| Summary: | 博士 === 國立臺北科技大學 === 機電科技研究所 === 98 === As chip power densities in electronic equipment increasing, improved cooling methods, including pool boiling and jet impingement using dielectric fluid, are demanded. A plain surface, four types of straight-finned surfaces, and six types of pin-finned surfaces were tested in this study to investigate the effects of fin dimensions. Fins were 0.1 ~ 0.4 mm thick and the fin lengths varied from 0.1 to 1.6 mm. Pool boiling and jet impingement experiments were conducted on 10-mm2 copper surfaces at three orientations form horizontal to vertical.
The nozzle orifice had 5 pores of 0.24 mm in diameter and jet distance was 5 mm in height. The jet heat transfer coefficient was better than boiling performance at low heat flux, and removed temperature overshoot. For the plain surface, the boiling heat transfer coefficient increased as the inclination angle increased at low heat fluxes for the increasing heat flux tests. No marked effect on CHF and jet boioling heat transfer coefficient during the decreasing heat flux tests was observed for all surfaces in the present tests. The pin fins made by wire cutting yield higher boiling performance than the wet etched surfaces because of the advantage of larger surface roughness and sharper fin base corners. The heat transfer coefficient of either jet impingemnt or boiling increased with increasing fin height/width ratio or surface enhamcement ratio. The best surface was the pin-finned surface having a fin width of 0.4 mm, a fin height of 1.6 mm and a fin pitch of 0.8 mm. It enhanced the boiling heat transfer coefficient about eight fold. For the same fin height and width, the straight fins and the pin fins yield similar performance at q” < CHF (critical heat flux). However, the CHF of the pin fins was greater than that of the straight fins because the opening area on the top of the pin fins was greater than that of the straight fins. For both straight fins and pin fins, the boiling heat transfer efficiency was mainly enhanced by increasing the total surface area at q” < CHF. The CHF of jet impingement increased with increasing the jet velocity. Correlations of heat transfer coefficient of the plain and fin surfaces in boiling and jet impingement are proposed. All prediction agrees with the experimental result within ± 25 %.
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