- 學位論文
全圓洞道內線性熱源位置對剖面溫度的效應
Effects of Position of Linear Heat Source on Cross-Sectional Temperature Distribution in a Circular Tunnel
摘要
近年來因都市美化的推行，地下洞道的發展及工程設計越來越受到重視，國內對地下洞道的工程經驗不足，且缺乏相關研究文獻，本研究以全圓洞道為實體模型進行研究，並以冷水管間接冷卻做為洞道內散熱的方法，利用棒狀加熱器模擬電纜輸電時所散發的熱量，探討相關的熱傳問題。 實驗中以四個加熱器的位置、加熱器的功率(600W、800W、100W)、冷水管流量(2LPM、4LPM、8LPM)、冷水管位置(冷1、冷2、冷3、冷4、冷5)及冷水管管數(單管、三管、五管)作為操縱變因。在洞道內部設熱電偶線量測洞道剖面的溫度及冷水入出口水溫，將所獲得的數據進行軸向溫度分佈、剖面溫度的分析及繪圖。 在單管冷卻及改變加熱器的實驗中發現，改變單管流量及加熱器溫度並不會對剖面溫度沒有多大的影響，而當流量最低時因對流效應增強使洞道內平均溫度降低。冷水管由洞道的右邊移至左邊時，洞道上方的局部高溫區會漸漸增大，在工程的應用上要特別注意，當冷水管置於冷4位置時冷水管帶走的熱傳率是所有單管冷卻中最大的，故冷水管放置在洞道上方冷4位置是單管冷卻系統的最佳佈設。在定流量改變管數的實驗中發現，冷水管數越多洞道內剖面溫度就越低，冷熱空氣的對流熱傳行為也越為激烈，而洞道剖面中有局部高溫存在是因為冷熱空氣會相交會有劇烈對流熱傳形成渦流所致。在改變加熱器位置的實驗中，隨著加熱器從高處向下移動，洞道剖面的溫度分佈越趨近一致。由實驗綜合結論可得─多管冷卻置於洞道上方且高壓纜線置於洞道下方有最佳冷卻效率。 在實驗中冷水前後溫度會有跳動現象，其因為洞道內空氣和壁面會有熱傳行為及加熱管並非維持等溫，故會有此現象發生。
並列摘要
In near future, the governments energetically beautify cities, and the engineering design of large underground tunnel becomes more general and worthy to take seriously. We don’t have enough engineering experiences of building large underground tunnel in Taiwan and lack for related literarure of a large underground tunnel. This research proceeds in a large circular tunnel model, in which air is cooled by indirect water cooling system. The linear heat source in the tunnel is simulated by electric heaters. The effect of the position of the heat source, the power of the heat source(600W,800W,100W), the flow rate of cooling water(2,4,8LPM), and the position and number of cooling-water pipes were investigated. Air temperature and temperature of axial direction in the tunnel were obtained with thermocouples, and used them to plot the temperature distribution of cross section of tunnel. The research shows that the temperature distribution of cross section didnot have strong change with changing the flow rate of single pipe of cooling water and power of heaters. The temperature of air of tunnel decreased when the flow rate is minima due to the effect of natural convection was increased. As the pipes of cooling water moved left side of tunnel from right side, the area of local higher temperature will spread. The application of engineering has to focus on it. When single cooling pipe fixed at left side, it have the most largest efficiency of heat exchange rate. In the experiment of fixed flow rate of the number of cooling pipes, the result shows that using multi-pipe to reach the lower temperature of air in tunnel than using single pipe. The vortex by cold air and hot air violently mixed due to the cross section of temperature distribution had area of local higher temperature. If the linear heat source is located the bottom of tunnel space, we have more uniform and lower air temperature in the tinnel. Using multi-pipe set up top of tunnel space and linear heat sources is located the bottom of tunnel is the best layout of indirect water cooling system. Moreover, the special phenomenon of temperature oscillation between cooling water inlet and outlet was found, which is due to the energy exchanges between the air of tunnel and wall of tunnel, and the linear heat sources do not keep the same temperature.