Adsorption heat pump modeling: the thermal wave process with local equilibrium

This paper describes a model for a thermal-wave adsorption heat pump cycle. Local equilibrium is assumed, providing the asymptotic best-case performance. The model is utilized to examine the performance of adsorption refrigeration cycles powered by low temperature waste heat sources of 373–393 K. The impact of varying system temperatures, bed cycling frequency, valve positioning, and sectioning of the bed are examined. Cycle coefficients of performance (COPs) were greater than 1.2 for the base case of a 393 K heat source, 303 K condenser temperature, and 278 K evaporator temperature for a cycle utilizing a water/NaX zeolite adsorbate/adsorbent pair. As an effect of the small temperature changes during the cycle, for some regions of the bed, the loading change was opposite of that expected; i.e., from the start to the end of the entire heating process some portions of the bed experienced loading increases. The location of the inlet/outlet valves in the bed was found to have an impact on the shape of the temperature and loading fronts. The introduction of partitions within the bed was found to have only a small impact on the performance of the cycle for the temperatures examined, with sections of the bed undergoing pressurization in a non-sequential order.