Sweeping air membrane distillation: Conjugate heat and mass transfer in a hollow fiber membrane tube bank with an in-line arrangement

A hollow fiber membrane tube bank (HFMTB) with an in-line arrangement is used for sweeping air membrane distillation. In the HFMTB, the brine flows inside the fiber tubes, while the sweeping air flows longitudinally between the tube voids in a counter flow configuration. Heat and water vapor can be exchanged through the membranes. The water vapor transferred from the hot brine side through the membranes is taken away by the sweeping air stream out from the HFMTB. The conjugate heat and mass transfer in the tube bank are investigated. An element consisting of two quarter-fibers, the brine stream in the tubes, and the sweeping air stream between the tubes, is selected as the computational domain. The equations governing the momentum and heat mass transports in tube side, membrane side, and shell side are established and solved based on the conjugate heat and mass transfer boundary conditions. The friction factors, local and mean Nusselt and Sherwood numbers in the element under various longitudinal and transverse pitch-to-diameter ratios (SL/(2ro) = ST/(2ro) or SL/(2ro) ≠ ST/(2ro)) are obtained and experimentally validated. It can be found that the effects of the various pitch-to-diameter ratios on the sweeping air side basic data are much larger than those on the brine side.