Experimental study on the heat and mass transfer of a combined absorber-evaporator exchanger

The present experimental study investigates the controlling mechanism involved in a new combined vertical film-type absorber-evaporator exchanger and deals with the experimental dependence of the overall heat and mass transfer rates on various operation conditions. The method of analogy between heat and mass transfer near the film surface is used to calculate the interfacial concentration and temperature, thus determining the heat and mass transfer coefficients. It is shown that the absorption process is controlled by a mass transfer mechanism on the liquid side and the mass transfer coefficients are higher than those obtained in isothermal absorption due to the convective effect arising from vapor absorption in the falling brine film. The correlations of mass transfer coefficient with respect to the inlet brine Reynolds number and physical properties have been derived. As to the heat transfer coefficient, it is found that the flow rate of water film and the absorber pressure have a minor effect on the overall heat transfer coefficient of the whole unit. In addition, a predictive model, based on the superposition of heat transfer near wall and near film surface, is proposed and has been successfully applied to evaluate the heat transfer coefficient of the absorber itself. Copyright (C) 1996 Elsevier Science Ltd.