A two-energy equation model for dynamic heat and mass transfer in an adsorbent bed using silica gel/water pair

Abstract

In this study, the influence of the adsorbent bed dimensions, convective heat transfer coefficient between the cooling fluid and adsorbent bed and the thermal conductivity of the solid adsorbent material on the transient distributions of the solid and gas phase temperature difference, differences in the adsorbate concentration predicted by the instantaneous equilibrium and linear driving force (LDF) models, solid phase temperature, gas pressure and adsorbate concentration inside the adsorbent bed of a solid sorption cooling system have been investigated numerically for a nearly isobaric adsorption process. Silica gel/water is selected as the working pair. A transient two-dimensional local thermal non-equilibrium model has been developed that takes into account both internal and external mass transfer resistances. The local volume averaging method has been used to derive the macro-scale governing conservation equations from the micro-scale equations. It has been found that generally, the effects of the parameters investigated on the transient distributions of the temperature difference between the phases, difference in adsorbate concentration between the instantaneous equilibrium and LDF models, and gas phase pressure gradients are negligible small. The thickness of the adsorbent bed for the given adsorbent bed length and thermal conductivity of the solid adsorbent material have a large influence on the transient distributions of the solid phase temperature and adsorbate concentration. On the other hand, the transient temperature and adsorbate concentration distributions are only slightly affected by the variation of the adsorbent bed length and convective heat transfer for the conditions studied.