Experimental Study on Natural Convection Heat Transfer of Indirect Water Cooling System in a Semicircular Tunnel
Date Issued
2007
Date
2007
Author(s)
Ho, Po-Ching
DOI
zh-TW
Abstract
In the large underground cables tunnel, the part of the electric energy carried by the cables will dissipate and transform into heat. Therefore, an effective cooling system is demanded to take the heat away for decreasing the air temperature in the tunnel as well as keeping a safe and pleasant environment.
In this work a semicircular tunnel were used as the main body to simulate the underground tunnel, within which an electrical heater could generate heat. Four PE water tubes were set to perform indirect water cooling. The air temperature distribution in the tunnel, the temperature change on the water tubes and the heater were all measured and analyzed. Both the non-dimensional variables Nusselt number, Nu, and Rayleigh number, Ra, were also calculated.
The effect of the cold water flow rate（8LPM, 12LPM and 16LPM）, number of cold water tube（four and single）, the relative positions of the single heater and cold water tubes, and the surface temperature of the heater（from 100℃ to 250℃）were discussed. The whole study was conducted for the Rayleigh number between 4.41 x 104 and 8.19 x 104.
In the experiment of four cold water tubes, the result shows that the larger the flow rate of cold water is, the larger the axial temperature gradient in the front section of the tunnel gets. However, the uniform air temperature in axial direction was obtained when the flow rate of cold water getting smaller. By the temperature distribution profile, a local relative high and low temperature area near the upper-right and lower-right of the semicircular wall of the tunnel can be found. In each cross-section in the axial direction, is maximized and minimized with the water flow rate at 16LPM and 8LPM, respectively, while rises in accordance with the increasing water flow rate. In the study of single heater and cold water tube, the tunnel temperature rises sharply at first and becomes uneven with increasing surface temperature of heater. rises to 5.2x104 from 4.7x104 when the surface temperature of heater is increased from 100℃ to 150℃. However, a large change in Rayleigh number（from 4.7 x 104 to 5.2 x 104） only makes small change in （from 10.1 to 10.3）. If the surface temperature of heater is raised to the range of 200℃ and 250℃, increases obviously. In addition, highest and can be obtained by arranging the cold water tube directly above the heater.
Subjects
地下洞道
間接水冷
溫度分佈
自然對流
紐塞數
雷利數
underground tunnel
indirect water cooling
temperature distribution
natural convection
Nusselt number
Rayleigh number
Type
thesis
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