本文為研製與測試可視化之迴路式虹吸熱管，其蒸發器內部為直徑35mm、長19mm，汽相流道外徑9mm、液相流道外徑6mm，管壁厚度各為1.5mm，冷凝器管路內直徑6mm、長81mm，加熱面積為31mm x 31mm。 迴路式虹吸熱管於內部壓力7 Torr(mmHg)下充填20%之去離子水，銅粉燒結毛細結構之直徑為35mm並製作成三種不同之厚度分別為0.4mm、0.7mm、1.0mm，銅粉平均粒徑與孔隙率分別為100μm及51%。輸入功率逐步由18W增加至236W，分別量測加熱表面溫度及汽相流道入口溫度以進行虹吸熱管的性能評估，並透過玻璃視窗拍攝記錄蒸發器內部毛細結構之汽泡生成與成長現象，包含蒸發器內部底面起始核沸騰、毛細結構起始核沸騰與穩態核沸騰及燒乾時汽泡生成的情形。 實驗結果顯示，起始核沸騰於加熱表面溫度43.3℃時發生；毛細結構表面之工作流體於56.7℃開始核沸騰，穩態核沸騰始於59.0℃；當輸入功率超過236W，則產生燒乾現象。當毛細結構厚度為1.0mm，輸入功率為235W時，加熱表面溫度為83.5℃，具有最低熱阻值為0.07℃/W，此時毛細結構表面為薄膜沸騰模式。 The purpose of this paper is to fabricate and study visualization of a loop thermosyphon. The size of the device are as the follow; the inner diameter of the cylindrical evaporator is 35mm with a length of 19mm; the inner diameter of the vapor flow passage and the liquid flow passage are 9mm and 6mm respectively, the thickness of tube-wall is 1.5mm; the inner diameter of condenser passage is 6mm and with a length of 81mm, and the heating area is 31mm x 31mm. DI water with 20% filling ratio was charged into the thermosyphon at a pressure of 7 Torr. Copper sinter wick structure with diameter of 35mm was fabricated with three different thicknesses of 0.4mm, 0.7mm and 1.0mm. The average diameter of copper powder and the porosity is 100μm and 51%, respectively. Heating surface temperature and inlet temperature at vapor flow passage were measured to evaluate performance of the thermosyphon when the heating input power is from 18W to 236W. Visualization of the loop thermosyphon is based on glass window. During video recording, we found that different power inputs causes variable bubble growth, including initial nucleate boiling of evaporator, initial nucleate boiling of wick structure, steady state boiling, and dried out. The experimental results show that the initial nucleate boiling occurred when the heating surface temperature was 43.3℃. When the temperature reached 56.7℃, the wick structure started initial nucleate boiling, and the steady state boiling status occurred at temperature of 59.0℃. Finally, the system dried out while power input is above 236W. The result show the loop thermosyphon with 1.0mm sinter thickness and 235W had a better performance with the lowest thermal resistance of 0.07℃/W, and the heating surface temperature was 83.5℃. We also found the phenomenon of thin film boiling was occurring in the same time.