Thermal conductivity measurement of activated carbon with granular graphite

The granular activated carbon used as adsorbent material in refrigeration systems and heat pumps often presents low thermal conductivity (in the order of 0.15 W/m2.K). Therefore the period of the adsorption/desorption cycle is longer, hence reducing the thermal efficiency of the heat pump/refrigeration system. In order to partially rectify this issue, activated carbon is often mixed expanded natural graphite (ENG) and compacted in order to enhance the thermal conductivity. The disadvantage of this technique is the reduction of gas permeability through the mixture over pure granular activated carbon. In order to overcome this negative effect, the proposed work is to mix granular activated carbon (GAC/208C) with granular graphite (GG) and to evaluate both the thermal conductivity of the mixture and the contact heat transfer coefficient between the matrix and the container (stainless steel tube). The preliminary test results with 20% GG and 80% GAC (not compacted) shows an increase of the thermal conduction with a factor of about 1.5 compared to ordinary GAC (with 0% GG)