Heat Transfer and Fluid Flows in Finned and Ribbed Channels with Cooling Applications to Electronic Chipsets
Date Issued
2008
Date
2008
Author(s)
Chiang, Kuei-Feng
Abstract
Heat transfer and fluid flow in the finned and rib-roughened channels for electronic cooling device are investigated through experimental and numerical study. Two passive heat transfer augmentation techniques are proposed to improve PC cooler and telecom air heat exchanger. Fan-fin channel roughened by 450 staggered ribs could enhance heat transfer coefficient comparing with conventional heatsink of PC industry. As well, twin flows in rib-roughened channel were proposed to enhance effectiveness and cooling capacity of air heat exchanger of telecom. The thermal physics and heat transfer correlation of above thermal mechanism are discussed. In what follows, the summaries from these two parts of experimental investigations were described. Fan-fin channel roughened by 450 staggered ribshe detailed heat transfer measurements of rectangular channel roughened by 450 full staggered ribs in both internal walls were performed using the infrared radiometer. The channel was three sides opened and bottom sealed. The present flow path simulated an enhanced coolant channel of the fin-type heat sinks for cooling of electronic chipsets such as CPU. The hydraulic diameter of three test experimental channels was 14.8 mm with different length-to-gap (L/B) ratios of 21.33, 17.11 and 13.56. The influences of L/B ratio on the local and spatially-averaged heat transfers over the rib-roughened surface at Reynolds numbers (Re) of 500, 1000, 2000, 3000 and 3300 were examined. Heat transfer results illustrated the combination effects of side-profile leakage-flow and the rib-induced flow, which were L/B ratio dependent. Heat transfer enhancement over the rib-roughened surface is consistently increasing as Reynolds number increasing and L/B ratio decreasing. 450 Rib-roughened test channel with twin blowshis series of experiment study performs the detailed heat transfer measurements over a skewed-rib roughened surface in a rectangular narrow channel with two equal-area flow entrances located on two adjacent edges of a channel-corner. The twin flow inlet was considered from the aspects of one big louder fan flow supplement replaced by two lower noise small fans. This flow configuration also allows for increasing the coolant-flow fed into the narrow channel without increasing the height of assembly in order to enhance the capacity of cooling duty for electronic chipsets. Four test scenarios, namely the single-blow from the side or upper entrance and the twin-blow with the coolant mass flow ratio of 1:1 or 2:1 between the side and upper blows are performed at Reynolds number of 500, 1000, 2000, 3000, 4000, 5000 and 6000 by conducting experimental tests; meanwhile, numerical studies were only performed for these four entrance conditions at Reynolds numbers of 4000. A commercial CFD software package, Star CD, was chosen as the numerical analysis tool to predict the velocity, turbulent kinetic energy distributions and heat transfer performances using RSM turbulence model. A selection of full-field heat transfer distributions over the rib-roughened surface illustrates that flow entry condition and Reynolds number affect the local and spatially averaged heat transfers. At fixed total coolant supplement, the twin-blow with coolant mass flow ratio of 2:1 between side and upper blows elevates the spatially averaged heat transfers to the levels of 150–180% of the single-blow references. A regression-type analysis is subsequently performed to develop correlation of spatially-averaged Nusselt numbers over rib-roughened surface to Reynolds number four test scenarios. For both single side and upper entry conditions, the predictions by RSM model show the good qualitative and quantitative agreements with the experimental heat transfer results. But the deviation of the RSM results for both twin blow conditions of Res=Reu and Res=2Reu are 31% and –34%
Subjects
Electronic Cooling
Heat Transfer
Skewed Rib-roughened Fin-flow
Twin-blow Ribbed Narrow Channel
Star CD
Type
thesis
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