An Experimental Study of Heat Transfer Performance Enhancement by Applying Oscillating Flexible Structures
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In this thesis, the effects of a flow-induced oscillating flexible structure on the convective heat transfer of a plate heat exchanger in a vertical rectangular wind tunnel were experimentally investigated. A variable speed fan was used to create an air flow with speed ranging from 9 m/s to 20 m/s. A flexible structure was placed in the front of the plate heat exchanger, which would oscillate in the air flow. Different shapes and dimensions of flexible structures were tested. The temperature of the plate was monitored, and the steady-state temperature was recorded for each experimental condition. The oscillating motions of the flexible structures were captured with a high-speed camera. Compared to the steady flow convection, the use of the oscillation flexible structure can enhance the mixing of the high-temperature boundary flow with the lower temperature flow and disrupt the boundary layer. The length and width of the rectangular structures were found to have large influence on the oscillating characteristics and the convective heat transfer enhancement. Dimensionless parameters including flow-induced oscillation frequency, f^*, and coverage ratio, A^*, were also studied in order to discover the relationship between them. Experimental results showed that the structures with a rectangular shape can most significantly improve the convective heat transfer among those various shapes used in the present study. The average heat transfer coefficient was improved from 113 [W/(m^2*K)] to 161 [W/(m^2*K)] when the inlet wind velocity was 17.2 m/s, and that specific rectangular structure had a length of 0.075 [m] and a width of 0.102 [m].In addition, highest heat transfer performance was found when 0.22≤f^*≤0.32, which could be used for possible further design optimizations.