COMBINED FREE AND FORCED CONVECTIVE HEAT TRANSFER OF GASES
Local measurements of wall heat flux and temperature in the entrance region of a vertical tube were obtained under conditions of free; convection aiding and opposing forced convection. Results show that, in aiding flow, within
the first 12 diameters or so of tube length, free convection effects are suppressed and Kays' constant property solution predicts closely the local heat transfer coefficients. At the point where the laminar flow becomes
disturbed by the effects of free convection the heat transfer coefficient is found to increase, but no evidence of turbulent flow axists. At higher values of Gr/Re transition to turbulent flow downstream is accompanied by a
reduction by some 20% in the heat transfer coefficient in the upstream laminar region.