Comparative Assessment of Falling-Film and Convective-Flow Absorption in Microscale Geometries

Abstract

A comparative assessment between two modes for ammonia–water absorption, microchannel falling-film absorption and microscale convective-flow, is presented in this study. The microchannel falling-film absorber consists of an array of short microchannel tubes arranged parallel to each other and stacked in several vertical rows to provide the necessary transfer area. Dilute solution flows in a falling-film mode around these cooled tubes while absorbing the counter-current vapor. The microscale convective-flow absorber consists of an array of parallel, aligned alternating sheets with integral microscale features, enclosed between cover plates. Several absorber variants were designed for each flow configuration, and optimal prototypes were identified based on design and operational constraints for a 10.5 kW cooling capacity chiller. Comparative assessments of heat and mass transfer characteristics are presented while accounting for fabrication considerations. This work will guide the development of miniaturized absorption heat pump components.