| Summary: | 碩士 === 建國科技大學 === 機械工程系暨製造科技研究所 === 98 === This work performed detailed measurements of heat transfer coefficients in the 180-deg turned channel by using the transient liquid crystal method. The fluid was air and the cross section of the channel was square. The divider of the 180-deg turned channel had several perforations with equal interval, then the fluid in the first duct can early flow into the second duct through the perforations, adjusting the heat transfer. Variable parameters were the Reynolds number (Re=2468-12340), the ratio of the perforation’s diameter to the channel’s hydraulic diameter (d/Dh=0, 1/4 and 2/4), the angle of perforation (=0, +45 and 45), the numbers of perforations (n=1, 2 and 3), and the arranged angle of the divider (=80, 85 and 90). The results indicated that, at the turned and second duct regions, the effects of fluid flow inertia and the impinging cooling induced better heat transfer on the outer side surface than the bottom one. Among all the test configurations, the non-perforation configuration had the best heat transfer capacity. The total heat transfer performance of the perforation mode with (d/Dh=1/4, q=45° and n=1) was most near that of the non-perforation one. Besides, the distribution of the Nusselt number (Nu) was strongly influenced by the angle of perforation () as d/Dh=2/4. Different from others configurations, the mode of (d/Dh=2/4 and =+45) grew the Nu along the streamwise direction in the second duct due to the biggest amount of bypass fluid, greatly improved the heat transfer at the downstream of the second duct. It demonstrates that the perforations of the divider did can adjust the spatial heat transfer of the 180-deg turned channel. Furthermore, for the mode of =80, the cross section of the channel is not uniform. It resulted in higher heat transfer enhancement at the upstream regions of the first and second ducts due to the bigger velocity than the mean value. If the arranged angle of the divider is changed to be negative, it should effectively smooth the spatial heat transfer distribution in the channel. This issue will be studied in the future.
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