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

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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