AIR HUMIDIFICATION WITH HOLLOW FIBER MEMBRANES: NEW IMPACTS ON CONJUGATED HEAT AND MASS TRANSFER

Fluid flow and conjugate heat and mass transfer in a hollow fiber membrane contactor used for air humidification are investigated. The contactor is like a shell-and-tube heat exchanger where the water stream flows in the tube side, while the air stream flows in the shell side in a counter flow arrangement. To overcome the difficulties in a direct modeling of the whole contactor, a representative cell comprising of a single fiber, the water flowing inside the fiber and the air stream flowing outside the fiber, is considered. The air stream outside the fiber has an outer free surface. Further, the equations governing the fluid flow and heat and mass transfer in the two streams are combined together with the heat and mass diffusion equations in membranes. The conjugate problem is then solved to obtain the velocity, temperature and concentration distributions in the two fluids and in the membrane. The local and mean Nusselt and Sherwood numbers in the cell are then obtained and experimentally validated.