THE MECHANISM OF HEAT-TRANSFER ENHANCEMENT FOR MINERAL-OIL IN 2 1 RECTANGULAR DUCTS/

A numerical study is performed to study the mechanism of heat transfer enhancement for mineral oil in 2:1 rectangular ducts. Three different heating conditions are considered: top wall heated, bottom wall heate d, and both top and bottom walls heated. For the three heating conditi ons, the present numerical results are all in good agreement with the experimental data. For the case of top wall heated, the heat transfer enhancement is caused mainly by the axial velocity distortion due to t emperature dependence of viscosity. For the case of bottom wall heated , the axial velocity distortion is the major factor to heat transfer e nhancement in the region near the entrance. While near the fully-devel oped region, the heal transfer enhancement is mainly caused by the buo yancy-induced secondary how. The mechanism of heat transfer enhancemen t for the case of top and bottom walls heated is more like that for bo ttom wall heated.