Browsing by Author "Lu, Ding Chong"

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Pool boiling heat transfer on artificial micro-cavity surfaces in dielectric fluid FC-72
(2006-10-01)
Yu, Chih Kuang
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Lu, Ding Chong
;
Cheng, Tsung Chieh
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機械工程學系
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Department of Mechanical Engineering
The boiling performance and flow mechanism on artificial micro-cavity surfaces with different geometric parameters are presented in the present study. The test surfaces are manufactured on a 625 mu m thick, 10 mm x 10 mm square silicon plate. The treated cavities are all cylinders with three diameters (200, 100 and 50 mu m) and two depths (200 and 110 mu m). The densities of the cavities were designed to be 33 x 33, 25 x 25 and 16 x 16 arrays with 100, 200 and 400 mu m spacings, respectively. The characteristics of heat transfer for pool boiling of FC-72 on artificial micro-cavity surfaces were also examined. In this paper, visualization of the flow patterns was conducted to investigate the characteristics of the bubbles in the growth and departure process. The results indicated that boiling incipience and temperature excursion of silicon-based surfaces are more significant than those of metal-based surfaces reported in the literature. The effects of cavity density are stronger in the high heat flux region than in the low heat flux region because of the bubble/ vapor coalescence near the heating surface. The heat transfer coefficient increases with heat flux and cavity density but a denser cavity will suppress the value of critical heat flux (CHF). Besides, in moderate and high heat flux regions, a larger cavity diameter surface shows earlier decay and a lower peak value of the heat transfer coefficient. The maximum value of CHF on the base area was 3 x 10(5) Wm(-2) (30 W m(-2)) for the test surface with a 33 x 33 cavity array, which is almost 2.5 times that of the plain silicon surface.
Pool boiling heat transfer on horizontal rectangular fin array in saturated FC-72
(2007-08-01)
Yu, Chih Kuang
;
Lu, Ding Chong
;
機械工程學系
;
Department of Mechanical Engineering
The flow patterns and pool boiling heat transfer performance of copper rectangular fin array surfaces immersed in saturated FC-72 were experimentally investigated. The effects of the geometry parameters (fin spacing and fin length) on boiling performance were also examined. The test surfaces were manufactured on a copper block with a base area of 10 mm x 10 turn with three fin spacing (0.5 mm, 1.0 mm and 2.0 mm) and four fin lengths (0.5 mm, 1.0 mm, 2.0 mm and 4.0 mm). All experiments were performed in the saturated state at I atmospheric condition. A plain surface was used as the reference standard and compared with the finned surfaces. The photographic images showed different boiling flow patterns among the test surfaces at various heat fluxes. The test results indicated that closer and higher fins yielded a greater flow resistance that against the bubble/vapor lift-off in the adjacent fins. Moreover, as the heat flux approached to critical heat flux (CHF), numerous vapor mushrooms periodically appeared and extruded from the perimeter of the fin array, causing dry-out in the center of the fin array. Closer and higher fins provide more heat transfer. The results also showed that overall heat transfer coefficient decayed rapidly as the fin spacing decreased or the fin length increased. The maximum value of CHF on the base area was 9.8 x 10(5) W m(-2) for the test surface with a 0.5 min fin spacing and a 4.0 min fin length, which has a value five times greater than that of the plain surface. (c) 2007 Elsevier Ltd. All rights reserved.