Study on Heat Transfer Augmentation in a Narrow Complex Flow Path Swept by Functional Fluid

为了研究流体的粘弹性是否能强化复杂狭窄流道中常见的空腔传热，对周期性膨胀/收缩流动中的流动与传热进行了基础性研究，首先研究了2，000 ppm的膨胀比为3的对称槽道进行了研究。作为流动条件，选择具有高斯坦顿数的层流。雷诺数的范围从1，420到5，000。在热流密度恒定的条件下对槽道进行加热，测量槽道底部壁面温度分布，计算槽道的换热系数。对空腔内形成的回流进行了空腔内流动显示实验，实验结果表明，在空腔上游区域换热得到了增强，但在空腔内形成回流时，换热系数随回流量的增加而增大， ...更多信息 在空腔下游区域，SFER严重下降。在空腔的上游区域，流线突然向空腔的底壁扩展，并且由于粘弹性流体的Barus效应，再循环流在那里消失。这在腔的上游区域中引起高的热传递。另一方面，由于流体的高拉伸粘度，在下游区域形成大规模回流区。这导致下游区域中的低传热。为了研究凹腔几何参数的最佳条件，在明渠中进行了流动显示实验，结果表明，当肋高较小时，凹腔尺寸为肋高的5倍宽时，凹腔下游区域形成的回流消失。这有望增强腔体中较宽区域的热传递。少

In order to investigate if the visco-elasticity of fluid can enhance the heat transfer from a cavity often observed in a narrow complex flow path, a fundamental study has been performed for flow and heat transfer in a periodic expansion/contraction flow.First of all, the effect of the visco-elasticity of dilute solution of bishydroxyethylmethylammonium chloride of 2,000 ppm was investigated for a symmetric grooved channel having the expansion ratio of 3. As a flow condition, the laminar flow that has high Stanton number was chosen. The Reynolds number ranged from 1,420 to 5,000. The grooved channel was heated at a condition of heat flux constant, and the wall temperature distributions in the bottom of the cavity were measured for calculating heat transfer coefficients. Flow visualization experiments in a cavity were also performed for the recirculating flow formed in a cavity.From the results, heat transfer in the upstream region of the cavity is found to be enhanced, but the heat tran … More sfer seriously decrease in the downstream region of the cavity. In the upstream region of the cavity, the stream-lines are suddenly expanded toward the bottom wall of the cavity and the recirculating flow disappears there by the Barus effect of the visco-elastic fluid. This causes high heat transfer in the upstream region of the cavity. On the other hand, the large-scale recirculating region is formed in the downstream region due to the high extensional viscosity of the fluid. This causes low heat transfer in the downstream region. However, the present methodology is found to be effective in the upstream region at least.In order to investigate the optimum condition of the geometric parameters of the cavities, flow visualization experiments were performed in an open channel.From the results, the recirculating flow formed in the downstream region of a cavity is found to disappear when the rib height is small and cavity size is 5 times wide of the rib height. This is expected to enhance the heat transfer in the wider region in a cavity. Less