CONVECTIVE AND RADIATIVE INTERNAL HEAT-TRANSFER AUGMENTATION WITH FIBER ARRAYS

A detailed numerical study is performed to investigate radiative and c onvective heat transfer enhancement in pipes filled with small diamete r (similar to 100 mu m) silicon carbide fibers. Radiation between fibe rs and the tube wall, conduction within fibers and convection from the fibers to the surrounding fluid drive the heat transfer enhancement. Macroscopic (porous media) modeling is used to determine the velocity, pressure, and temperatures fields for periodic fiber arrays of variou s porosites under laminar flow conditions (Re-D = 1000). Key features of the macroscopic model include two-dimensional effects, nongray radi ative exchange, and the relaxation of the local thermodynamic equilibr ium assumption. Results show that fiber arrays increase heat transfer largely by the radiative mode, with significant enhancement shown for porosities as high as 0.99. The increased pressure drop due to the pre sence of the fibers rises monotonically as the porosity is reduced. (C ) 1998 Elsevier Science Ltd. All rights reserved.