Three dimensional Fluid Flow and Heat Transfer Characteristics of a Backward-Facing Step Flow in a Rectangular Duct

摘要

Various fundamental researches have been done in the backward-facing step flow that can easily produce separation and reattachment. While the relationship between fluid flow structure and heat transfer on the bottom wall is yet completely understood when the effect of side wall is taken into consideration. Here, a duct of 30mm height and of 240 mm width with a step of 15mm height were introduced. Velocity measurements have been done by PIV for various low Reynolds numbers based on the step height from 400 to 900. Distributions of local heat transfer coefficients were measured by making use of a thermosensitive liquid crystal sheet that showed the different color distribution for various temperature values. Large attention was paid to the relationship between fluid flow structures and heat transfer. The local Nusselt number changes not only in streamwise direction but also spanwise direction, the maximum Nusselt number always appear near the side wall region even if the flow Reynolds number is varied. As the Reynolds number increases, the average heat transfer coefficient on the bottom wall increases. The heat transfer coefficient increases near the reattachment region while is higher on the slightly downstream side of the reattached region. The region with the large velocity fluctuation intensity on the bottom wall surface is located slightly downstream of the reattachment region. And the high heat transfer region is in good agreement with that with large flow fluctuation. The reason why the maximum heat transfer area is located on the side wall is mainly related to the strong flow fluctuation.