Effective thermal conductivity and permeability of compact compound ammoniated salts in the adsorption/desorption process

Abstract

For halide salt-ammonia working pairs, thermal conductivity and permeability always change with the adsorption/desorption concentration because of swelling and agglomeration phenomena during the processes of complexation and decomposition. Correspondingly, heat and mass transfer performance, which both affect the adsorption refrigeration performance, will be influenced. To provide an overview of the process mentioned above, solidified composite adsorbents that utilize expanded natural graphite (ENG) as the matrix were developed for eight different salts. Thermal conductivity and permeability were investigated for three different ratios between ENG and salt in the ammoniating process. The resulting data were compared with the data for the adsorbents that did not adsorb ammonia. The results indicate that the thermal conductivity and permeability of ammoniated salts have a strong dependence on the salt ratio and the consolidated density of the compound adsorbent. In regard to the adsorbent that was not adsorbed, the optimal thermal conductivity was 1.73 W/(m K) for the adsorbent of CaCl2-ENG with a density of 550 kg/m3 when the salt ratio was 75%. The optimal permeability was 9.02 × 10−11 m2 for the adsorbent of BaCl2-ENG with a density of 450 kg/m3 when the salt ratio was 83% in converging mode. Furthermore, the thermal conductivity and permeability of the compact compound ammoniated salts varied significantly with different concentrations of ammonia. The largest increase in thermal conductivity was as high as 1.25 W/(m K)during the adsorption process, whereas the largest decrease in permeability was as high as 5.08 × 10−11 m2 for different adsorption states. For the different adsorption working pairs, the thermal conductivity and permeability ranged from 0.62 to 2.98 W/(m K) and 1.47 × 10−14–8.13 × 10−11 m2, respectively.