Unsteady Evaporation of Water from Wire Mesh Structures at Sub-Atmospheric Pressures

摘要

Evaporator development for adsorption heat pumps and chillers with water as refrigerant is a challengingtask since the required sub-atmospheric pressure level usually impedes efficient evaporation. A promisingconcept for one-chamber adsorption modules is a combined evaporator-condenser heat exchanger in cyclicoperation with external capillary structure. In this work the interplay between dewetting and evaporationdynamics of an innovative copper wire mesh structure for such an evaporator-condenser is analyzed bymeans of unsteady evaporation measurements and simulations with a simple resistance-capacitance model.The results reveal that for large and medium characteristic pore sizes (2.5 mm and 0.8 mm) a dewettingpattern in the shape of a receding front is formed. In contrast, a smaller pore size (0.375 mm) apparentlypromotes a cluster-like dewetting pattern. The fine-porous sample reaches overall effective heat transfer coefficients of up 23…28kW/(m~2K) which makes the wire mesh structures a promising approach forefficient evaporation.