2017 Volume 2 Pages 41-46
Experimental investigations have been carried out on the fluid flow and heat transfer of opposing flows induced over a vertical heated plate placed in a uniform downward flow of water. The vertical plates of lengths L = 50 and 100 mm, heated with uniform heat flux were utilized in the experiments. The Reynolds and modified Rayleigh numbers based on the plate length were ranged as; ReL = 4×102 - 4×103 and RaL* = 4×106 - 3×1010, respectively. The flow fields around the heated plates were first visualized with dye. The result showed that the separation of the laminar boundary layer of forced convection appears first at the bottom edge of the plate and the separation point shifts from the bottom to the leading edge of the plate with the surface heat flux. We also found that the separations of flow at the bottom and upper edge can be predicted with the non-dimensional parameter as; (GrL*/ReL2.5) = 0.4 and 3, respectively, where the parameter (GrL*/ReL2.5) stands for the ratio of the buoyancy to the inertia force. The local heat transfer coefficients from the plates were subsequently measured with thermocouples. The result showed that the coefficients deviate from those of the pure-forced convection with the onset of flow separation at the bottom edge. We have also found that the overall Nusselt numbers from the plate show minima at around (GrL*/ReL2.5) = 1.0. Moreover, by comparing the overall Nusselt numbers to those of the forced and natural convections, the combined convection region was determined as; 0.35< (GrL*/ReL2.5) <4.0.
