本論文主要探討擴散吸收式冷凍系統中氣泡幫浦的熱流特性與效率。根據本實驗團隊研究成果，本研究使用漸深(擴)流道為氣泡幫浦中升流道的部份，期改善目前氣泡幫浦低效率和系統低穩定性的缺點。本實驗在一大氣壓下，選用乙醇水溶液作為工作流體，並且以機械(定流量)及重力(定壓力頭)兩種驅動模式，改變加熱功率、溶液濃度和進口流速，觀察其對氣泡幫浦熱流特性及效率之影響。同時針對本實驗設計之氣泡幫浦建立均質雙相流的理論模式，並將分析數據與實驗結果相互比較。
本研究的功率範圍為130W，實驗結果顯示進口流量約為10ml/min時，能量效率會隨著功率增加而上升，質量效率也有同樣趨勢。在相同高功率下，機械推動的質量效率優於重力驅動。重力驅動循環時，進口流率隨著加熱功率增加而上升至最高值後，持續提高加熱功率反而使進口流率減少。當等液位水槽內乙醇水溶液高度為20公分，能量效率與質量效率皆優於40公分，推測由進口流率影響質量效率。液位高度20公分的效率上升至一高加熱功率(120W)後，能量與質量效率隨著加熱功率增加而些微下降。但是液位高度40公分時，能量與質量效率皆隨著加熱功率增加而上升。機械推動下，乙醇溶液莫耳濃度為20%的效率優於濃度30%。
理論計算與實驗的進口流率相當接近，理論計算顯示液位高度20公分的質量效率優於40公分。
綜合以上實驗觀察結果，以120W加熱莫耳濃度20%乙醇水溶液且以重力驅動、液位高度為20公分時其質量效率最好，此時流譜型態為擾動流或環狀流。

In this study, the two-phase flow and heat transfer in a bubble pump, which is used in a diffusion absorption refrigeration system, with parallel diverging channels is investigated to improve the efficiency. Based on the findings of our previous studies, a diverging channel may enhance the transport of bubble and significantly stabilize the two-phase flow. The experiment was operated at atmosphere pressure and using ethanol solution as the working fluid. To investigate their effects on the bubble pump efficiency, the heating power, ethanol concentration in the solution and inlet flow rate were varied under two kinds of driving modes: constant flow rate using high performance liquid chromatography pump, and constant pressure head with constant height liquid reservoir. In addition, a theoretical model based on the homogeneous two-phase flow for the bubble pump was developed to compare the model prediction with the experiment results.
The results show that when inlet flow rate was 10ml/min and the heating power was gradually increased to 130W, the energy efficiency increases as the heating power increases. The mass efficiency shows the same increasing tendency as of the energy one. Under high power conditions, the constant velocity mode demonstrates a higher mass efficiency than that driven by a constant liquid height. For the gravity-driven mode with constant liquid height, the inlet flow rate increases with increasing the heating power until a maximum value, and then the inlet flow rate decreases as the heating power increases. The efficiency for the bubble pump is better at the reservoir height of 20 cm than that for the reservoir height of 40 cm. At the reservoir height of 20 cm, the efficiency increases with increasing the heating power until the highest value, and then the efficiency decreases as the heating power increases. The efficiency at the reservoir height of 40 cm increases with increasing the heating power monotonically. The efficiency for the ethanol solution with mole fraction of 20% is better than that for 30% under constant inlet velocity. The inlet mass flow rate versus heating power predicted by the theoretical model is similar to the experiment observation under constant pressure head. The theoretical analysis also shows that the mass efficiency at the reservoir height of 20cm is superior to 40cm.
Based on the experiment results of this study, the optimal condition for the present bubble pump with diverging channels is using the 20% ethanol solution at the reservoir height of 20 cm and heated at 120W. The flow pattern under such a condition is churn flow or annular flow.

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