Experimental study of a liquid desiccant regeneration system: performance analysis for high feed concentrations

Abstract

Liquid desiccant air-conditioning is an energy-efficient alternative to conventional vapor compression systems due to its ability to handle sensible and latent heat loads independently. Membrane-based processes are prevalent in desalination research due to their superior abilities to separate fluids. The membrane-assisted separation process is also suitable for use in liquid desiccant air-conditioning systems as it can minimize the problems of corrosion, which has so far prevented the widespread use of liquid desiccant systems. In this study, we have utilized the flat-sheet polytetrafluoroethylene membranes for liquid–vapor separation and combined multieffect design with vacuum conditions, for enhanced liquid–vapor separation across the membrane. Preliminary experiments and literature surveys indicate that the conventional vacuum multieffect membrane distillation system exhibits poor performance when the feed concentration is above 26%. Therefore, efforts are made to enhance its performance when operating at higher concentrations (30% and 34%) by employing flat-plate-type heat exchangers to preheat the liquid desiccant and by maintaining high air-side vacuum. The regeneration process can be optimized based on increase in concentration (ΔC) and performance ratio (PR), by controlling the operating conditions. The evaluations of the regenerator performance for different operating parameters including heat source temperature, circulation cross-flow rate are presented along with analysis. Preheating the LiCl solution before regeneration resulted in improved performance; PR of 0.58 and ΔC of 2.4% are achieved for 34% LiCl concentration. Schematic representation of the membrane-assisted LDAC test bed