Experimental studies by the electrochemical method were made to investigate the heat transfer problems of combined free and forced laminar convection for high Pr fluid in the thermal entrance region of rectangular ducts with the aspect ratio Υ=0.5, where the boundary condition of uniform wall temperature has been used.
Experimental data for the local and mean Nu were compared with analytical solutions obtained by developing Leveque''s method and the numerical one, and the following conclusions were reached: i) for the region of forced convection in which the effect of free convection approaches zero, the experimental results are well-correlated with the analytical results obtained by developing Leveque''s method; ii) for the region where the effect of free convection exists, the experimental results are in satisfactory agreement with the numerical ones; and iii) for the onset of free convection effects, both experimental and numerical results are also in good agreement with the original correlative equation suggested by Ou et al.