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增强狭窄复杂流道中常见的空腔的换热，对周期性膨胀/收缩流动中的流动和换热进行了基础研究。首先，研究了2000 ppm双羟基乙基甲基氯化铵稀溶液对膨胀比为3的对称槽状通道的粘弹性影响。作为流动条件，选择斯坦顿数较大的层流。雷诺数从1420到5000不等。在热流密度恒定的条件下对槽形通道进行加热，测量槽形通道底部壁面温度分布，计算换热系数。对在空腔内形成的再循环流进行了空腔内流动可视化实验。结果表明，腔体上游区域的换热得到增强，而腔体下游区域的换热严重降低。在空腔上游区域，由于粘弹性流体的巴鲁斯效应，流线突然向空腔底壁扩展，再循环流动在此消失。这导致腔体上游区域的高传热。另一方面，由于流体的高拉伸粘度，在下游区域形成了大规模的再循环区域。这导致下游地区的低传热。然而，目前的方法至少在上游地区是有效的。为了研究空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，空腔尺寸为肋高宽度的5倍时，在空腔下游区域形成的再循环流动消失。这有望在更大范围内增强腔内的传热。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