全圓洞道內具雙線性熱源之冷卻水溫度及流量對熱傳之影響

Abstract

近年來基於安全以及美觀等考量，各式纜線的地下化成為都市計畫中很重要的一環，但是國內對於這一方面的經驗較少且缺乏相關研究。有鑒於此，本研究以圓形洞道作為實體模型，架設雙線性棒狀加熱器以模擬高壓電纜工作時散失之熱量，並透過冷水管間接冷卻系統將洞道內纜線所產生的熱量攜出洞道，希望藉此了解洞道內之熱傳問題。 本實驗之操作變因包括加熱器功率(250、600、1100、1400、1800W)、冷卻水管管數(兩支、四支)、冷卻水總流量(4、6、8、10、12、14LPM)及冷卻水入水溫度(11、14、17、20℃)。並在洞道內架設熱電耦線以量測溫度剖面、冷水入出口水溫及洞道內外壁溫，且將其繪圖及分析。 在未開冷卻系統的實驗中發現，加熱器位於洞道中120°位置且不高於一定功率時，洞道下方區域之相對溫度將低於15℃，但洞道頂端區域將達到相對溫度38℃以上，而加熱器上方靠近壁面處的相對溫度將達到50℃以上。 在改變冷卻水管管數以及冷水總流量的實驗中發現，相同冷水總流量下多管數者對洞道中高溫聚集的現象有較明顯的抑制，但少管數者之溫度剖面對冷水總流量的變化較為敏銳。隨著冷水總流量增加，對洞道中高溫區的抑制效果在低加熱器功率時較為明顯，而對低溫區的影響則是在高加熱器功率時較為明顯。對內外壁溫之差值而言是否開啟冷卻系統有很大的影響，但是開啟冷卻系統之後隨流量增加其差值變化較小。 在改變冷卻水入水溫度的實驗中發現，隨著入水溫度的增加洞道上方高溫聚集的現象會加劇，此時提高冷水流量對此一現象會有改善，其中低功率之改善效果較為明顯。同時隨著入水溫度的增加，冷水入出口的水溫差值會逐漸下降且流量較高者其下降幅度較小。

In recent years, for safety reasons and the consideration of landscape, the development of underground cables tunnel becomes a very important part in urban planning. In Taiwan, we have less experience in this area and lack of related research. Therefore, in this research, we use a large circular tunnel as a model, in which we use double linear heat sources to simulate the heat lost of high-voltage cables at work. In the same time, with the indirect water cooling system, the lost heat will be taken out of the tunnel. Through this way, we hope we can understand the mechanism of heat transfer in the tunnel. The effects of the power of the heat sources (250, 600, 1100, 1400, and 1800W), the numbers of cooling pipes (two or four), the flow rate of cooling water (4, 6, 8, 10, 12, and 14 LPM), and the temperature of cooling water (11, 14, 17, and 20℃) will be discussed. In the tunnel, the thermocouples were installed to measure the temperature of the cross section of the tunnel, the cooling water at inlet and outlet of the water pipes, and inside and outside the tunnel wall. Then, we made drafting and analysis. In the experiment without cooling system, we found that when the heat sources at the angle of 120° in the tunnel and the power is not too high, the related temperature will below 15℃ in the area below the tunnel. But at the top of the tunnel, the related temperature will be over 38℃, and the area above the heat sources will be over 50℃. In the experiment of changing the numbers of the water pipes and water flow rate, we found that the one with more water pipes will obviously suppress the area of high temperature in the tunnel at the same water flow rate, but to the one with less water pipes, its cross section of temperature will be more sensitive to the water flow rate. As the water flow rate increasing, the suppression of the area of high temperature in the tunnel will be more evident at lower heat sources power, but to the area of low temperature in the tunnel, the one with higher heat sources power will be more evident. There is a marked difference between the temperature inside and outside the tunnel wall whether the water cooling system is working. But after the cooling system turning on, the difference will be unapparent as the water flow rate increasing. In the experiment of different cooling water temperature, we found that as the temperature of water increasing, the phenomenon of heat accumulation at the top of the tunnel will be more significant, and then increasing the water flow rate will modify this phenomenon especially for the lower heat sources power. As the water temperature increasing, the difference of temperature between inlet and outlet of the water pipes will decrease, and the one with higher water flow rate will decrease slowly.