Effect of residual gas on the dynamics of water adsorption under isobaric stages of adsorption heat pumps: Mathematical modelling

A mathematical model of the coupled heat and mass transfer in an adsorbent layer was developed to study the effect of a non-adsorbable gas (air, hydrogen) on kinetics of water adsorption on loose grains of the composite adsorbent SWS-1L (silica modified by calcium chloride). The adsorbent monolayer was placed on the surface of an isothermal metal plate at T = 60 °C and equilibrated with the mixture of water vapor at constant P = 10.3 mbar in the presence of the non-adsorbable gas at a variable partial pressure PA = 0.06–14.3 mbar. After that the metal plate is subjected to a temperature drop down to 35 °C that initiates water adsorption. It is shown that the adsorption of water causes effective gas sweeping to the surface where it was accumulated as a gas-rich layer. This results in dramatic slowing down of the adsorption and heat transfer processes.