Mass transfer enhancement of falling film liquid desiccant dehumidification by micro-baffle plates

Abstract

Mass transfer enhancement of falling film liquid desiccant dehumidifier (LDD) is of significance for efficiency improvement of liquid desiccant air-conditioning (LDAC). This study investigated liquid film patterns and dehumidification processes of falling film LDD for smooth and baffle plates. Five baffle plates with different baffle height and spacing were adopted in the study. The CFD simulation with VOF model was adopted for the moist air and liquid desiccant two-phase flow. Moreover, the heat and mass transfer model based on the penetration theory was developed by UDF program to predict the dehumidification process. After numerical validation with previously experimental measurement, the liquid film patterns, water vapor concentration fields, outlet water vapor mass fraction, gas-liquid flow fields and liquid film waves were obtained and analyzed. The results showed that the moisture removal enhancement ratio reaches 7.3%, 18.3%, 25.1%, 19.4% or 16.8% for the baffle plate A, B, C, D or E respectively, compared with the smooth plate case. Therefore, the dehumidification performance of the LDD can be significantly improved by the baffle plate. The liquid film waves, the flow eddies and high-value TKE distribution near the gas-liquid interface induced by the baffle plates are the main mechanisms to enhance the dehumidification performance of the falling film LDD. Moreover, the above enhancement mechanisms will be more significant for higher baffle height and smaller baffle spacing under the present conditions. The simulation results may be useful for the dehumidification performance enhancement in the realistic falling film LDD applications.