Effect of heat exchanger materials on the performance of adsorption chiller

The effect of adsorber heat exchanger (adHEX) material on the system performance of a silica gel-water, fin-tube type adsorption chiller was investigated for three typical materials, aluminum (Al), copper (Cu) and stainless steel (SS), following both the first and second laws of thermodynamics. High thermal conductivity was expected to shorten switching time and prolong adsorption/desorption period, and consequently result in a larger amount of water vapor, and lower thermal mass. In other words, since the product of density and heat capacity increases the heat supplied to the system, higher thermal performance was expected for Cu. However, preliminary calculations failed to confirm the expectation. This study examined the causes by artificially changing the Al thermo-physical properties to those of the Cu and SS. Above a threshold thermal conductivity, the main cause was found to be the material’s density, and below the threshold, thermal conductivity was most important. The Al adHEX showed 0.518 of COP, 221 W/kg of SCP and 0.115 of ηe, which were 6.85 % and 6.53 % higher in COP and exergy efficiency than the Cu adHEX.