Composite materials for solid sorption heat pumps: measurements, model calculations and consequences for system performance

摘要

The performance of adsorption heat pumps is strongly related to the properties of the used sorbents. Not only the pressure - temperature relations that determine the operating window but also the heat and mass transfer properties, which determine cycling time and hence power density, are of great importance. The use of composite materials, such as sorbent with ENG or metal foams, can greatly enhance the heat and mass transfer of sorbent materials. In this paper various heat and mass transfer properties of ammonia salts in a porous composite material are measured and analyzed. Its consequences in terms of cycle time and power density are discussed in the light of the system's design. The determined heat and mass transfer parameters include adsorption and desorption rates of various ammonia-salts under a range of pressure and temperature conditions, the thermal conductivity of composite materials in relation to their state-of-charge and the long-term stability of the composite material related to the number of adsorption-desorption cycles.