Performance investigation of a natural circulation membrane-based liquid dehumidification system

A natural circulation membrane-based liquid dehumidification system, driven by the solution density gradient, eliminates the reliance on conventional mechanical pumps while mitigating the additional costs and failure risks associated with the strong corrosiveness of the desiccant solutions. For this system, a natural circulation flow model in the loop and a heat and moisture transfer model within the membrane module are developed and validated with the tested values. Based on the proposed model, the effects of heat exchanger power, solution channel diameter, and system inclination angle on the natural circulation of the solution stream and the performance of heat and moisture transfer across membranes were investigated. The results show that the system can achieve a flow rate comparable to that provided by a solution pump, with the solution flow rate in the channel ranging from 98 to 341.4 L/h under natural circulation conditions. The regeneration temperature ranges from 42.7 °C to 45.2 °C, and increasing the regeneration rate can enhance the potential for utilizing lower-grade energy. In addition, the solution density gradient in the dehumidification system is primarily determined by solution temperature. It is because the moisture transferred across the membrane is negligible compared to the solution flow rate (less than 2%), resulting in a minor concentration difference of the solution stream within the channel. In miniaturized systems or scenarios with a significant concentration gradient, the effect of the concentration gradient on solution flow rate becomes more pronounced.