The effects of Cooling Water Temperature and Flow Rate on Heat Transfer in a Circular Tunnel with Double Linear Heat Sources
Date Issued
2011
Date
2011
Author(s)
Tan, Jie-Yau
Abstract
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.
Subjects
Circular enclosure
Natural convection
Underground tunnel
Indirect water cooling
Double linear heat sources
Type
thesis
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