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Water Vapor Adsorption Kinetics on Small and Full Scale Zeolite Coated Adsorbers; A Comparison
Abstract
A possibility to enhance both heat and mass transfer characteristics of an adsorber heat exchanger is to apply the adsorbent directly to its surface in form of a consolidated layer. As the majority of the available publications on the effect of both coating technology and adsorbent layer thickness on the adsorption kinetics deals with small scale adsorbent samples, the results obtained can only represent the best case design of an adsorber heat exchanger. This article presents, therefore, a comparison between the adsorption kinetics of water vapour on small as well as two different full scale coated adsorber heat exchanger types with AQSOA-Z02 layers of Mitsubishi Plastics Incorporation under quasi isobaric conditions of adsorption heat pumps. The small scale coated samples have a zeolite dry mass of 200 mg and layer thicknesses of 200, 300 and 500 μm while the full scale adsorbers have a coated zeolite mass between 1.5 and 2.5 kg and layer thicknesses of 150, 200, 300, 400 and 500 μm. In the investigated adsorption heat pump module, up to 52.7 and 57.3% of the equilibrium differential water loading measured with the small scale coated substrates have been obtained after an adsorption-evaporation times of 300 and 600 s, respectively.
... In addition, the adsorption kinetic measurements of the small-scale adsorbent sample have been utilized in a 3-D mathematical model built to simulate the introduced APHE. The authors reported that, the introduced APHE outperformed a coated aluminium finned, flat tube adsorber HEX as well as an extruded aluminium adsorber heat exchanger [36]. Strictly speaking, an enhancement of 310 % in the differential water uptake obtained 300 s after adsorption start has been measured and simulated compared to [36]. ...
... The authors reported that, the introduced APHE outperformed a coated aluminium finned, flat tube adsorber HEX as well as an extruded aluminium adsorber heat exchanger [36]. Strictly speaking, an enhancement of 310 % in the differential water uptake obtained 300 s after adsorption start has been measured and simulated compared to [36]. The extremely reduced volume of the HTF domain compared to the adsorbent domain, while keeping the uniformity of the temperature distribution over the heat exchanger's plates are the key design advantages of the introduced APHE [34,35], which explain its superior performance. ...
... Although several studies addressed the influence of adsorbent bed thickness (the HTCL) on the adsorption and desorption dynamics using small-scale adsorbent samples of loose grains [39][40][41] or consolidated layers [36], no experimental study so far has treated the influence of the length of the refrigerant vapour diffusion path (MTCL) on the adsorption or desorption dynamics inside a plate heat exchanger. This deems urgently required, if plate heat exchangers shall be designed and optimized for adsorption heat transformation processes. ...
The effect of both heat and mass transfer characteristic lengths (HTCL, MTCL) of two different adsorber plate heat exchangers (APHE), for application in an adsorption chiller, on the adsorption and desorption kinetics is investigated. Three representative test frames (TF1-TF3) are prepared to examine small-scale adsorbent samples of the microporous silica gel (Siogel of Oker-Chemie, Germany) applying the volumetric large-temperature-jump methodology at different operating conditions. Based on the obtained kinetic data, an analytical model has been developed to predict the specific cooling power (SCP) and the coefficient of performance (COP) of a single-bed adsorption chiller comprising the studied APHEs. It turned out that, within the tested range of HTCL and MTCL, it can be concluded that, the adsorption kinetics are mainly influenced by the MTCL, while the desorption kinetics are dominated by the HTCL of the adsorbent domain. Applying Siogel as loose pellets inside a newly introduced APHE results in SCP s of 423.3 and 182.7 W∙kg⁻¹, at the evaporator temperatures of 15°C and 5°C, respectively. Herein, the condenser and adsorber-end temperatures amount to 30 °C and the desorption-end temperature to 90°C. The corresponding COP s amount to 0.50 and 0.40, respectively, which represent quite promising results for further design optimizations.
... Table 2 depicts average readings of U, m ads /V AHEx (an indicator of compatibility), and m ads /m metal for the two designs employing loose grains or coating structures: finned tubes/loose grains, 94 finned tubes/coatings, 122 extended surface/loose grains, 136 or extended surface/ coatings. 148 Employing coated finned tubes rather than loose grains raised U by about 4.5 times, nearing 106 W/m 2 K, resulting in higher h ads and l ads , and lowered d (Table 1)). ...
... Dawoud et al. 148 revealed that the SHPs for loose pellets in the finned tube AHEx were smaller than a fourth of the tested utilizing coatings. Thus, when employing loose grains rather than coatings, a more significant amount of adsorbent can be incorporated per unit volume of heat exchanger (m ads /V AHEx ) regardless of shape ( Table 2). ...
... finned tubes/coatings, 122 extended surface/ loose grains,136 or extended surface/coatings.148 ...
Adsorption heat pumps (AHPs) have gained noticeable attention in recent years. The review discusses significant research in the domain of adsorption heat pumps focusing on heating applications, the working principle, adsorption equilibrium and kinetics, the design of adsorbent beds, physical models, operating parameters, and physical and thermodynamic characteristics of adsorbents. A comparison is presented among AHPs and traditional heating technologies and systems for AHPs that certain market participants have created. The review focuses on the most appropriate conditions for each measurement technique and the constraints of the modeling processes that are an essential element for the comprehensive performance evaluation of adsorption cooling units. For adsorption bed applications, it is suggested to use various bed designs and heat exchanger structures. Moreover, significant literature gaps and constraints in designing AHPs for heating applications are identified and analyzed. The heat and mass transfer resistance should be reduced by developing novel adsorbent materials and an improved interface among the duct wall and the bed, where heat transfer fluid circulates to increase adsorption heat pump system performance. Furthermore, optimum operational modes for the intended application might significantly enhance system performance.
... Adsorbents are also expected to have large adsorption capacities, good thermal stability and high affinity for the adsorbate (Li, 2013). The wide application of zeolites besides silica gel has led to innovative designs of heat exchanger systems as well as increasing optimization of the material (Dawoud, 2013;J. Janchen & Stach, 2011). ...
... The tendency of zeolites to agglomerate at the surface contributes greatly to this. Thus, increasing zeolite thickness leads to a slower adsorption kinetics (Dawoud, 2013) and lead to longer cycle times for the attainment of equilibrium (Chan, Chao, & Bahrami, 2012). To reduce the effect of agglomeration at the surface, the use of the lowest possible grain size would be effective. ...
... To reduce the effect of agglomeration at the surface, the use of the lowest possible grain size would be effective. This, however, may require an infinite number of heat exchanger fins (Dawoud, 2013). Consequently, leading to the increase the thermal mass of the adsorber and require more energy to heat the system. ...
Zeolites based on the numerous applications can be utilised in providing solutions to some challenges of our world. With the ability to store thermal energy as chemical potential, zeolites are able to store thermal energy for long periods. This can occur with very minimal loss of energy and indefinitely unless the zeolite comes into contact with an adsorbate. The use of zeolite - water as adsorbent - adsorbate pair in thermal energy storage (TES) applications have been studied and have shown good results. However, the cost of zeolites synthesized from reagents continue to hamper the effective use of this adsorbent. Zeolite A was synthesized from kaolin from Wassa in Ghana based on a modified synthesis route. The adsorption properties of the zeolite utilising a designed and fabricated TES system using amounts of 100g, 200g, 300g, 400g and 500g of zeolite with a 1:1.5 ratio to water. Adsorption isosteres were plotted with the temperature and pressure values recorded and results showed correlation to adsorption behaviour of zeolites. Langmuir adsorption isotherms with r-squared values greater than 90% confirmed the affinity of water for zeolites. isosteric heat of adsorption was calculated with the minimum being 5,655.84 J/g and the maximum being 8,113.44 J/g. This confirms that the Zeolite A synthesized from Was kaolin has the structural properties needed for TES applications.
... The binder used in this system is not publically available. 76,77 He simulated kinetics of coated DDZ70 layers of 700 and 550 µm in 2007 and compared coated small scale samples to full scale adsorbers. He found, that for thicker coatings the power decreased and postulated a mass transfer limitation. ...
... In literature values from 116 kgS/m 3 to 226 kgS/m 3 can be found. 77,117 For the construction of compact modules, adsorbers with a high fill factor are advantageous. This is especially important for wall mounted or mobile adsorption devices. ...
... In literature so far it was reported that this gain in energy efficiency would have to go hand in hand with a loss in power output because of a decrease in mass and heat transfer in the thicker coatings. 20,76,77,117 It could be shown in this work, that with the coating and conditions used this is not the case. The adsorbent fill factor on the heat exchanger could be raised up to 382 kgS/m 3 without sacrificing power output. ...
The earth as we know it can only continue to exist if humanity finds a way to switch to a sustainable use of energy and resources. This work contributes to the research carried out to achieve this goal by improving the coating of adsorptive materials. These are used in heat transformation and drying processes that allow for efficient temperature and humidity control in buildings. A central component of these adsorptive coatings is the binder that acts as “glue” in the manufacturing of the coating. In this work the methods to evaluate binder performance regarding their thermal stability under the process conditions, their mechanical stability and their influence on the adsorptive properties of the coating were established. The coatings have to meet special requirements due to the thermal stresses and low pressure atmosphere they experience in these applications. A selection of silicone binders was then characterized with the established tests according to these requirements. Additionally a selection of inorganic binders was investigated because they allow for the use of high desorption temperatures and thus a high energy efficiency of the process. Out of these binders Silres® MP50E emerged as the most promising one due to very good adsorptive properties of the coating, its good temperature stability and ease of use. While some of the inorganic binders showed very good adsorptive properties and temperature stability the mechanical stability of all inorganic binders was not sufficient for their use in adsorption heat transformation technology. This is the first time that a broad selection of binders was evaluated with regards to adsorptive coatings and the results published in literature. With a suitable binder identified, the next step was to optimize the coating of the heat exchangers in order to work out how to manufacture the most efficient and powerful heat exchangers. Samples with different coating thicknesses were manufactured in small scale and full scale and their adsorption behavior was characterized. It could be shown for the first time that it is possible to increase energy efficiency by improving the mass ration of adsorber to coating and increase the delivered power at the same time. This was shown for small and full scale samples. It was shown that under the corresponding conditions the heat transfer from the coating layer to the adsorber metal substrate is the limiting step in the process. These results can now be used for the planning and construction of adsorbers. With knowledge of a suitable binder and how to coat efficient, powerful adsorbers, the coating process itself was improved to allow for industrial scale manufacturing. A central point here is the ability to control slurry rheology. Out of many rheology additives those that are suited for the application in adsorption heat transformation were identified and their influence on the slurry rheology thoroughly characterized. Additionally the process of slurry preparation could be simplified for several different adsorbents. Here it was shown that the supersonic deagglomeration step is not necessary to prepare a slurry. Extending the possible coating techniques and in addition to the dip coating process used so far, the spray coating of adsorptive coatings was established for the first time in literature. This process is widely used in the industry and allows for easier plugin into existing coating processes. For the coating of high resolution patterns a proof of concept of the screen printing process was carried out.
... They can be glued to the heat exchanger to improve the thermal conductance (Stefan Jäschke 2005). An improved contact with heat exchanger surfaces is possible by skipping the adsorbent granulation step and directly coating the HX surface instead, thereby improving the thermal contact while maintaining a high surface area for vapor accessibility (Freni 2015;Dawoud 2013). To achieve this coating, two distinct approaches are known: direct crystallization and binder-based coating. ...
... Developing adsorbent heat exchangers with high power densities and high COPs represents one of the recent challenges (Freni 2012b;Dawoud 2013;IMPRES006-cd.dvi;IMPRES006-cd.dvi;IMPRES006-cd.dvi;Meunier 2013). ...
... The introduced procedure in (Mikhaeil et al., 2020) is followed to prepare a test frame for the small-scale loose grain sample and to evaluate the matching between the obtained experimental adsorption and desorption kinetic results of the full-scale and small-scale adsorbers. The adsorption and desorption kinetics of the small-scale adsorbent sample are measured in the existing V-LTJ kinetic setup (Dawoud, 2007;Aristov et al., 2008;Dawoud, 2013) at similar operating conditions of the investigated APHE. A slight modification to the introduced thermal response LTJ methodology (Tokarev, 2017), is introduced; namely, to estimate the instantaneous water loading from the measured evaporator or condenser power during adsorption or desorption processes, respectively, rather than carrying out a blind (disconnecting the evaporator from the adsorber) and an active adsorption process and estimate the temporal water uptake from the measured temporal heat of adsorption. ...
... The details of the V-LTJ kinetic setup, the experimental procedure and the evaluation of the instantaneous water uptake can be read elsewhere (Dawoud, 2007;Aristov et al., 2008;Dawoud, 2013). The tests have been carried out at the same operating temperatures, under which the full-scale APHE has been tested. ...
This paper introduces the results of an experimental study on the adsorption and desorption kinetics of a commercially available, open-structured asymmetric plate heat exchanger adapted to act as an adsorber/desorber for the application in adsorption heat transformation processes. In addition, a volumetric large temperature jump (V-LTJ) kinetic setup was applied to measure the adsorption and desorption kinetics of a small-scale adsorbent sample prepared dedicatedly to be representative for the adsorbent domain inside the investigated adsorber plate heat exchanger (APHE). All kinetic results of the small-scale adsorbent sample and the APHE were fitted into exponential forms with a single characteristic time constant (τ) with a coefficient of determination (R 2) better than 0.9531. A very good matching between the small-scale and full-scale adsorption kinetic measurements was obtained, with an average relative deviation of 12.3% in the obtained τ-values. In addition, the kinetic data of the small-scale adsorbent sample were utilized for estimating the expected specific instantaneous and moving average powers of the evaporator/condenser heat exchanger. The average relative deviation (ARD) between the moving average specific evaporator powers obtained from the small-scale and the full-scale measurements amounts between 5.4 and 15.1%.
... The adsorbent material is normally packed inside the adsorber bed in the form of granular particles and needs to be restrained using fine metal mesh. Recently coating the adsorbent material onto the adsorber bed showed the potential of better performance compared to the packed one as it offers enhanced heat and mass transfer through the thin adsorbent material coating layer [9][10][11][12]. Fig. 1 shows the schematic diagram of the adsorption system. ...
... Table 2 illustrates different published numerical models to study the packed finned tube adsorber beds. For the coated adsorbent on finned tube, most of the studies were only carried out experimentally [10,22]. The maximum water uptake of the coated adsorbent material is less than the packed one due to the addition of the binder to the adsorbent powder [38]. ...
A transient numerical model has been developed using the segregated solution approach to study the performance of packed and coated finned tube in adsorber beds for desalination and cooling applications. Published isotherms and kinetics of the Aluminium Fumarate in granular packed and powder-coated forms are used in the model to investigate the adsorber bed design. The fin configurations (fin spacing and fin height) were investigated at different operating conditions to obtain the optimum geometrical design for the packed and coated adsorber beds in terms of the specific daily water production (SDWP) and the specific cooling power (SCP). A comprehensive comparison of the SDWP and SCP was carried out at different fin height and coated thickness. The results showed that the maximum SCP and SDWP for the packed bed are 300 W/kg and 12.5 L/day/kg, while they are 825 W/kg and 34.2 L/day/kg respectively for the coated bed. The optimum design of the heat exchanger was found using the coated finned tube with an adsorbent material thickness of 0.3mm.
... Poor heat and mass transfer effectiveness involves the use of a large quantity of solid adsorbent with the consequent need to produce bulky and heavy adsorption units. Nowadays, many studies proved that intensification of heat transfer properties of the adsorbent bed can be efficiently achieved though preparation of thin adsorbent coatings [3,4], highly conductive foams [5] or fibers [6,7], which permitted to design adsorbent units with enhanced power density [8, 9]. A recent research line aims at improving the mass transfer rate through the adsorbent coating by directed mass transfer channels [10]. ...
... The above equations can be combined with the saturation temperature pressure relationship to provide the time derivative of temperature or pressure. 8 ...
Adsorption chillers can provide energy efficient cooling and have large potential for performance increase and cost reduction compared to conventional chillers. Among the different R&D activities currently in progress in the field, the development of advanced cascading adsorption cycles is an effective way to improve the performance of standard adsorption units, making this technology especially interesting in applications where waste heat for driving the adsorption chiller is a widely available, such as many industrial processes, cogeneration plants, I.C. engines, district heating networks. In this paper, a novel modelling tool able to simulate complex adsorption cycles is presented and validated with literature data. The simulation tool is used to investigate numerically the performance of a cascade adsorption cycle consisting of a twin adsorber high-temperature cycle with heat recovery coupled with an intermittent adsorber low-temperature cycle. A parametric analysis is carried out showing the optimization potential in terms of Coefficient Of Performance (COP) and specific cooling power (SCP) with varying cycle periods, step time ratios and adsorbent mass ratios. COP of 0.97 with SCP of 142 W/kg are found for water-zeolite 4A (high-temperature) and water-CaCl2/Silica gel (low-temperature cycle). These results are in line with previous findings reported in literature. Finally, useful recommendations for further performance improvement are provided.
... Preliminary studies [55,57] have confirmed that fluidization improves the heat transfer conditions in the adsorption bed. This paper aims to evaluate average convective heat transfer coefficient values for packed and fluidized bed samples based on the results of experimental studies. ...
Sustainable development policy focuses on reducing the carbon footprint generated by the global industry and energy sector. Replacing conventional energy sources with environmentally friendly ones requires advanced research to increase energy efficiency and reduce the instability and intermittence of renewable sources. Moreover, adsorption chillers are an opportunity to introduce net-zero emission technologies to the refrigeration, air-conditioning, and desalination industries. Adsorption devices could be popularized if a method of effective heat transfer in the volume of the adsorption bed is developed. The innovative concept of introducing fluidized beds into the adsorption system can achieve the most promising results in improving energy efficiency. To confirm the adopted assumption, heat transfer coefficient calculations for the packed and fluidized bed were carried out in this paper based on experimental tests and literature data. The empirical research aims to extend the fundamental knowledge in the implementation of fluidization under low-pressure conditions, characteristic of the adsorption systems’ working cycle. Experiments were conducted on a unique test stand equipped with the Intensified Heat Transfer Adsorption Bed (IHTAB) reactor prototype. Five adsorption bed samples were analyzed. The reference sample consisted only of silica gel, and the subsequent ones contained aluminum or carbon nanotubes with 5 and 10% additions. In the case of samples with admixtures, the fluidized state increased the heat transfer coefficient on average from approx. 36.9 W/m2 K to approx. 245.4 W/m2 K.
... The influence of adsorbent shapes on sorption kinetics is unneglectable. In addition to spherical particles with various grain sizes mostly used under industrial conditions [69,96], adsorbents can also be manufactured into other functional shapes, such as thin coatings through dipping [97], spraying [98], binder-based adhering [99][100][101], in-situ crystallization [102,103], freeze-drying method [104,105] or thermal gradient synthesis [106][107][108], and complex structures by 3D printing technology [109][110][111][112]. These advanced approaches have created great flexibility for structural design and functional manipulation of adsorbent materials in the field of material engineering. ...
Adsorption thermal storage, which can store heat like a battery, reserve it when it is unneeded and release thermal energy on users’ demands, has been acknowledged as a promising strategy for heat reallocation, especially water based adsorption thermal battery (ATB). This review aims to summarize the recent advances in this domain and provide perspectives for the further development of ATB, focusing on the design of adsorbent materials and the optimization of system configurations in the light of different application scenarios. Here, we start with introducing the fundamental mechanisms concerning thermodynamics and adsorption kinetics. Next, we elaborate properties and performances of various adsorbents and system configurations developed for ATB, with their advantages and limitations as well as design strategies discussed. Importantly, we introduce the application-oriented selection principles of diversified materials and system cycles, which could provide practical guidelines for overall design in various application scenarios. In the last section, we outline the challenges in this field from fundamental research and practical application aspects, and provide a future outlook for the development of ATB technology.
... In [15] author demonstrated that SCP of SWS-1L adsorption bed increases by about 48% when aluminum particles are added to adsorbent grains. Consolidation of zeolite with Hex also can lead to enhancement in the adsorption speed that can reach 7% as reported in [16]. For composite sorbent consolidation is also possible and specific power can reach 319W/kg [17]. ...
Adsorption heat transformation (AHT) makes it possible to accumulate and use renewable energy and waste heat. This emerging technology is based on the reversible adsorption-desorption of vapour by an adsorbent. One of the most crucial factors affecting the AHT efficiency is heat transfer in the system "adsorbent-heat exchanger"(AdHex), which depends on the AdHex geometrical parameters. For designing compact and efficient units, it is necessary to maximize the AHT useful power per AdHex unit volume. Therefore, the optimization of AdHex geometry is an essential and urgent task. In this purpose the intensity of heat transfer and heat generation inside the restricted volume of AdHex have to be properly balanced. The aim of this work is to find out the optimal geometry of AdHex for adsorption chilling application with use of “methanol-LiCl/SiO2” working pair. The procedure for defining the optimal AdHex geometry is based on finding the compromise between the volume of the adsorbent granules placed inside the AdHex and number of plate channels and fins. The results of calculations were experimentally verified.
... In the past few years, aluminophosphate based AQSOA zeolites have been immersed as high-performance adsorbent materials [19,20]. They have been widely used in different adsorption chillers and desiccant wheels [21]. ...
This work reports the synthesis and use of zeolites based super-porous hydrogel composites (SPHCs) as solid polymer desiccants to capture water vapors from moist air. The SPHCs were composed of super-porous hydrogels (SPHs) of acrylic acid and methacrylamide (i.e. P(AA-co-MAM)-SPHs) as polymer matrix and AQSOA type zeolites, i.e. AQSOA-Z01, AQSOA-Z02 and AQSOA-Z05 zeolites as reinforcing materials. Different structural and morphological properties of SPHCs were characterized using techniques like XRD, SEM, FTIR and TGA-DTG. Desiccant properties of P(AA-co-MAM)-SPH and SPHCs were explored in terms of adsorption isotherm and kinetics. All the desiccants exhibited type-III adsorption isotherm, suggesting water vapors’ adsorption via capillary condensation mechanism and correlated well with GAB and FHH isotherm models. P(AA-co-MAM)-SPH exhibited maximum adsorption capacity of 0.72 gw/gads. However, after reinforcing different zeolites, adsorption capacity increased to 0.80, 0.84 and 0.91 gw/gads in SPHC/AQSOA-Z01, SPHC/AQSOA-Z02 and SPHC/AQSOA-Z05, respectively at 90% relative humidity and 25 °C. Further, the adsorption kinetics data correlated well with linear driving force and intraparticle diffusion models and the adsorption equilibrium was achieved much quicker at 70% relative humidity as compared to 90% relative humidity. SPHCs showed much better re-use efficiency as compared to parental SPH, therefore, reinforcement of zeolites improved the re-use efficiency of P(AA-co-MAM)-SPH.
... In such a context, several research activities have been focused on developing adsorbent HEXs coated with thin adsorbent layers (typically 0.1-0.3 mm thickness) with suitable adsorption performance and effective coating/metal interface [1][2][3]. In this way, the global heat transfer coefficient is reduced thanks to the reduction of the thermal contact resistance between the adsorbent coating and the heat exchange surface compared to the standard grain-sized configuration [4]. ...
In the present work, the optimization of a new coating formulation was investigated, taking attention to an industrially focused research approach used for the engineering design of the adsorber. The adsorbent was a composite zeolite or silica-gel based coating applied by using new flexible polymer matrices. The FC-80 formulation represents a good compromise between mechanical stability and absorption capacity. Using the developed coating process, a new compact HEX design was developed to reach the AHP target performance with easy and fast manufacturing. The specific cooling power of the coated heat exchanger was estimated to be about 500 W/kg of adsorbent. The new coated HEX was integrated in a new adsorption chiller and has been tested by a laboratory test-rig under realistic operating conditions. Results of preliminary testing demonstrated that the prototype provides a cooling capacity of around 10 kW with a COP of 0.54.
... The coating approach reduced the heat transfer contact resistance between adsorbent and metal of heat exchanger remarkably. Dawoud [16] compared the adsorption kinetics (i.e., adsorption rate) of different coating thicknesses, range from 0.2 to 0.5 mm. His conclusion showed that the adsorption rate increases as the coating thickness decreases and vice versa. ...
Using an eco-friendly system to provide cooling power for buildings is a great challenge. The adsorption cooling (AC) cycle is a promising thermally driven technology to provide green cooling energy for buildings. It uses environmentally friendly working fluids and could be powered by low-grade thermal energy. Despite these advantages, it suffers from low performance compared to electrical-driven cooling systems. Achieving high performance of the AC cycle relies basically on the state of operation that needs to be optimized to get the compromise between the specific cooling power (SCP) and the coefficient of performance (COP). So, the key objective of the paper is to model the outputs (SCP and COP) of the cooling cycle in terms of its operating conditions using artificial intelligence. The evaporator temperature, chilled water cycle time, chilled water mass flow rate are the main operating parameters (inputs) of the system that are optimized. An accurate Adaptive Network-based Fuzzy Inference System (ANFIS) model of COP and SCP is created based on experimental datasets. ANFIS can accurately grasp the trend of the data and hence produce an accurate model even if the data describes a highly nonlinear system. To verify the performance superiority of the fuzzy model, the attained findings are compared with ANOVA. The ANOVA uses the linear regression method to obtain the mathematical model of the system. For the COP model and during the training phase, the coefficient of determination is increased from 0.7477 by using ANOVA to 0.9997 by using ANFIS (33.7% increase). Also, during the testing phase, the coefficient of determination is increased from 0.6522 to 0.9725 (32.9% increase). Regarding the SCP model, the coefficient of determination is increased by 27.66% and 46.6% for training and testing, respectively. The RMSE values are found to be 0.0026 and 0.0437, respectively, for training and testing for modeling the ANFIS model of COP. These values prove the superiority of fuzzy modeling compared with ANOVA. Also, the RMSE values are decreased by 97.37% and 80.91% using ANFIS compared with ANOVA, respectively, for COP and SCP models. Therefore, the obtained results demonstrated the excellence of the ANFIS model of implementing the AC cycle in comparison with ANOVA.
... ese machines use CFCs for their operation which causes the depletion of the ozone layer [2]. In this context, the use of renewable energies as an alternative to fossil fuels is becoming increasingly essential [1,3]. Nowadays, adsorption heat pump (AHP) has received much attention as a sustainable energy solution using environmentally friendly refrigerants such as water, methanol, and ammonia [4,5]. ...
Heat and mass transfers inside an adsorbent bed of an adsorption heat pump (AHP) are considered poor; consequently, they can cause low system performance. They should be enhanced so as to increase the coefficient of performance of the cooling machine. The aim of this work is to study an adsorbent bed coated with the zeolite SAPO-34. A simulation model based on governing equations for energy, mass, and momentum transfers is developed using COMSOL Multiphysics software. The system zeolite SAPO-34/water has been considered. Modeling results are validated by experimental database available at the Institute for Advanced Energy Technologies “Nicola Giordano,” Italy. It has been shown that the adsorption heat pump performance is affected by both heat and mass transfer. The enhancement of heat transfer solely is not sufficient to attain high values of specific cooling power. In the case of water vapor/SAPO-34 pair, mass transfer has a significant impact on the duration of the cooling step which should be shortened if one would want to increase the specific cooling power. The sole way to do it is to enhance mass transfer inside porous adsorbent.
... The technique for preparing consolidated composite adsorbents consists of adding material with greater thermal conductivity [10] to the powder of the classic solid adsorbent. These techniques make it possible to design cooling units with improved power densities, [11] [12]. Other recent studies show that the use of directed mass transfer channels [13] [14] or structures with metal organics [15] [16] [17] in the adsorber bed make it possible to capitalize the heat and mass transfers. ...
... If the adsorbent particle size is decreased further (<100 µm) the adsorbent can be mixed with a binder and this slurry can be used for coating various heat exchanger geometries [10,24]. A flat tube-lamella heat exchanger is coated with a zeo-type material TiAPSO by Bendix et al. [24], and with SAPO34 by Freni et al. [25] and Dawoud [26]. In addition, Ammann et al. performed research on the reduction of heat and mass transfer resistances of binder-based SAPO-34 coatings for the use in heat exchangers [23,27,28]. ...
In adsorption heat pumps, the adsorbent is typically combined with heat conducting structures in order to ensure high power output. A new approach for the direct integration of zeolite granules into a copper structure made of short copper fibers is presented here. Zeolite NaY granules with two different grain sizes are coated with copper fibers and powder and sintered to larger structures. The sorption dynamics of these structures were measured and evaluated in terms of heat and mass transfer resistances and compared to the loose grain configuration of the same material. We found that the thermal conductivity of such a composite structure is approximately 10 times higher than the thermal conductivity of an adsorbent bed with NaY granules. Sorption equilibrium measurements with a volumetric method indicate that the maximum uptake is not altered by the manufacturing process. Furthermore, the impact of the adsorbent–metal structure on the total thermal mass of an adsorption heat exchanger is evaluated. The price of the superior thermal conductivity is a 40% higher thermal mass of the adsorption heat exchanger compared to the loose grain configuration.
... The directly crystallized sample showed an 85% higher final loading than the reference sample, which was glued to the metal support. Dawoud [32] compared the adsorption speeds for various coating thicknesses from 200 µm to 500 µm and loose pellets with a moderate radius from 0.7 mm to 2.6 mm. He reported that the adsorption speed decreased sharply as the zeolite layer thickness increased. ...
Most previous studies on adsorption chillers were conducted using the same adsorption and desorption times. Instead, this study analyzed various adsorption/desorption time allocations, and systematically examined the effect of cycle time allocation on system performance. The results provide physical insights for 3-bed adsorption chillers. The effect of hot water temperature and cycle time on the optimum adsorption/desorption time ratio was also examined. Setting the proper adsorption and desorption times was much more important for smaller cycle times. The highest degradation in COP (coefficient of performance) found was 36 % at 300 s of cycle time, compared with the conventional 1:1 ratio. When the temperature of the heat source is low, the ratio of adsorption/desorption time was not significantly affected, however, for higher performance at high temperature, a longer adsorption time than desorption time was required.
... AQSOA-Z02 is a crystalline microporous silico aluminophosphate (AlPO 4 ) zeolite having Chabasite (CHA) phase type structure [18,19]. AQSOA-Z02 zeolite has already been used in many desiccant cooling and dehumidification applications and it was found to adsorb and regenerate water vapor at comparatively much lower temperatures than silica gel and other conventional zeolites [19,20]. Sun and Chakraborty [21] studied the water vapors adsorption behavior of AQSOA-02 zeolite in details and proposed a thermodynamic formulation to calculate the amount of water vapor uptake on different solid adsorbents including AQSOA-02 zeolite. ...
Deliquescent salts have high water vapor adsorption capacity, but they dissolve in water by forming crystalline hydrates. That restricts their use in different water vapor adsorption applications. However, this limitation can be overcome by incorporating deliquescent salts within a polymer matrix which will keep the salt solution in place. Furthermore, if the polymer matrix used is also capable of adsorbing water vapor, it will further improve the overall performance of desiccant system. Therefore, in this work, we are proposing the synthesis and use of a highly effective new solid polymer desiccant material, i.e. superporous hydrogel (SPHs) of poly(sodium acrylate-co-acrylic acid (P(SA-co-AA)), and subsequently its composite with deliquescent salt, i.e. calcium chloride (CaCl2), to adsorb water vapors from humid air without the dissolution of the salt in the adsorbed water. Parental PAA-SPHs matrix alone exhibited an adsorption capacity of 1.02 gw/gads which increased to 3.35 gw/gads after incorporating CaCl2 salt in the polymer matrix. Both materials exhibited type-III adsorption isotherm and the experimental isotherm data fitted to the Guggenheim, Anderson and Boer (GAB) isotherm model. However, the adsorption kinetics followed linear driving force model which suggested that this extremely high adsorption capacity was due to the diffusion of water molecules into the interconnected pores of SPHs via capillary channels followed by the attachment of adsorbed water molecules to the CaCl2 salt present in the polymer matrix. Furthermore, the adsorbents were used successively for six cycles of adsorption with a very little loss in adsorption capacity. Therefore, the proposed polymer desiccant material overcomes the problem of dissolution of deliquescent salts and opens the doors for a new class of highly effective solid desiccant material.
... Interestingly, when the target is to develop adsorption machines characterized by high energy efficiency (e.g., thermal COP), the employed coatings are designed to be thicker, in order to maximize the amount of adsorbent material that is embedded per each HEX. This is reflected in the lower metal-to-adsorbent ratios and higher achievable COP [72]. Similar considerations were also reported recently by Gluesenkamp et al. [77], analyzing the effect of inert masses on adsorption technologies. ...
The use of adsorbent heat pumps as heating and cooling systems is particularly relevant thanks to their ability to exploit low-grade heat (e.g., below 90 °C) from renewable energy sources and waste energy streams with prospective applications in several fields, e.g., industrial and residential. Their development began in the 20th century and is still in full evolution. The great interest in their improvement and optimization was determined by some key factors inherent to their sustainability compared to traditional refrigeration systems (e.g., low electricity consumption and the low environmental impact of the employed refrigerants). Recently, strong efforts have been dedicated to increasing the achievable heating/cooling power density of this technology through the development of innovative adsorbent coating technologies. Indeed, the deposition of thin coatings on the surface of the heat exchanger could reduce the heat transfer resistance existing on the adsorbent material side, thus increasing the overall adsorption dynamics. Three main approaches have been assessed, namely a thick consolidated bed, binder-based composite coatings and in situ directly crystallization coatings. This paper provides a brief overview of some of the main achievements related to adsorbent coating technology developments for adsorption heat pump applications.
... The water evaporation rate in the evaporator was noticeable based on the sorbed water in the aluminum composite. Composite 1AP-H and aluminum-coated zeolite were introduced to evaluate the SCP value at sorption ratios of 0.7, 0.8, and 0.9 by varying the spacing between fins, L. The experimental data for aluminum-coated zeolite (ACZ) has been collected by Dawond [29]. The ACZ sorbs water vapor at a constant heat-sink temperature of 35 C. Additional information on sorption characteristics and isotherms of the zeolite has also been published [30]. ...
Recently, increasing research attention has been given to the development of an absorber to enhance the coefficient of performance (COP) and the capacity of an adsorption heat pump by improving the sorbent in the sorption chamber or reactor. This study introduces the preparation method for an efficient adsorbent with a high thermal conductivity. Three types of host matrix aluminum composite sorbents were prepared through anodizing and pore widening treatment (PWT). This created an aluminum oxide film that was 92 μm thick with a mean pore diameter of 76 nm on an aluminum plate. To improve the sorption ability, the anodized aluminum was impregnated with calcium chloride. The sorption isotherm of the aluminum composite demonstrated its ability to uptake 7.5 mol-H2O/mol-CaCl2 water at a relative pressure of 0.33 at 30 °C. A numerical method was used to predict water sorption and temperature distribution in the aluminum composite layer via a heat and mass transfer model. The specific cooling power (SCP) was used to indicate the cooling performance of a sorption heat pump that employed the aluminum composite as laminate sorbent fins by varying the spacing between each fin.
... AQSOA-Z02 is a crystalline microporous silico aluminophosphate (AlPO 4 ) zeolite having Chabasite (CHA) phase type structure [18,19]. AQSOA-Z02 zeolite has already been used in many desiccant cooling and dehumidification applications and it was found to adsorb and regenerate water vapor at comparatively much lower temperatures than silica gel and other conventional zeolites [19,20]. Sun and Chakraborty [21] studied the water vapors adsorption behavior of AQSOA-02 zeolite in details and proposed a thermodynamic formulation to calculate the amount of water vapor uptake on different solid adsorbents including AQSOA-02 zeolite. ...
A promising and highly efficient new solid desiccant material composted of superporous hydrogel (SPHs) of polyacrylamide (PAM) and AQSOA-Z02 zeolite was fabricated to capture water vapor from moist air. The synthesis method of PAM-SPHs involved the gas blowing and foaming technique which insured a uniform distribution of zeolite particles throughout the polymer matrix. The presence of three dimensional porous structure, interconnected macropores in SPHs and the highly hydrophilic functional groups of AQSOA-Z02 particles enabled the synthesized SPHs composite to exhibit excellent water vapor adsorption capacity. The introduction of AQSOA-Z02 zeolite in the polymer matrix increased the water vapor adsorption capacity from 0.77 gw/gads to 0.89 gw/gads. Both materials exhibited type-III isotherm and followed Frenkel-Halsey-Hill and Guggenheim, Anderson and Boer (GAB) adsorption isotherm models. The high adsorption capacity was attributed to the combined effects of capillary condensation in interconnected macropores and the attachment of water molecules to the hydrophilic functional groups present in the zeolite structure. The water vapor adsorption capacity was found to decrease with increasing temperature. Adsorption kinetics studies suggested that the water vapor adsorption followed first-order kinetics models and the mechanism of water molecules diffusion into the internal structure of SPHs was case-II type of diffusion mechanism.
... An intermediate behavior, between loose grains and in situ crystallized configurations is represented by the binder-based coating technique. 21 Indeed, in this case, the heat transfer is enhanced since the contact between the coating and the HEX is good while the coating thickness is higher than the one obtained for the in situ crystallization, thus it is possible loading a sufficient amount of adsorbent material inside the HEX. ...
This article evaluates the hydrothermal and mechanical stability of an adsorbent composite foam based on zeolite silicone for application in adsorption heat pump. The adsorption properties of the fresh composite adsorbents and their morphological features were already presented in previous papers. In the present work, hydrothermal aging of composite foams, at varying SAPO‐34 zeolite contents and under real operating conditions, was carried out in order to verify the stability of the synthetized material. This improvement of knowledge is a key point for the industrial application. This evaluation was successfully performed by means of adsorption measurements and compression test on aged samples, up to 1500 aging cycles. The adsorption properties of composite foams are effective and stable up to the maximum number of cycles of the aging process. Instead, from the mechanical point of view, composite foams with high content of zeolite, aged at long cycles, evidenced a slight stiffening that stimulates mechanical brittle behavior. The composite foam with 67% zeolite filler represents a threshold value beyond which the action of the hydrothermal aging implies a significant loss of flexibility and mechanical integrity, which limits its applicability under typical conditions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48311.
... Zeolite coatings directly crystallized on metal supports are beneficial to be used in various applications, especially when the fast heating/cooling of the adsorbent presents a significant advantage. The use of adsorbents in the form of coatings on metal surfaces have been demonstrated to be very favorable for adsorption heat pump/cooling systems, which provide heating/cooling effects [1][2][3]. Besides the elimination of heat transfer resistances, the quality of mass transfer in the coating also plays role in determining the performances of these materials [4]. ...
Coatings of NaA and NaX zeolites with various thicknesses were grown by direct crystallization on stainless steel plates. As a next step, ion exchange was applied to obtain the Li forms of the coatings. The materials obtained were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), inductively coupled plasma (ICP), thermal gravimetry (TG), and N2 adsorption. The stabilities of the coatings in the ion exchange process were also determined. Li⁺ ions were observed to be readily exchanged with Na⁺ ions in zeolite coatings of various thicknesses but the percentage of exchange did not attain 100%. Favorable ion exchange conditions for obtaining both zeolite LiNaA and LiNaX coatings were determined. After Li exchange, the surface area of zeolite X increased by about 56% while the water capacities of zeolites X and A were enhanced by about 15 and 14%, respectively, for the conditions investigated. The ion exchange process resulted in some detachment from the coatings, which increased with enhanced coating thickness. Significant improvement was obtained in coating stability by using plates with roughened surfaces. Zeolite coatings in Li form may improve the performances of adsorption heat pumps, provided that relatively thick coatings remain stable to a desired extent during ion exchange.
... Other types of zeolites that have been investigated are zeolite 13X/H 2 O [18] with regeneration temperature of 110°C and some novel porous materials which will be discussed in the following sub-section. Dawoud [19] provided an insight into water vapour adsorption kinetics on small AQSOA (Aqua Sorb Adsorbent) FAM-Z02(SAPO-34)-coated aluminium substrates for adsorption heat exchangers The equilibrium differential water loading was up to 57.3% in the investigation. Meanwhile, a new experimental protocol to evaluate thermodynamic performance of AQSOA-FAM-Z02 as a desiccant for advanced working pair in adsorptive heat transformers have been investigated by Frazzica [20], Frazzica [21]. ...
Thermochemical heat storage (THS) systems have major advantages over other thermal storage systems, notably high energy density and low heat loss when hermetically sealed. There are several review papers available that discuss THS. Unlike other published review articles, this paper presents a literature survey and a review that add insights into the current state-of-the-art THS technologies, covering: the THS materials, THS reactor design and THS as thermal batteries. Emphasis is placed on THS for solar thermal energy storage and also for industrial waste heat recovery. At the materials level, in addition to a review on THS material sorbents, emphasis is placed on innovative composite THS materials with salt mixtures and metal-organic frameworks materials. Reactor design is one of the major fields of THS system development. In this paper, we also review several types of innovative reactor designs, including hybrid THS systems, towards obtaining advanced reactor concept, numerical studies in THS studies mainly covering the heat and mass transfer in the reactor designs, and also the implementation of THS systems as thermal batteries. Among the main conclusions, it is found that, although several advancements have been achieved in these fields in the last decade, further research is needed for advancing THS technology to be commercially viable. This paper will provide a wide range of information including the research gaps and critical issues in this field. The authors aim to allow readers to identify gaps/issues in the current research towards improving the practicality of THS systems.
To achieve simultaneous ammonia adsorption and microscale zeolite recovery, zeolite was coupled with dynamic membrane technology to establish a composite zeolite-dynamic membrane system, and its ammonia removal rate and zeolite recovery efficiency were evaluated. At initial ammonia concentration of 10 mg·L−1, 67% ammonia could be removed effectively with 10 g·L−1 zeolite dosing. The adsorption kinetics and isothermal model indicated that the adsorption fitted well with the pseudo-second-order model, and the theoretical maximum adsorption capacity was 4.12 mg·g−1 predicted by Langmuir model. Zeolite and diatomite were mixed in the zeolite-dynamic membrane system at a mass ratio of 1:1, and the composite zeolite dynamic membrane could rapidly form under the conditions of 1 g·L−1 dosage, 40 mL·min−1 flow rate and 38 μm supporting membrane. After the formation of DM layer, the effluent turbidity remained stably below 1 NTU, and ammonia removal rate was 56%. Ammonia removal and zeolite recovery were achieved at the same time, which laid the foundation for simultaneous ammonia adsorption and adsorbents recovery for the composite zeolite dynamic membrane system in future.
Recently adsorbent coating technique was pointed for the aluminum fin in the ad/desorption chamber of an adsorption heat pump/chiller. This research proposes an aluminum substrate adsorbent coating method including examination of characteristics and adsorption isotherms. An aluminum substrate was dipped into the adsorbent suspended solution to form a composite adsorbent layer on its surface. The adhesion of the adsorbents onto the aluminum substrate was evaluated by the peeling test. The aluminum oxide film on the aluminum substrate promotes the adhesion between adsorbent and aluminum substrate refer to residual ratio. The suitable anodization condition of the aluminum oxide film is 150 volts for 2 min yielded the thin aluminum oxide film layer upon the aluminum substrate 67 nm of thickness. The suspended adsorbent solution was prepared at a mass ratio of 3 g-adsorbent g⁻¹-coupling agent that provided the thickest adsorbent coated layer by dip coating. Zeolite AQSOA-Z01 is a good choice to coat the aluminum substrate due to satisfier adhesion strength and specific cooling capacity evaluated at 239.4 kJ kg⁻¹ under operating relative pressure range of adsorption heat pump/chiller.
Currently, there is an increasing interest in the development of HVAC systems based on solid desiccant materials to achieve efficient and affordable air dehumidification and humidification processes. Many research efforts deal with the development of novel composite materials suitable to manufacture such devices. In this work we present a novel silica gel-based desiccant compound, which can be used to prepare different products, such as sheets, monolithic components, and coatings. The proposed formulation is based on a combination of silica gel, sodium polyacrylate, vinyl glue and polypropylene fibers. The preparation procedure of the sorbent material and its characterization (adsorption capacity, morphology and surface analysis, mechanical properties by pull-off test, structural and thermal stabilities of new and aged samples and volatile compounds emissions) are described in detail. A small-scale prototype has been also manufactured and experimentally tested under typical operating conditions of air dehumidification processes. Results show that the proposed material has a suitable sorption capacity (maximum water uptake equal to 0.32 kg kg⁻¹), good mechanical properties (pull adhesion strength around 2.74 MPa) and stability (decomposition threshold of 400 °C). The performances achieved by the prototype are comparable with those of a reference silica gel packed bed system, highlighting that the desiccant material performs adequately also at system scale.
Silica adsorbents with controlled porosity were produced by sol-gel technique without using catalyst. Mesoporosity and water vapor adsorption properties were evaluated for the synthesized silica materials. This study was supported by several characterizations, including FTIR, SEM and Nitrogen sorption. It has been shown that the mesoporous structure and the water adsorption performance of the silica are entirely dependent of the solvent type used and gelation temperature. The present study shows that for the adsorption parameters used in this work, the control of the sol-gel parameters can give rise to silica adsorbents with greater adsorption capacity than the commonly used commercial silica. The highest adsorption capacities were measured for silica structures synthesized with tert-butanol and gelled at 90 °C, which absorbs up to 65% more than its mass due to both high mesopore volume and big pore size. The silica materials were synthesized in this work by a simple sol-gel synthesis, which represents an important advantage in terms of safety and environmental sustainability, besides reinforcing the simplicity and novelty of the processing route employed herein to obtain silica adsorbents with a controlled porous structure.
Zeolite coatings were directly crystallized on stainless steel substrates, which included double layer wire mesh cylinders and tubes, by induction heating. X-ray diffraction (XRD), thermal gravimetry (TG) and scanning electron microscopy (SEM) analyses were performed to characterize the materials obtained. Thermal and ultrasonic treatments were performed to assess the mechanical stabilities of the coatings. The desorption kinetics of the coatings were also investigated and compared to those obtained for zeolite NaX in various pellet and powder forms. Coatings of up to about 1.2 mm mass equivalent thickness, consisting mainly of NaX, could be prepared on various substrates using new clear solution compositions. The coatings grown on double layer wire mesh cylinders as well as double layer meshes welded to tubes were observed to be highly stable, especially when covered by an additional polymer layer. Utilizing the zeolite as a coating on metal surfaces, instead of in pellet or powder form, improved heat transfer properties significantly, mainly due to the firm contact between the metal and zeolite provided by direct crystallization. Consequently, the desorption kinetics of the zeolite NaX coatings were also much superior to the other forms of zeolite NaX investigated in this study. This may be very beneficial for various applications, such as for use in adsorption heat pumps. The coating thickness affected the heat and especially mass transfer properties of the zeolite.
In this work, the adsorption/desorption kinetics of a consolidated bed, for adsorption heat pumps application, coated with a new composite adsorbent material based on SAPO-34 zeolite in a matrix of sulfonated poly(ether-ether-ketone) was investigated. The heat exchanger was coated by drop casting with a composite zeolite/polymer mixture containing 90 wt% of SAPO-34 powder. The adsorption/desorption kinetic was investigated using the Thermal Large Temperature Jump method and compared with the same heat exchanger filled with loose grains of SAPO-34. The coated heat exchanger exhibits very high specific cooling capacity with a very fast adsorption kinetic. The characteristic times were approximately 39% lower compared to zeolite grains filled adsorber. Analogously, the obtained maximum specific power value was 85% higher than that of the uncoated one.
The adsorber bed design and the method of integrating the adsorbent material in the bed have a major effect on the overall performance of the adsorption system. This study numerically investigates the performance of wire finned tube adsorber bed with aluminium fumarate metal-organic framework material integrated either using coating, packing, or combination of coating and packing. A 3D heat and mass transfer model using the coupled solution approach with a variable vapor pressure through the adsorbent voids between the particles is developed. Results showed that the coated wire finned heat exchanger outperforms the packed and the combined packed and coated in terms of the specific daily water production (SDWP) and specific cooling power (SCP). Also, a parametric study was carried out of the coated wire finned heat exchanger geometry including different tube diameters, fin height, and number of fins to predict the best geometrical parameters that produce maximum output using different coating thicknesses. Results revealed that using tube diameter of 22 mm, fin height of 20 mm, 44 fins per loop, and coating thickness of 0.5 mm can provide maximum water daily water production of 300 L/day and cooling power of 8.3 kW.
Water vapor has been one of the vital problems in purification of volatile organic compounds. In this study, the adsorption-desorption equilibrium of water vapor were conducted at 298, 308, 318 and 328K on three adsorbents: hypercrosslinked polymeric adsorbents (HPA), activated carbon fiber (ACF) and granular activated carbon (GAC). The obtained isotherms were type V and the adsorption capacity at the same condition was as follows: GAC>ACF>HPA. Cluster Formation Induced Micro-pore Filling (CIMF) model was adopted to fit the adsorption isotherms and the fitting parameters showed that adsorption capacities of water vapor on micropores and functional groups had a negative logarithmic linear relationship with temperature. The existence of functional groups could weaken the negative influence of temperature on the water adsorption performance, while the influence of temperature had negligible relationship with microporous volume. The hysteresis loops at different temperatures on three adsorbents had similar shape, the size of which were also as follows: GAC>ACF>HPA. They mainly occurred in micropore adsorption, but their size had positive relationships with both functional groups and microporous volume. The hysteresis became smaller along with the increase of temperature, closely related with the stability of water clusters. In conclusion, temperature, functional groups and porous structure played crucial roles for water vapor adsorption and the formation of hysteresis.
Adsorption heat pumps offer the possibility to provide cold from waste heat, and can therefore be an important component for an environmentally friendly and sustainable cooling supply. A new accurate measurement method is developed to evaluate the progress of performance improvement in this area through new material and heat transfer concepts. The new method covers the entire sample range from very small to large sample sizes and also allows measurements in the poorly accessible transition region of medium sample sizes in the range from 1 to 10 g. A comparison with the conventional volumetric method in large temperature jump adsorption experiments is carried out using granular TiAPSO-34 in a flatbed configuration as adsorbent. The sample mass is varied from 300 mg to 1709 mg and the influence on the adsorption rate is compared using the characteristic time constants describing the dynamics of the adsorption reaction. It can be shown that the time constant for the new method is almost constant with a maximum deviation of 9 % while the characteristic time constant for the conventional method varies up to 64 %. The difference in adsorptive loading per adsorbent varies from 0.193 to 0.197 for the new method and from 0.100 to 0.190 for the conventional method. The new measurement method thus provides significantly more reliable results for the design of adsorption heat pumps than the previous volumetric measurement method. From the experimental results it can also be concluded that the new measurement method can be used in the present case up to sample sizes of 600 g which makes the gravimetric version of the large temperature jump method obsolete in this case.
SAPO-34 and Y are two of the most commonly investigated zeolites for adsorption heat pump/cooling applications, due to their favorable adsorption properties. Some observations that mass transfer may be a limiting factor for SAPO-34 and faujasite (X/Y) coatings deserve further inquiry to understand better the performance limits of these materials. In this study, a theoretical investigation was made to predict the performances of zeolite Y and SAPO-34 coatings for an adsorption cooling system operated by waste heat, under various conditions. A mathematical model developed and tested previously for coatings of A and X type zeolites on various substrates was used for this purpose. SAPO-34 generally provided relatively high maximum cooling power, owing to its high water sorption capacity coupled with the relatively low regeneration temperature. However, mass transfer resistances became quite significant at relatively high coating thicknesses, originating from the rather slow water diffusion in this zeolite. Utilizing a relatively low desorption temperature of 100 °C, instead of 150 °C, favored the relative performance of SAPO-34 coatings. The strong temperature dependence of water diffusion in zeolite Y reduced the performance of this material. The enhancement of the adsorption temperature from 25 °C to 60 °C resulted in improved performances for NaY coatings. When enhanced diffusivity values were used in the calculations, to represent coatings with more open texture, the cooling power increased notably for both zeolites.
In this work, a new composite adsorbent coating on aluminum support, based on SAPO34 zeolite filler embedded into sulfonate polyether ether ketone matrix is investigated for adsorption heat pumps (AHP) applications. Composite zeolite/polymer mixtures, with 80–95 wt% content of SAPO‐34 zeolite filler have been prepared and coated on aluminum substrates. The as prepared coatings showed a pull‐off adhesion strength up to 2.0 MPa, significantly higher than conventional values of composite zeolite coatings reported in the literature. Scanning electron microscopy analysis demonstrated that the coating has a homogeneous morphology with zeolite filler well interconnected in the composite coating structure. Water adsorption isobars were carried out at equilibrium in the temperature range 30–120°C. The best adsorption performances for AHPs applications were observed for the PZ‐95 batch, where a maximum water uptake of ∼29.0 wt% was reached, highlighting that the polymer matrix presence does not alter the zeolite adsorption capability (31.3 wt%).
A numerical analysis was conducted to examine the effect of a coating technique on adsorption cooling system (ACS) performance compared to a fully-filled grain configuration. The main interest was the effect of coating thickness, binder and cycle time for adsorption cooling applications. Validation of the numerical model was confirmed by comparison with experiment. The coating configuration resulted in a larger interfacial area to open space and also a shorter length of vapor flow path compared to the fully-filled configuration, which enhanced the vapor flow and resulted in higher performance. The optimal coating thickness was found to be 0.2–0.5 mm. A short cycle time was enough for the coating configuration, which improved system performance. For example, at coating thickness t = 0.2 mm, a 34.17% enhancement in specific cooling power (SCP) was achieved with a shorter cycle time of 480 s rather than 840 s, with the penalty of 9.87% decrease in coefficient of performance (COP). The coating technique with reduced cycle time is a good design approach for adsorption cooling systems. The binder had a negative effect on system performance, but the coating technique had clear advantages compared to the fully-filled configuration, and there was no other way of binding the adsorbent particles together. Thus, it is recommended that the binder content be kept as small as it can be.
Adsorption heating/cooling became an alternative to vapour compression system due to low ozone depletion potential (ODP) and global warming potential (GWP). However, more investigation is required due their low efficiency when compared to conventional heating/cooling systems. This review emphasizes on the mathematical modelling simplification and heat transfer enhancement method that applied by many researchers to improve the performance of adsorption heating and cooling technologies. Various techniques investigated by many researchers on solving low thermal conductivity and the different methods for enhancing heat and mass transfer in the adsorbed bed/pipe also discussed. Common techniques used to enhance heat and mass transfer in the adsorbed bed/pipe include the fin type adsorbent tube/ heat exchanger, amalgamated adsorbent bed with a metal foam, consolidated adsorbent, adsorbent coating and adsorbent with multi cooling tubes. Other than that, recent advancements in adsorption cooling/heating systems also discussed in this review.
An innovative adsorber plate heat exchanger (APHE), which is developed for application in adsorption heat pumps, chillers and thermal energy storage systems, is introduced. A test frame has been constructed as a representative segment of the introduced APHE for applying loose grains of AQSOA-Z02. Adsorption kinetic measurements have been carried out in a volumetric large-temperature-jump setup under typical operating conditions of adsorption processes. A transient 2-D model is developed for the tested sample inside the setup. The measured temporal uptake variations with time have been fed to the model, through which a micro-pore diffusion coefficient at infinite temperature of 2 E−4 [m²s⁻¹] and an activation energy of 42.1 [kJ mol⁻¹] have been estimated. A 3-D model is developed to simulate the combined heat and mass transfer inside the APHE and implemented in a commercial software. Comparing the obtained results with the literature values for an extruded aluminium adsorber heat exchanger coated with a 500 μm layer of the same adsorbent, the differential water uptake obtained after 300 s of adsorption (8.2 g/100 g) implies a sound enhancement of 310%. This result proves the great potential of the introduced APHE to remarkably enhance the performance of adsorption heat transformation appliances.
Water adsorbent AQSOATM FAM-Z02 (Z02) coatings and pellets were evaluated in our custom-built lab-scale sorption chiller with two adsorber beds. Two finned-tube heat exchangers (HEX) (4.08 L) were coated with Z02 by Mitsubishi Plastics and compared with two other HEX that were packed with Z02 pellets. When tested with 15, 30, 30 and 90 °C operating temperatures for the evaporator, condenser, adsorption and desorption, and 5 to 30 min cycle times, the sorption chiller had a peak volumetric specific cooling power of 90 ± 5 kW/m³ with Z02-coated HEX compared to 59 ± 2 kW/m³ for HEX packed with Z02 pellets. The specific cooling power (SCP) and coefficient of performance (COP) were greater for Z02 coatings compared to pellets.
This review presents the state-of-the-art in adsorption heat pumps (AHPs) for heating applications. Crucial aspects like operating conditions, working pairs, performances, adsorbent bed forms, adsorbent heat exchanger geometries and cycle features are discussed. A comparison of AHPs with conventional heating technologies is provided, and concepts of AHPs developed by some market players are presented. Important achievements, gaps and trends of the R&D in this field are discussed.
In this work, at first, an overview on SAPO-34 zeolite coating for adsorption heat pumps is presented, highlighting current quality standard and open technological issues (i.e. the need for good mechanical and hydrothermal stability, high aging stability, etc.). Afterwards, we present an improved formulation of adsorbent composite coatings on aluminum support, having improved thermal and mechanical properties, especially when subjected to an impulsive stress. Specifically, the coated samples were prepared by dip-coating method starting from a water suspension of SAPO-34 zeolite and a hybrid polymer binder. Adhesive and mechanical properties were evaluated by pull-off test confirming the good interaction between metal substrate, filler and matrix. Adsorption equilibrium of water vapor on the adsorbent coating was measured in the range T = 30–150 °C and partial pressure of moisture equal to 11 mbar. It was found that binder does not affect the water adsorption capacity and adsorption rate of the original SAPO-34 zeolite.
The monolithic adsorbent is a key unit for adsorptive rotary dehumidification system. It is usually prepared by dip-coating adsorbent on glass fiber paper. In this study, a new in-situ synthesis strategy of Aluminum fumarate MOF (A520) monolithic adsorbent based on glass fiber paper was introduced. The influences of the mole ratio of fumaric acid to H2O, the reaction temperature and time on the crystal phase, pore structure and adsorption performance of the monolithic adsorbent were systematically discussed. The morphology of the adsorbent was characterized by Scanning Electronic Microscopy (SEM). And the adsorption and desorption performances were evaluated by DVS water adsorption and Differential Thermogravimetric Analysis (DTG). The results showed that under the conditions of the mole ratio of fumaric acid to H2O of 0.02, reaction temperature of 50℃ and the reaction time of 60 min, the obtained A520 monolith exhibited the highest BET surface area (740 m2g-1) and high adsorption capacity (0.3906 gg-1). The monolithic adsorbent carries about 76% A520 powder with facile fabrication process, high adsorption capacity, rapid adsorption rate and low desorption temperature providing a guidance for the fabrication of highly efficient desiccant dehumidification wheel.
This study presents a simple and reasonable experimental methodology for separating the effects of interfacial and internal mass transfers from an overall mass transfer. First, the mass transfer in the range of thickness with negligible internal mass transfer resistance is experimentally observed. It was assumed that the effect of the internal mass transfer can be neglected if the sorption dynamic data of two thin-coated samples correspond with each other. Then, the internal mass transfer resistance is calculated by subtracting the interfacial mass transfer resistance from the overall resistance. The adsorbent, named Wakkanai Siliceous Shale (WSS) impregnated with lithium chloride of 20 wt%, was coated on sample plates with different thicknesses (27 μm, 65 μm, 0.19 mm, 0.38 mm and 0.71 mm). The large pressure jump (LPJ) method was used, and adsorption dynamic characteristics were gravimetrically measured. Based on the experimental data, the adsorption dynamics of composite WSS-coated layers were compared with those of the layers coated by an A-type silica gel to verify the applicability of a composite adsorbent using WSS on adsorption heat pump systems.
To overcome the problem of peak electricity demand caused by the use of air-conditioning in the summer, researchers have been focusing their interest on adsorption chillers, which are an environmentally friendly technology in that they use waste heat as their power source and water as a refrigerant. In the present study, to improve the performance of an adsorption chiller, FAPO4-5 adsorbents were synthesized using two hydrothermal synthetic methods, and then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption/desorption isotherms and water adsorption isotherms.
Coatings of the adsorbent were applied to an aluminum substrate. Six different coating solutions were used, with a 5.0 wt%, 10.0 wt%, and 15.0 wt% content of epoxy-based and silicone-based binders, respectively. The surface features of adsorbent coating were observed with scanning electron microscopy (SEM). To determine the variation in the water adsorption properties of the adsorbents according to the binder type, each adsorbent was subjected to water adsorption isotherm analysis at 25 °C. The coating thickness was calculated by three dimension coordinate measuring machine. Cross-cut tests (performed according to ISO 2409:2013) were carried out to assess the strength of the adhesion of the coating to the aluminum substrate.
An adsorption heat pump is provided in Which Water vapor can be ef?ciently adsorbed and desorbed using a heat source having a loWer temperature than ones heretofore in use because the pump employs an adsorbent Which has a large difference in Water adsorption amount in adsorption/desorp tion and can be regenerated (release the adsorbate) at a loW temperature.
In this paper we proposed and tested a new methodology of studying the kinetics of water vapour sorption/desorption under operating conditions typical for isobaric stages of sorption heat pumps. The measurements have been carried out on pellets of composite sorbent SWS-1L (CaCl2 in silica KSK) placed on a metal plate. Temperature of the plate was changed as it takes place in real sorption heat pumps, while the vapour pressure over the sorbent was maintained almost constant (saturation pressures corresponding to the evaporator temperature of 5°C and 10°C and the condenser temperature of 30°C and 35°C). Near-exponential behaviour of water uptake on time was found for most of the experimental runs. Characteristic time τ of isobaric adsorption (desorption) was measured for one layer of loose grains having a size between 1.4mm and 1.6mm for different heating/cooling scenarios and boundary conditions of an adsorption heat pump. Maximum specific power estimated from the τ-values can exceed 1.0kW/kg of dry adsorbent, that gives proof to the idea of compact adsorption units for energy transformation with loose SWS grains.
Thermochemical storage of heat has general advantages: long-term storage without degradation, adjustable discharging temperature level, which can even be higher than the previous charging temperature, energy densities of about 100 to 1000 kWh/m 3 (sensible heat storage in water under atmospheric pressure yields about 60 kWh/m 3 ). (change-para-here) We report on a system with zeolites and water vapor as adsorbate, working under atmospheric pressure, with air as carrier gas. Operated as heat storage system, energy densities of about 200 kWh/m 3 are realised. Charging temperatures of about 200 °C are required. During discharging water vapor in humid air is adsorbed while flowing through a bed of dry zeolite pellets. The adsorption enthalpy is utilized by producing warm dry air. The charging process uses hot air for desorbing the water. (change-para-here) An analogous system can be used for air conditioning. In isothermal adsorption dry air of ambient temperature is produced. Then by adiabatic evaporation air is chilled. The desorption process is identical with the one applied in storage. Experimental results obtained in laboratory pilot plants are reported and technical problems are discussed.
The kinetics of water vapor adsorption/desorption under quasi isobaric conditions have been studied on one layer of loose pellets of FAM-Z02 placed on a metal plate. Temperature of the sample holding plate has been changed as it takes place in real adsorption heat pumps (AHPs), while the vapor pressure over the adsorbent was maintained almost constant (saturation pressures corresponding to an evaporator temperature of 5°C and a condenser temperature of 35°C). Adsorption- and desorption-end temperatures have been adjusted to 35 and 90°C, respectively. Measurements have been carried out on grains having the following size distributions: 0.7 to 1.0 mm, 1.4 to 1.6 mm and 2.0 to 2.6 mm. An average equilibrium differential water loading of 19.2 g/100 g has been measured during desorption compared to 16.4 g/100 g during adsorption. The adsorption/desorption rates have been characterized by the times required to reach 50, 80 and 90% of the equilibrium loading. It has been found that the adsorption kinetics are mainly dominated by inter-crystalline diffusion, while the desorption kinetics are mostly influenced by surface resistance to the heat and mass transfer. Average specific evaporator cooling/condenser heating capacities in the order of 1 kW/kg have been estimated for the grain size 0.7 to 1.0 mm, putting in evidence the possibility of developing highly compacted AHPs with FAM-Z02 for heating and cooling applications. The influencing parameters on the combined heat and mass transfer process have been discussed.
CHA-type structure silicoaluminophosphate zeolite (SAPO-34) was examined as an AHP adsorbent and the influence of silicon content on its adsorption performance was evaluated. SAPO-34 with silicon content of 7.5 mol% (Functional Adsorbent Material-Zeolitc 02; FAM-ZO(2)) was selected for further testing. The water vapor adsorption isotherm of FAM-ZO2 was S-shaped and highly dependent on temperature, and a small hysteresis was observed with adsorption/desorption at 363K. No changes were observed in the properties of FAMZO(2) after 100000 cycles of water vapor adsorption-desorption, indicating that FAM-ZO(2) is Suitable durable for practical use. When the AHP was operated under conditions of T,(L)/T-M/T-H=283 K/313 K/363 K, the adsorption capacity of FAM-ZO(2) was 4.8 times and 3.8 times those of Y zeolite and silica gel.
This paper describes the prototype of a small adsorption heat pump working on the adsorption pair silica gel-water. The developed system consists of two modules, each containing an adsorption reactor and a second heat exchanger for evaporation and condensation of the working fluid. The two modules are operated periodically in order to obtain a quasi-continuous heating or cooling output. A reliable control unit has been developed and implemented in the machine. Hot water provided at temperatures of 80°C to 95°C is used to drive the machine, and heat from the low-temperature heat source (10°C to 20°C) is upgraded to the intermediate temperature level of about 35°C to 45°C, which is suitable for low-temperature heating systems such as wall or floor heating installations. For cooling applications, chilled water of 10°C to 15°C is produced in an almost continuous mode. The first prototypes have been tested. Heating coefficients of performance (COPs) of more than 1.3 and cooling COPs for air-conditioning purposes (12°C to 15°C) of 0.5 have been achieved. The machine provided a mean heating power of up to 15 kW and a cooling power of up to 8 kW.
A zeolite-water adsorption module, which has been originally constructed for an adsorption heat pump, has been experimentally investigated as an adsorptive thermal energy storage unit. The adsorber/desorber heat exchanger contains 13.2 kg of zeolite 13X and is connected to an evaporator/condenser heat exchanger via a butterfly valve. The flow rate of the heat transfer fluid in the adsorber/desorber unit has been changed between 0.5 and 2.0 l min−1, the inlet temperature to the evaporator between 10 and 40°C. It turned out that the higher the flow rate inside the adsorber/desorber unit the faster and more effective is the discharge of heat. However, at lower flow rates higher discharge temperatures are obtained. Storage capacities of 2.7 and 3.1 kWh have been measured at the evaporator inlet temperatures of 10 and 40°C, respectively, corresponding to thermal energy storage densities of 80 and 92 kWh m−3 based on the volume of the adsorber unit. The measured maximum power density increases from 144 to 165 kWh m−3 as the flow rate in the adsorber increases from 0.5 to 2 l min−1. An internal insulation in form of a radiation shield around the adsorber heat exchanger is recommended to reduce the thermal losses of the adsorptive storage. Copyright © 2006 John Wiley & Sons, Ltd.
The working pair zeolite-water has very good characteristics for the heat pump application. It is non-poisonous, non-flammable and low-corrosive so that the use of a zeolite-water heat pump in the large field of domestic heating is very promising.
The poor heat and mass transfer of the zeolite has to be considered by an appropriate design of the adsorber heat exchanger. Compact zeolite layers directly linked with the heat exchanger enable a high specific thermal output (thermal output related to the mass of zeolite) which is the main shortcoming of these machines. Additionally the coefficient of performance (COP) can be improved significantly by a modular design of the machine consisting of six to eight heat pump modules. Due to the periodical operating mode which is required by the zeolite-water pair the single module is built up in a simple way without any moving parts. The different modules, each of them operating in another phase of the sorption cycle, are connected in series by a heat transfer medium circuit so that a continuous thermal output together with high COP is achieved by this zeolite-water heat pump.
First experimental investigations focus on the layout of the different components of the heat pump, e.g. the single module, the adsorber/desorber and the evaporator/condenser. The paper will present the design of these components as well as the design of the entire modular machine. Furthermore there will be a theoretical discussion of the COPs of the modular heat pump depending on the ambient temperature, on the number of modules and on the heating system.
This article presents a numerical study of the dynamic performance of an adsorption cooling system for automobile waste heat recovery. A new lumped parameter non-equilibrium model is developed and used to investigate and optimize the waste heat cooling system, which is estimated to be operated in quicker cycles when compared with the time needed to reach equilibrium. The effects of the operating temperatures and the overall heat transfer coefficient on the system performance are extensively investigated. It is found that the SCP is more sensitive to parameter changes than the COP. And improving the UA is the most effective way to obtain an increased SCP, but only in the ranges below the threshold value, which is determined by the overall mass transfer coefficient.
Various applications are discussed for the civil use of a device based on the adsorption/desorption of water vapour in a zeolite. Experimental work carried out with a testing system is described. Technical and economical development of such a system depends mainly on the solution of heat- and mass-transfer problems. To assess these problems, a special heat exchanger was designed and tested in a small-scale demonstration unit. We also describe the design procedure for a prototype heat exchanger and provide a description of a shell and finned-tube heat exchanger located in a zeolite bed. Details of plant assembly and experimental results are included.
Zugl.: Aachen, Techn. Hochsch., Diss., 2002.
Numerische Untersuchung einer periodisch arbeitenden adsorptionswärmepumpe
- T Westerfeld
T. Westerfeld, Numerische Untersuchung einer periodisch arbeitenden adsorptionswärmepumpe, Ph.D.-Thesis, RWTH Aachen University, Germany, Shaker Verlag, 1996.
Experimental Investigations of the kinetics of water vapor adsorption into MOLSIVTM DDZ-70 under typical operating conditions of adsorption heat pumps
- B Dawoud
- S Dunne
- R Lang
B. Dawoud, S. Dunne, R. Lang, Experimental Investigations of the kinetics of water vapor adsorption into MOLSIVTM DDZ-70 under typical operating conditions of adsorption heat pumps, Proc. Int. Sorp-tion Heat Pump Conf. "ISHPC 02", Shanghai, China, September 24e27, 2005, pp. 603e608.