漸深流道氣泡幫浦之效率提升研究

Performance enhancement of a bubble pump with multiple divergent channels

洪兆進(Chao-Chin Hung)

指導教授 ： 潘欽 ； 李進得

國立清華大學/原子科學院/工程與系統科學系/碩士(2017年)

摘要

氣泡幫浦是擴散吸收式冷凍循環中一個重要的元件，他扮演了推動整個循環並分
離出冷媒蒸氣的角色。本論文研究延續之前實驗室氣泡幫浦的研究，改善氣泡幫浦的
設計，將出口液體位置移至氣泡幫浦上方和分離器相連，從分離器後面收集出口液體。藉此改善原本設計所發生液體在單相時就會從出口流出。並且針對氣泡幫浦幾個重要的參數，像是蒸發的蒸氣流量、蒸氣帶動的液體流量、氣泡幫浦的效率等進行進一步的探討，期望改善氣泡幫浦低效率的缺點。
本研究以乙醇水溶液作為工作流體，將乙醇-水作為冷媒-吸收劑二元流體，設計一氣泡幫浦，包含產生器、上升管及分離器，其中產生器為加熱的位置，加熱總面積為27mm×50mm，其連接6 條漸深的上升管，上升管的截面積為2mm×2mm 漸深至2mm×3.3mm、長度為15cm，漸深角度為0.5 ﾟ，之後和分離器相連，分離器為23mm×28mm×12.5mm 的矩形空間，可以將氣體與液體分離。實驗以三種不同濃度( m X = 0.1、0.2 及0.3)及兩種驅動高度(H=10cm、15cm) 且與均勻截面積的上升管做比較，探討濃度、驅動高度及上升管截面積對氣泡幫浦的效應。並且使用高速攝影機以500frame rate 拍攝氣泡幫浦底部、中間及上方流譜進行分析。
實驗結果顯示，蒸氣質量流率會隨著濃度與加熱功率增加而上升。出口的液體質量流率會隨著加熱功率增加而上升到一最大值，然後下降，這是因為流譜的改變。實驗中定義了質量效率與能量效率，質量效率會隨著加熱功率增加而上升；能量效率會隨著加熱功率增加而上升，而在高功率時趨近水平。在實驗中主要觀察到的流譜為Slug flow，隨著功率增加，產生的氣體變多，流譜會轉變為Annular flow。從均勻與漸深上升管的比較結果，出口的液體質量流率大於均勻的設計，漸深的設計收集到的蒸氣質量流率也較大，因此有比較高的能量效率。

關鍵字

氣泡幫浦 ； 漸深流道 ； 能量效率 ； 質量效率

並列摘要

The bubble pump is a critical component of a diffusion absorption refrigeration system, which is driven mainly by heat and buoyancy effect. This paper continues to study bubble pump of previous study and improves the design of bubble pump. The outlet liquid position is moved to the top of bubble pump and connect with separator. In this way, it can reduce the heat loss. The vapor flow rate, outlet liquid flow rate and efficiency etc. are important parameters to the bubble pump. Therefore, this information are record and analyze to enhance the bubble pump performance.
The present study investigates experimentally the performance of a bubble pump with multiple diverging lift channels operating with a binary mixture (ethanol/water) as working fluids. The bubble pump contains generator, lift tube and separator. The heating area of the generator is 27mm×50mm with depth 2mm and the generator is connected with 6 lifting tubes. The depth of the lifting tube at the inlet is same as the generator and is 3.3mm at the outlet and diverging angle of 0.5ﾟ. The separator is a 23mm×28mm×12.5mm space to separator vapor and liquid. Three concentration of molar fractions ( =0.1, 0.2 and 0.3) and two driving head (H=10cm and 15cm) are tested and compared with the uniform lifting tubes. Moreover, a visualization window is placed on the surface of channel for flow visualization using a high speed video camera with 500 frame rate.
The results indicate that the vapor mass flow rate raises with increasing the concentration and heating power. Similarly, the outlet liquid mass flow rate increases to a maximum and then decreases with increasing heating power. This is due to the transition of flow pattern. The mass efficiency increases with increasing heating power. The energy efficiency increases with increasing power and concentration and it seems to reach an asymptotic value if the heating power get high. The flow pattern observed in the experiment is most slug flow and it changes to annular flow at the high heating power. The outlet liquid flow rate and vapor flow rate of the diverging channels is higher than the uniform design. Therefore, the energy efficiency of the diverging design is high than the uniform.

並列關鍵字

Bubble pump ； Diverging channels ； Energy efficiency ； Mass efficiency

參考文獻

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Standard Reference Data Program, (2013).

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