Studies on Heat Transfer in Buoyancy-Affected Separated Flows

流动分离和回流区的存在 对传热特性有显著影响， 工程设备中的传热性能，例如 紧凑型热交换器，电子设备，数字 计算机和燃气轮机 在某些情况下， 在传热装置的设计中增加了流动区域 以增强传热，但其有效性并没有 已通过实验证明或验证浮力- 影响层流。 在某些情况下， 温差大，流速大， 小，浮力效应变得显著。 的作用 浮力在这种复杂的流动结构中起作用 涉及流动分离和再附着的 作者最近仅在有限的范围内进行了数值计算， 并且还没有被实验研究过。 拟议 研究，包括协调的实验和数值 涉及阶梯形渠道中分离流的研究， 沿着阶梯式平板， 水平位置，旨在提供定量 （测量和预测）流量和热量的结果 在分离和再附着流动区域中的转移， 这些流动配置。 重点将放在 实验研究和流动和传热的结果将 可获得浮力辅助和反向 在均匀壁温加热或 均匀表面热通量 据估计，根据 浮力辅助流动条件，再附着长度 将随着浮力的增加而减小， 当几何形状是倾斜的或水平的时， 三维非定常涡流可能发生。 实验 观察将定义这些区域和条件， 在这种流动几何形状中形成了特征。 两个都向后- 具有不同台阶高度的面向和面向前的台阶 将在拟议的研究中处理。 结果 拟议的研究将与提供建设 在处理热传递过程中所需的模块， 受浮力影响的复杂分离流， 在许多工程设备中。

The existence of a flow separation and a recirculating region has a significant effect on heat transfer characteristics and heat transfer performance in engineering devices, such as compact heat exchangers, electronic equipment, digital computers, and gas turbines. In some cases these separated flow regions are added to the design of heat transfer devices to enhance the heat transfer, but their effectiveness has not been justified or verified experimentally for buoyancy- affected laminar flows. In situations in which the temperature difference is large, and the flow velocity is small, buoyancy force effects become significant. The role the buoyancy force plays in such a complex flow configuration involving flow separation and reattachment has been studied only numerically in a limited scope by the authors recently, and has not been explored experimentally at all. The proposed research, consisting of coordinated experimental and numerical studies involving separated flows in stepped channels and along stepped flat plates oriented in vertical, inclined, and horizontan positions, is aimed at providing quantitative (measured and predicted) results for the flow and heat transfer in the separated and reattached flow regions for these flow configurations. Emphasis will be placed on the experimental study and the flow and heat transfer results will be obtained for both buoyancy assisting and opposing conditions under heating by uniform wall temperature or by uniform surface heat flux. It is expected that, under the buoyancy assisting flow conditions, the reattachment length will decrease with an increase in buoyancy forces and that when the geometry is inclined or horizontal, a three- dimensional unsteady vortex flow could occur. Experimental observations will define the region and conditions where these characteristics develop in this flow geometry. Both backward- facing and forward-facing steps with different step heights will be treated in the proposed research. Results from the proposed research will be correlated to provide the building blocks that are needed in dealing with heat transfer in complex, buoyancy-affected separated flows that are prevalent in many engineering devices.