| Summary: | 碩士 === 國立交通大學 === 機械工程系 === 91 === The characteristics of evaporative heat transfer coefficient and two-phase flow pressure drop for FC-72 at saturation pressure 1.15atm in a small-gap annulus were investigated experimentally and observed by flow pattern observation. The test section was a horizontal annulus with inside diameter 22mm, outside diameter 25mm with a gap 1.5mm. The range of mass flux was from 50 to 100 and heat flux from 1.0 to 5.0 . The results showed that the heat transfer coefficients and pressure drops both increased with quality, mass flux and heat flux. For pressure drops, the effect of mass flux was noticeable at high vapor quality, but the effect of heat flux was much smaller than that of mass flux. When compared with experimental data for proposed correlations reported in the literature, Wattelet&Chato’s(1994) heat transfer correlation predicted well within ±40%, but Friedel’s(1979) and Souza’s(1993) pressure drop correlation predicted very poorly. For mass flux of , heat flux of and quality of 0.09, the flow pattern was plug flow. For quality of 0.399, the flow pattern was wavy flow or slug flow. For quality of 0.65, the liquid film almost dried out and just had few liquid at the bottom portion of the annulus.
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