Entropy and exergy analysis of an internally-cooled membrane liquid desiccant dehumidifier

Abstract

The internally-cooled membrane-based liquid desiccant dehumidifier (IMLDD) has good performances for air dehumidification, which is a kind of a parallel-plate membrane contactor with cooling channels. The feed air and the solution streams exchange heat and water vapor through the membranes in a form of a cross-flow arrangement. The water in the cooling channel separated by the plate flows vertically along the plate surfaces to form the falling films, while the sweeping air flows over the films. A lumped parameter heat and mass transfer model, an entropy generation model, and an exergy destruction model in the IMLDD are established and numerically solved. The dehumidification rate, dehumidification efficiency, total heat flux, and heat transfer efficiency are calculated. The effects of the structural parameters, operating conditions, and membrane parameters on the performances are analyzed. The pressure drops, entropy generation rate, and exergy destruction are calculated and analyzed. It can be found that the channel height of about 2 mm is a better choice with the pressure drop of about 69.3–94.2% lower than that of 1 mm. The efficiencies of the IMLDD increase about 69.3–94.2% with the diffusivity increasing from 1.0 × 10−6 m2/s to 4.0 × 10−6 m2/s. In addition, increasing the driving forces of the heat and mass transfer can improve the performance, but the entropy generation and exergy destruction also increase.