鰭片構造之滴淋蒸發熱傳性能研究

A Study of Fin Geometry on Falling Film Evaporation Performance

陳榮鴻(Rong-Hong Chen)

指導教授 ： 簡良翰

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2009年)

https://doi.org/10.6841/NTUT.2009.00084

摘要

滴淋式蒸發器利用薄膜蒸發之高熱傳模式提升蒸發器的傳熱效率，並需搭配各式高熱傳效率之蒸發管以提升性能。本研究以實驗的方法探討不同測試管的滴淋薄膜蒸發熱傳性能，使用圓管打孔滴淋裝置滴淋於三根上下垂直排列之水平測試管以模擬滴淋式蒸發器，工作流體為R-134a，在飽和溫度10、20、26.7℃下，測試管種類為光滑管、鰭片密度60FPI (Fins Per Inch) 鰭片高0.4mm之鰭片管與纏繞黃銅 #100目網格之網格鰭片管，改變熱通量範圍為4.5~48.5kW/m2，流量範圍為0.0075~0.0375kg/ms。
實驗結果發現，光滑管在未發生乾枯現象前熱傳係數受熱通量、溫度增加而上升，而流量只有些微的影響；鰭片管在低流量(0.0075、0.015kg/ms)時可形成薄膜蒸發之高熱傳效率模式，熱傳性能大幅增加，在高流量(0.0225、0.03、0.0375kg/ms)時滴淋蒸發與池沸騰的性能相當接近；網格鰭片管熱傳性能在未發生乾枯現象前熱傳係數隨熱通量增加而上升，受溫度、雷諾數影響不大。三種測試管中以鰭片管之性能最佳，相對於光滑管的熱傳性能，在飽和溫度為10、20與26.7℃時，低流量之鰭片管平均熱傳性能分別提升8.29、6.32與6.55倍，高流量之鰭片管平均熱傳性能則分別提升3.74、3.13與2.99倍。

關鍵字

滴淋式蒸發器 ； 薄膜蒸發 ； 鰭片 ； 乾枯現象 ； 流場型態

並列摘要

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.

並列關鍵字

falling film evaporation ； thin film evaporation ； fin ； dry-out ； flow pattern

參考文獻

[1] Chien, L. H., and Shih, T.H., 2006, "Thermal performance evaluation of a spray type evaporator using elemental NTU-ε method," Proceedings of the 13th International Heat Transfer Conference.

[3] Chien, L. H., and Webb, R. L., 1998, "Parametric studies of nucleate pool boiling on structured surfaces, part I: Effect of tunnel dimensions," Journal of Heat Transfer, Vol. 120, pp. 1042-1048.

[4] Chien, L. H., and Webb, R. L., 1998, "Parametric studies of nucleate pool boiling on structured surfaces, part II: Effect of pore diameter and pore pitch," Journal of Heat Transfer, Vol. 120, pp. 1049-1054.

[5] Chun, K. R., and Seban, R. A., 1971, "Heat Transfer to Evaporating Liquid Films," Journal of Heat Transfer, Vol. 93, pp. 391-396.

[6] Alhusseini, A. A., Tuzla, K., and Chen, J. C., 1996, "Falling Film Evaporation of Single Component Liquids," Int. J. Heat Mass Transfer, Vol. 41, pp. 1623-1632.