HEAT AND MASS-TRANSFER IN SEPARATED FLOW REGION FOR HIGH PRANDTL AND SCHMIDT NUMBERS UNDER PULSATILE CONDITIONS

Heat and mass transfer phenomena were studied in the sudden expansion region of a pipe under steady and pulsatile conditions. The Prandtl number was varied from 100 to 12 000 and the flow was characterized for both uniform and parabolic entrance velocity profiles. A uniform velocity profile was used for pulsatile flow. It was found that heat transfer in the recirculation region was maximal near the area where wall shear was minimal. Blunting of the inlet profile caused the point of maximum heat transfer to move upstream. There was a nonlinear effect of Prandtl number on heat transfer which plateaued for Pr > 10(3). The wall shear rate in the separation zone varied markedly with pulsatile flows, but the wall heat transfer remained relatively constant. The time-averaged pulsatile heat transfer at the wall was approximately the same as with steady flow with the mean Reynolds number. However, the isotherms within the pulsatile flow were markedly different from steady flow. The results demonstrate the complexity of separation flows and identify characteristic regions of high and low heat/mass transfer for high Prandtl/Schmidt pulsatile flow.