STAGNATION POINT HEAT-TRANSFER FROM TURBULENT LOW REYNOLDS-NUMBER JETS AND FLAME JETS

The flow structure and heat transfer of impinging flame jets as well as impinging isothermal jets from two rapid-heating burners were measured. The separation distance between burner and plate varied from 1 to 12 burner diameters. The Reynolds numbers of the examined isothermal jets were 3300-10,000. From the flame jets Re = 1700-4250. Stagnation point Nusselt numbers were determined in two ways: from heat flux density measurements and from measurements of the radial velocity gradient in the vicinity of the stagnation point. With this last parameter a first estimate could be made of the heat transfer coefficient. It is shown that heat transfer from isothermal and flame jets can be described in the same way with this velocity gradient and a turbulence enhancement factor. The results from flame jets agreed quantitatively with the results from isothermal jets if the fluid properties in the heat transfer correlation were taken at a temperature belonging to the averaged enthalpy of the boundary layer along the plate.