Theoretical investigation of performances of zeolite Y and SAPO-34 coatings for adsorption heat pump applications
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ORIGINAL
Theoretical investigation of performances of zeolite Y and SAPO-34 coatings for adsorption heat pump applications Melkon Tatlier 1 Received: 21 May 2020 / Accepted: 19 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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 SAPO34 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. Keywords Zeolite . Coating . Adsorption . Heat pump . Cooling
Nomenclature CA concentration of water vapor in adsorbent, mol/kg adsorbent CAS equilibrium concentration of water vapor on adsorbent surface, mol/kg adsorbent Cp specific heat capacity, Jkg−1 K−1 DAe effective diffusivity, m2/s ΔHads/des heat of adsorption/desorption, Jmol−1 k thermal conductivity, J/smK L latent heat of vaporization, Jmol−1 M mass, kg P cooling power, W Qu useful cooling effect, J r radius, m t time, s
* Melkon Tatlier [email protected] 1
Department of Chemical Engineering, Istanbul Technical University, 34469 Istanbul, Maslak, Turkey
T ΔW α ρ
temperature, K amount of water circulating in the system, kg(kg zeolite)−1 thermal diffusivity, m2/s density, kg/m3
1 Introduction The common use of fossil fuels for maintaining everyday life has become a major problem regarding environmental issues. Carbon dioxide is produced when fossil fuels are burned, leading to an increase in the temperature of the Earth. Ozone depletion is another serious environmental issue originating from chlorofluorocarbons (CFCs), commonly employed in refrigeration and air-conditioning systems. Ozone depletion enhances the amount of ultraviolet radiation that reaches Earth’s surface and it
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