| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 97 === 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.
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