EXPERIMENTAL INVESTIGATION OF OPPOSING MIXED CONVECTION HEAT TRANSFER IN A VERTICAL FLAT CHANNEL IN THE TRANSITION REGION. 1. ANALYSIS OF LOCAL HEAT TRANSFER

In this paper, the results of experimental investigation into the local opposing mixed convection heat transfer in a vertical flat channel in the transition region are presented. Variation of the local heat transfer rate at different air pressures (0.1-0.4 MPa), i.e., in the case of different buoyancy effects, was analyzed. The analysis of the results revealed a significant increase in the heat transfer rate on increase in the buoyancy effect at a certain value of x/d(e). This is related to the change in the flow regime, i.e., formation or disappearance of vortices. Moreover, it was determined that in the case of vortical flow, the heat transfer rate is significantly higher than in the case of turbulent flow, and the transition to turbulent flow occurs at higher Re numbers. Therefore, the results obtained change the concept of the transition from laminar to turbulent flow under a significant buoyancy effect.