Heat transfer enhancement with porous inserts in recirculating flows

This investigation explores the use of porous inserts for heat transfer enhancement in recirculating flows, specifically flow over a backward-facing step. Numerical computations are performed for laminar flow with high porosity inserts, which are composed of small-diameter (150 mu m) silicon carbide fibers aligned transverse to the streamwise flow. The inserts are varied in length and porosity in order to determine the most favorable combinations of maximum temperature reduction and head loss penalty. In general, the porous inserts reduce or eliminate the lower wall recirculation zone; however, in some cases the recirculation zone is lengthened if the inserts are short and extremely porous. Excellent heat transfer characteristics are shown within the inserts themselves due to the high-conductivity fiber material. Non-Darcy effects are shown to be important primarily as the porosity is increased Deviation from local thermodynamic conditions between the inserts and the fluid is most apparent for the shortest inserts considered.