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Novel Water Vapor Adsorbent FAM-Z01 and its Applicability to an Adsorption Heat Pump
Abstract
AFI-type structure ferroaluminophosphate zeolite (FAPO-5) was examined as an AHP adsorbent. FAPO-5 with iron content of 2-8mol% (Functional Adsorbent Material-Zeolite 01; FAM-Z01) was selected for further testing. The water vapor adsorption isotherm of FAM-Z01 was S-shaped and highly dependent on temperature, and almost no hysteresis was observed with adsorption/desorption at 333 K and 348 K. No changes were observed in the properties of FAM-Z01 after 200,000 cycles of water vapor adsorption-desorption, indicating that FAM-Z01 is suitably durable for practical use. When the AHP was operated under conditions of TL/TM/TH= 283 K/303 K/333 K, the adsorption capacity of FAM-Z01 was 4 times that of silica gel.
... Moreover, the specific heat is higher in samples with lower SAPO34 loading, ranging from about 0.85 kJ kg −1 • C −1 (foam Z60) to about 1.6 kJ kg −1 • C −1 (foam Z20). This behavior is due to the higher specific heat of the polymeric phase with respect to the pure SAPO34 fraction, which is characterized by relatively low specific heat (0.82-0.94 kJ kg −1 • C −1 [28]). The low specific heat of the Z60 foam is a physical property of interest for the application of thermal energy storage. ...
... Moreover, the specific heat is higher in samples with lower SAPO34 loading, ranging from about 0.85 kJ kg −1 °C −1 (foam Z60) to about 1.6 kJ kg −1 °C −1 (foam Z20). This behavior is due to the higher specific heat of the polymeric phase with respect to the pure SAPO34 fraction, which is characterized by relatively low specific heat (0.82-0.94 kJ kg −1 °C −1 [28]). The low specific heat of the Z60 foam is a physical property of interest for the application of thermal energy storage. ...
In this work, novel silicone-SAPO34 composite materials are proposed for application in adsorption thermal energy storage systems. The innovative composite materials were obtained through a mold foaming process activated by a dehydrogenative coupling reaction between properly selected siloxane compounds. Morphology analysis by optical microscopy and measurement of the mechanical properties of the foamed materials at varying zeolite content demonstrated a quite homogeneous open-cell structure and good structural stability of the foam. Water adsorption isotherms of the adsorbent foams expanded in free space and inside paperboard were measured by a gravimetric adsorption apparatus, demonstrating that the presence of the polymeric fraction does not affect the adsorption capacity of the SAPO34 fraction added in the composite foam. Finally, main adsorption and thermodynamic properties of the proposed foam have been compared with those of other adsorbent materials, confirming the possible use of these new composite foams as adsorbent materials for adsorption thermal energy storage systems.
... In this work, we report a new CSPM prepared from porous matrix named AQSOA-Z01, a partially Fe-substituted material from aluminophosphate AlPO 4 -5 (named FAPO 4 -5) [10,11], and CaCl 2 . The study aims to combine the advantages of the host and the salt which are the high water adsorption capacity in AHP working relative pressure and the stability in that condition. ...
... FAPO 4 -5, an iron-doped aluminophosphate zeolite with the AFI structure which is a one-dimensional pore structure, and pore size of 0.74 nm [11], was studied as the host matrix. It was synthesized by following the recipe from literature [10] (see Supplementary data for more detail). ...
New composite materials were prepared by impregnating CaCl2 into FAPO4-5 to enhance the water adsorption capacity of the FAPO4-5 and limit the deliquescence of CaCl2. The structure of the FAPO4-5 was not changed after impregnation, as confirmed by the corresponding X-ray diffraction (XRD) patterns. The composite materials exhibited enhanced water adsorption capacity (up to 08 g/g-sorbent at 50.0 wt% loading) within the working relative pressure range of water vapor of adsorption heat pump (AHP) systems (0.1–0.3 of water vapor relative pressure). The composite material with CaCl2 loading up to 15.9 wt% can also minimizes deliquescence of the salt which is not preferable in AHP applications. Despite partial pore filling of CaCl2 in the matrix, the adsorption capacities of the composites were comparable to the sum of the adsorption capacities of CaCl2 and FAPO4-5 without significantly affecting that of the pristine FAPO4-5.
... An adsorption chiller cycle using H 2 O or NH 3 refrigerant is considered to be an environment-friendly product. In a previous study, Kakiuchi et al. [6] introduced a new Functional Adsorbent Material-Zeolite 01 (FAM-Z01), which is an AFI-type structure Ferroaluminophoshate Zeolite (FAPO-5) with iron content of 2 -8 mol% [6]. It was suggested that the adsorption capacity of FAM-Z01 was four times than that of silica gel at a desorption temperature of 60˚C. ...
... An adsorption chiller cycle using H 2 O or NH 3 refrigerant is considered to be an environment-friendly product. In a previous study, Kakiuchi et al. [6] introduced a new Functional Adsorbent Material-Zeolite 01 (FAM-Z01), which is an AFI-type structure Ferroaluminophoshate Zeolite (FAPO-5) with iron content of 2 -8 mol% [6]. It was suggested that the adsorption capacity of FAM-Z01 was four times than that of silica gel at a desorption temperature of 60˚C. ...
Large amounts of waste heat below 100˚C from the industrial sector are released into the atmosphere. It has been suggested that energy system efficiency can be increased with adsorption chillers. However, the cooling power and coefficient of performance (COP) of conventional adsorption chillers significantly decrease with the desorption temperature. In this paper, we proposed a mechanical booster pump (MBP)-assisted adsorption chiller cycle, and evaluated its performances. In the cycle, a MBP was incorporated into a zeo-lite-water-type adsorption chiller for facilitating water vapor transportation between an adsorber and an evaporator/condenser. We have experimentally studied the effect of the input electrical power of MBP on the performances of adsorption chiller cycle. It has been demonstrated that the heat input achieved by using MBP at the desorption temperature of 50˚C was 1.6 times higher than that of without MBP at the desorption temperature of 60˚C. And the increase of pump power was found to be effective in increasing the heat input. Therefore, it was confirmed that the operation range of desorption temperature , which can be generated by using the waste heat, was extended and the cooling power was increased directly by using MBP.
... Novel adsorbent materials ''AQSOA Ò ", belonging to the class of (Silico)aluminophosphates, have been developed and commercialized by Mitsubishi Plastic Inc. (MPI) for desiccant and AHP systems [12]. Adsorption equilibrium and durability studies of adsorbents AQSOA Ò -FAM-Z01 and AQSOA Ò -FAM-Z02 are presented in [13][14][15][16]. Both materials present S-shaped isotherms, are able to exchange large amount of water (up to 0.25 g g À1 ) within narrow temperature and humidity ranges and conveniently low desorption temperature (60-90°C). ...
... In this sense, an optimal application may be refrigeration in fishing boats where seawater is widely available for heat dissipation. [19,22] X X X X X Composite LiBr-silica [19,21,23] X X X X X X Composite LiCl-silica [21] X X X Zeolite CBV-901 [17] X X X Activated Carbon SRD 1352/3 [26] X X X Carbon Fibers FR20 [26] X X X Zeolite 4A [7] X X Zeolite AQSOA Ò -FAM-Z02 [14] X X X Zeolite DDZ-70 UOP [16] X X X Zeolite SAPO-34 [10] X X X Composite Ca(NO 3 ) 2 -silica [20] X X Zeolite AQSOA Ò -FAM-Z01 [13] X X Microporous silica gel [6] X X Fig. 7 shows the heating COP and heating enthalpy Q 4 + Q c for the heat pumping case H2 at T max = 150°C. Utilization of methanol or ethanol is not recommend in heat pumping mode, due to the possible thermal decomposition effects. ...
In this study, the most promising working pairs are evaluated for utilization in thermal driven adsorptive heat pumping, air conditioning and refrigeration applications employing water, ethanol and methanol as refrigerant. With this aim, a comparative study was carried out for different currently available (silica gels, zeolites, aluminophosphates, activated carbons) and recently developed materials (composite adsorbents). A simple mathematical model was developed in order to evaluate the performance of various working pairs for different sorption cycles. Among the considered adsorbents, the Mitsubishi product AQSOA®-FAM-Z02, the composite adsorbents LiBr-silica and CaCl2-silica appeared the best water adsorbents for air conditioning and heat pumping purpose, providing heating/cooling COP up to 1.62/0.71 and heating/cooling enthalpy up to 1080/570 kJ kg-1. Also the LiCl-silica/methanol working pair showed high performance for air conditioning cycles, especially in terms of cooling enthalpy (Qev= 640 kJ kg-1).
... 31 Commercially applied sorbents that perhaps show most advantageous adsorption isotherms, when contacted with water, are those of the FAM Z-series (functional adsorbent material zeolite). FAM Z05, 45 and especially both Z01 46 and Z02 47 as commercialized by Mitsubishi Plastics, although referred to as the AQSOA tm series, 48 show very suitable adsorption character- istics. Adsorption isotherms of commercially used adsorbents are shown in Figure 4. ...
... The list is completed with selected or benchmark materials. For water as working fluid, these are commercially applied AQSOA-Z01 46 and -Z05, 45 both AlPO 4 -5-based zeotypes (Z01 is partially iron-exchanged) with the AFI-structure, AQSOA-Z02, based on the SAPO-34 zeotype (CHA-structure), and silica gel (Grade 40, Davidson). 362 For methanol as working fluid, research in academia has focused primarily on various activated carbons. ...
... Two AIPO-type adsorbents have been tested under over 100,000 cycles to demonstrate their suitable durability for practical use [132,133]. Among them, FAM-Z01 with 0.73 nm windows can obtain 0.2 g g − 1 of water uptake with adsorption/desorption at 30 • C and 75 • C, while FAM-Z02 with a small pore size of 0.38 nm can absorb a larger amount of water (0.3 g g − 1 ) but need to be regenerated at 90 • C. FAM-Z05 developed by Shimooka et al. [134] is able to adsorb water vapor at an ultra-low temperature of 50 • C. Recently, Liu et al. [123] studied an AlPO-type adsorbent with SFO topology, namely EMM-8, for water adsorption refrigeration. ...
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.
... Aluminophosphate-based molecular sieves possess similar properties as zeolites and they can be prepared in three types as Aluminophosphate (AIPO), Silicoaluminophosphate (SIPO), and, Ferroaluminophosphate (FAPO) [14]. Various researchers [15][16][17] have used FAPO-5 or also known as Functional Adsorbent Material Zeolite-01 (FAM-Z01) as desiccant material in the desiccant wheel. The performance of this wheel is more compared to Silica gel desiccant and it gives further research statement to work ahead in this field. ...
Desiccants play a major role in dehumidifiers operated using desiccant wheels. Performance improvement of desiccant wheels is mostly depending on the desiccants. Good desiccant materials should have high adsorption capacity and low regeneration temperature. Researchers in the past have made several attempts to review desiccant materials that possess good adsorption capacities and low regeneration temperature but not many have reviewed the class of nanoporous inorganic desiccant materials. This class of desiccants covers three novel types – Aluminosilicate zeolites, Aluminophosphate-based molecular sieves, and Aerogels. Detail review of nanoporous inorganic desiccants is presented in this paper in the context of the applicability of desiccants in the dehumidifiers operated using desiccant wheels. Authors have attempted to cover a work of researchers who have synthesized and utilized this novel class of desiccants for dehumidification. It is important to note that nanoporous inorganic desiccants have high adsorption capacity than conventional desiccants such as Silica-gel, activated carbon, zeolites, etc., and also, it possesses regeneration temperatures in the range of 50 to 90 °C which can be easy to achieve using low-grade energy or waste heat.
... The transport properties of adsorbent bed can be accelerated utilizing fins, and/or metal additives [16][17][18][19][20] or coated bed designs [21][22]. The example of new adsorbents can be given as SWS-1L [23], FAM Z01 and Z02 [24,25], AQSOA-Z05 [26], metal-organic frameworks (MOFs) [27], and Maxsorb III [28]. Although the new adsorbent can enhance the adsorption chiller performance, the endurance of new adsorbents under vacuum conditions and thermal treatment during cycles should be well researched. ...
The main objective of this study is to design a low-grade heat driven ethanol-silica gel adsorption chiller. The low-grade waste heat is utilized in an adsorption chiller. For this purpose, an innovative bed heat exchanger including a condenser embedded inside the adsorbent bed is uniquely designed. The silica gel/ethanol pair is examined both analytically and numerically in this article. The cycles of the adsorption chiller are performed experimentally. The obtained isotherm for the silica gel/ethanol fitted to Type III isotherm behavior. The obtained equations of isotherm are also validated numerically. The new adsorption chiller design used in this study has reduced the desorption temperature for silica gel/ethanol pair to 37°C which will widen the application area of adsorption chillers. The COMSOL Multiphysics program is used for 2-D numerical analysis of adsorbent bed. The mass transfer inside of the particle, the heat transfer in porous media, and Darcy law are used for analyzing the heat and mass transfer of the bed. Temperature and concentration distributions of adsorbent bed during the duration of adsorption and desorption processes are examined numerically. The specific cooling power and volumetric cooling power values of the system are found as 20.2 Wkg-1 and 4.5 kWm-3, respectively.
... Besides, new adsorbents are another way to improve performance. These newly developed adsorbents such as SWS-1L, FAM Z01 and Z02, AQSOA-Z05, and metal-organic frameworks (MOFs) [6][7][8][9][10][11][12][13] are new ways to improve the performance of the AHPs. On the other hand, new adsorbents which are suitable for vacuum and AHP working principle are limited in the literature or have not commercialized yet. ...
One of the most common adsorbents used in adsorption heat pumps (AHP) is silica gel. Many studies on adsorptive working with silica gel such as water, R134a, etc. can be found. On the other hand, the studies for another adsorptive working with silica gel as a pair are limited in the literature. Thus, this study is focusing on the acetone and ethanol adsorption rate on silica gel as an adsorptive. To calculate the COP values of these silica gel RD/acetone and silica gel RD/ethanol pairs, the isotherm equations should be defined, and the necessary calculations should be performed. With the help of the limited studies found in the literature on the adsorption rate of acetone and ethanol on silica gel, the isotherm equations are found, and the COP values are calculated for these pairs.
... Furthermore, the phenomenon of hysteresis is undesired for the adsorption process as this will cause a loss of inefficiency. Many researchers have used silica gel [37,38], zeolite [39,40], and functional adsorbent material such as FAM Z05 [41], Z01 [42], Z02 [43], and [44] for different applications. All these adsorbents show good adsorption characteristics, especially silica gel and zeolites. ...
The reduction of carbon dioxide emissions has become a need of the day to overcome different environmental issues and challenges. The use of alternative and renewable-based technologies is one of the options to achieve the target of sustainable development through the reduction of these harmful emissions. Among different technologies thermally activated cooling systems are one which can reduce the harmful emissions caused by conventional heating, ventilation, and air conditioning technology. Thermal cooling systems utilize different porous materials and work on a reversible adsorption/desorption cycle. Different advancements have been made for this technology but still a lot of work should be done to replace conventional systems with this newly developed technology. High adsorption capacity and lower input heat are two major requirements for efficient thermally driven cooling technologies. In this regard, it is a need of the day to develop novel adsorbents with high sorption capacity and low regeneration temperature. Due to tunable topologies and a highly porous nature, the hybrid porous crystalline materials known as metal–organic frameworks (MOFs) are a great inspiration for thermally driven adsorption-based cooling applications. Keeping all the above-mentioned aspects in mind, this paper presents a comprehensive overview of the potential use of MOFs as adsorbent material for adsorption and desiccant cooling technologies. A detailed overview of MOFs, their structure, and their stability are presented. This review will be helpful for the research community to have updated research progress in MOFs and their potential use for adsorption-based cooling systems.
... Silica gel (Fuji Silysia Chemical Ltd.) and iron aluminophosphate (FAM-Z01, Mitsubishi Chemical Corp.) were employed as conventional adsorbents for desiccant humidity control systems to evaluate the applicability of the cross-linked NIPA gel to the system [17]. The silica gel had a Brunauer-Emmett-Teller (BET) surface area (S BET ) of 632 m 2 / g and total pore volume (V total ) of 0.372 cc/g, while the corresponding values for FAM-Z01 were 357 m 2 /g and 0.32 cc/g. ...
Water vapor adsorption characteristics and the thermosensitivity for vapor adsorption of poly(N-isopropylacrylamide) gel (NIPA gel) cross-linked with N, N′-methylenebisacrylamide (MBAA) (cross-linked NIPA gel) were investigated for application in desiccant humidity control systems. The cross-linked NIPA gels were prepared via copolymerization of NIPA monomers and MBAA monomers, which were used as crosslinkers, at various reagent concentrations and polymerization temperatures in the range of 283–323 K. The water vapor adsorption isotherms of NIPA homopolymer, MBAA homopolymer, and cross-linked NIPA gels were obtained at adsorption temperatures in the range of 298–323 K using a volumetric gas adsorption apparatus. The water vapor adsorptivity of the cross-linked NIPA gel increased with increasing MBAA monomer concentration and decreasing NIPA monomer concentration. NIPA homopolymer under dry conditions showed weak thermosensitivity for water vapor adsorption between 298 and 313 K. Meanwhile, MBAA homopolymer showed almost no change in water vapor adsorptivity above adsorption temperatures of 298 K. The cross-linked NIPA gels had a similar thermosensitivity to NIPA homopolymer, but its sensitivity might be shifted to higher temperature than NIPA homopolymer. Thermosensitivity of the cross-linked NIPA gel was effective in improving polymer water adsorptivity, necessary for desiccant humidity control systems; however, the adsorption performance of the polymer gel systems investigated require further improvements before practical application will be possible.
... 16 As an alternative, the CHA-type silicoaluminophosphate material SAPO-34 has emerged as a commercially-viable adsorbent for adsorption-driven chillers due to its high water uptake at low relative pressure, combined with its very high durability and robustness. 17,18 However, efforts to develop more advanced water adsorbents are both critical and timely since the working capacities of these commercial adsorbents at low pressure (P/P 0 = 0.15-0.35) are not large enough. ...
The development of new water adsorbents that are hydrothermally stable and can operate more efficiently than existing materials is essential for the advancement of water adsorption-driven chillers. Most of the existing benchmark materials and related systems in this field suffer from clear limitations that must be overcome to meet global requirements for sustainable and green energy production and utilization. Here, we report the energy-efficient water sorption properties of three isostructural metal-organic frameworks (MOFs) based on the simple ligand pyridine-2,4-dicarboxylate, named M-CUK-1 [M3(3-OH)2(2,4-pdc)2] (where M = Co2+, Ni2+ or Mg2+). The highly hydrothermally-stable CUK-1 series feature step-like water adsorption isotherms, relatively high H2O sorption capacities between P/P0 = 0.10─0.25, stable cycling, facile regeneration, and most importantly, benchmark coefficient of performance (COP) values for cooling and heating at low driving temperature. Furthermore, these MOFs are prepared under green hydrothermal conditions in aqueous solutions. Our joint experimental-computational approach revealed that M-CUK-1 integrates several optimal features, resulting in promising materials as advanced water adsorbents for adsorption-driven cooling and heating applications.
... Mesoporous silicate-based zeolites with uniform pore size in the range of 2-10 nm, such as MCM-41 [10], SBA-15 [11], etc., and aluminophosphate based zeolites with uniform pore size in the range of 0.38-0.73 nm, named FAMs, such as AlPO-5, SAPO-34, FAPO-5, etc. [12][13][14][15], show a typical type V (S shape) water vapor isotherm. They do display lower desorption temperature, however, the adsorption capacity is much lower than that of conventional zeolites in the whole humidity range, especially in low humidity. ...
With a characteristic of type I water adsorption isotherms, NaA zeolite has been considered as a very promising candidate for the utilization in adsorptive rotary wheel dehumidification system for deep dehumidification. However, high desorption temperature of the zeolite is not conducive to the system energy saving. In this research, the La-modified, Nd-modified and the binary La/Nd-modified NaA zeolites were synthesized by microwave-assisted ionexchangemethod to reduce the desorption temperature. The structural and the composition of the modified products were characterized using X-ray diffraction (XRD) and X-ray Energy Dispersive Spectrometry (EDS), and their adsorption/desorption performances were evaluated by static adsorption, thermogravimetry (TG) and temperature programmed desorption (TPD). TG results exhibited that, Nd-modified zeolite with the highest ion-exchange degree (α) of 63.35% was more effective in reducing the desorption temperature of NaA zeolite. TPD analysis also demonstrated that the binary modified adsorbent had a lower desorption activation energy (Ed), which indicates that the binary modified zeolite as deep dehumidification adsorbent has an excellent desorption performance.
... These materials have S-shaped isotherms meaning that they have a high water exchange capacity for low temperature differences [18,21,22]. Recently, Mitsubishi Plastic Inc. developed and commercialized new adsorbent materials, AQSOA ® -FAM-Z01 and AQSOA ® -FAM-Z02 [23,24]. Both materials work with desorption temperatures in the range of 60-90 0 C and seem to be a promising solution for heating applications. ...
A review of the most relevant work on the field of adsorption heat pumps with emphasis on heating applications is presented, covering the working principle, physical models, adsorption equilibrium and kinetics, adsorbent material physical and thermodynamic properties, adsorbent bed designing and operating conditions. The major literature gaps and development challenges of adsorption heat pumps for heating applications are identified and discussed. A bridge between materials and system level studies is lacking. The simultaneous investigation of the adsorption kinetics, adsorbent bed specifications, operating conditions and interaction between all the system components is missing in the literature. Detailed information required for the development and validation of physical models is often not provided in the experimental studies. A physical model that considers an entire adsorption heat pump system, which is required for performance predictions and system's optimization, cannot be found in the literature. To improve the adsorption heat pump system's performance the heat and mass transfer resistances need to be minimized by developing new adsorbent materials and better interaction between the adsorbent bed and the wall of the duct where the heat transfer fluid flows. In addition, operation modes optimized for the desired application can also contribute to improving the system's performance.
... As the isotherm shape is very sensitive to such kind of substitution, this approach has great potential for adsorption performance (Kornatowski 2005). Recently, Ferroaluminophosphate (FAPO), known as FAM-Z01, had been proposed by Kakiuchi for commercial applications (Kakiuchi et al. 2005). It is expected to possess the essential characteristics for sorption cycles such as high affinity to water vapor, lower regeneration temperature (< 85 °C) and the ability to sustain uptake process at relatively higher adsorption temperature. ...
With a characteristic of S-shape isotherms for water vapor adsorption, aluminophosphate molecular sieve with AFI type (AlPO-5) has been considered as an up-and-coming adsorbent for the utilization in the adsorption cooling and heating (ACH) system. In order to improve its adsorption performance, iron doped AlPO-5 (FeAPO-5) with variable Fe loading was synthesized by microwave hydrothermal method. The effects of the iron doping content on the structure and adsorption performance were systematically investigated. The analysis results of X-ray diffraction (XRD), UV–visible spectroscopy (UV–Vis-DR) and scanning electron microscopy (SEM) showed that the iron ion was incorporated into aluminophosphate molecular sieves with a typical AFI structure as that of AlPO-5 through the isomorphous substitution. As the iron content of FeAlPO-5s increased, the isolated FeIII decreased, while oligonuclear FeIII and nanosized FeIII increased, besides, the static adsorption curves showed that the adsorption capacity of FeAlPO-5 increased first and then decrease. After iron modifying, the crystallinity and morphology of crystals was improved, and the adsorption performance increased from 0.185 g/g (AlPO-5A) to 0.235 g/g (FeAlPO-5), while the desorption performance of FeAlPO-5 (95.69 kJ/mol) was close to that of AlPO-5A (81.59 kJ/mol).
... We performed a regression analysis with respect to temperature on Y 1 , Y 2 , Y 3 , Y 4 and Y 5 , which were set to approximate literature values [13][14][15]; the generalized function is expressed by the following equation. Utilized parameters are indicated in the figure. ...
In order to improve the efficiency of the adsorption refrigeration cycle, this study proposes a triple-effect adsorption refrigeration cycle equipped with a compressor. This cycle can run in order to create a large variation in adsorbent concentration range by the compressor, even if there is little temperature variation in the desorption and adsorption processes. The objective of this study is to clarify the effect that regulating adsorption pressure using a compressor has on the adsorption refrigeration cycle, and to that end cycle efficiency was calculated using a static analysis based on a state of equilibrium. As a results from the simulation, the triple-effect cycles can operate by regulating adsorption pressure. Both COP and exergy efficiency can be improved by a factor of 1.2 if the cycled is regulated the adsorption pressure of each cycle rather than using a shared adsorption pressure. For heat sources in the temperature range of 70–100°C, this method is superior in terms of COP and exergy efficiency. COP values of approximately 1.7–1.8 can be obtained, which is three times higher than single-effect cycles. The triple-effect cycles have one-third the SCE of single-effect cycles but about the same SCE as double-effect cycles.
... This is why the H 2 O vapor diffusion resistance on the adsorbent packed bed was different for 20 kPa in the first adsorber desorption step and 4.2 kPa on the second adsorber desorption step. Mitsubishi Plastics, Inc [7]. Figure 12 illustrated the effect of the desorption temperature on the coefficient of performance. ...
Here, we propose a double-effect adsorption chiller with a zeolite adsorbent (FAM-Z01) for utilization of waste heat. The FAM-Z01 adsorbent has the potential to recover waste heat in low temperatures ranging from 353 to 333 K and shows good potential in the adsorption chiller in terms of the high cooling output. A double-effect adsorption chiller could provide a higher Coefficient Of Performance (COP) than that of a single-effect chiller. In this paper, we developed a measuring method for the amount of adsorption in the first and second adsorber in a double-effect adsorption chiller and measured the adsorption and desorption rate based on the volumetric method. We calculated the COP of the adsorption chiller with the quantity of adsorbent obtained in the experiment. In the experiments, the quantity of adsorbent in the first adsorber was 0.14 g-H2O/g-Ads at the pressure 20 kPa and a desorption temperature over 100℃. The amount of adsorbent in the second adsorber was equal to that of the first adsorber. By analyzing the COP with the experimental results, the COP value was calculated to be over 1.0 (–) at any desorption temperature. The COP of the double-effect cycle was higher than that of single-effect cycle.
... Crystalline aluminophosphates which exhibit isotherm type V with properly positioned isobars and relatively low desorption temperature (60-90°C) make up a family of adsorbents that have only in the past 5 years been considered for heat pumping and cooling applications [7]. Ferroaluminophosphate zeolite (FAPO-5), known as FAM-Z01, has been examined as an ACH adsorbent of which the adsorption capacity was 4 times greater than that of silica gel and already commercialized for ACH systems due to no changes after 200,000 cycles of water adsorption-desorption [19,20]. Moreover, FAM-Z05 (FAPO-34) could also obtain a higher dehumidification value in direct cooling and heating desiccant device system (DCHDS) [20]. ...
With a characteristic of S-shaped water sorption isotherms, AlPO4-5 molecular sieves have been considered as up-and-coming adsorbents for the utilization in adsorptive cooling and heating systems. In order to avoid toxicity and corrosion of fluoride, this paper introduced a fluorine-free microwave hydrothermal synthesis strategy of pure AlPO4-5 crystals. The effects of hydrothermal conditions including template agent, crystallization temperature and time on the performances of AlPO4-5 adsorbents were systematically investigated. Fourier transform infrared spectroscopy, X-ray diffraction (XRD), ²⁷Al and ³¹P solid state magic angle spinning nuclear magnetic resonance (MAS NMR), pore size analyzer and Scanning electron microscopy (SEM) were used to determine the chemical structure, crystalloid phase, framework, pore structure and the morphology. Adsorption and desorption performances were measured by static adsorption, thermogravimetry and temperature programmed desorption. XRD results indicated that both triethylamine and tetraethylammonium hydroxide as templates, AlPO4-5 crystals could quickly be synthesized within 30–45 min under fluorine-free microwave irradiation. By comparison, the adsorption and desorption performance of the former (recorded as AlPO4-5A) was superior to that of the latter (recorded as AlPO4-5H). FT-IR, MAS NMR and SEM results revealed that AlPO4-5 crystals have the frameworks of alternating AlO4 and PO4 units and typical hexagonal rod-like morphologies.
... 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]. Also, the novel zeolite for purpose of cooling cycle has been an interesting topic in the past decade [16,17]. ...
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.
... Currently, some of these zeolite-like molecular sieves have been utilized in practical desiccant cooling systems by various researchers [19e21]. Kakiuchi et al. [22] applied FAPO-5 adsorbent material to an adsorption heat pump. When the heat pump was operated under evaporation, adsorption and regeneration temperatures of 10 C, 30 C and 60 C, the adsorption capacity of the FAPO-5 heat pump was 4 times that of silica gel one. ...
A DCHE (desiccant coated heat exchanger) is a novel solid desiccant component with desiccant coated onto the surface of a fin-tube heat exchanger, in which desiccant coated aluminum-fin is an important part. It has an impact on overall performance of the whole desiccant cooling system. In this study, different zeolite-like powders (SAPO-34 and FAPO-34) coated aluminum sheets were fabricated. Their performance was tested and analyzed to investigate the feasibility in a DCHE system. Experimental values of surface area and pore parameters for desiccant coatings had a slight reduction because of the existence of binder solution. Adsorption kinetics indicated that the binder solution would not affect water adsorption capacity or adsorption kinetics of original desiccant powder. Moreover, SAPO-34 and FAPO-34 coated aluminum sheets had higher adsorption capacity than that of silica gel. Sorption isotherms were also measured and fitting equations were developed based on Polanyi principle. Finally, their dehumidification performance in DCHE systems was predicted with a mathematical model. Simulation results indicated that the DCHE prepared from FAPO-34 can have 2–3 times larger dehumidification capacity than those from SAPO-34 and silica gel at low regeneration temperatures.
Adsorption desalination is prescribed as a promising and eco-friendly solution for mitigating water scarcity, owing to its utilization of low-grade thermal waste and zero liquid brine discharge. The keystones that regulate the performance of the adsorption desalination system (ADS) include nature of adsorbents, system design, and operating conditions. The present study aims to provide a state of the art review on the keystones of ADS. Metal-organic frameworks (MOFs) hold remarkable adsorption capacity and tunable structure. However, hydrothermal instability, high cost, and complex synthesizing procedures are the potential challenges that need to be addressed. The technological advancements in ADS have been classified into: (i) Conventional Approach, (ii) Heat and Mass Recovery Approaches, (iii) Hybridization Approaches, (iv) and Adsorbent Substituting Approach. The study provides critical insight and compares the performance of each approach based on specific daily water production (SDWP), specific cooling power (SCP), and coefficient of performance (COP). The conventional ADS produce SDWP of 4.7 m3/ton/d, however producing zero and/or minimal SCP while using payable energy of 1.50 kWh/m3. In heat/mass recovery approaches, pressure equalization-valve delay schemes and master–slave configuration provide ∼ 5 % additional water adsorption/desorption on/from silica-gel and reduce ∼ 50 % thermal heating load, respectively. Evaporator-condenser amalgamation emphasizes the evaporator temperature of 30–42 °C leading towards ∼ 69 % higher SDWP with zero SCP. Dual stage, multi evaporators/condensers scheme is found supportive in cogenerating feature of ADS thereby improvising COP to ∼ 0.87. In hybridization approach, ejector integrated ADS produces SDWP of 80 m3/ton and COP of 2.22 using payable energy of 0.92 kWh/m3, however, needs experimental validation. In the adsorbent substituting approach, CPO-27(Ni), Emim-Ac/Syloid 72FP, and composite adsorbent manifest the SDWP to higher levels. The operating conditions are sensitive and need to optimize depending on the configuration of ADS. Possible future research directions may include efficient designing/ sizing of evaporators/ condensers, minimizing the heat and mass transfer resistances in adsorber/desorber reactor, optimize the thickness of the adsorbent layer in heat exchangers, and investigating wide range of adsorbent classes that can be driven with very low regeneration temperature.
This study investigates the performance of double effect adsorption refrigeration cycle that utilizes the adsorption heat of a high-temperature adsorbent heat exchanger for desorption of a low-temperature one. Because there is a freedom to select an adsorbent for each adsorbent heat exchanger, the combination of adsorbents such as silica gel, FAM-Z01, FAM-Z02 and FAM-Z05 were examined. The temperature of an external heat source was assumed to be 90°C. Dynamic cycle simulation was employed to estimate the performance in terms of coefficient of performance (COP) and specific cooling power (SCP). The results show that the combination of the adsorbents FAM-Z01 and FAM-Z02 for the low-temperature heat exchanger and high-temperature one, respectively, is the most effective to achieve high COP as well as high SCP. The results also indicate that the COP=1.0 is attainable when the mass allocation of the adsorbents and the cycle time are selected appropriately. From the viewpoint of maximizing the cooling power, COP=0.9 is suggested for the best design, where the mass of high-temperature side is equal to the mass of low-temperature side.
This study focuses on the adsorption heat pump cooling performance enhancement. The corrugated heat exchanger (HEX) has been employed in recent years owing to its excellent heat transfer; however, its filling method require improvement. Therefore, a filling method called dip-coating method is introduced to improve its heat transfer and packing density. The dip-coating method is adapted to accommodate the Wakkanai siliceous shale composite adsorbent, and two types of adsorbent filled-HEX (ad-HEX), i.e., the dip-HEX and dip-filled-HEX, are compared with the conventional ad-HEX of the filled-HEX. The dip-HEX comprises a few mass transfer channels and has a packing density similar to that of the filled-HEX. Meanwhile, the dip-filled-HEX exhibits a 30% higher packing density compared with the filled-HEX. A basic performance experiment is performed, and the results indicate that the dip-HEX outperforms the filled-HEX owing to its higher coefficient of performance (COP) and specific cooling power (SCP). The dip-filled-HEX exhibits a slightly lower SCP than the filled-HEX; however, it exhibits the highest COP among three types of ad-HEXs. Subsequently, mass recovery is applied to enhance the cooling performance. In a typical mass recovery period of 10 s, the COP and SCP of the dip-HEX increases to 0.46 and 0.74 W/g, respectively.
Dehumidification performance of a high-efficient compact desiccant cooling component named desiccant-coated heat exchanger (DCHE) highly depends on coated desiccant materials. Currently, mesoporous silica gels and salt-supported silica gels have been extensively studied. Silica gels have limited adsorption quantity in the middle relative pressure range, while salt-supported silica gels have potential threat of corrosion. In this work, a metal–organic framework UiO-66 that can achieve good adsorption quantity without corrosion is reported. The equilibrium adsorption test shows that UiO-66 has promising water uptake, especially in the relative pressure range of 0.35–0.65. The adsorption kinetics test displays that UiO-66 exhibits desirable dynamic water uptakes and adsorption rate constant. Dehumidification capacities of a DCHE using UiO-66 are estimated via a mathematical model and compared with silica gel- (SG) and LiCl-supported silica gel (SG/LiCl). Simulation results show that UiO-66 has better dehumidification performance than both SG- and SG/LiCl-coated samples for semiarid and semihumid climates when outdoor temperature is lower than 36 °C. Especially, when the temperature and relative pressure of inlet air are set as 30 °C and 0.35, respectively, its dehumidification capacity can be 2.7 times the amount of the SG-coated one and 1.3 times of the SG/LiCl-coated one. However, it should be more prudent in choosing UiO-66 under hot and humid climates.
Cyclic physical adsorption and desorption processes on porous materials can be used for the conversion of heat in heat transformation processes, which is the working principle in adsorption heat pumps (AHPs). Environmentally benign water with its high enthalpy of evaporation is the working fluid of choice in AHPs. Metal‐organic frameworks, MOFs can adsorb large amounts of water or methanol, up to their own weight. MOFs could be alternative materials to silica gels, zeolites, or aluminum phosphates for low‐temperature heat transformations in AHPs.
Ferroaluminophosphate (FAPO4‐5)/MgSO4 composites were prepared as a series of new materials with low charging temperatures and improved volumetric heat storage capacities. A microporous zeolithic compound FAPO4‐5 was used as an adsorbent of water vapor and a matrix of MgSO4 salt particles. Composites with various MgSO4 contents (5‐40 wt%) were then prepared using a wet impregnation method. The MgSO4 salt particles were impregnated into the micropores and textural pores of FAPO4‐5 without the crystal structure of the host material, confirmed by XRD patterns. Although nitrogen adsorption isotherms of the composites showed approximately a half of FAPO4‐5 pore was blocked by MgSO4, the water uptake of the composites reached the sum of those from FAPO4‐5 and MgSO4. The dehydration temperature of MgSO4 in the FAPO4‐5 matrix decreased with its decreasing content due to the easier dehydration of FAPO4‐5. The heat storage recovery of the 25 wt% loaded sample at 80°C was 85.5% while that of MgSO4 was 52.2%. The swelling and agglomeration of the composites containing 25 wt% and less salt were suppressed by the micro and textural pores of FAPO4‐5. The composite at 25 wt% of MgSO4 loading exhibited a total volumetric heat storage capacity of 174 kW h m−3 based on the volume in the hydrated state. Composites with various MgSO4 contents (5‐40 wt%) in the micropore and textural pore of a ferroaluminophosphate (FAPO4‐5) were prepared using a wet impregnation method. Limited swelling of the confined MgSO4 salt particles in the pore allowed the composites to exhibit highly improvement of volumetric heat storage capacity. Moreover, the dehydration temperature of MgSO4 in the composites decreased due to the easier dehydration of FAPO4‐5 and thus heat storage recovery at low temperature was improved.
This study aims to develop a low-cost and highly efficient adsorption chiller (AHP). A laboratory-scale AHP with a capacity of 1 kW and transparent body was developed to observe the valve's operation and condensed water. A natural mesoporous material, WSS impregnated with 20 wt % LiCl was used as an adsorbent to reduce the initial cost and filled into aluminum corrugated heat exchangers (HEX). Foundation performance experiments were conducted, and the COP of 0.45 and SCP of 0.41 kW/kg were obtained under the following experimental conditions: regeneration at 80 °C, condensation, and sorption at 30 °C, chilled water of 15 °C, and cycle time of 14 min. Further, heat recovery was introduced and experimentally studied to reduce the regeneration heat amount, and the heat balance for this AHP was evaluated. It was confirmed that two types of heat recoveries could improve the COP for this AHP up to 0.54 when the outlet temperature of both adsorbers was 55 °C. The COP could be further improved to 0.57, based on the calculation for the heat balance. This AHP has advantages of high SCP as compared with AHPs in other formal studies, although some details need to be studied in the future.
The composite adsorbent of natural mesoporous powder of Wakkanai siliceous shale (WSS) impregnated with LiCl has been investigated. In this study, the slurry of WSS–LiCl with acryl resin as a binder was prepared for fabricating an adsorbent-filled heat exchanger (HEX). The optimal LiCl content for the impregnation with WSS was 20 wt%, which was chosen from the relation between water uptake and pore volume. The theoretical sorption amounts were estimated from various sorption isotherms, and the value was 0.34 g/g at the temperature conditions of 80 °C (regeneration), 30 °C (condensation and adsorption), and 15 °C (evaporation). From the analysis of sorption heat, it was found that water adsorption and desorption occurred repeatedly at the lower region of 45–50 kJ/mol at the driving conditions for the adsorption heat pump. To evaluate the coefficient of cooling performance (COP) and a specific cooling power (SCP), the adsorbent-filled HEX was prepared using a small-sized corrugated-fin-type aluminum HEX and the slurry. The COP and SCP were 0.41 and 498 W/kg at 80 °C of regeneration, respectively.
This study was focused on the evaluation of the adsorption kinetics of water vapor onto silica-gel with and without an acoustic field, in an objective to reveal the enhancement mechanisms of water vapor adsorption by an acoustic wave. Adsorption uptake curves of water vapor from humidified air onto the silica-gel with and without acoustic field were measured at room temperature under various conditions, after which the adsorption kinetic parameters (fluid film mass transfer coefficient and intraparticle diffusivity) were determined from the uptake curves with the aid of numerical calculations. The results demonstrated that the acoustic field exhibited no effect on the intraparticle diffusion, because the fluid film mass transfer was the rate-limiting step under the condition of this study. In contrast, the fluid film mass transfer was enhanced by the velocity amplitude of the acoustic field. However, the diminished mass transfer was also observed in some cases. For the enhancement and diminution of adsorption rate by the acoustic wave, it was suggested that the ratio of the oscillation flow (U) to the steady flow (u), U’ = U/u, was an important factor. Moreover, the enhanced adsorption kinetics was observed under the conditions of U’ > 2, whereas the adsorption rate was diminished or invariant under the condition of U’ < 2. This would be understood from the viewpoint of the thinning and thickening of fluid film by the oscillation flow caused by the acoustic wave. Even when the direction of the oscillation flow is countercurrent to the steady flow, the thinning of fluid film by the oscillation flow is still possible under U’ = U/u > 2.
Nitrogen-doped porous carbons were prepared via chemical activation of chitosan using alkali-metal carbonates (Na2CO3, K2CO3, Rb2CO3, and Cs2CO3), and the water adsorption isotherms of prepared carbons were measured to estimate the performance of the carbons in adsorption heat pump/desiccant cooling. Pre-doping of an alkali carbonate activator into the chitosan precursor resulted in a highly developed micropore structure and the introduction of macropores. The macropore structure clearly depended on the alkali carbonate activator. Na2CO3 resulted in two-dimensional macropores because of the hard-template effect, whereas the other alkali carbonate activators resulted in three-dimensional macropores with different cell sizes. A density functional theory calculation study based on X-ray photoelectron spectroscopy analyses of nitrogen-doped activated carbons indicated that pyridinic (pyridine, pyridone, and pyridine N-oxide), amide, and quaternary N groups might be effective for low-pressure water adsorption. Although the water adsorption capacities of the prepared carbons at P/P0 > 0.5 increased with increasing micropore volume, those at the low-pressure region (P/P0 < 0.1) were dependent on the surface density of nitrogen or oxygen functional groups. In addition, the shape of water isotherms preferable for adsorption heat pump/desiccant cooling was observed for the carbons with an appropriate surface density of nitrogen functional groups.
The adsorption–desorption behavior of a fin-tube heat exchanger coated with Functional Adsorbent Material Zeolite (FAM-Z01) was investigated to experimentally determine the influence of the temperature of the hot water circulating in the heat exchanger and cycle time on adsorption-desorption behavior and heat flow. It was found that dehumidification performance increased significantly as the water temperature increased from 50 to 60°C and to a lesser degree from 60 to 70°C, in the temperature range in which the performance control step switches from regeneration to adsorption. Heat-flow analysis revealed that in the regeneration region the heat exchanger did not effectively use its heat supply, and preheating of the regeneration air was shown to improve the regeneration performance. Coefficient of performance COPth, which indicate the cooling efficiency, and COPlat, which indicate the dehumidifying efficiency, were significantly improved at a hot-water temperature of 50–60°C. Thus, preheating of air was shown to be quite effective in improving dehumidifying performance at the lower range of hot-water temperatures.
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.
Adsorption cooling system is driven by low‐grade heat sources and is an eco‐friendly system, is therefore considered a potential alternative to the traditional vapor‐compression refrigeration system. An exergy analysis is a tool for identifying the details of energy degradation of each process and component, but there is a critical limitation in previous works which assumed there was no spatial variation in the adsorption beds, i. e., the lumped capacity method. We have conducted both an energy and exergy analysis of an adsorption cooling system. The exergy analysis was conducted based on detailed information obtained from the CFD results of energy analysis. The numerical results provide detailed information which varies in time and space, free of the assumptions used in lumped capacity methods, by including the effects of geometric features (fin height, fin spacing, tube diameter, and thickness) and, the contact resistance between sorbent material and metallic finned tube, which affirmatively enhance the accuracy of the exergy analysis. Finally, we analyze the effect of several main parameters from the view point of the 2nd law of thermodynamics. The results show that increases in the temperature of the heat sources leads to an increase in energy performance while the exergy efficiency decreases; increases in the cooling water temperature reduces the COP, SCP, and ηex. An increase in cycle time improves the COP and ηex but reduces the SCP. The exergy analysis was conducted based on detailed information obtained from the CFD results of energy analysis. The numerical results provide detailed adsorption bed information which varies in time and space, free of the assumptions used in lumped capacity methods. The effect of several main parameters on system performance from the view point of the 2nd law of thermodynamics was discussed, herein.
This paper presents static analyses of two stage adsorption cycle using FAM Z01 & FAM Z05 as the adsorbents. The conventional two stage system consists of four adsorbent beds. In contrast, in new scheme three beds were used assigning FAM Z01 and FAM Z05 combination for low and high pressure sides, respectively. The objectives of this study were to evaluate the performance of two stage cycle with the Z01 & Z05 combination of adsorbent pair, and to compare the performance with that of the conventional two stage cycle using Silica-gel. Static analysis based on Dühring diagram was employed to estimate the performances of specific cooing effect (SCE) and COP. It was found that the cycle with new combination gives SCE more than twice compared with the conventional Silica-gel-water system at the heat source temperature of 55°C. The sensitivity analysis was also performed for optimal mass allocation to adsorbent beds.
A system which is driven by low-grade heat around 60–90 °C is expected to enhance the use of the solar heat and waste heat. The adsorption refrigeration is capable of operating at low-grade heat while the challenge is how to increase the efficiency of current implementations of adsorption refrigerators. The double-effect cycles have higher COP than a conventional single-stage adsorption cycle because the heat generated from an adsorption process is recovered and reused as a heat source. The double-effect cycles consist of two adsorbers, and there exists freedom to select adsorbent for them. The water adsorbent isotherm of FAM was S shaped and highly dependent on adsorption pressure, and the combination of FAM will be effective for the double-effect cycle according to the adsorption pressure. However, operating temperature range of the double-effect cycles is higher than the conventional single-effect adsorption cycle; the double-effect cycles have lower COP below 80 °C because the condition of adsorption pressure at this temperature range is not suitable for any adsorbents. This study suggests using the double-effect adsorption cycles combined a compressor with a view to improving COP below 80 °C. The compressor sets up, and the adsorption pressure is controlled by compressed refrigerant vapor. The adsorption cycle can work under a lot of changes due to adjusting the adsorption pressure regardless of the external temperature like the heat source. The effect of the combination of adsorbents on adsorption cycle and installation position of a compressor is not clear. The objective of this study is to investigate the COP, SCE, and exergy efficiency of double-effect adsorption cycles with various installation position of a compressor and various adsorbent pairs FAM Z01, FAM Z02, and FAM Z05. The double-effect cycle is examined by means of the static cycle simulation assuming equilibrium stats where the cooling effect is dominated by driven heat source temperature, cooling water temperature, evaporator pressure, condenser pressure, and adsorption pressure. The results from the static cycle simulation imply that the hybrid double-effect adsorption refrigeration cycle is the efficient refrigeration cycle and can enhance the performance. For heat sources in the temperature range of 60–90 °C, the method is superior when the compressor is installed on the high-pressure side and adsorbent pair is Z02-Z01. COP amounts to 1.2, SCE amounts to 350 kJ/kg, and exergy efficiency amounts to 0.45 by supplying a minimal power consumption to the compressor. As a result, this system is expected to increase the non-utilized heat such as solar heat or waste heat utilization.
A numerical simulation of the performance of a fin-tube-type adsorption bed with silica gel/water working pairs was conducted. Three models of the heat recovery cycle, the mass recovery cycle, and a combined heat and mass recovery cycle were closely examined. The main goals were to determine 1) the conditions under which these advanced cycles were most effective and 2) the optimum recovery time. Mass recovery enhanced both the coefficient of performance (COP) and specific cooling power (SCP) by up to 24 and 37.5 %, respectively, at 60 °C, and the enhancements of the COP and SCP were 5.0 and 16.0 %, respectively, at 90 °C. Heat recovery increased the COP by 12.56 %, but reduced the SCP by 10.84 % at 60 °C, whereas, at 90 °C, the COP increased by 11.83 % and SCP decreased by 5.96 %. The mass recovery is more influential at a low heating temperature than that at a high heating temperature. Therefore, in the combined heat and mass recovery cycles, the main contribution to the enhancement of the COP comes from mass recovery at lower water temperature. However, at a high heating temperature, the COP increases mainly due to heat recovery.
The objectives of this paper are to analyze adsorption heat pump (AHP) systems using different working pairs such as silica gel/water, zeolite/water, SAPO-34/water, FAPO-34/water and activated carbon/ammonia, and to carry out their boundary conditions. According to the Clapeyron diagram, adsorption equilibrium equations and energy balance equations, feasibility and economic studies under various working conditions are made. Silica gel/water, SAPO-34/water and FAPO-34/water AHPs can feasibly operate for space heating and domestic hot water. Beyond that, zeolite/water and activated carbon/ammonia AHPs can even feasibly operate for heating network or industrial heating/preheating. However, ranges of economic operation are much stricter than that of feasible operation. Silica gel/water, SAPO-34/water and FAPO-34/water AHPs are not convenient for cold winter except zeolite/water and activated carbon/ammonia AHPs. Activated carbon/ammonia AHP even can economically operate in the cold winter with −15 °C ambient temperature. Floor heating is the most convenient technique for silica gel/water, SAPO-34/water and FAPO-34/water AHPs. Zeolite/water and activated carbon/ammonia AHPs require more than 130 °C and more than 140 °C driving source for economic use, respectively. The sequence according to the value of COPH is as follows: silica gel/water, FAPO-34/water, SAPO-34/water, zeolite/water and activated carbon/ammonia AHPs.
A cross-flow heat exchanger type adsorber was investigated for a desiccant humidity control system. The aim of the adsorber was to improve dehumidification performance by forcibly cooling an adsorbent with flowing air. Aluminophosphate (AlPO) zeolite was coated on the heat exchanger, because it was expected to regenerate sufficiently even with a low-temperature heat source of around 333 K. Fundamental dehumidification behavior with the adsorber was experimentally investigated at various inlet absolute humidities, regeneration temperatures, and air flow velocities. Dehumidified water in an equilibrium state was kept even at a regeneration temperature of 333 K, indicating that the adsorber coated with AlPO zeolite could be driven using low-temperature heat at 333 K. The dehumidification rate was found to increase as the cooling and process air velocities increased. However, the increase in the dehumidification rate decreased when cooling air flowed at a velocity of 2 m/s or more. Heat removed by the cooling air increased as the cooling air velocity increased and the process air velocity decreased. It was also found that dehumidified air could be supplied for a longer period at a sufficiently low absolute humidity suitable for practical use as the cooling air velocity increased.
The working pair is one of the main influencing parameter on performance of an adsorption heat pump (AHP). Researchers started to synthesize different adsorbents in order to improve the adsorption rate. Even the adsorption rate could seem very well, the new adsorbent could not be suitable for an AHP for given conditions. In this context, the effect of new adsorbent materials with isotherm Type V on adsorption-desorption processes of an unconsolidated adsorbent bed works for refrigeration are investigated. The adsorbate is taken as water. Type V isotherm equations for each adsorbent are predicted and the influence on the performance is analyzed. The constants in the equation that simulate the isotherm shape are found. The average temperature/concentration in the rectangular bed during the adsorption/desorption processes are plotted for different novel adsorbents; FAM-Z01, FAM-Z02, MIL101@GO5, and NH2-MIL-125(Ti). The performed numerical solutions for the case which is taken into account for this paper (evaporator temperature and bed heating temperature are 2 °C and 77.5 °C) showed that, MIL101(Cr)@GO5 has the best Specific Cooling Power for the volume of the bed which is 21.13 kJ/kga but has worst COP as 1.20. FAM-Z01 has 53.85 kJ/h evaporator capacity where this value is the best for the case.
An adsorption refrigeration chiller has great potential for improving energy conservation. It uses adsorbing materials with low regeneration temperatures that can be regenerated by waste heat from a gas engine or hot water from a solar heat collector. To optimize the operation of an adsorption refrigeration chiller, a performance prediction method is required. In this study, a model of an adsorption refrigeration chiller was developed for annual building energy simulation.
Models have been developed to calculate the thermodynamic properties of an adsorbent. Many of the adsorption refrigeration chillers currently available in the market use an AFI-type structure ferroaluminophosphate zeolite (FAPO-5) as the adsorbent. As the adsorption isotherms of FAPO-5 have sigmoidal characteristics in contrast to those of general zeolite or silica gel, they were approximated using a logistic function (Eq.(1)). Fig. 2 shows the adsorption isotherms of FAPO-5. To increase the calculation speed, a linear regression model (Fig. 3) was also proposed. The correlations between relative pressure [-], adsorbent temperature [K], and adsorption [kg/kg] were expressed in the model. The relative and absolute error rates of adsorbent temperature were 0.009% and 0.024%, respectively, in the range of applications. To calculate the temperature of saturated water from relative pressure and adsorbent temperature, a linear regression model of saturated water and vapor was also developed.
The model of the adsorption refrigeration chiller consists of four components: a condenser, an evaporator, an adsorber, and a desorber. Fig. 4 shows the heat balance diagram of the adsorption refrigeration chiller. Heat flow was modeled using cooling water, chilled water, and hot water. Heat flow inside the chiller occurred by vaporization, condensation, desorption, and adsorption of refrigerant water. The heat exchange at each component was expressed with the NTU (number of transfer units) effective method as expressed in Eqs. (15), (22), (25), and (27). The changes in adsorption at the adsorber and desorber were expressed using differential equations as shown in Eq. (18) and Eq. (24). Fig. 5 shows the time series of the adsorption refrigeration cycle assumed in this model. Eq. (18) and Eq. (24) can be solved to Eq. (36) and Eq. (40) by using the linearity assumption of adsorption isotherms. Fig. 6 shows the calculation flow diagram of the model. Three iterative computations were required. The co-efficient of performance (COP) of the chiller was calculated iteratively in the outer loop. The hot water outlet temperature and desorb temperature were calculated iteratively in the inner loop. When the value of adsorption exceeded the linear range in the iterative calculations, the value was corrected as shown in Fig. 7.
A sensitivity analysis was performed to evaluate the developed model. Fig. 8 shows the results of sensitivity analysis. The cooling capacity and COP were calculated by varying the temperature and flow rate of cooling water, hot water, and chilled water. The plot in Fig. 8 represents the actual measured data from a previous study. The lines in Fig. 8 are the calculated results for the developed model. The solid lines denote the results that have the same boundary conditions as the measured data. The results of the sensitivity analysis on flow rates were consistent with the measured data. Sensitivity analysis on the hot water inlet temperature shows slightly different trends compared to measured data.
All source codes developed in this study are distributed under General Public License and can be downloaded from the website ( http://www.hvacsimulator.net ).
This paper investigates the characteristics of ferroaluminophosphate (FAM-Z01) compared to various types of conventional silica gels in the performance of an adsorption bed. FAM-Z01 has high potential to replace silica gel due to some key advantages, including a low heating temperature and high adsorption rate resulting from its S-shaped isotherm. We conducted a performance simulation on a fin-tube type adsorption bed with FAM-Z01/water and silica gel/water working pairs and compared the results in terms of coefficient of performance (COP) and specific cooling power (SCP). In the partial pressure range of typical operating condition for silica gels, there was no advantage with FAM-Z01. However, in the partial pressure range of 0.14 < P/P0 < 0.29, which corresponds to a lower evaporation temperature (15°C → 10°C) and lower heating temperature (80°C → 70°C) compared to the typical operating condition for silica gels, the COP of FAM-Z01 was almost similar (3.72 % decreased) to that of Type-RD silica gel, while the SCP was significantly increased by 35.0 %. This indicates that without a change of system efficiency, FAM-Z01/water has a high cooling capacity with small size as compared to Type-RD silica gel/water. This confirms that the adsorbent FAM-Z01 has a high potential to address one of the adsorption chiller’s disadvantages, i.e., system size.
A heat pump process is a thermodynamic process having the main target to pump heat from a heat reservoir at a low temperature (ambient heat source) to a heat sink at a higher temperature (heating net). According to the second law of thermodynamics, this target can only be realized if a driving energy is applied. Contrary to the vapor compression heat pump process, where mechanical work is applied as a driving energy to run the compressor, thermally driven heat pumps (TDHP) make use of heat at a higher temperature (driving heat source), compared to the heat sink temperature, as a driving energy.
Shaped MIL-101 and ethanol were selected as a working pair for adsorption refrigeration in this work. The adsorption isotherm of ethanol on shaped MIL-101 (MIL-101-3) was obtained by high vacuum gravimetric method. The desorption performance of ethanol on MIL-101-3 was measured by Thermo Gravimetric Analyzer. The adsorption refrigeration performance and cyclic adsorption stability of MIL-101-3–ethanol were investigated on the simulation device of adsorption refrigeration. The results show: (1) the equilibrium adsorption capacity of ethanol on MIL-101 is 0.74 kg/kg at 25 °C. (2) The desorption peak temperature of ethanol on MIL-101-3 is 54.0 °C, and temperature of complete desorption is about 100 °C. (3) At the desorption temperature of 80 °C, the refrigeration capacity of MIL-101-3–ethanol working pair reaches 283 kJ/kg, which is 2.2 times as much as that of activated carbon–ethanol. (4) MIL-101-3 shows no significant reduction of ethanol uptake after 60 cycles, and the Brunauer−Emmett−Teller (BET) surface area only decreases by 3.3%.
A large fraction of global energy is consumed for heating and cooling. Adsorption driven heat pumps and chillers could be employed to reduce this consumption. MOFs are often considered as ideal adsorbents for heat pumps and chillers. While most published works to date on this topic have focused on the use of water as working fluid, the instability of many MOFs to water together with the fact that water cannot be used at sub-zero temperatures pose certain drawbacks. The potential of using alcohol-MOF pairs in adsorption driven heat pumps and chillers is investigated. To this end, eighteen different selected MOF structures in combination with either methanol or ethanol as working fluid are considered, and their potential is assessed based on adsorption measurements and thermodynamic efficiencies. If alcohols are used instead of water (1) Adsorption occurs at lower relative pressures for methanol and even lower for ethanol, (2) larger pores can be utilized efficiently, as hysteresis is absent for pores smaller than 3.4 nm (2 nm for water), (3) larger pore sizes need to be employed to ensure the desired step-wise adsorption, (4) the effect of (polar/apolar) functional groups in the MOF is far less pronounced, (5) the energy released or taken up per cycle is lower, but heat and mass transfer may be enhanced, (6) Stability of MOFs seems less of an issue and (7) cryogenic applications (e.g. ice-making) become feasible. From a thermodynamic perspective, UiO-67, CAU-3 and ZIF-8 seem to be the most promising MOFs, for both methanol and ethanol as working fluid. Although UiO-67 might not be completely stable, both CAU-3 and ZIF-8 have potential to be applied, especially in subzero temperature adsorption chillers (AC).
Adsorption chillers are capable of utilizing inexpensive or free low grade thermal energy such as waste heat and concentrated solar thermal energy. Recently developed low regeneration temperature working pairs allow adsorption chillers to be driven by even lower temperature sources such as engine coolant and flat plate solar collectors. In this work, synthetic zeolite/water was implemented into a 3 kW adsorption chiller test facility driven by hot water at 70 degrees C. The zeolite was coated onto two fin-and-tube heat exchangers, with heat recovery employed between the two. Cyclic steady state parametric studies were experimentally conducted to evaluate the chiller's performance, resulting in a cooling coefficient of performance (COP) ranging from 0.1 to 0.6 at different operating conditions. Its performance was compared with published values for other low regeneration temperature working pairs. The physical limitations of the synthetic zeolite revealed by parametric study results were then discussed. A novel operating control strategy was proposed based on the unique characteristics of synthetic zeolite. In addition, a physics-based COP prediction model was derived to predict the performance of the chiller under equilibrium loading, and was validated by the experiment results. This analytical expression can be used to estimate the cyclic steady state performance for future studies.
CAU-10-H displays a highly suitable step-wise water adsorption behaviour for application in adsorption driven heat pumps and chillers. For actual application, manufacturing of coatings of this material on thermally conductive surfaces is highly desired. Direct, single-step, crystallization of CAU-10-H on either metallic or anodized aluminium yields a significant amount of by-product(s) and an inhomogeneous substrate coverage. Although adequate pretreatment of the substrates before crystallization improves the quality of obtained coatings, significant improvements are achieved only when crystal nucleation and growth are separated. More specifically, application of a reactive seeding approach with anodized aluminium leads to full coverage of the substrate surface, high MOF loading and high purity of the crystalline phase, homogeneous layer thickness, narrow crystal size distribution, and good stability in repeated water adsorption-desorption cycles.
The adsorption equilibria of water and ethanol vapour on three kinds of silica gels (SG) and active carbons (AC) with different pore size distributions were measured in the temperature region of 303 to 383K at reduced pressure of less than 0.1MPa. 1) The adsorption equilibrium curves of both adsorbates on SGs correspond to those expected from their pore size distributions. Those for SGs with mono- and di-modal micropores had the shape of one- and two-step increases respectively. The amount of ethanol adsorbed for super-AC is more than six times that for conventional ACs. 2) Heat of adsorption of water vapour on SGs is larger in the case of SG with smaller micropore. 3) Three combinations of adsorbent/adsorbate, i.e. SG and AC with smaller micropore/water vapour and super-AC/ethanol, can be applied to the adsorption heat pump. © 1993, Society of Chemical Engineers, Japan. All rights reserved.
To apply the adsorption/desorption behavior of water on zeolite to a heat storage system which can generate both warm and cold heat, equilibrium data under low relative vapor pressure were measured. Based on the data the adsorptivities under adsorption/desorption are estimated. Heat storing/releasing characteristics were also studied by using an experimental heat storage device with 20 wt-% sodium chloride solution and zeolite 13 X. Heat storing/releasing cycles which have adsorptivity higher than 0.1 kg·kg -1 per cycle even under relative vapor pressure as low as 0.1 and an evaporation process at temperatures lower than 0°C, are achieved. A water-zeolite type heat storage system using a slight amount of sodium chloride for lowering the solidification point of water is proposed for heating and freezing applications.
Adsorption equilibria of ethanol and methanol vapors on activated carbon fibers (ACF) and granular one (GAC) were measured at 30 and 50degreesC, and adsorption isotherms over a wide temperature range were predicted from the experimental equilibrium curves. The cooling effect in an ideal cycle of adsorption refrigerators was estimated under the typical operating temperature conditions from the predicted isotherms. The results obtained showed that the ACF with large surface area has high adsorptive capacity for both ethanol and methanol vapors. The cooling effect estimated for the ACF/methanol pair exceeded 300 kJ/kg, and these values were greater than those for the GAC/methanol pair. Furthermore, we could successfully prepare ACF with high bulk density (HD-ACF) from phenol resin fibers without adding any binders. The prepared HD-ACF has a dense structure with smooth fibers, and has micropores mainly in the range of the radius below 2 nm. The HD-FAC adsorbed rapidly ethanol and methanol vapors comparable to the felt-type ACF. The cooling effect on the apparent volume basis showed an extremely high value of 177 MJ/m(3) for the HD-ACF/methanol pair. Therefore, we concluded that it is feasible to apply this working pair to adsorption refrigerators.
The micropores and surface characteristics of aluminophosphate-type zeolite, AlPO4-5, were analyzed by examining the adsorption behavior of water and other adsorbates. Water adsorption on AlPO4-5 occurred on both structural defects and nonpolar surfaces. Adsorption on structural defects, accompanied by high heats
of adsorption, is attributed to adsorption to surface hydroxyls. Water adsorption increased steeply at a certain relative
pressure depending on the adsorption temperature, and this was considered attributable to capillary condensation. The contact
angle of water on AlPO4-5 micropore surfaces can be determined quantitatively by applying the Kelvin equation. The surface free energy of AlPO4-5 calculated on the basis of the contact angle was revealed to be about 120 mJ/m2, in agreement with accepted values of the dispersion component of the surface free energy of metal oxides. Adsorption heat
values of adsorbates with different polarities indicate that the AlPO4-5 surface is essentially nonpolar and interacts only with dispersion interaction. In the case of n-hexane the contact angle was assumed to be zero, showing high affinity with the result of enhanced adsorption due to pore
filling.