global warming. Moreover, the efficient system is expected to have low adsorption and desorption time. This review presents different types of desiccants and various integrated techniques available to enhance the effectiveness of the adsorption-based cooling system, including ultrasound, microwaves, solar energy, etc. The present study critically reviews different modeling techniques of integrated adsorption cooling systems, using recent advancements in power techniques like microwave energy and ultrasound.
... The sorption performance of the silica gel in the adsorption chiller system inevitably deteriorates due to the impurity ions and solid particles pollutions [38]. Silica gel's sorption/desorption capacity degradation will affect the adsorption chiller system [21]. ...
An adsorption chiller system is one of the most promising technologies that utilize waste thermal energy to simultaneously produce cooling and potable water. However, the energy utilization optimization and detection of desiccant’s sorption capacity degradation are two unresolved issues that have severely impeded the development and commercial applications of adsorption chiller technologies. This study is pioneered to develop a digital twin platform specifically designed for an experimental four-bed two-evaporator adsorption chiller system prototype. Leveraging this platform, system monitoring, performance prediction, and optimization functions are achieved. Relying on the monitoring function, the digital twin can detect the capacity degradation of desiccant-coated heat exchangers. By employing the prediction and optimization functions, the application performance of the adsorption chiller system under varying ambient and load conditions can be simulated and optimized under real-time operating conditions. Additionally, this work projects a first-time experimental parametric study analysis for a four-bed two-evaporator adsorption chiller system prototype under a heat recovery scheme that considers fourteen operating parameters. Key results revealed that COPth reaches 0.68 when the cycle time is 2240 s. Case studies also showed that the adsorption chiller system can yield significant energy-saving performance for climatic conditions in Malaysia and Saudi Arabia. The proposed digital twin optimization method demonstrates that COPth is enhanced by 8.5 %, 9.5 %, and 8.5 %, respectively. In contrast to the conventional method, optimizing the adsorption chiller’s performance through the digital twin platform enables a reduction of the annual electricity consumption by up to 10.3 %.
... When selection is done, there must be compromise between the high porosity required for rapid vapor diffusion and the high density suitable for good thermal conductivity (Wang et al., 2012). The most commonly used adsorbents are activated carbon, zeolite and silica-gel. ...
... In another study Wang et al. [17] analyzed the adsorption performance deterioration in silica gel/water adsorption refrigeration and studied the possible factors influencing. The authors concluded that pollution caused by impurity ions and solid particles was the primary factor to lessen the adsorption capacity. ...
In this study, a completely new adsorption refrigeration system powered by biomass boiler, under condition of lower than 85°C driving hot water temperature was proposed. A numerical model of the whole system including the model of silica gel-water adsorption chiller, water tank, which reveals the transient operation process of the adsorption cooling system, is developed and verified by experiments. Parametric studies were performed using the model to determine the effect of parameters matching of components configuration and operation process on the cold generation capacity, the performance and the cyclic characteristics of the system, such as the chiller startup temperature, cooling and chilled temperatures, not only in the conventional cycle mode but also in direct cycle mode. The fluctuation of temperature in conventional cycle mode was significantly smoother than that in the direct cycle mode at heat source temperatures below 65°C. The cold delivered in the direct cycle mode was a little more fluctuating of the former but doesn't significantly reduce the performance of the machine. It was also found that the adsorption chiller could work efficiently on direct cycle mode under the conditions of heating temperatures of 60-65°C, with the COP of 0.33-0.4 and the cooling power of 3.8-4.15 kW while producing 10°C chilled water.
... Solar adsorption cooling system (SACS) is considered as a promising solution because it has many advantages compared with conventional refrigerators, such as it can be driven without electricity and it can be powered by low heat driving sources as solar heat energy, industrial/automobile waste heat, and geothermal heat. [1][2][3] SACSs are also considered as zero ozone depletion potential, and zero global warming potential, because it uses environmentally friendly materials 4 or alternative refrigerants of chlorofluorocarbures (CFCs), hydrochlorofluorocarbures (HCFCs), or hydrofluorocarbons (HFCs) 5 such as activated carbon (AC)-methanol, 67 AC-ethanol, [8][9][10] AC-ammonia, [11][12][13] silica gel-water, [14][15][16] and zeolite-water. [17][18][19] The first study on solar adsorption cooling appeared in 1848 20 before conventional refrigeration when Faraday demonstrated a system using ammonia and silver chloride as the working pair. ...
This article presents the modeling of the solar adsorption cooling system to predict its performance at each hour of the day. The model was implemented to improve the performance of the existing prototype built in Morocco that employs activated carbon–methanol as the working pair. The comparison between the numerical results and experimental data indicates that the model predicts the dynamic performance of the system well as a good agreement was obtained. Several main factors affecting system performance are discussed according to the results given by the simulation. New submodels have been added to predict the performance of the continuous cycle. The results show that the performance of the system could be enhanced by 68% with the continuous cycle. And by 88% with double glazed collector configuration.
... Miyazaki and Akisawa [16] examined the operating parameters of silica gel-water adsorption chiller based on single-bed design and observe that although increasing the size of adsorbent bed can decrease the coefficient of performance (COP) due to the shorter cycle time, it can also increase the specific cooling power (SCP). Wang et al. [17] measures how the pollution by the impurity ions or solid particles would increase the adsorption deterioration of silica gel, and found that soaking in acidic solution along with washing via distilled water would be a very good solution to restore the silica gel adsorption capacity. Effect of grain size and grain layers on the adsorption performance of silica gel was numerically examined by Chakraborty et al. [18]. ...
In solar-thermal adsorption/desorption processes, it is not always possible to preserve equal operating times for the adsorption/desorption modes due to the fluctuating supply nature of the source which largely affects the system's operating conditions. This paper seeks to examine the impact of adopting unequal adsorption/desorption times on the entire cooling performance of solar adsorption systems. A cooling system with silica gel-water as adsorbent-adsorbate pair has been built and tested under the climatic condition of Iraq. A mathematical model has been established to predict the system performance, and the results are successfully validated via the experimental findings. The results show that the system can be operational at unequal adsorption/desorption times. The performance of the system with equal time is almost twice that of the unequal one. The roles of adsorption velocity, adsorption capacity, overall heat transfer coefficient, and the performance of the cooling system are also evaluated.
... However, silica gel requires higher desorption temperature (>200 °C) and exhibits lower stability over adsorption/desorption cycles. 57 On the other hand, MOFs currently face scalability challenges, because their crystallization is a slow batch process that calls for highly controlled temperature and pressure conditions. For example, Furukawa et al. described a 6-hour long synthesis to produce 10 g of MOF-801, followed by a 7day period of rinsing and drying. ...
... The above analysis results also provide ideas and direction for the improvement of silicone rubber. Through investigation, it was found that the change of viscosity of rubber solution or composition of silica gel would cause the change of hole size inside the rubber [12]. So the main indexes that affect the filling effect of silicone rubber on circuit board are viscosity and surface dry time of rubber. ...
In this paper, the failure mechanism of sulfide corrosion of a batch of silver electrodes was studied by means of environmental simulation test, scanning electron microscopy (SEM), energy spectrum analysis (EDS), micro-CT, infrared spectroscopy analyzer(FTIR), pyrolysis gas chromatography mass spectrometry (Py-GC-MS) and specific surface area (BET) analysis. The results showed that the H 2 S in the air entered the silver electrode surface through the rubber by the adsorption and permeation effects, and corroded the silver electrode. What’s more, The change of pore size in silicone rubber will affect the H 2 S corrosion reaction. The smaller the pore, the higher the specific surface area and the more polar H 2 S molecules adsorbed by rubber. So the special pore distribution of the size of the intercalation was beneficial to reduce the diffusion resistance of H 2 S molecules in rubber. The above analysis results also provided ideas and direction for the improvement of silicone rubber. The pore distribution of silicone rubber could be controlled by controlling the viscosity and the surface drying time of the glue solution, so as to ensure the filling effect of the silicone rubber and prevent the corrosion failure of the silver electrode.
... On the other hand, the performance of adsorption was explored with deteriorated samples after they are being processed with the help of acid solution to find out the possible routes to recondition the performance of adsorption. [10] In a performance study of adsorption air conditioner using zeolite-water, 8-12 0 C chilled water was obtained from the conditioner to be supplied to the fan coil and where system was driven with a temperature of 350-450 0 C of exhaust gas. The achieved COP and refrigerating power were 0.25 and 5kW. ...
In the current scenario, for majority of the people and industry needs of the globe, cooling processes such as refrigeration as well as air conditioning are important and major requisites. On the other hand, the conventional vapour compression systems require high electrical energy input and employ refrigerants with negative environmental impacts like ozone layer depletion and climate change resulting from the emission of harmful gases such as CO 2 , Hydro fluorocarbons and Chlorofluorocarbons with the usage of conventional refrigerants. The solar energy being a renewable source is one of the key solutions to pollution problems and can be used to drive the adsorption cooling machines. With the heat source temperature of even 50° C which is obtained from the low grade energy like solar energy or waste heat energy is feasible to run the adsorption refrigeration system to reduce the operating cost. In the present work, a single bed adsorption refrigeration system is developed and tested using working pair as silica gel and water. From the experimental results, it was observed that this system can be used as alternative to the conventional vapour compression refrigeration system to produce cooling effect. However, the performance of the adsorption system studied is lower than the vapour compression refrigeration system.
... Amongst all these mentioned adsorbents activated carbon is the best suited option for adsorption of CO 2 , as it has good adsorption qualities such as high BET surface area, better pore size distribution, good surface chemistry, strong affin-ity for CO 2 , hydrophobic nature and good thermal stability ( Saxena et al., 2014, Singh and Kumar, 2016, Lal, 2008, Himeno et al., 2005, Sircar et al., 1996. Previously, many researchers have studied the performances of ADCSs for different adsorbate-adsorbent pairs: (i) Silica gel-water based adsorption cooling systems ( Luo et al., 2006, Saha et al., 2001, Wang et al., 2012, Saha et al., 1995, Lu et al., 2013, (ii) Activated carbon-methanol based cooling systems ( Boubakri, 2003, Anyanwu et al., 2001, Wang et al., 2003, El-Sharkawy et al., 2009 ), (iii) Activated carbon-ammonia based cooling systems ( Tamainot-Telto andCritoph, 1997 , Al Mers et al., 2006 ), (iv) Activated carbon-ethanol based cooling systems , El-Sharkawy et al., 2006, Kyaw et al., 2018, (v) Activated carbon-CO 2 based cooling systems ( Jribi et al., 2008, Jribi et al., 2014, etc. experimentally studied adsorption of CO 2 onto different grades of commercially available Norit activated carbons. A thermodynamic analysis was done taking 80 °C as source temperature, 25 °C as condenser temperature and 15 °C as evaporator temperature. ...
In the present investigation, thermodynamic analysis of four different adsorption cooling cycles; basic, internal heat recovery, mass recovery, and heat & mass recovery cycles are carried out employing CO2 as the refrigerant. The said investigation is done for five different adsorbent materials i.e. a highly microporous activated carbon (Maxsorb III), Maxsorb III based composite, Activated carbon fibre (ACF) A-20, BPL activated carbon (AC), and Norit AC. The study stretches the analysis from subcritical to supercritical zone for evaporator temperature ranging from −5 °C to 15 °C. For subcritical cycle, generator and condenser temperatures are varied between 65 °C to 91 °C and 20 °C to 30 °C, and for transcritical cycle, generator and gas cooler exit temperatures are varied from 90 °C to 120 °C and 35 °C to 40 °C, respectively. The maximum COP and specific cooling effect (SCE) achieved by incorporating both heat and mass recovery to the basic cycle are 0.305 and 105 kJ/kg, respectively. The improvement in COP and 2nd law efficiency of the same cycle w.r.t. other cycles are in the range of 7% to 84% and 38% to 77%, respectively for subcritical cycles. Similarly, for transcritical cycles, improvements in COPs of HMRC are in range of 17% to 75%. Analysis showed better system performance for Maxsorb III and it's composite as compared to other adsorbents. Various regression equations are developed to predict the different intermediate temperatures and COP for the mentioned modified subcritical and transcritical cycles.
... Wang et al. [14] said that the adsorption deterioration must greatly impact the performance of the silica gelwater adsorption refrigeration system. For investigating the adsorption deterioration of silica gel, many different silica gel samples were prepared according to the application surroundings of silica gel in adsorption refrigeration systems. ...
Adsorption refrigeration systems are developed due to the need of replacing the conventional systems which utilizeenvironmentally harmful refrigerants and consume high grade electrical power. Solar adsorption refrigerationdevices are of significance to meet the needs for cooling requirements such as water chiller, air-conditioning, ice-making and medical or food preservation in remote areas. They are also noiseless, non-corrosive and environmentallyfriendly. For adsorption refrigeration there is different refrigeration pair available. In this review paper, we havestudied various research papers on silica gel-water adsorption -refrigeration. From the study, we found that thissystem is compatible with low generation temperature around 70-80°C and chilled water is around 10-20°C. Pressurerange of the system is 1-12 kPa. COP of the adsorption chiller is in range of 0.3-0.5.
... Adsorption heat pump applications in cooling refer to useful cooling [4]; chilled water circuits [5,6]; electric vehicle air conditioners [7]; heat rejection systems, such as dry or wet cooling towers or ground coupled heat exchangers [8]; and solar systems as the driving heat source [9,10]. Heating applications of adsorption heat pumps are found in heating systems, waste heat utilization [3,5], low-temperature heat sources (e.g., ground heat exchangers and geothermal water installations [11]) and driving heat sources (e.g., gas furnace) [12]. ...
The main aim of this paper was to find the correct method of calculating equations of heat and mass transfer for the adsorption process and to calculate it numerically in reasonable time and with proper accuracy. An adsorption heat pump with a silica gel adsorbent and water adsorbate is discussed. We developed a mathematical model of temperature and uptake changes in the adsorber/desorber comprising the set of heat and mass balance partial differential equations (PDEs), together with the initial and boundary conditions and solved it by the numerical method of lines (NMOL). Spatial discretization was performed with equally spaced axial nodes and the PDEs were reduced to a set of ordinary differential equations (ODEs). We focused on the comparison of results obtained when the set of heat and mass balance ODEs for an adsorber was solved using: (1) the Runge–Kutta fixed step size fourth-order method (RKfixed), (2) the Runge–Kutta–Fehlberg 4.5th-order method with a variable step size (RK45), and (3) the Gear Backward Differentiation Formulae numerical (Gear BDF) methods. In our experience, all three types of ODE numerical methods (RKfixed, RK45, and Gear BDF) can be applied in simple models to model an adsorber with attention on their limitations. The Gear BDF method usually requires much fewer steps than the RK45 method for almost the same calculating time. RK methods require many more steps to obtain results, and the calculating time depends on accuracy or defined time step. Moreover, one should pay attention to the number of nodes or possible oscillations.
... Effects of the average radius of the silica gel grain ranging from 0.6 mm to 0.9 mm and of the temperature regeneration ranging from 77°Cto 107°C were studied. Wang et al. [11] showed that a silica gel acts as a key role in adsorption refrigeration systems. It was found out that the silica gel/water adsorption refrigeration system is greatly influenced by the adsorption deterioration. ...
The performance of an 8.0 kW Solar Adsorption Refrigeration System (SARS) under Jordanian climate conditions was evaluated experimentally and theoretically. The solar cooling system under study consists of four subsystems, namely silica gel/water adsorption chiller, solar thermal collector, cooling tower and fan coil unit. The ambient temperature, global solar radiation, relative humidity, wind speed and the temperatures of the solar adsorption system at different locations of experimental setup were measured.
Simulation of the solar adsorption system was carried out using the TRaNsientSYstem Simulation software (TRNSYS). The solar adsorption system is based on adsorption chiller operated by hot water produced by flat plate solar collectors with a total surface area of 41m2.
The obtained results revealed chilling power and thermal COP of 4.5 kW and 0.34, respectively when the average chilled water outlet temperature, cooling water inlet temperature, and hot water inlet temperatures were 16.8 °C, 28.1°C and 80.2 °C, respectively.
... Solid-gas sorption heat powered cycles appear to be an attractive alternative for cooling [16] or air conditioning applications [17]. Cogeneration of fuel cell and sorption air conditioning systems was widely analysed in [18]. ...
In the paper, comparison of an analytical and a numerical model of silica gel/water adsorber/desorber is presented. Adsorber/desorber as a part of the two-bed single-stage adsorption heat pump is discussed. The adsorption heat pump under consideration consists of an evaporator, two adsorber/desorber columns and a condenser. Only heat and mass transfer was taken into account during operation of assumed adsorption heat pump. Adsorption equilibrium was described by the Dubinin-Astachov model. The presented mathematical models, both analytical and numerical, were created to describe the temperature, heat and concentration changes in the adsorber/desorber and consequently to describe the performance of the adsorption heat pump. Heat and mass transfer equations of the model were solved analytically and calculation parameters were entered in the common spreadsheet. The numerical model was established comprising of the set of heat and mass balance partial differential equations, together with the initial and boundary conditions and was solved by the numerical method of lines. The developed analytical model is very basic and can be used only for the initial estimates of mean cyclic temperature of the cooling/heating water in the adsorber/desorber bed. Validation of the numerical model shows reasonable agreement between the numerical and experimental averaged bed temperatures and is an indication of the proper mathematical modeling and the accuracy of the numerical analysis. © 2017, International Centre for Sustainable Development of Energy, Water and Environment Systems SDEWES. All rights reserved.
... Due to the use of solid adsorbents in these systems, they are preferred in fishing boats, locomotives etc. where there are chances of serious vibration and shocks. In these physical adsorption systems, commonly used working pairs are activated carbon-methanol [8][9][10], activated carbon-ethanol [11][12][13], activated carbon-ammonia [14][15][16], silica gel-water [17][18][19], and zeolite-water [20][21][22]. Despite the above advantages, these systems have still some drawbacks, such as low COP, low SCP, large size and high capital cost. ...
With increasing social and economic developmental activities, high grade energy sources are depleting at faster rate and also inviting menace of environmental problems. Therefore, to reduce dependency on high grade energy sources for cooling applications and to protect environment, adsorption cooling systems are promising alternatives that are powered by low grade heat sources like solar heat, industrial/automobile waste heat etc. and also use environment friendly refrigerants. But, these systems have still low performances, large size and high cost. Therefore, in order to overcome these difficulties, many researchers are focussing on different ways to improve heat and mass transfers in the heat exchangers of the system to enhance its performance. These strategies include the use of advanced adsorbent material and advanced adsorption cycles, design improvement in heat exchangers and development of mathematical models for optimization of design/operating parameters of the cooling systems. In this paper, various mathematical models for adsorption systems are presented that include thermodynamic models, lumped parameters models; and heat and mass transfer models. These models include equations governing the heat and mass transfer in the main components of the cooling systems. The advantages of this method are that it can produce large volumes of results at no more cost and it is very cheap to perform parametric studies, for instance, to optimize equipment performance. The various numerical methods and experimental validations have been also presented and discussed.
... Blue Silica-gel can be easily regenerated at a temperature below 85 °C, at higher vacuum pressures, and easily available in the market. The capacity of adsorption of silica-gel granules can be easily restored by soaking it in the acidic solution followed by washing with distilled water [11]. Water is non-inflammable and non-toxic as well. ...
A working model of a double-bed Adsorption
refrigeration system using Silica-gel as Adsorbent and Water as
an eco-friendly Adsorbate is developed for the application of
vehicle air conditioning. This system is designed for 1 TR cooling
capacity which is most suitable for hatchback vehicles. Here, Hot
water in the temperature range of 45 to 60°C is used as a hot source
while water at atmospheric temperature and pressure is used as a
cold source. A chilled water is obtained as the output from the
system which would be the input for the Air-handling unit.
Adsorber bed heat exchangers used in the system acts as a
compressor. It consists of Mass Transfer Channel (MTC), an
integrated structure which is made up of coiled Copper tubes and
an array of rectangular shaped aluminium fins to increase heat
and mass transfer rates. Silica-gel is mixed with Copper chips in
1:10 proportion and filled compactly around the copper tubes to
reduce thermal resistance. Metallic net is wrapped around the
MTC to hold the contents and enclosed in a leak-proof outer
casing. The system is analyzed through series of experiments
against different operating conditions to obtain the performance
parameters as, Specific Cooling Power (SCP) and Coefficient of
Performance (COP). Adsorber bed to Adsorbent Mass Ratio
(AAMR) is calculated to analyze the fabrication of Adsorber bed
heat exchanger. A sophisticated and well-understood method is
adopted here to minimize the errors in experimentation. Effects of
operating conditions on the performance parameters are analyzed
and presented with the help of graphical tools to understand the
overall working of the system.
... Wang et al. [12] verified adsorption deterioration of silica-gel/Water pair in ADCS. From experimental results, it has been concluded that the water uptake capacity of silica-gel decreases around 45%, when Solid particulates blocks the micropores present in silica-gel. ...
Adsorption cooling technology gained attention of researchers as soon as Montreal protocols adopted in 1987 and Kyoto protocols in 1997. Adsorption refrigeration system do not increase global warming as well as it has zero Ozone depletion potential. The interesting thing about this system is that; it can be powered by low grade energy and uses natural refrigerant. In this way, no protocols could be violated. This 'Green technology' evolved as an emerging technology in various applications involving air conditioning. This technology is the best suitable option for existing harmful cooling technologies. This cooling system works on the Adsorption principle. Compressor of vapour compression refrigeration system is replaced by adsorber bed. Adsorber bed is filled with adsorbents which has micro-pores on the surface. Refrigerant molecules; well known as Adsorbate, adheres to adsorbents. The design of adsorber bed heat exchangers needs to be taken care of in such a way that, the heat and mass transfer rate should be as high as possible. This paper presents a review of different types of adsorber bed, variety of adsorbents and the adsorbate. This paper focuses on the selection of adsorbents and adsorbate pair according to temperature of hot and cold source, further advancements required to be done in future to make the technology compatible with the present technologies to achieve an objective of pollution free cooling technology.
... In recent years, reports with respect to the operating effect on the silica gel system [9,10], or to the effect as a metal component was added [11], were openly published. Wang et al. reported that the adsorption chiller of silica gel-water could experience the COP deterioration after 1 year's performance [12,13]. On the other hand, the property of the silica gel was possible to be improved by doping it with the alumina [14] or the lithium chloride [15]. ...
In this work, the macro adsorption characteristic of water vapor by the allochroic silica gel and the zeolite 5A and ZSM-5 were investigated experimentally. BET analysis method presented the difference of the porosity, the micro pore volume, and the specific surface area of the material. The dynamic and the equilibrium characteristics of the sample were measured thermo-gravimetrically in the moist air. In general, the ZSM-5 zeolite showed an inferior feature of the adsorption speed and the equilibrium concentration to the others. By comparison to the result of SAPO-34 zeolite in the open literature, the 5A zeolite showed some superiorities of the adsorption. The equilibrium concentration of the ZSM-5 zeolite was higher than that of the SAPO-34 calcined in the nitrogen, whereas it was lower than that calcined in the air. The adsorption isotherm was correlated and the relation of the isotherm to the microstructure of the material was discussed. With more mesopore volume involved, the zeolite presented an S-shaped isotherm in contrast to the exponential isotherm of the silica gel. In addition, the significance of the S-shaped isotherm for the application in adsorption heat pump has also been addressed.
Adsorption refrigerators can prove to be a viable alternative to compression refrigerators. Producing cooling water using this unit decreases reliance on traditional electric-driven cooling systems, which contribute to global warming and ozone layer depletion while also consuming a lot of energy. Solar adsorption cooling systems are environmentally friendly and do not deplete the ozone layer. The activated carbon granules were used as an adsorbent, and ethanol was used as an adsorbate in the current study. Many studies on adsorption cooling systems have been conducted on numerical simulation, operation strategy, and system performance at various regeneration temperatures. Many further experiments on adsorption cooling systems have been carried out using a variety of adsorbent materials such as silica gel, zeolite, and others. Water, ammonia, and methanol are perfect adsorbates for adsorption cooling systems. Water cannot be used for the applications below 0 °C, whereas ammonia is highly toxic. Methanol is highly toxic and inflammable, and it also has the dissociation problem above 120 °C in the presence of copper. Therefore, an environment-friendly refrigerant with better adsorption/desorption characteristics needs to be explored in detail. After going through the various journal and research paper, we found carbon-ethanol pair is most suitable for adsorption cooling system because ethanol having low freezing point, non-toxic, and zero ozone-depletion potential is considered to be a better choice for solar-adsorption cooling systems, and also, they are easily available. In this paper, our motive is to provide solution to the low performance of adsorption cooling systems.KeywordsAdsorptionEnergy savingCarbon ethanolSolar energyAdsorption cooling
Advances in Phytochemistry, Textile and Renewable Energy Research for Industrial Growth
Advances in Phyto Chemistry, Textiles, Renewable energy and Industrial Growth
Proceedings of the International Conference of Phytochemistry, Textile and Renewable Energy for Sustainable development (ICPTRE 2020), August 12-14, Eldoret, Kenya
Solid waste management is among the environmental challenges facing many industries in the world today. Biogas production is one of the most cost-efficient renewable energy technologies that use biodegradable wastes as feedstock. Furthermore, it is one of the methods for reducing greenhouse gas emission. Cotton Yarn Wastes (CYW) is among the biodegradable wastes that are commonly managed by dumping onto the open land or disposing in sanitary landfills where they undergo anaerobic decomposition. However, CYW could be used as substrate to generate energy in the form of biogas that can be utilized in other activities like powering textiles production. The aim of this study was to investigate the use of CYW as a substrate for biogas production using anaerobic batch reactor. The experiment was carried out in reactors of two-liter capacity. The CYW and inoculum were characterized before and after digestion. The CYW contained 93.18% total solids, 82.48% total volatile solids and 6.82% moisture content while the respective values for digested sludge were 21.61%, 23.61% and 78.38%, respectively. The carbon to nitrogen (C/N) ratio of inoculum was 20.5, which is in the suitable range to keep the anaerobic digestion in a stable condition. However, the CYW had high carbon content; resulting in a C/N ratio of 42.5. The effect of TS concentration at different ratios of CYW on biogas volume produced was investigated. The reactors loading was differentiated using a mixture with concentration corresponding to R1 (1:1), R2 (1:1.5), R3 (1:2), R4 (1:2.5), R5 (1:3), R6 (1:3.5), R7 (1:4), R8 (1:5), R9 (1:6), and R10 (1:10) on TS content basis i.e. 50%, 40%, 33%, 28%, 25%, 22%, 20%, 18%, 14%, and 10% respectively. The total biogas yield was 6307 mL, 6519 mL, 6711 mL, 7178 mL, 4878 mL, 3868 mL, 3720 mL, 3306 mL, 1164 mL, and 932 mL respectively after 36 days. The results indicated that biogas production increased with increase in TS content. The ratio that provided 28% of TS content had the highest biogas yield. The average reduced TVS at the end of digestion was 88.49%. The results of this test indicated that CYW is a suitable substrate for AD due to its high biodegradability. Therefore, the reactors should run at 28% TS, for maximum biogas generation.
Sorption heat storage systems are gaining more and more research attention due to the efficient heat supply for building space heating and domestic hot water. These systems are promising technologies for the utilization of low-temperature energy sources, such as solar energy, waste industrial heat, and the transport sector. Open sorption systems have a simple structural design, high energy density of the system, controlled heat transfer. Therefore, the basic principles of open sorption systems and the operating cycle are described in this chapter. The sorption materials used for sorption heat storage systems are briefly overviewed. Finally, this article provides the heat storage system design and existing prototypes.
Adsorption refrigeration technology is being increasingly investigated over the past few decades as a sustainable technology option for meeting the fast-growing cooling needs for refrigeration and air-conditioning. What is attractive about adsorption technology is the opportunity to use low grade thermal energy such as solar heat and industrial waste heat. The present study is an attempt to provide readers a comprehensive update on status and challenges of adsorption refrigeration. The effects of working parameters like evaporator temperature, condenser temperature, regeneration temperature, cycle time, and inter-stage pressure on coefficient of performance and specific cooling power are covered with an objective to include experimental as well as theoretical research work reported thus far. Research work consolidated in this study includes the integrated cycles of adsorption cooling, adsorber design with extended surfaces, multi-stage and/or multi-bed scheme, and heat and/or mass recovery scheme either in combination or individually for thermal performance enhancement. Furthermore, work on a state of the art of various commercially available adsorption chillers highlighting their cooling capacity, working temperature range, novelties, and applications are reported in detail. This review also reveals an opportunity for research in optimizing the mechanism, design, orientation of the heat exchangers, functioning, and customizing the vapour adsorption refrigeration system for widespread applications in various sectors like automobiles and agriculture. Authors present this study with an expectation to provide beginners a quick review in the area of adsorption cooling technology.
As an effective way to improve the performance of heat and mass transfer, Composite adsorbent used in adsorption refrigeration has attracted increasing research attention. The aim of the research is to reveal composite theory of silica gel composite adsorbent and to understand adsorption refrigeration system mechanism running by above composite adsorbent. Coarse porous silica gel with different particle diameters was selected as the matrix of composite adsorbent and calcium chloride was selected as additive. The results showed that composite adsorbent's thermal conductivity and adsorption capacity increased significantly compared with pure silica gel. The thermal conductivity could be increased by 58.2%, and the adsorption capacity could be increased by 4-10 times. Finally, the adsorption refrigeration system using silica gel-calcium chloride composite adsorbent was studied. A two-bed adsorption refrigeration cycle running by above composite adsorbent was adopted. The experimental results the optimal values of system cooling capacity and COP were not at the same time. The system cooling capacity reached its maximum at 1500s and the system COP reached its maximum at 1200s. The best heat recovery time was 20s. The SCP of the system was up to 288.1W kg⁻¹, which could reduce the volume of the adsorption refrigeration system effectively.
In the current scenario, for all human beings and industry needs in the world, cooling processes such as refrigeration as well as air conditioning are essential and major requisites. On the other hand, the conventional vapour compression systems require high electrical energy input and employ refrigerants with negative environmental impacts like ozone layer depletion and global warming caused by the emission of harmful gases such as carbon dioxide, Hydro fluorocarbons and Chlorofluorocarbons with the usage of conventional refrigerants. The solar energy being a renewable source is one of the key solutions to pollution problems and can be used to drive the adsorption cooling machines. With the heat source temperature of even 50° C which is obtained from the low grade energy like solar energy or waste heat energy is feasible to drive the adsorption refrigeration system to reduce the operating cost. In the present work, a literature review was undertaken to find out the performance of single and multi bed adsorption cooling system using the suitable adsorbent-adsorbate pair reported in the literature review which can be operated successfully to produce the cooling effect using low grade heat energy.
As a technology of the green energy utilization, solar adsorption cooling is a promising way to make use of the solar energy in the future. Aiming to the efficiency improvement of such kind system, the performance of the solar adsorption cooling system that employed the silica gel-water as the working pair was evaluated experimentally. With a mono-axial solar collector of tracking parabolic trough to provide the heat supply to the adsorption bed, the effect of the adsorption time on the system performance was mainly addressed in the study. The experimental results revealed that the performance of the system reached the maximum as the adsorption time was 45 min. Correspondingly, the coefficient of performance of the system reached 0.258. In addition, a comparison of the optimal performance of the silica gel system to the SAPO-34 zeolite system was conducted. It was revealed that both the cooling capacity and the performance coefficient of the silica gel system depended more strongly on the adsorption time than those of the SAPO-34 zeolite system did. At the optimal adsorption time, the coefficient of performance of the silica gel system was 1.93 times as that of the SAPO-34 zeolite system. In general, the silica gel-water pair has shown better performance as compared to the SAPO-34 zeolite-water pair as used in the solar adsorption cooling system.
Solid waste management is among the environmental challenges facing many industries in the world today. Biogas production is one of the most cost-efficient renewable energy technologies that use biodegradable wastes as feedstock. Furthermore, it is one of the methods for reducing greenhouse gas emission (GHG). Cotton Yarn Wastes (CYW) is among the biodegradable wastes that are commonly managed by dumping onto the open land or disposing in sanitary landfills where they undergo anaerobic composition. However, CYW could be used as substrate to generate energy in the form of biogas that can be utilized in other activities like powering textiles production. The aim of this study was to investigate the use of sized CYW as a substrate for biogas production. The experiment was carried out in reactors of two liter capacity. The substrates were characterized before and after digestion. Proximate analysis before digestion showed that total solids (TS), total volatile solids (TVS) and moisture content (MC) were 93.18%, 82.48%, and 6.82% respectively. Analysis of digested sludges showed that TS solids, TVS and MC were 21.61%, 23.61% and 78.38% respectively. The carbon to nitrogen (C/N) ratio of inoculum was 20.5, which is in the suitable range to keep the anaerobic digestion in a stable condition. However, the sized CYW had high carbon content; resulting in a C/N ratio of 42.5. The effect of TS concentration at different ratios of sized CYW on biogas volume produced was investigated. The reactors loading was differentiated using a mixture with concentration corresponding to R1 (1:1), R2 (1:1.5), R3 (1:2), R4 (1:2.5), R5 (1:3), R6 (1:3.5), R7 (1:4), R8 (1:5), R9 (1:6) and R10 (1:10) on TS content basis i.e 50%, 40%, 33%, 28%, 25%, 22%, 20%, 18%, 14% and 10% of solid content respectively. The biogas produced was measured on daily basis using the water displacement method. The average biogas productions were 6307, 6519, 6711, 7178, 4878, 3868, 3720, 3306, 1164 and 932 ml respectively after 36 days of digestion. The results indicated that biogas production increased with increase in TS content. The ratio that provided 28% of TS content had the highest biogas yield. The average reduced TVS at the end of digestion was 88.49%. The results of this test indicated that sized CYW is a suitable substrate for AD due to its high biodegradability. Therefore, the reactors should run at 28% TS, for maximum biogas generation.
Key words: RIVATEX, total solids, textile waste, anaerobic digestion, moisture content.
To reduce combustion harmful emissions such as CH 4 , CO 2 and NO, low calorific renewable biofuels are found to be the best candidate. Combustion of biofuels gives a weak unstable flame which can be enhanced by hydrogen addition. The latter can also be obtained from a renewable source like syngas. In this context the mixture biogas-syngas is studied to overcome combustion emissions issues. A two-dimensional numerical procedure has been used to investigate the opposed jet turbulent flame structure of biogas-syngas mixture. The standard k-ε model is adopted for turbulence modeling and the Steady Laminar Flammelettes Model (SLFM) to handle turbulent combustion. The combustion kinetics is modeled by the detailed Glarborg's N-mechanism. Equimolar biogas-syngas mixture is considered, namely: biogas 0.25CH 4 + 0.25CO 2 and syngas 0.25H 2 + 0.25CO. Injection velocity is equal for both jets and it is varied from 3 to 12 m/sec. It has been noticed that when injection velocity increases, the flow residence time and non-equilibrium effects are enhanced. This improves incomplete reaction species production and reduces final combustion products volume, temperature and NO species emission. As a summary, the NO emission can be avoided by using important injection velocities.
Renewable energy helps to mitigate the tension between the energy demands and public concerns on environmental pollution (Al-Badi and Albadi 2012).
This paper presents the first attempt to investigate of natural zeolite for cooling adsorption application. Representative samples were collected from Bayah-Banten, Indonesia. As known that zeolites can be used as an adsorbent. Unfortunately, natural zeolite has many limitation, among them contains a lot of impurities. To improve the characteristic of natural zeolite, activation and modification should be conducted beforehand. Activation was conducted by reducing grain size (1-2mm), washed by aquadest and heated using microwave. While the chemical activation is done through acidification by adding HCl solution. Finally, the activated natural zeolite was calcined gradually initiated at room temperature to 150°C for 2 hours and then heating continued from 150°C to 300°C for 4 hours. The final zeolite activated product was characterized by X-Ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) and Transmission Electron Microscopy (TEM). The result showed that the morphology of the natural zeolte was cubic shave as observed by TEM and the surface area of activated natural zeolite is geater than the raw material.
Sorption is used for absorption/adsorption heat pumps (sorption refrigeration) and sorption for thermal energy storage (TES). This paper is the first review where the research on both applications is shown together. Sorption has advanced very much due to the immense amount of research carried out around heat pumping and solar refrigeration. Moreover, sorption and thermochemical heat storage attracted considerable attention recently since this technology offers various opportunities in the design of renewable and sustainable energy systems. The paper presents the operation principle of the technology and the materials used or in research are listed and compared. Absorption heat pumping and refrigeration research is today more focussed in the decrease of unit costs and increase of energy efficiency, adsorption is focussed in finding more efficient working pairs, and storage is testing the first prototypes and designing new ones with different or enhanced storage materials and new reactor concepts to optimize energy output.
The urgency to look for promising sustainable alternatives to the conventional vapour compression technique for cooling applications has been strong. As the result, the gas-solid adsorption system has been considered as one of the alternatives to generate cooling effect. This paper reviews the development of this adsorption cooling technique in three different aspects: mathematical modelling, intrinsic, and extrinsic developments, in order to present an overview of this field from basic mathematical representations and designs to current research trends as well as innovative applications and configurations. Various adsorption equilibria, diffusion models, kinetics, and system modelling are reviewed. On the other hand, the roles of both the heat exchanger design parameters and the adsorbent materials are discussed followed by the different bed configurations and schemes. The impact of various operating parameters on the system performance is also covered.
This paper presents experimental data on methanol sorption on new composite sorbents which consist of mesoporous silica gels
and calcium chloride confined to their pores. Sorption isobars and XRD analysis showed the formation of a solid crystalline
solvate CaCl2⋅2MeOH at low methanol uptake, while at higher uptake the formation of the CaCl2–methanol solution occurred. The solution confined to the silica pores showed the sorption properties similar to those of
the CaCl2–methanol bulk solution. Calorimetric and isosteric analyses showed that the heat of methanol sorption depends on the methanol
uptake, ranging from 38±2 kJ/mol for the solution to 81±4 kJ/mol for the solid crystalline phase CaCl2⋅2MeOH. The above mentioned characterizations allowed the evaluation of the methanol sorption and the energy storage capacities,
clearly showing that the optimal applications of these new composite sorbents are the methanol removal from gaseous mixtures,
heat storage and sorption cooling driven by low temperature heat.
In this paper, a novel composite water sorbent “silica modified by calcium nitrate” (SWS-8L) has been tested for utilization in adsorption chillers driven by low-temperature heat. The isosteric diagram of the working pair under investigation has been calculated from experimental adsorption data measured at equilibrium. The equivalent specific heat of the sorbent as a function of the water loading was experimentally measured by a calorimetric technique. Thermodynamic cooling COP was estimated to be 0.51–0.71, with desorption temperature lower than 90°C. Real performance was measured by testing a SWS-8L based sorbent bed in a lab-scale adsorption chiller. With this aim, SWS-8L grains were embedded inside a compact aluminium heat exchanger with high thermal efficiency. Experimental cooling COP, mass specific cooling power SCP and volumetric specific cooling power VSCP obtained are 0.18–0.31 (cycle time 10min), 190–389W/kg dry sorbent and 104–212W/dm3, respectively.
This paper presents the achievements gained in solid sorption refrigeration prototypes since the end of the l970s, when interest in sorption systems was renewed. The applications included are ice making and air conditioning. The latter includes not only cooling and heating, but also dehumidification by desiccant systems. The prototypes presented were designed to use waste heat or solar energy as the main heat source. The waste heat could be from diesel engines or from power plants, in combined cooling, heating and power systems (CCHP). The current technology of adsorption solar-powered icemakers allows a daily ice production of between 4 and 7 kg m−2 of solar collector, with a solar coefficient of performance (COP) between 0.10 and 0.16. The silica gel–water chillers studied can be powered by hot water warmer than 55 °C. The COP is usually around 0.2–0.6, and in some commercially produced machines, it can be up to 0.7. The utilization of such chillers in CCHP systems, hospitals, buildings and grain depots are discussed. Despite their advantages, solid sorption systems still present some drawbacks such as low specific cooling power (SCP) and COP. Thus, some techniques to overcome these problems are also contemplated, together with the perspectives for their broad commercialisation. Among these techniques, a special attention was devoted to innovative adsorbent materials, to advanced cycles and to heat pipes, which are suitable devices not only to improve the heat transfer but also can help to avoid corrosion in the adsorbers. Recent experiments performed by the research group of the authors with machines that employ composite adsorbent material and heat pipes showed that it is possible to achieve a SCP of 770 W kg−1 of salt and COP of 0.39 at evaporation temperatures of −20 °C and generation temperature of 115 °C.
This paper is the second part of a study on the use of adsorption refrigeration cycles driven by waste heat of near-ambient temperature. Experiments were conducted with several heat transfer fluid operating temperatures (hot, cooling, and chilled water), flow rates, and adsorption-desorption cycle times, and good qualitative agreement was obtained with the simulated results. Both experiments and simulation showed that the silica gel-water adsorption cycle is well suited to near-environmental-temperature heat sources and small regenerating temperature lifts, which help reduce the heat losses intrinsic to batched cycle operation. The chiller was operational with a hot water inlet temperature (Thot in) of 50°C (122°F), and the highest experimental values of the coefficient of performance (COP) (more than 0.4) were obtained with Thot in = 50°C (122°F) in combination with cooling water at 20°C (68°F).
Adsorption refrigeration systems are commercially developed due to the need of replacing the conventional systems which utilise environmentally harmful refrigerants and consume high grade electrical power. This paper presents the key equations necessary for developing a novel empirical lumped analytical simulation model for commercial 450 kW two-bed silica gel/water adsorption chiller incorporating mass and heat recovery schemes. The adsorption chiller governing equations were solved using MATLAB (R) platform integrated with REFPROP (R) to determine the working fluids thermo-physical properties. The simulation model predicted the chiller performance within acceptable tolerance and hence it was used as an evaluation and optimisation tool. The simulation model was used for investigating the effect of changing fin spacing on chiller performance where changing fin spacing from its design value to minimum permissible value increased chiller cooling capacity by 3.0% but decreased the COP by 2.3%. Furthermore, the effect of generation temperature lift on chiller performance and the feasibility of using it as a load control tool will be discussed. Genetic Algorithm optimisation tool was used to determine the optimum cycle time corresponding to maximum cooling capacity, where using the new cycle time increased the chiller cooling capacity by 8.3%.
A new composite adsorbent SiO2·xH2O·yCaCl2 which is composed of macro-porous silica gel and calcium chloride is introduced. In order to analyze its adsorption theory, adsorption and desorption isotherms, BET surface areas, pore volumes and average pore diameters of macro-porous silica gel and four composite adsorbent samples with different CaCl2 content are measured using SEM and Asap2010 apparatus. From the adsorption isotherms, desorption isotherms and lag loops, it can be deduced that the main pore structure in macro-porous silica gel and the new composite adsorbent have two shapes: taper with one top open and taper or hyperbolic taper with both ends open. Based on the analysis of pore diameter distribution and lag loop, a sketch map showing calcium chloride filled in pore of macro-porous silica gel is presented. The adsorption isotherms at 25°C are measured. Experimental results show that the new composite adsorbent can adsorb more water than common adsorbents (macro-porous silica gel, micro-porous silica gel and synthetic zeolite 13X). In the light of the results of pore structure, adsorption isotherms and lyolysis phenomenon are analyzed.
Desiccant coated heat exchanger (DCHE) system can handle latent and sensible load simultaneously by removing the released adsorption heat in dehumidification process. The system can also be driven by low grade thermal energy such as solar energy. In this paper, a dynamic one-dimensional mathematical model validated by experimental data is established to predict the performance of DCHE system, using conventional silica gel as desiccant material. Cooling performance of DCHE system is calculated under ARI (American Air-conditioning and Refrigeration Institute) summer and humid conditions. Simulated results show that the operation time in dehumidification process is a crucial factor for cooling capacity of DCHE system, which can be enhanced by eliminating the initial period with higher outlet air temperature, the largest cooling power of DCHE system increase from 2.6kW to 3.5kW by eliminating first 50s of operation time under ARI summer condition. The results also prove that the system can provide cooling power to indoor condition with selective operation time when regeneration temperature varies from 50°C to 80°C. Besides, the model is adopted to analyze the effects of some structural parameters on system performance under simulated condition. The system performs well in smaller cobber tube external diameter condition, while both transient heat and mass transfer capacity can be enhanced under the condition of smaller distance between the fins.
A measurement of moisture uptake curves in silica gel–calcium composite adsorbents is performed by using the thermal gravimetrical method in a relative vapor pressure range from 0.5 to 0.9 at different temperature levels of 25, 35 and 45°C, respectively. Also, dynamic adsorption curves individually corresponding to the temperature and relative pressure conditions of (25°C, 0.7), (35°C, 0.7) and (35°C, 0.5) have been measured. This experimental study shows that the sorption rate is highest for non-impregnated macroporous silica gel; however, the same silica gel impregnated with calcium chloride has a much greater final water loading. This confirms that composite adsorbents result in a better adsorption performance compared with non-impregnated silica gel, leading to a trade off in finalizing the content of CaCl2 in the composite. Through theoretical analysis on the experimental data, it is found that the saturated adsorption data can be well fitted by the FHH model and the dynamic adsorption data well fitted by the Crank diffusion model, simultaneously yielding the effective solid side mass diffusivities. A comparison with these obtained diffusion coefficients further supports that the mass diffusivity in the composite adsorbent also increases with an increase in temperature, as well as in humidity, but drastically decreases due to the presence of salt inside the matrix pores compared with the non-impregnated host matrix.
A novel silica gel–water adsorption chiller with two chambers has been built in Shanghai Jiao Tong University (SJTU). This chiller combines two single bed systems (basic system) without any vacuum valves. One adsorber, one condenser and one evaporator are housed in the same chamber to constitute one adsorption/desorption unit. In this work, the chiller is developed and improved. The improved chiller is composed of three vacuum chambers: two adsorption/desorption vacuum chambers (the same structure as the former chiller) and one heat pipe working vacuum chamber. The evaporators of these two adsorption/desorption units are combined by a heat pipe. So, no valves are installed in the chilled water sub system and one vacuum valve connects the two adsorption/desorption chambers together to improve its performance. The performance of the chiller is tested. As the results, the refrigerating capacity and the COP of the chiller are, respectively, 8.69kW and 0.388 for the heat source temperature of 82.5°C, the cooling water temperature of 30.4°C and the chilled water outlet temperature of 11.9°C. For a chilled water outlet temperature of 16.5°C, the COP reaches 0.432, while the refrigerating capacity is near 11kW. There is an improvement of at least 12% for the COP compared with the former chillers.
Experimental comparison between two honeycombed desiccant wheels, namely, a conventional one treated with silica gel and a new one fabricated with a new kind of composite desiccant material, was made in this paper. It is found that the newly developed composite desiccant wheel performs better than the conventional one and can remove more moisture from air by approximately 50%. Also encouraging is that the new desiccant wheel can be driven by a lower regeneration temperature for acquiring the same amount of moisture removal. The reason is that the composite desiccant materials, which are constructed with LiCl and silica gel solutions in an optimal way, behave better than silica gel in moisture adsorption, according to the findings from the scanning electron microscope (SEM) pictures as well as the equilibrium adsorption test results. Some parameters, such as inlet air humidity, regeneration temperature, air mass flow rate, etc., which may affect the performance of the desiccant wheels, are also analyzed and discussed. It is further identified that the new composite desiccant wheel has potential for dehumidification applications in many fields.
Regeneration of dehumidizers (a typical drying process) is the most important stage in the working cycle of desiccant system. Ultrasonic technology, as a non-heating method, can enhance drying kinetics and improve energy utilization efficiency in the drying process. This work has made an investigation on five different drying models, i.e., the Lewis, the Henderson & Pabis, the Logarithmic, the Weibull and the Gaussian model, that quantify the drying kinetics of silica gel during the regeneration by hot air combined with power ultrasonic according to the experimental data. The experiments were performed under different drying air temperatures (i.e. 45 °C, 55 °C, 65 °C and 75 °C) plus power ultrasonic with three kinds of frequencies (i.e. 21 kHz, 26 kHz and 38 kHz) and three power levels (20 W, 40 W and 60 W). The models were identified by fitting the experimental data with Matlab’s curve fitting tool, and the suitability of these models for predicting the moisture ratio evolution in silica gel during the regeneration was evaluated by the percent error (PE, %). The results showed that the Gaussian and the Weibull model were much more accurate than the other ones in describing the drying kinetics of silica gel assisted by the power ultrasonic. The parameter, β, in the Weibull model, which is like the drying rate constant (K) in the semi-theoretical models (e.g., the Lewis, the Henderson & Pabis and the Logarithmic model), can be found to have a regular relation with the drying temperatures, and hence, will be more convenient for modeling.Highlights► We examine five models for the silica gel regeneration assisted by ultrasonic. ► The Gaussian and the Weibull model are superior to the others for the modeling. ► The Weibull model is recommended for its parameters can be identified more easily. ► The validity of the model depends greatly on that of the equilibrium moisture content.
A low-grade waste heat driven solid/vapour adsorption chiller has been successfully designed and tested. A simple model was developed to aid the design and predict the performances. The system comprised two identical sorption reactors operating out of phase in order to ensure continuous cold production. One sorption reactor consisted of six commercially available automotive plate/fin heat exchangers in which silica gel grains were accommodated between the fins. The system was tested as to the power delivered at 12 °C and the power density. The average cooling power was 3.6 kW. This is only 72% of the design value and can be largely attributed to the lower heat transfer fluid flow rate through the sorbent reactor. The thermal efficiency, COP, was 0.62 and the power density was 17 kW/m3 for the system as a whole. Higher power densities are possible. At present, the adsorption chiller is integrated in a prototype trigeneration system, which is tested at CRF’s Eco-building in Turin.
A compact silica gel-water adsorption chiller without vacuum valves was manufactured and experimentally studied. This chiller contains two adsorption/desorption chambers and one chilled water tank. Each adsorption/desorption chamber consists of one adsorber, one condenser and one evaporator. The chilled water tank is adopted to mitigate the variation of the chilled water outlet temperature. A mass recovery-like process, which is a heat recovery process between the two evaporators, was carried out in this chiller. A novel heat recovery process was also fulfilled after the mass recovery-like process to improve the coefficient of performance (COP). The cooling power and COP were 9.60 kW and 0.49 respectively when the average hot water inlet temperature, cooling water inlet temperature, and chilled water outlet temperature were 82.0, 31.6 and 12.3 °C, respectively.
A novel micro CCHP system, which is based on a two bed silica gel–water adsorption chiller, is constructed in this work. To reveal the chiller characteristic in this system, a transient model of the adsorption chiller is developed. According to the comparison of the simulated results and experimental data, the presented model shows a good performance in predicting the chiller performance, with both stable and variable heat source temperature. With the analysis of simulated results, it is found that the cooling capacity and the coefficient of performance (COP) of the chiller are influenced significantly by the average value and variation rate of electric load, as well as the average value of cooling load. The water tank also shows a great effect on the chiller performance. To get better performance of the chiller, the water tank should be adopted when the electric load is low or its variation rate is positive, and should not be utilized when the electric load is high or its variation rate is negative. A 500 L water tank is recommended in order to get better performance and acceptable start-up time. Furthermore, to get better performance as well as higher security, a cold accumulator should be adopted.
Different adsorbents, such as physical, chemical and composite adsorbents are analyzed. Three types of working pairs, activated carbon–methanol, chemical adsorbent-ammonia and composite adsorbent-ammonia can be used for adsorption ice makers on fishing boats. The advantages, disadvantages and performances of three types of adsorption ice makers, with activated carbon–methanol, CaCl2–NH3 and compound adsorbent (made by CaCl2 and activated carbon)-NH3 as adsorption pairs, are compared at the condition of two bed systems. The activated carbon–methanol ice maker shows the advantage of reliable safety, and the composite adsorption ice maker shows the best adsorption performance. The cooling power of 20.32 kW can be obtained from the composite adsorption ice maker when the volume for each adsorber is 0.288 m3, which is about 10 times that of the physical adsorption ice maker and 1.38 times that of the chemical adsorption ice maker.
This study aims at improving the performance of thermally activated silica gel–water adsorption refrigeration cycle by applying multi-bed scheme. In this paper, a three-bed non-regenerative silica gel–water adsorption chiller design is outlined along with the performance evaluation of the innovative chiller. The three-bed chiller will be able to work as high efficient single-stage adsorption chiller where driving source temperature is between 60 and 95 °C along with a coolant at 30 °C. The three-bed cycle comprises with three adsorber/desorber heat exchangers, one evaporator and one condenser. Waste heat or renewable energy sources will power the high temperature desorber. If two beds are in desorption mode, the hot water outlet from the lead desorber will drive the lag desorber before being released to ambient. This facilitates the maximum utilization of the waste stream. On the contrary, if two adsorber or desorber beds are in adsorption mode, the cooling water outlet from the lead adsorber will cool down the lag adsorber. In this circumstance, two adsorber beds will be connected with the evaporator and will enhance evaporation.A cycle simulation computer program is developed to analyze the influence of operating temperatures (hot and cooling water temperatures, adsorption/desorption cycle time) on cooling capacity and coefficient of performance (COP) of the innovative three-bed cycle in parallel flow configuration of the heat transfer fluids. The cycle simulation calculation indicates that the COP value of the three-bed chiller is 0.38 with a driving source temperature at 80 °C in combination with coolant inlet and chilled water inlet temperatures at 30 and 14 °C, respectively. The delivered chilled water temperature is about 6 °C with this operation condition. Simulation results also show that from the two to three beds, waste heat recovery efficiency, η is boosted by about 35%.
As one kind of environmentally friendly refrigeration, the adsorption refrigeration has attracted many attentions in resent decades. This paper introduces the researches of adsorption refrigeration systems with the commonly used working pairs, advanced adsorption cycles, heat and mass transfer enhancement and attempts of adsorption refrigeration applications. Poor heat and mass transfer problem is a bottleneck to prevent the improvements of the adsorption refrigeration technique. Two ways to enhance the heat and mass transfer are discussed in this paper. The adsorption deterioration of adsorbent, another obstacle to physical adsorption refrigeration applications, is also pointed out. And the possible reasons and the possible methods are analyzed.
Shanghai is characteristic of subtropical monsoonal climate with the mean annual temperature of 17.6 °C, and receives annual total radiation above 4470 MJ/m2 with approximately 2000 h of sunshine. A solar energy system capable of heating, cooling, natural ventilation and hot water supply has been built in Shanghai Research Institute of Building Science. The system mainly contains 150 m2 solar collector arrays, two adsorption chillers, floor radiation heating pipes, finned tube heat exchangers and a hot water storage tank of 2.5 m3 in volume. It is used for heating in winter, cooling in summer, natural ventilation in spring and autumn, hot water supply in all the year for 460 m2 building area. The whole system is controlled by an industrial control computer and operates automatically. Under typical weather condition of Shanghai, it is found that the average heating capacity is up to 25.04 kW in winter, the average refrigerating output reaches 15.31 kW in summer and the solar-enhanced natural ventilation air flow rate doubles in transitional seasons. The experimental investigation validated the practical effective operation of the adsorption cooling-based air-conditioning system. After 1-year operation, it is confirmed that the solar system contributes 70% total energy of the involved space for the weather conditions of Shanghai.
The prototype of a novel silica gel–water adsorption chiller is built and its performance is tested in detail. The experimental results show that the refrigerating capacity (RC) and COP of the chiller are 7.15 and 0.38 kW, respectively, when the hot water temperature is 84.8 °C, the cooling water temperature is 30.6 °C, and the chilled water outlet temperature is 11.7 °C. The RC will reach 6 kW under the condition of 65 °C hot water temperature, 30.5 °C cooling water temperature and 17.6 °C chilled water temperature. The results confirm that this kind of adsorption chiller is an effective refrigerating machine though its performance is not as fine as the prediction results. Also it is well effectively driven by a low-grade heat source. Therefore, its applications to the low-grade heat source are much attractive.
Adsorption technology
- S Kondou
- H Ishikawa
- Abe
Kondou S, Ishikawa H, Abe I. Adsorption technology [Guoxi Li, Trans.]. 2nd ed. Beijing: Chemical Industry Press of China; 2006 [in Chinese].