Effects of adsorbent conductivity and permeability on the performance of a solid sorption heat pump

Solid sorption heat pumps can improve the effectiveness with which energy resources are used for heating and cooling. These systems operate by alternately heating and cooling beds of adsorbent material to produce a flow of refrigerant. The research presented here evaluates the effects of adsorbent thermal conductivity and permeability on the performance of a thermal wave solid sorption heat pump. In order to evaluate these effects, a numerical model of the thermal wave heat pump is developed. This model incorporates not only the effects of the conductivity and permeability, but also the effects of the adsorption equilibrium properties, refrigerant properties, application parameters, operating parameters, and bed geometry. For a typical air conditioning application, the model is used to study the influence of conductivity and permeability on the COP for systems using ammonia as a refrigerant. The results indicate that for the geometry considered, increasing the thermal conductivity of the adsorbent to 1 W/m-K can improve the COP to approximately 0.75. Further increases in conductivity do not yield improved performance. Furthermore, the reduced permeability associated with high conductivity adsorbents can impair vapor flow and lead to decreased performance.