Experimental assessment of alternative compact configurations for ammonia-water desorption

Heat and mass transfer during ammonia-water desorption in miniaturized desorbers using microscale geometries was investigated. Two heat transfer fluid coupled test sections (a vertical column configuration and a branched tray configuration), consisting of an array of alternating plates with integral microscale features, enclosed between cover plates, were fabricated. Due to the counter-current flow configuration, refrigerant vapor with a high purity of ammonia (as high as 99.9% ammonia mass fraction) was generated in these components. Compact adiabatic analyzers and solution-cooled rectifiers with microscale features were also integrated with the two desorber concepts to further increase refrigerant purity. These components were installed in a breadboard test facility consisting of all components of a single-effect ammonia-water absorption chiller and investigated over a range of solution and vapor flow rates. The measured experimental data were analyzed to estimate component duties, solution- and coupling fluid-side resistances, and conduct a comparative assessment of the two miniaturized desorption concepts. The branched-tray configuration performed better than the vertical column design and led to higher purity refrigerant. Potential causes for differences in the performances are discussed.