Reconcentration of Aqueous Solutions in a Packed Bed: A Simple Approach

Abstract

In recent years attempts have been made to use packed beds in open-cycle liquid desiccant cooling systems for the dehumidification process and/or for regenerating weak aqueous solutions. The possibility of reconcentrating the aqueous solution in a packed bed by means of solar-heated air was investigated. The schematic of the reconcentration process is shown. The weak absorbent solution, which leaves the absorber, is pumped to the top of the packed bed after passing through a solution-to-solution heat exchanger where it is preheated by the strong solution. solar-heater air enters the packed bed at the bottom. Since the weak solution vapor pressure exceeds the vapor pressure of water in air, the moisture transfer takes place from the solution to the air. Cooled and humidified air exists at the top and warm, concentrated solution leaves the bottom of the packed bed. For each kilogram of water evaporated from the solution in the packed bed, one kilogram may be absorbed in the absorbed and thus evaporated in the evaporator to provide cooling. Hence, the performance of the cooling system is directly related to the amount of water evaporated from the weak solution in the packed bed. A step-wise heat and mass balance across themore » bed is used to determine the performance of the reconcentration process. In this paper dimensionless vapor pressure and temperature difference ratios suitable for application in the reconcentration of aqueous solutions are defined. Further, a closed-form analytical solution is obtained to predict the mass of water evaporated from the weak absorbent solution, through a simplified vapor pressure correlation and the dimensionless vapor pressure correlation and the dimensionless vapor pressure and temperature difference ratios.« less