Investigation on Fluid Flow, Heat and Mass transfer Characteristics in a LiCl-H2O Falling Film Absorber

A 2-D transient numerical model of falling film absorber is proposed in the present work with coupled heat and mass transfer. The simulation uses penetration theory to estimate the mass transfer process, whereas volume of fluid (VOF) is used to track the liquid-gas interface. Lithium chloride (LiCl) is selected as the liquid desiccant for its superior dehumidification effect. To align the model with real-time situation the variation of different thermophysical properties (viz. density, viscosity, diffusivity, specific heat, conductivity and surface tension) as well as interfacial area on the dehumidification process are taken into account with the help of some custom auxiliary functions known as UDFs written in conjunction with the FLUENT solver. Moreover, the source terms in the governing equations are also written with similar UDFs. To model the flow accurately, RNG k-e turbulence model is used. Pressure velocity coupling is done with SIMPLE scheme. Finite volume method based software package ANSYS FLUENT 18.2 is used to solve the nonlinear governing equations viz. continuity, momentum, energy, species transport and turbulence equations. The present model is validated with an earlier work and found to be in good agreement with a deviation of 6.25% in the predicted outlet specific humidity. The air side surface has been modified to a wavy structure in order to enhance the dehumidification performance. It was found that the surface modification at the air side led to a significant enhancement of % in the moisture removal rate enhances the turbulence intensity by 7.53% and moisture removal by 10.7%.