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In lots of application to heat exchanger systems, closed two-phase thermosyphons are tited from a horizontal. If the tilt angle, especially, is less than 30°, the operational performances of thermosyphon are highly dependent on tilt angle.
The present study was conducted to better understand such operational behaviors as mechanisms of phase change, and flow patterns inside a tilted thermosyphon.
For experiment, an ethanol thermosyphon with a 35% of fill charge rate was designed and manufactured, using a copper tube with a diameter 19㎜ and a length 1500㎜. Through a series of test, the tilt angle was kept constant at each of 4 different values in the range 10~25deg. and the heat supply to the evaporator was stepwisely increased up to 30㎾/㎡. When a steady state was established to the thermosyphon for each step of thermal loads, the wall temperature distribution and vapor temperature at the condenser were measured.
The wall temperature distributions demonstrated a formation of hot dry patch in the top end zone of the evaporator, with a values of temperature 20~40℃ higher than the wetted surface for a moderate heat flux q≒20㎾/㎡. Inspite of the presence of hot dry patch, however, the mean values of boilling heat transfer coefficient at the evaporator wall were still in a good agreement with those predicted by Rohsenow's formula, which was based on nucleate boiling. For the condenser, the wall temperatures were practically uniform, and the measured values of condensation heat transfer coefficient were 1.7 times higher than the predicted values obtained from Nusselt's film condensation theory on tilted plate. Using those two expressions, a correlation was formulated as a function of heat flux and tilt angle, to determine the total thermal resistance of a tilted thermosyphon. The correlation formula showed a good agreement with the experimental data within 20%.
The present study was conducted to better understand such operational behaviors as mechanisms of phase change, and flow patterns inside a tilted thermosyphon.
For experiment, an ethanol thermosyphon with a 35% of fill charge rate was designed and manufactured, using a copper tube with a diameter 19㎜ and a length 1500㎜. Through a series of test, the tilt angle was kept constant at each of 4 different values in the range 10~25deg. and the heat supply to the evaporator was stepwisely increased up to 30㎾/㎡. When a steady state was established to the thermosyphon for each step of thermal loads, the wall temperature distribution and vapor temperature at the condenser were measured.
The wall temperature distributions demonstrated a formation of hot dry patch in the top end zone of the evaporator, with a values of temperature 20~40℃ higher than the wetted surface for a moderate heat flux q≒20㎾/㎡. Inspite of the presence of hot dry patch, however, the mean values of boilling heat transfer coefficient at the evaporator wall were still in a good agreement with those predicted by Rohsenow's formula, which was based on nucleate boiling. For the condenser, the wall temperatures were practically uniform, and the measured values of condensation heat transfer coefficient were 1.7 times higher than the predicted values obtained from Nusselt's film condensation theory on tilted plate. Using those two expressions, a correlation was formulated as a function of heat flux and tilt angle, to determine the total thermal resistance of a tilted thermosyphon. The correlation formula showed a good agreement with the experimental data within 20%.
목차
Abstract
1. 서론
2. 작동유체의 유동형태와 상변화 대류 열전달
3. 실험장치 및 방법
4. 결과 및 고찰
5. 결론
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