EXPERIMENTAL INVESTIGATION OF OPPOSING MIXED CONVECTION HEAT TRANSFER IN A VERTICAL FLAT CHANNEL IN THE TRANSITION REGION. 2. ANALYSIS OF LOCAL HEAT TRANSFER IN THE CASE OF THE PREVAILING EFFECT OF BUOYANCY AND GENERALIZATION OF DATA

This paper presents the results of experimental investigation of local opposing mixed convection heat transfer in a vertical flat channel in the transition region. Local heat transfer was analyzed at various air pressures (0.7-1.0 MPa), i.e., under the prevailing effect of buoyancy. Analysis of experimental results showed tendencies in heat transfer at higher pressures similar to those revealed at smaller pressures (0.2-0.4 MPa). But at higher pressures (i.e., when there is a higher buoyancy effect), the transition from a vortical flow regime to a turbulent one does not cause such a drastic decrease in heat transfer as is the case at lower air pressures. This is due to the significant increase in turbulent heat transfer with increase in the buoyancy effect in the case of a turbulent (nonvortical) flow. Also, it was determined that with increase in buoyancy the Re number also increases, with minimum heat transfer being observed (transition from a vortical to a turbulent flow). A correlation was suggested for calculating this critical Re number (Re-cr2) in the case of a stabilized flow.