Experimental study of the film thickness in the dehumidifier of a liquid desiccant air conditioning system

Abstract

A liquid desiccant air conditioning system is one possible substitute for the high energy consumption of the conventional system. The dehumidifier performance is of great importance as it is the key component of such systems. Film thickness plays a vital role in determining the heat and mass transfer performance of a falling film dehumidifier. However, no experimental studies on the liquid film thickness of the dehumidifier within liquid desiccant air conditioning systems have been conducted. Therefore, the film thickness of LiCl solution flow in a single channel dehumidifier is chosen to be investigated in this study. It was found that the mean film thickness without air flow followed the same trend as that predicted by the Nusselt relation, but was about 20% greater. The opposite air flow exerted a shear force on the liquid film to increase the mean film thickness non-linearly. The mean and changing film thickness over time are studied and comparisons made between the lower and upper points of the film. When no air flow existed, the mean film thickness at the lower point was found to be about 10.7%–16.3% thicker than at the upper point. An increase of the air velocity enhanced the wave at both the upper and lower points. The falling film statistical characteristics are also analyzed, and the probability density of the film thickness was found to effectively describe the flow condition. It was also shown that an increase in both the solution flow rate and air velocity enhanced the surface wave velocity.