Experimental investigation on the flow resistance characteristic of the entrance region of mixed convection in rectangular channel

The flow resistance characteristic of the entrance region of mixed convection in rectangular channel was studied by the experiment of the air flowed through a rectangular duct with a uniformly heated plate in the middle section. The rules of the friction factors variation connected with the Reynolds number, the Grashof numbers and inclination angles were obtained. The results reveal that when Re is less than 1500, the friction factor increases with Re and decreases with Gr^*. Moreover, when the Re is greater than 1500, the friction factor is little affected by Re and Gr^*. Furthermore, the friction factor increases with inclination angles. Considering the influences of Re, Gr^*, inclination angle and length to diameter ratio, correlations of friction factors were fitted when Re was greater or less than 1500. Comparison of the friction factors calculated from the fitted correlations and the experimental results satisfactory reached agreement, with the deviations being less than 10%.