Effects of cross-sectional aspect ratio of V-shaped ribs and blockage ratio on heat transfer in a channel at a low Reynolds number

초록

V-shaped ribs were investigated with the objective of enhancing heat transfer at the high-temperature side of a fin-plate type heat exchanger used in a railway vehicle compressor. The high-temperature side supplied with compressed air has a Reynolds number of approximately 4000, which is not sufficiently high to generate strong turbulence. When a 3D printer is used to fabricate a heat exchanger, the cross-sectional aspect ratio or blockage ratio of the ribs should be greater than the optimum value in order to attain a certain value of strength. In this study, a series of numerical analyses were conducted to investigate whether increasing the aspect ratio or the blockage ratio was more advantageous for achieving high heat transfer. Ribs with cross-sectional aspect ratios ranging from 0.3 to 5 were investigated. The investigated blocking ratios were 0.1 and 0.3. The results of computational fluid dynamics calculations were used to investigate the influences of flow separation-reattachment, secondary flow, and turbulence on heat transfer. The results demonstrated that the introduction of V-shaped ribs with a high blockage ratio into the channel at a low Reynolds number resulted in greater heat transfer enhancement compared with the effect of introducing ribs with a high cross-sectional aspect ratio.

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