碩士 / 國立臺北科技大學 / 能源與冷凍空調工程系碩士班 / 97 / This study investigates the evaporation heat transfer performance of R-134a falling film on three horizontal tubes in a vertical column. This study tested three kinds of tubes, a smooth tube, a fin tube of 0.4mm fin height, 60FPI (Fins Per Inch), and a new enhanced tube made by wrapping a brass mesh of 100 meshes per inch on the 60 FPI finned tube. Experiments were performed at saturation temperatures of 10, 20 and 26.7℃. The liquid flows through a liquid feeder with a row of circular holes at a rate of 0.0075~0.0363kg/ms, and heat fluxes varied from 4.5 to 48.5kW/m2.
The test results show that the heat transfer coefficient of the smooth tube increases with increasing heat flux, fluid temperature, and it increases slightly with increasing flow rate before dry-out occurs. At low flow rates (0.0075 and 0.015kg/ms), the fin tube is in thin film evaporation mode, which is revealed by its high heat transfer coefficient, and at high flow rates (0.0225, 0.03, and 0.0375kg/ms) the falling film evaporation curves are similar to those in pool boiling. The heat transfer coefficient of the mesh tube increases with increasing heat flux. The fluid temperature and the flow rate have only minor influence on heat transfer coefficient before dry-out occurs. The fin tube has the best heat transfer performance. It enhances the heat transfer coefficient by 8.29 folds in average as compared with the smooth surface at 26.6oC saturation temperature. As the saturation temperature decreases the enhancement ratio decreases from 6.32 folds at 10oC to 6.55 folds at 5oC.
| Identifer | oai:union.ndltd.org:TW/097TIT05703009 |
| Date | January 2009 |
| Creators | Rong-Hong Chen, 陳榮鴻 |
| Contributors | 簡良翰 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 131 |
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