碩士 / 國立交通大學 / 機械工程系所 / 93 / An experiment is carried out in the present study to investigate the FC-72 flow boiling heat transfer performance and associated bubble characteristics on a heated micro-pin-finned silicon chip flush mounted in the bottom of a rectangular channel. The test section is a horizontal rectangular-channel with the cross section 20 mm in width and 5 mm in height (hydraulic diameter Dh = 8 mm). The silicon chip of surface area 10 mm × 10 mm is flush mounted around the geometric center of the bottom plate of the test section. Besides, three different micro-structures of the chip surface are examined, namely, the smooth, pin-finned 200 and pin-finned 100 surfaces. The pin-finned 200 and 100 surfaces are respectively equipped with micro-pin-fins of size 200 200 70 (Wf Lf Bf) and 100 100 70 (Wf Lf Bf). The space between the two adjacent fins is equal to its width for both pin-finned 200 and pin-finned 100 surfaces. The micro-structures are fabricated on silicon chips through MEMS procedures. The experiment intends to explore the effects of the FC-72 mass flux, inlet liquid subcooling, imposed heat flux, and surface micro-structure of the silicon chip on the FC-72 flow boiling characteristics. In the experiment the coolant mass flux G ranges from 280 to 502 kg/m2s, inlet liquid subcooling ranges from 0 to 4.3 oC, imposed heat flux of the silicon chip q” ranges from 0.1 to 10 W/cm2, and the system pressure is at atmospheric pressure, covering the saturated and subcooled flow boiling.
The experimental results show that increases in the FC-72 coolant mass flux and / or inlet liquid subcooling causes a delay in the boiling incipience. The subcooled flow boiling heat transfer coefficient is reduced at increasing inlet liquid subcooling but is slightly affected by the coolant mass flux. Besides, adding the micro-pin-fin structures to the chip surface can effectively lower the surface temperature in both single- and two-phase regions and raise the single-phase convection and flow boiling heat transfer coefficients. Moreover, the mean bubble departure diameter and active nucleation site density are reduced for rises in the FC-72 mass flux and inlet liquid subcooling. Higher coolant mass flux or lower inlet liquid subcooling results in a higher mean bubble departure frequency. Furthermore, larger bubble departure diameter, higher bubble departure frequency, and higher active nucleation site density are observed as the imposed heat flux is increased. We also note that adding the micro-pin-fins to the chip decrease the bubble departure diameter and increase the bubble departure frequency. However, due to the relatively small space between the fins on the pin-finned 100 surface, the departing bubbles are larger for the pin-finned 100 surface than the pin-finned 200 surface but the bubble departure frequency is lower on the pin- finned 100 surface than the pin-finned 200 surface.
Finally, empirical correlations for the FC-72 single-phase liquid convection, saturated flow boiling, and subcooled flow boiling heat transfer coefficients for the boiling flow over the silicon chips are proposed. Besides, the experimental data for the mean bubble departure diameter, mean bubble departure frequency, and active nucleation site density are also correlated.
| Identifer | oai:union.ndltd.org:TW/093NCTU5489030 |
| Date | January 2005 |
| Creators | Jau-Han Ke, 柯召漢 |
| Contributors | Tsing-Fa Lin, 林清發 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 154 |
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