Fluid flow and heat transfer across an elliptical hollow fiber membrane tube bank for air humidification

•An elliptical hollow fiber membrane tube bank (EHFMTB) is employed for air humidification.•Fluid flow and heat transfer across the EHFMTB are investigated.•Heat transfer of the air flow across the EHFMTB along the minor semiaxis is intensified.•The heat transfer enhancement is more obvious with the semiaxis ratios (b/a) decreasing.

In order to improve the performances of a hollow fiber membrane tube bank (HFMTB) used for air humidification, an elliptical hollow fiber membrane tube bank (EHFMTB) is proposed and employed. Fluid flow and heat transfer across the EHFMTB are investigated. Due to the higher heat and mass transport effectivenesses of a regularly populated tube bank as compared to a randomly spaced one, the tube bank with in-line and staggered arrangements are considered. Ten rows of the fiber tubes and the air stream across the tubes are selected as the computational domains. The equations governing the momentum transfer and the heat transfer are established via a renormalization group k–ɛ (RNG KE) turbulence model with enhanced wall treatment. The friction factor and Nusselt number across the EHFMTB under various fiber arrangements (in-line or staggered), pitch to diameter ratio (S/d), semiaxis ratio (b/a), and Reynolds numbers (Re) are numerically obtained, experimentally validated, and analyzed. It is found that compared to the HFMTB, the heat transfer of the air stream flowing across the EHFMTB along the minor semiaxis direction is enhanced. Further, the heat transfer enhancement is more obvious with a decrease in the semiaxis ratios (b/a).