以紅外線測溫儀探討微流道內之熱傳機制

Investigation of two-phase boiling heat transfer in microchannels using infrared thermography

林芝瑞(Chih-Jui Lin)

指導教授 ： 潘欽

國立清華大學/原子科學院/工程與系統科學系/碩士(2014年)

https://doi.org/10.6843/NTHU.2014.00319

摘要

本研究使用紅外線測溫儀探討微流道內的雙相沸騰熱傳機制，測試段採用鋁材質當作微流道的基底，流道尺寸為長、寬、深分別為111mm、1.5mm及0.6mm，且在流道上方覆蓋3mm厚的鍺玻璃，做為適用本實驗紅外線測溫儀的可視化視窗。具有高靈敏度的紅外線測溫儀提供了一個非侵入性的量測方法，可直接透過視窗量測流體的溫度分佈。
本研究中，首先建立紅外線測溫儀量測的校正系統，使用高效能層析幫浦以固定流率推動乙醇，並藉由T-型熱電偶與紅外線測溫儀量測流體溫度，相互同步記錄溫度，進行分析校正。另外，本實驗也設計一套微流道雙相流實驗設備環路，利用高效能層析幫浦控制工作流體的進口流量，探討在不同質量流率下的沸騰熱傳機制，而壁面溫度及進出口區之流體溫度使用T-型熱電偶量測，並使用紅外線測溫儀觀察微流道內流動沸騰時溫度暫態變化的情形。
本實驗結果，將呈現使用紅外線測溫儀拍攝出微流道內流動沸騰的雙相流譜，並且探討彈狀氣泡和其周遭的液袋區以及環狀流液膜形成至乾化的熱場變化和熱傳機制。從觀察到的流譜中，發現在兩彈狀氣泡間的液體帶區有不對稱的渦流，且不同的相變化數會影響渦流的形成。另外在環狀流譜中發現，液膜的形成到乾化的時間非常快速，當質量通率為20.4kg/m2s，壁熱通率為104.6kW/m2，其液膜平均的蒸發熱通率為127.4 kW/m2

關鍵字

紅外線測溫儀 ； 雙相流 ； 熱傳

並列摘要

The objective of this study is to investigate the boiling two-phase heat transfer in a single rectangular microchannel by using a high thermal sensitivity, non-invasive infrared thermography(IR).The temperature of the working fluid, i.e.enthanol of 95%, in liquid state measured by IR is calibrated by a T-type thermocouple immerse in the bulk liquid. The microchannel is made of aluminum, with a dimension of 0.6 mm in depth, 1.5 mm in width, and 111 mm in length. The test section with the microchannel is adhered on top of a heating module with variable heating power. Five T-type thermocouples are embedded in the test section below the channel bottom surface for the measurement of the local wall temperature. To measure the fluid temperature distribution along the microchannel using an IR thermography, the microchannel is covered with a germanium window with a thickness of 5 mm. The germanium window is transparent for the transmission of long-wavelength (LW) IR. The infrared images of this study are recorded with a frame rate of 200 fps, which facilitates the observation of the transient temperature behavior during flow boiling in the microchannel. The calibrated process for the IR thermography to measure temperature is also discussed.
The experimental results show that the infrared images capture the transient two-phase flow patterns as well as the fluid temperature along the channel. Thermal field analysis of slug and liquid slug as well as annular film formed to desiccation are presented and discussed.
By observing the flow patterns in the channel, a pair of vortexes with liquid flow forward along the side wall and backward in the center have been identified in the liquid slug between two bubbles. Moreover, the effect of phase change number on the formation of vortexes has also been studied. In addition, the drying out of annular liquid film is also studied based on the isotherms from IR. The average liquid film evaporation rate is 137.8 kW/m2.for the case of qꞌꞌ=104.6kW/m2,G=20.4kg/m2s.

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