| 摘要: | 本研究使用外徑6mm、內徑3mm玻璃管製作震盪式熱管，使用去離子水及90、270、450 ppm之四氧化三鐵磁性奈米流體，填充率固定70 %，冷凝端溫度固定在25°C，輸入加熱功率20、55、90、125、160W，並分別在無磁場及磁場設置於蒸發端中央、兩側及全部三種不同磁場設置下進行實驗，利用數位攝影機拍攝記錄，觀察管路中工作流體的作動情形，並量測溫度變化，以及奈米流體及磁場對震盪式熱管之影響，並分析熱阻之變化。
結果顯示，震盪式熱管會因奈米流體之加入而性能提升；在所有實驗參數下，熱阻會隨著加熱功率增加而降低，125W至160W時，各實驗中皆有環狀流發生，且各熱阻值皆較相近，因此高功率下磁性奈米流體與磁場對震盪式熱管之作用並不明顯。在低加熱功率20W時，與無磁場設置比較，由於磁場之設置，奈米顆粒於蒸發端管壁上有較顯著的附著與較低的熱阻。另外在磁場設置於蒸發端兩側及全部比設置於中央有較顯著的奈米顆粒附著與較低的熱阻，但在高濃度450 ppm下磁場設置於蒸發端全部反而會因奈米顆粒過度附著而有較高之熱阻。最後使用田口法分析預測奈米流體濃度及磁場設置對震盪式熱管性能的提升。
Abstract:
The present research a pulsating heat pipe (PHP) is made of glass material with an inner and outer diameters of 3 mm and 6 mm for 70 % fill ratio was employed. The heat input was applied at 20, 55, 90, 125 and 160 W. Distilled Water and Fe3O4 nanofluid with different concentrations of 90, 270, 450ppm were used as working fluid, and cooling water temperature was set at 25 °C. Experiment was conducted under no magnetic field and three different magnetic fields that magnet located in the middle area of evaporator (Mid mag), both sides of evaporator (Both mag) and along the evaporator (Along mag). In order to investigate the effects of nanofluid and magnetic field on the thermal resistance of PHP, a video camera was set to observe the motion of working fluid in PHP, and temperatures were measured.
The results show that the thermal performance enhanced with PHP filled magnetic nanofluid, and thermal resistances reduced with an increase of heat input for all experimental parameters. With high heat input from 125 to 160 W, annular flows were observed and the thermal resistances tend to be approximately the same in all the tests. It indicates that magnetic nanofluid and magnetic field have no obvious effects on PHP in high heat input. At low heat input of 20 W, compared with no magnetic field was set, nanoparticles were observed to have a more significant attachment on the evaporator side wall when a magnetic field was applied, and the thermal resistance of the PHP was lower. It was also found that more nanoparticles attachment and lower thermal resistance happened both in the case of (Both mag) and (Along mag) than in the case of (Mid mag). However, a high concentration of 450 ppm in the case of (Along mag), excessive nanoparticles attached and PHP had higher thermal resistance. Finally, enhancement of heat transfer in a PHP utilizing magnetic nanofluid and magnetic field has been designed and predicted using Taguchi method. |
