Heat Transfer in Adsorption Heat Exchangers between Fins and Monolayer Pellet Beds

Adsorption heat exchangers (AdHXs) are important components in adsorption heat pumps and chillers, often build as fin-and-tube type heat exchangers with beds of adsorbent pellets. For design and optimization the governing transport phenomena in AdHXs need to be quantified as functions of design parameters like geometry or material properties. In this work the heat transfer between fin surface and adsorbent pellet is analyzed using a three-dimensional COMSOL model. The model is evaluated for generic material combinations with a variation of parameters: pellet size (0.2-4 mm), pellet roughness (20-100 µm) and thermal conductivity of gas (0.01-0.03 W/(m K)) and pellet (0.1-0.3 W/(m K)). The calculated effective heat transfer coefficient is in the range of 16-670 W/(m2 K). From the simulation results a general Nusselt correlation is deduced allowing a direct calculation of the heat transfer coefficient within the parameter space.