| 摘要: | 本篇論文共有三大主題，其一是描述將銀奈米流體應用於銅質震盪式熱管之研究，其二乃是利用聚二甲基矽氧烷應用於震盪式熱管之製作及其三最後之可視化探討。
第一部份是將二種不同濃度(100ppm及450ppm)之銀奈米流體，充填於內徑2.4mm的銅管中，以作震盪式熱管性能之測試；其填充率各為20%、40%、60%及80%四種，功率從5W加熱至85W，比較不同濃度及填充率之熱管性能為何；最後實驗結果顯示，濃度相同之最佳填充率是為60%，填充率相同之最佳濃度則為100ppm；如加熱功率與填充率相同(85W、60%)， 則100ppm之銀奈米流體，其加熱段與冷凝段之溫差較純水低7.79°C、熱阻值亦較純水少0.092°C /W。
第二部份是利用聚二甲基矽氧烷(Polydimethylsiloxane, PDMS)翻模製作震盪式熱管，三維尺寸各為長56mm、寬49mm及流道內徑2mm；完成震盪式熱管製作、真空處理、充填、封裝及測試平台等，本實驗使用之工作流體為甲醇及乙醇、填充率是為60%，功率從3W加熱至8W，實驗過程中並使用高速攝影機，拍攝工作流體在流道內之作動情形暨性能效果之分析。最後測試結果顯示，甲醇之工作流體在垂直放置時性能較優，輸入功率為3W時，熱阻值較乙醇少4.5°C/W；輸入功率為4W時，加熱段平均溫度亦較乙醇低15°C，由實驗觀察本震盪式熱管，垂直放置較水平放置容易啟動(重力影響)。
第三部份是利用聚二甲基矽氧烷之可視化透明效果，配合高速攝影機，觀察汽-液柱在流道內之作動情形與探討流場之運行模式；隨著不同之加熱功率，亦可清楚觀察工作流體在流道內之作動情形、流場型態之變化(如由細泡型流場轉變為彈狀型流場再轉變為連續之彈狀型流場)、汽泡在加熱段成核、汽泡與汽泡之結合或分裂與汽泡之崩潰或消失等。另當輸入較高之熱通量時，汽-液柱則會開始朝一固定方向在流道內作大幅度之循環。
This dissertation has three parts. The first part describes the nano-fluid applicable to the study of PHP with copper tubes. The second part discusses the materials used in PDMS applying to PHP research and finally a discussion of observations made in the research project.
The first part presents preliminary experimental results on using copper tube having internal and external diameter with 2.4mm and 3mm respectively to carry out the experimental pulsating heat pipe. The working fluids include the silver nano-fluid water solution and pure water.
In order to study and measure the efficiency, we compare with 20nm silver nano-fluid at different concentration (100ppm and 450ppm) and various filled ratio (20%, 40%, 60%, 80% respectively), also applying with different heating power (5W, 15W, 25W, 35W, 45W, 55W, 65W, 75W, 85W respectively). According to the experimental results in the midterm value (i.e. 40%, 60%) of filled ratio shows better performance results. In the majority 60% of efficiency is considered much better. The heat dissipation effect is analogous in sensible heat exchange, where 60% has more liquid slugs that will carry more sensible heat, so in 60% of filled ratio, the heat dissipation result is better than 40%, and the best filled fluid is 100ppm silver nano-fluid.
We observed through the measurement comparison in thermal performance with pure water. When the heating power is 85W, the average temperature difference and the thermal resistance of evaporator and condenser are decreased by 7.79ºC and 0.092ºC /W respectively.
The second part reports on preliminary experimental results of using polydimethylsiloxane (PDMS) to manufacture a visual pulsating heat pipe with length, width and internal diameter are 56mm, 49mm and 2mm respectively, including the manufacturing process and the vacuuming management for filling and packaging. The experiment used methanol and ethanol as the working fluid. A fix filled ratio (about 60%) and different heating power values (3W to 8W) were used to test thermal performance. A high-speed video camera was used to record the working situation of the working fluid inside the channel. The results are discussed and analyzed.
The experiment discussed in the third part shows that methanol, in a vertical orientation, shows the most efficient results. When the heating power is 3W, the thermal resistance is more than 4.5ºC/W below the value for ethanol as the working fluid. For a heating power of 4W, the average temperature decreases to 15ºC in the evaporator. Also gravity will have impact on the PHP performance: The vertical orientation is the better one, as compared to the horizontal orientation.
Inside the channel of the PDMS PHP, different heating powers were employed to observe the working situation, flow direction of the vapor plug, liquid slug and the structure form of the flow. A high speed video camera was used to record the formation, combination, collapse, flow direction and the different kinds of flow of the bubble. At the same time, we can find out the vapor plug and liquid slug are unstable and uneven in growth and distribution which caused the PDMS PHP to oscillate and work. |
