Adsorption Heat Pump Applications Research Articles

Desorption kinetics of thick zeolite coatings prepared by induction heating for adsorption heat pump applications

Desorption kinetics of thick zeolite coatings prepared by induction heating for adsorption heat pump applications

High-throughput Screening of Aluminophosphate Zeolites for Adsorption Heat Pump Applications

High-throughput Screening of Aluminophosphate Zeolites for Adsorption Heat Pump Applications

A case study of a multidisciplinary approach for facing new challenges for adsorption heat pump applications

In this paper, a new zeolite/silicone foam for AHP applications was evaluated as a case study of a multidisciplinary teaching approach for addressing a science education experience from the pedagogical point of view. The interdisciplinary approach promotes the improvement of scientific knowledge among different materials science disciplines allowing to develop a performing adsorbent foamed HEX. In such a context, a flipped classroom approach was identified as the most suitable method for the students to develop their individual and collaborative improvement of knowledge. Changing the classroom lesson from teaching to students learning can be an effective strategy for stimulating students’ interest and learning. This approach, based on a 5E teaching model, opens up to an active and dynamic discussion phase of problem solving which, although contextualized on a practical experience, can be effectively extended in wider contexts.

Theoretical investigation of performances of zeolite Y and SAPO-34 coatings for adsorption heat pump applications

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.

Recent Developments in Coating Technologies for Adsorption Heat Pumps: A Review

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.

New SAPO-34-SPEEK composite coatings for adsorption heat pumps: Adsorption performance and thermodynamic analysis

In this paper, a new adsorbent composite coating by using SAPO-34 filler in a sulfonate polyether ether ketone matrix is proposed for thermally efficient adsorption heat pumps. Composite SAPO-34 zeolite based coatings with 80–95 wt% SAPO-34 content were realized. Preliminary morphological analysis, by scanning electron microscopy, highlighted that the coating microstructure is homogeneous and permeable to water vapor diffusion. Water vapor adsorption isobars were measured at equilibrium for all samples in the temperature range 30–120 °C. The results showed the typical S-shaped trend, which is suitable for adsorption heat pump applications. The highest adsorption value was observed for the coating with highest zeolite filler amount, 95 wt%. This batch exhibited a maximum water uptake of about 29.0 wt%, demonstrating that the S-PEEK matrix does not hinder the SAPO-34 adsorption performance. Finally, starting from obtained experimental data of composite materials adsorption capacities the, a simple energy balance based thermodynamic analysis was performed for air conditioning application by using an aluminum finned-flat tube heat exchanger, as reference. Results highlight that this composite coating technology allows cooling COP up to over 5% higher than that of the conventional loose adsorbent grains configuration, indicating the proposed technology promising for practical application in adsorption heat pumps.

Ion exchange of zeolite coatings for adsorption heat pump applications

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.

Adsorption performance and thermodynamic analysis of SAPO-34 silicone composite foams for adsorption heat pump applications

In the present work, adsorption performances of an innovative composite adsorber, based on SAPO-34-silicone composite macro-cellular foams, are reported. The choice of a foamed structure was assessed to improve the water vapor access towards the embedded zeolite keeping good adsorption heat pump dynamic performance. Depending on zeolite amount used as filler, zeolite/silicone foams evidenced a soft and open cell configuration (low zeolite content) or rigid and closed one (high zeolite content). Morphological analysis evidenced that the cellular structure of the foam is homogeneous and well distributed along the foam cross section. Adsorption tests showed that the adsorbent foamed samples have very effective adsorption capabilities indicating that the porous structure of the filled pure zeolite was not obstructed. SAPO-34 filler contributed actively, with an efficiency above 90%, to the adsorption performances of the composite foam. Starting from experimental equilibrium data, a simple thermodynamic analysis based on energy balances was carried out for air conditioning application. Results of the analysis demonstrated that foam technology can guarantee cooling COP up to 7% higher than that estimated for the typical adsorber solution based on loose adsorbent grains inside an aluminum finned-flat tube heat exchanger, which is very promising for practical application in adsorption heat pumps.

Water adsorption capacity enhancement of ferroaluminophosphate (FAPO4-5) by impregnation of CaCl2

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.

Synthesis of SAPO-34 zeolite filled macrocellular foams for adsorption heat pump applications: A preliminary study

In this work, a new approach for an innovative adsorber is presented, not necessarily alternative to the zeolite coated absorbers, based on the use of composite SAPO-34 filled silicone foams that can improve the adsorption surface area without altering the adsorption pump dynamic performances. Flexible, semirigid or rigid zeolite/silicone foams, obtained with different zeolite amount, were produced ranging from mixed open/closed cell configurations to closed cell configurations. The cells are homogeneously distributed along the foam cross section, consequently mechanically unstable regions were not identified. Adsorption measurements evidenced that the adsorbent foams have effective adsorption capacity without obstruction of the porous structure of the pure zeolite, indicating its potential application in adsorption heat pump. In particular composite foam with 70wt.% of zeolite evidenced a water adsorption of 21.6%. Considering that SAPO-34 powder evidenced an adsorption of 31.7% thus indicating that above 96% of zeolite in the foam is active and the zeolite porosity was maintained also in silicone binder as matrix.

Ionic liquid as a new binder for activated carbon based consolidated composite adsorbents

Consolidated composite adsorbents have gained much attention as next generation adsorbents in adsorption heat pump (AHP) applications due to some of their salient features such as improved uptake to volume ratio and high thermal conductivity. Synthetic polymers, which are generally used as binders for the composite adsorbents impose negative impact on adsorption capacity resulting from poor affinity for the refrigerant and pore blockage. To address these issues, a polymerized ionic liquid (IL) was explored as a potential binder in making consolidated activated carbon composite. Polymerized IL [VBTMA][Ala] (vinylbenzyltrimethyl ammonium alanate) was synthesized and characterized. The composite adsorbent was prepared with a mass ratio of 90% Maxsorb III and 10% of Poly IL [VBTMA][Ala]. It is observed that surface area and pore volume of new composite were increased to more than 11% and 18%, respectively, compared to polyvinyl alcohol (PVA) as a binder. Sorption tests for ethanol uptake were performed using thermogravimetric technique at 303.15K, 323.15K and 343.15K with various evaporator pressures. For a typical operating condition of AHP system, composite using polymerized IL as binder showed 22% higher net ethanol uptake than the net uptake of parent material Maxsorb III whereas a remarkably high 85% increase in thermal conductivity was observed. Thus, polymerized IL could be considered as strong candidate for making consolidated composite adsorbents in AHP applications.

Silicone composite foams for adsorption heat pump applications

The development of multi-functional adsorbent materials and systems is an important design step to improve engineering and technology of adsorption heat pumps (AHP).In this work a new engineering solution was proposed in order to better manage classical needs in AHP. The proposed idea is based on the development of an innovative multi-functional composite silicone-zeolite foams. In particular foamed zeolite-silicone structure is obtained by combined crosslinking and foaming reactions due to dehydrogenative coupling of siloxane constituents.The physico-chemical characterisation of the composite material aimed to evaluate its industrial applicability is discussed. The results obtained evidenced that the morphology of the composite foams is related to the interaction between zeolite filler and silicone matrix. Furthermore adsorption tests evidenced that zeolite embedded in the foam is effectively able to participate to sorption and desorption processes, giving to these adsorbents materials greater advantages than other zeolite containing systems (e.g. coating, picking, direct growth etc.…) for heat pump applications.

Development of MIL-101(Cr)/GrO composites for adsorption heat pump applications

Adsorption heat pumps can be used for generating heating, cooling, seasonal energy storage and water desalination applications. Metal-organic frameworks (MOFs) are hybrid porous materials with high surface area and superior adsorption characteristics compared to conventional adsorbents. MIL-101(Cr) has a large pore size with water vapour adsorption capacity up to 1.5 gH2O gads−1 and high cyclic stability, and thus has the potential to be used in adsorption heat pumps. This work investigates the enhancement of the thermal conductivity and water adsorption characteristics of MIL-101(Cr) using hydrophilic graphene oxide. Two methods have been used to develop MIL-101(Cr)/GrO composites. The first method was through the physical mixing of GrO and MIL-101(Cr) while the other was through incorporating the GrO during the synthesis process of MIL-101(Cr). The composites and neat MIL-101(Cr) were characterized in terms of their structure, water adsorption uptake, BET surface area, particle size, thermal gravimetric analysis, SEM images and thermal conductivity measurements. Results showed that introducing low amounts of GrO (2%) to the neat MIL-101(Cr) enhanced the water adsorption characteristics at high relative pressure but enhanced the heat transfer properties by 20–30% while using more than 2% of GrO reduced the water adsorption uptake but significantly enhanced the thermal conductivity by more than 2.5 times.

Development and characterization of silane-zeolite adsorbent coatings for adsorption heat pump applications

The enhancement of the efficiency of adsorption heat pumps depends on the adsorption capacity of the adsorbent materials as well as on heat transfer efficiency between the adsorbent material in contact with the heat exchanger and the heat transfer fluid. The heat transfer efficiency can be improved by coating the heat exchangers with a thin layer of adsorbent material consolidated by means of a proper binder. In the present paper, three innovative silane-based adsorbent coating compositions, employing a commercial SAPO 34 as adsorbent material, are presented. Their physico-chemical and the mechanical features have been deeply studied, demonstrating promising characteristics which make them as an attractive solution to enhance achievable power density of adsorption machines.

High Methanol Uptake Capacity in Two New Series of Metal–Organic Frameworks: Promising Materials for Adsorption-Driven Heat Pump Applications

Two new series of metal–organic frameworks (MOFs), termed M-VNU-74-I and -II (where M = Mg, Ni, Co; VNU = Vietnam National University) were designed to expand the methanol uptake capacities with polar amide functionalities. The resulting MOFs, isoreticular to MOF-74, exhibited high porosity (up to 3000 m2 g–1) as well as the highest reported methanol uptake [>1 g g–1 or >400 cm3 cm–3]. As a representative example, Mg-VNU-74-II was shown to maintain a remarkably high stability and methanol mass transfer capacity for at least 42 ad/desorption cycles (3 days). Indeed, these findings highlight the potential of such materials for practical use in adsorption heat pump applications.

Aluminium fumarate and CPO-27(Ni) MOFs: Characterization and thermodynamic analysis for adsorption heat pump applications

Metal-organic framework (MOF) materials are new porous materials with high surface area, pore size and volume, and tunable pore geometry thus providing high adsorption capacity. Currently, limited MOF materials with high water adsorption capabilities and hydrothermal stability are available on a large scale. Two MOF materials, namely CPO-27(Ni) and aluminium fumarate, have been identified to have a high hydrothermal stability, high water uptake of 0.47 gH2O.gads−1 and 0.53 gH2O.gads−1 at a relative pressure of 0.9 and are commercially available.This work aims to measure the water adsorption characteristics of these two MOF materials in terms of isotherms, kinetics and cyclic stability. Also the thermodynamic cycle performance of such materials based on their equilibrium adsorption data was investigated under different operating conditions for various adsorption applications such as heating, cooling and water desalination.Results showed that the CPO-27(Ni)/water pair outperformed the aluminium fumarate/water pair at low evaporation temperatures (5 °C) and high desorption temperatures (≥90 °C), while the aluminium fumarate/water pair was more suitable for applications requiring high evaporation temperature (20 °C) and/or low desorption temperature (70 °C).

Investigations of optimum heat exchanger shape for adsorption heat pump applications

Investigations of optimum heat exchanger shape for adsorption heat pump applications

Effects of Using Different Polymers in Post-Synthesis Treatments of Zeolite a Coatings

Zeolite A coatings were prepared by the substrate heating and repeated conventional syntheses methods, targeting their use especially in adsorption heat pump applications. The coatings, grown on stainless steel, were then covered by polyvinyl acetate, polyvinyl alcohol, and cellulose acetate as post-synthesis treatments for improving the stabilities of the coatings. The water desorption properties of the metal-zeolite-polymer integrated systems were investigated by thermogravimetry (TG). Their stabilities were determined by the application of consecutive ultrasonic treatments and heating/cooling cycles. The zeolite coatings prepared by substrate heating contained void fractions of about 45%, significantly higher values than those obtained by repeated syntheses, which remained below 10%. When the former coatings were covered by polymer, they exhibited water desorption of about 0.13–0.15 g/g sample which was higher than the amount of water desorbed from both pure zeolite (0.12–0.14 g/g sample) and pure polymer (0.038–0.083 g/g sample) under the conditions investigated. Such behavior was absent for the more compact zeolite coatings prepared by repeated syntheses. This might signify that the zeolite coatings with larger intercrystalline void regions provided higher amount of surface and/or interactions between the polymer and zeolite phases, which mostly favored water desorption properties of composite coatings. Zeolite coatings prepared by both synthesis methods exhibited high stabilities after the post-synthesis treatments applied.

Zeolite coated copper foams for heat pumping applications

The preparation of a metal supported in situ grown adsorbent bed for adsorption heat pump applications is discussed. The active phase, the zeolite 4A, was directly grown by hydrothermal synthesis on a on-purpose prepared, open-cell, copper foam. The metal foam was obtained by foaming a mixture of epoxy resin, copper powder and a foaming agent in a microwave oven. Subsequently, the metal/polymer foamed composite was heated up to burn the resin matrix and to sinter the metal powder. The so prepared copper foam was preliminary seeded and then exposed to a low temperature (368 K) hydrothermal synthesis in a reactor flask. The accretion treatment was repeated again and an extensive multilayer zeolite 4A coating covering the copper foam surface was obtained. The coating was characterized by SEM, XRD analysis and water adsorption measurements by a Cahn thermobalance. The results in terms of zeolite water uptake in the range of temperatures (328–493 K) and pressures (10–65 mbar) tested, demonstrated a promising performance of the zeolite/foam composite.

Effects of fractality on the accessible surface area values of zeolite adsorbents

The effects of the molecular sizes of adsorbates on the accessible surface area values of the zeolites 13X, 5A, silicalite and NaY as well as the modified forms of NaY are investigated by taking into account the concept of fractality. For this aim, a relationship developed by combining the Pfeifer–Avnir and the surface area equations, which relates the surface areas of adsorbents to the molar volumes and the cross-sectional areas of adsorbates is utilized. The expected relationship, signifying that the accessible surface areas of adsorbents having fractal dimensions above and below 2, increase and decrease, respectively, with decreasing size of the adsorbate, is quantified in this study for the above zeolite adsorbents. Modifying the properties of adsorbents by using various treatment methods is seen to be potentially useful for enhancing the performances of processes involving adsorption, e.g. adsorption heat pump applications. Since the treatments employed may change the fractal dimension of the original sample, adsorbates having proper sizes should be used with the modified forms in order to achieve a good result. The modified hydrogen form of NaY provides the opportunity to increase the efficiency of the adsorption heat pumps by almost 40% with respect to the utilization of the original sample when methanol is used as the adsorbate.