Fluid Flow and Heat Transfer of Mixed Convection and Its Application to Thin Film Formation by CVD

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Fluid flow and heat transfer of mixed convection over upward-facing horizontal heated plates placed in a uniform downward flow of forced convection were investigated experimentally. The experiments were carried out with air and with the test plates of 50 and 100mm wide, which were heated with uniform heat flux. The Reynolds and modified Rayleigh numbers ranged as: Rew =37-2000 and Raw^*=6.2x10^4-5.3x×10^7.The flow fields over heated plates were visualized with smoke. The results showed that the laminar wedge flow from the center to the edges of the plate appears when the heat fluxes are small, while that the flow turns its direction from the edges to the center with increasing the heat flux, and, finally, the flow detaches from the center of the plate as a buoyant plume when the heat fluxes are high enough. The local heat transfer coefficients from the plates were also measured. The results showed that the coefficients under the fixed velocity of the forced flow are increased monotonously with the heat fluxes. It was also found that the overall Nusselt numbers of the plates, Nun, were predicted well with the non-dimensional parameter, (GrW^*/d/Num Rew^2.5), where Grw^* stands for the Grashof numbers. Moreover, the parameter well classify the regions of the forced, mixed and natural convection, and the mixed convection region is determined as : 0.3< (Grw^*/Num Rew^<2.5>) <15