Experimental and Theoretical Analysis of the Kinetic Performance of an Adsorbent Coating Composition for Use in Adsorption Chillers and Heat Pumps

The present work aims at the experimental evaluation of the kinetic performance achievable by an innovative binder-based coating developed for application in adsorption chillers or heat pumps. It employs a commercial SAPO 34 as adsorbent material and a clay as binder. Samples with different thickness were prepared at the CNR-ITAE labs and their adsorption kinetics has been tested with a volumetric apparatus based on the Large Pressure Jump (LPJ) approach, available at the Fraunhofer ISE labs. For comparison purposes, also two representative loose adsorbent grain configurations, namely monolayer and multilayer, have been tested. The experimental evolutions have been fitted by means of a heat and mass transfer model, which allowed the determination of the effective diffusion coefficients and the effective heat conductivity as a function of the thickness of the samples. The effective diffusion coefficients showed a linear increase with the square of the coating thickness, which demonstrates that mass transfer is mainly limited by diffusion inside adsorbent grains. Finally, employing the obtained effective parameters, half-cycle simulations (adsorption after temperature jump) in real operating conditions of an adsorption chiller have been carried out for the tested adsorber configurations. A coating thickness of 0.6 mm was identified to be the most promising in terms of achievable Volumetric Specific Cooling Power (VSCP)