半圓洞道內冰水管間接冷卻系統之自然對流熱傳研究

Experimental Study on Natural Convection Heat Transfer of Indirect Water Cooling System in a Semicircular Tunnel

何柏慶(Po-Ching Ho)

指導教授 ： 蘇金佳

國立臺灣大學/工學院/機械工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.00709

摘要

在大型地下高壓電纜洞道內，當纜線在輸送電流時，由於本身存在電阻的緣故，損耗之能量會以熱能的形式散失於洞道之內，故必須仰賴適當的冷卻系統帶走熱量以降低洞道內空氣的溫度，才能維持安全及舒適度。

本研究根據工程實績，以半圓形洞道為主體，用加熱器模擬高壓電纜，並採用PE冷水管實行間接冷卻。在實驗過程中量測洞道內空氣溫度、冷水管溫度及加熱器表面溫度等，並在實驗結束後分析洞道內空氣的縱向溫度分佈、剖面溫度分佈及重要熱傳參數Nu（Nusselt number）和Ra（Rayleigh number）等。研究中所探討的參數有冷水的總流量（8 LPM、12 LPM及16 LPM）、冷水管的管數（四管和單管）、單一冷熱管實驗（加熱器分別和不同位置之單一冷水管組合）並改變加熱器表面溫度（100℃至250℃），整個實驗Ra的範圍為4.41 x 104至8.19 x 104。

實驗結果顯示，當冷水管數為四管時，冷水流量大者在洞道前半段所造成的縱向溫度梯度較大，冷水流量小者，在洞道內縱向整體的溫度分佈較為平均，並由剖面溫度圖可觀察出洞道內在靠近半圓壁面右上方有一溫度較高的區域，右下方接近半圓壁面的最低點則有ㄧ比較低溫的區域。且當冷水管數為四管時，在每一個斷面X處，冷水流量為16LPM時的 值最大，8LPM時的 值最小，且冷水流量越大，則 越大，冷水流量越小，則 越小。單一冷熱管實驗時，當加熱器表面溫度提高，除了洞道溫度提高外，溫度變化亦較為劇烈，也較不均勻。當加熱器表面溫度由100℃升高為150℃時， 由4.7x104提升至5.2x104，但 只從10.1增加到10.3左右，之後當表面溫度提升至200℃和250℃時， 明顯提升。又在單一冷熱管實驗時，則冷水管位於加熱器上方時所造成的 和 最大。

關鍵字

地下洞道 ； 間接水冷 ； 溫度分佈 ； 自然對流 ； 紐塞數 ； 雷利數

並列摘要

In the large underground cables tunnel, the part of the electric energy carried by the cables will dissipate and transform into heat. Therefore, an effective cooling system is demanded to take the heat away for decreasing the air temperature in the tunnel as well as keeping a safe and pleasant environment.

In this work a semicircular tunnel were used as the main body to simulate the underground tunnel, within which an electrical heater could generate heat. Four PE water tubes were set to perform indirect water cooling. The air temperature distribution in the tunnel, the temperature change on the water tubes and the heater were all measured and analyzed. Both the non-dimensional variables Nusselt number, Nu, and Rayleigh number, Ra, were also calculated.

The effect of the cold water flow rate（8LPM, 12LPM and 16LPM）, number of cold water tube（four and single）, the relative positions of the single heater and cold water tubes, and the surface temperature of the heater（from 100℃ to 250℃）were discussed. The whole study was conducted for the Rayleigh number between 4.41 x 104 and 8.19 x 104.

In the experiment of four cold water tubes, the result shows that the larger the flow rate of cold water is, the larger the axial temperature gradient in the front section of the tunnel gets. However, the uniform air temperature in axial direction was obtained when the flow rate of cold water getting smaller. By the temperature distribution profile, a local relative high and low temperature area near the upper-right and lower-right of the semicircular wall of the tunnel can be found. In each cross-section in the axial direction, is maximized and minimized with the water flow rate at 16LPM and 8LPM, respectively, while rises in accordance with the increasing water flow rate. In the study of single heater and cold water tube, the tunnel temperature rises sharply at first and becomes uneven with increasing surface temperature of heater. rises to 5.2x104 from 4.7x104 when the surface temperature of heater is increased from 100℃ to 150℃. However, a large change in Rayleigh number（from 4.7 x 104 to 5.2 x 104） only makes small change in （from 10.1 to 10.3）. If the surface temperature of heater is raised to the range of 200℃ and 250℃, increases obviously. In addition, highest and can be obtained by arranging the cold water tube directly above the heater.

並列關鍵字

underground tunnel ； indirect water cooling ； temperature distribution ； natural convection ； Nusselt number ； Rayleigh number

參考文獻

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