圓形洞道內雙線性熱源位置對於剖面溫度之效應

Abstract

近年人們基於使用空間需求及美化市容景觀之考量，使得地下化洞道發展及工程設計越來越受到重視，但國內對地下洞道的工程經驗不足，且缺乏相關研究文獻，因此本研究以圓形洞道來進行實體模型研究，並以冷水管間接冷卻系統做為洞道內散熱之方法，且使用雙支線性棒狀加熱器，來模擬電纜線輸電時所散失的熱量，進而探討相關之熱傳問題。 實驗中以加熱器位置(30°、60°、90°、120°)、加熱器功率(2600W、1950W、1300W)、冷水管流量(4LPM、8LPM、12LPM)、五種冷水管位置及冷水管管數(單管、雙管、多管)作為操縱變因。在洞道內部設熱電耦線，量測洞道剖面的溫度及冷水出入口水溫，將所獲得之數據進行軸向溫度分佈、剖面溫度之分析及繪圖。 在單管冷卻實驗中發現，當加熱器位置越低時，吸收的熱傳量會越多、冷卻率會越好，缺點則是整體洞道剖面溫度會變高；若冷水管位置較靠近某邊加熱器，該加熱器上方高溫區受抑制現象明顯。當流量增加時，冷水管帶走之熱傳量也會增加，但不是呈正比增加。以單管而話，在雙加熱器位置30°、90°、120°時，皆為冷水管D有最佳冷卻率；反觀，雙加熱器位置60°則是在冷水管C有最佳冷卻率。在定流量改變管數的實驗中發現，冷水管位置佈設分散，對於冷卻洞道剖面溫度，比冷水管佈設集中之冷卻效果會來得更好；佈設越多支冷卻水管，對於降低剖面溫度以及縱向軸心溫度，有明顯助益。在改變加熱器位置之實驗中，隨著加熱器從下往上移動，低溫區範圍會越來越大；而當加熱器功率減少，洞道整體剖面溫度會降低。由實驗綜合結論可得：最佳冷卻系統應佈設多支冷水管於洞道上方；而最佳電纜線放置位置則在洞道越上方越好。

In recent years, people demands the use of space needs and beautifying the landscape of cities. The underground tunnel development and engineering design get much attention. We don’t have enough engineering experiences of building large underground tunnel in Taiwan and lack for related literarures of a large underground tunnel. Therefore , this research proceeds in a large circular tunnel model, in which air is cooled by indirect water cooling system. Using two linear heat sources in the tunnel is simulated by electric heaters. In order to investigate the related heat transfer issues. The manipulated variables of this research are the positions of two heat sources( 30°, 60°, 90°, and 120°), the powers of heat source ( 2600W , 1920W , and 1300W ) , the flow rates of cooling water (4LPM , 8 LPM , and 12LPM) , the number of cooling-water pipes( single , double , multi-pipe ) , and cooling-water pipes with five positions. Air temperatures , temperatures of axial direction and cooling-water pipes in the tunnel are obtained with thermocouples, then useing them to plot the temperature distribution of cross section in tunnel. The research shows that if the position of the lower heaters , the absorption of heat transfer rate and the cooling rate will be better in single pipe. The disadvantage is that the overall temperature of the tunnel will become high. If the location of pipes are closer to the heaters , The high temperatures at the top of heaters significantly affected by inhibition. When increasing the flow rate of the pipe , the heat transfer rate will increase , but it’s not proportional to increase. When the positions of the two heat sources( 30°, 90°, and 120° ) , the D pipe is optimun cooling rate in single pipe. But the optimum cooling rate of heat sources in 60° is the C pipe. In the experiment of changing the number of cooling pipes with fixed flow rate, the distributed installation of pipes is better then the concentrated installation of pipes. Installing multi-pipe is useful for cooling the temperatures of cross section and the temperatures of axial direction. In the experiment of changing the positions of heaters , moving from the bottom to top with the heaters , the area of lower temperatures becomes larger. When the power of the heater is decreased , the temperatures of cross section will be lower. The optimum layout of indirect water cooling system is using multi-pipe and the electric heaters placement in the top of the tunnel is optimum.