碩士 / 國立臺北科技大學 / 冷凍空調工程系所 / 93 / This thesis discusses the effect of surface geometries and inclination angle on the falling film evaporation performance. Falling film evaporation experiments were conducted on a smooth plate and two finned plates using refrigerant R-134a at 10.5+-0.5 oC system temperatures, and R-141b at 15.5+-0.5 oC. The fin pitch = 0.6 mm and the fin thickness = 0.3 mm for both finned surfaces. The fin height is 0.5 mm for Fin-A, and 0.3 mm for Fin-B. All plates are tested with an inclination angle between 10o and 40o, and the heat fluxes are varied between 17.9 and 45.7 kW/m2. The local heat transfer coefficients are measured at four different heights, and the falling film flow distribution is observed through a sight glass. The test results showed that the falling film evaporation heat transfer coefficient increases as the heat flux increases. For the finned surfaces, the heat transfer coefficient increases as the inclination angle increases. However, the inclination angle showed negligible effect on the smooth surfaces for both R-134a and R141b. The finned surface yields better falling film evaporation heat transfer performance than the smooth surface for R-134a an R141b. For the R-134a, the Fin-A surface, having 0.5 mm fin height, yields 2~4 times enhancement of the heat transfer coefficient over the smooth surface, and the Fin-B surface enhanced the heat transfer by 2.5~4.8 folds. For the R-141b, the Fin-B surface yields 1.5~1.8 times heat transfer coefficients of the smooth surface. The visualization observation showed that bubble nucleation is more pronounced on the finned surface than the plain surface. The enhancement of the falling film evaporation is mainly attributed to the bubble nucleation effects on the finned surfaces.
| Identifer | oai:union.ndltd.org:TW/093TIT05703040 |
| Date | January 2005 |
| Creators | Hung-Ta Lin, 林宏達 |
| Contributors | Liang-Han Chien, 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 | 93 |
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