Falling Film Absorption Around Microchannel Tube Banks

Abstract

An experimental investigation of heat and mass transfer in a fallingfilm absorber with microchannel tube arrays was conducted. Liquid ammonia–water solution flows in a fallingfilm mode around an array of small diameter coolant tubes, while vapor flows upward through the tube array countercurrent to the falling film. This absorber was installed in a test facility consisting of all components of a functional singleeffect absorption chiller, including a desorber, rectifier, condenser, evaporator, solution heat exchanger, and refrigerant precooler, to obtain realistic operating conditions at the absorber and to account for the influence of the other components in the system. Unlike studies in the literature on benchtop, singlecomponent, singlepressure test stands, here the experiments were conducted on the absorber at vapor, solution, and coupling fluid conditions representative of spaceconditioning systems in the heating and cooling modes. Absorption measurements were taken over a wide range of solution flow rates, concentrations, and coupling fluid temperatures, which simulated operation of thermally activated absorption systems at different cooling capacities and ambient conditions. These measurements are used to interpret the effects of solution and vapor flow rates, concentrations, and coupling fluid conditions on the respective heat and mass transfer coefficients.