| Summary: | 碩士 === 國立交通大學 === 機械工程系所 === 107 === To enhance heat transfer performance, rib has been widely applied to channel wall. In our research, vertical cooling channel with cross section of right angle trapezoid has been considered. Heater and rib were applied to the right angle wall and inclined wall with rib height-to-hydraulic diameter as 0.128. Ribs with V-shaped, full X-shaped and modified X-shaped which pointing upstream and downstream had been investigated. Dry air was applied as the cooling fluid, and the Reynolds numbers were from 10000~40000. Infrared camera (IR camera) has been used to capture the temperature distribution of different rib types, including single rib and staggered arrangement with two rib spacing (P/e=10 and 20). Result shows, at right angle wall of the trapezoid channel, zones near the shorter side with smaller cross section area, fluid has been squeezed and speeded up, causing higher heat transfer. At the bottom edge of the inclined wall, the flow was blocked by the sharp angle of the corner, resulting in lower heat transfer comparing to upper edge of the inclined wall. For the case of single rib, full X type has the larger high heat transfer region located at middle part of the rib and downstream area. Its Nusselt number ratio is 11~15% higher than V-shaped rib. For staggered arrangement, full X with P/e=20 has comparable heat transfer comparing to V rib with P/e=10. However, the friction factor of X rib is a drawback because higher friction factor causes lower thermal performance. In conclusion, in single rib and staggered arrangement, despite full X rib has larger and higher heat transfer region, modified X ribs decrease the friction factor and successfully maintain acceptable thermal performance.
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