Numerical Modeling of an Air Gap Membrane Distillation Regenerator for Liquid Desiccant Air-Conditioning Applications

Liquid desiccant cooling is a promising alternative to vapor compression cycle due to its lower electricity consumption. Regeneration process is the principal source of the overall energy consumption which aims to concentrate the diluted desiccant. Conventional direct/indirect regenerators use flowing air to remove the moisture and yield a relatively low thermal efficiency. Based on this, this paper presents a liquid desiccant regenerator which uses air gap membrane distillation to simultaneously concentrate the weak desiccant and produce potable water. A heat and mass transfer model is developed and validated to explore the regenerator performance under various operation conditions as well as the effects of heat transfer enhancement. The simulation results show that the regeneration rate and thermal efficiency increase remarkably with the rise in both the temperature and flow rate of the desiccant. Decreasing both the temperature and flow rate of the coolant can obtain an obvious increase in the regeneration rate but slight fall in the thermal efficiency. In addition, it is found that the convection inside the desiccant channel plays a dominant role in the overall heat transfer performance. By contrast, enhancing condensation heat transfer on the cooling plate surface has a negligible influence on the regenerator performance. This study provides a guideline for the design and optimization of the air gap membrane distillation based liquid desiccant regenerator.