Fluid flow and heat transfer in hexagonal parallel-plate membrane channels (HPMC): Effects of the channel heights and fluid parameters

Membrane-based air humidity control technology offers a potential alternative for addressing the vital problem of liquid droplet entrainments encountered in a traditionally direct-contacting approach. A parallel-plate membrane contactor has been extensively used for this application. It is comprised of a series of plate-type membranes to form the channels. The processing air and the liquid (water/liquid desiccant) streams flow in a pure cross-flow arrangement. To improve the performances, hexagonal parallel-plate membrane channels (HPMC) are proposed. Effects of the deformation heights (2H) and fluid parameters on fluid flow and heat transfer in the HPMC are investigated based on a unit cell, which includes one piece of membrane and half a channel. The equations governing the fluid flow and heat transfer are established together with a uniform temperature boundary condition and solved by a finite volume method. The mean friction factors (fm) and Nusselt numbers (Num) in the channels under various channel heights (2H) and fluid varieties are obtained. It has been found that when the fluids and Re are fixed, the larger the 2H are, the smaller the fm are. For the fixed 2H and Re, the Num for the LiCl solution stream are about 1.21-1.38 and 1.51-2.85 times of those for the water and the air streams, respectively.