冷媒R-152a應用於滴淋式蒸發器之熱傳性能研究

A Heat Transfer Study of Falling Film Evaporator Using R-152a

潘俊宏(Chung-Hung Pan)

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(2014年)

摘要

本研究以實驗量測的方式測試冷媒R-152a滴淋於三根垂直排列銅製水平管的滴淋蒸發熱傳性能，測試管以紅銅製管徑19mm，在飽和溫度分別為15、20、26.7℃下測試光滑管及鰭片密度60FPI(Fin Per Inch)鰭片高0.4mm、鰭片間隙約0.233mm之鰭片管，並以圓管上打孔之方式滴淋至孔下三根垂直排列之水平測試管上，並改變流量範圍為0.01065~0.03097kg/ms，熱通量範圍為8.05~43.89kW/m2。實驗結果發現，光滑管熱傳係數受熱通量增加而上升，隨著熱通量的上升薄膜破裂降低有效熱表面，使上下測試管間的熱傳係數差異增加。在鰭片管可發現下管的性能優於中管及上管；主要由於特徵表面鰭片上容易產生薄膜，而因冷媒流經上兩排管時因受熱蒸發而使越下排的冷媒流量越少、薄膜越薄，增強了薄膜蒸發沸騰機制，使熱傳係數大幅提升。鰭片管的滴淋蒸發熱傳性能明顯高於池沸騰；而光滑管的滴淋蒸發僅與池沸騰熱傳相近。流量對於兩種管子的熱傳性能都只有些微的影響。在兩種測試管中可發現鰭片管性能較佳，以光滑管為基準，上管約提升4.68倍、中管5.45倍、下管 6.34倍。R-152a的溫室效應係數遠低於R-134a。鰭片管在R-152a的滴淋蒸發性能高於R-134a，但光滑管在這兩種冷媒的蒸發性能則相反，顯示本研究之鰭片適合R-152a之滴淋蒸發特性。

關鍵字

滴淋式蒸發器 ； R-152a ； 薄膜蒸發

並列摘要

The study investigates the evaporation heat transfer performance of R-152a falling film on three horizontal tubes in a vertical column. This study used copper with outer diameter of 19mm, and tested two kinds of tubes, a smooth tube, and a fin tube of 0.4 fin height, 60FPI(Fin Per Inch), 0.233 mm fin gap. The liquid flows through a liquid feeder with a row of circular holes at a rate of 0.01065 ~ 0.03097kg/ms, and heat flux varied from 8.05 to 43.89kW/m2 at saturation temperatures of 15, 20 and 26.7℃.
The test results show that the heat transfer coefficient of the smooth tube increases with increasing heat flux. The film ruptured at high heat fluxes, and the difference of heat transfer coefficient increases with increasing heat flux. Falling film flow rate has minor influence of heat transfer coefficient for both smooth and fin tubes. The fin geometry improved the wetting on the fin tube, which is revealed by its high heat transfer coefficient at the bottom tube. The falling evaporation heat transfer performance of the fin tube is significantly greater than its pool boiling performance. Yet, the heat transfer coefficient of falling film evaporation of the smooth tube is similar to that of pool boiling. As compared with the smooth tube, the heat transfer performance of the fin tube is enhanced by 4.68 folds at top tube, 5.45 folds at center tube, and 6.34 folds at bottom tube. The global warming potential of the R-152a is significantly smaller than that of R-134a. The falling film evaporation heat transfer coefficient is greater than that of R-134a for the fin tube, but contrary for smooth tube. This implies that the fin geometry of the present study is more suitable for R-152a than for R-134a.

並列關鍵字

falling film type ； R-152a ； thin film evaporation

參考文獻

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