DEWATERING OF THIN LIQUID-DESICCANT FILMS CONSTRAINED BY A VAPOR VENTING MEMBRANE: ROLE OF SOLUTION AND AIR TRANSPORT CONDITIONS

The dewatering rate and energy efficiency of the membrane-based liquid-desiccant regeneration process are complex functions of thermo-hydraulic characteristics of both liquid-desiccant and air streams that have not yet been fully examined. Particularly, while the dewatering rate increases at higher liquid solution flow rates, the desorption energy efficiency decreases with the solution flow rate. This indicates the importance of other parameters including air transport conditions for the engineering of advanced membrane-based desorber modules. In this study, the effects of air flow velocity and liquid desiccant velocity and thickness at different operating temperatures on the dewatering rate and energy efficiency of the membrane-based liquid desiccant regeneration process are experimentally investigated. This allows understanding the underlying physics of the membrane-based desorption process and identifying the sub-mechanism limiting the process. To understand the role of the air stream in the regeneration process, two air flow velocities of 0 and 1 m/s were studied. Additionally, two solution film thicknesses of 0.5 and 1.5 mm, and two solution flow velocities of 2 and 4 cm/s were considered to reveal the effect of the liquid solution stream on the regeneration process. The results showed that the dewatering rate increases with the air and solution velocities, and decreases with the solution film thickness. Furthermore, the results indicated the energy efficiency of the desorption process is improved at thinner solution films, but adversely affected at higher air and solution flow velocities. The new insights are key to the design of compact, energy-efficient membrane-based liquid-desiccant regenerator modules for future air conditioning systems exhibiting high-performance energy metrics