• Journal of Power System Engineering
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• v.5 no.1
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• pp.27-34
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• 2001

관 외벽에 낮은 핀을 가진 수직 및 경사 열사이폰의 열전달 성능에 관한 실험적인 연구를 하였다. 관 외벽에 낮은 핀을 가진 이상밀폐 열사이폰의 열전달 성능을 비교 분석하기 위하여 동일한 규격의 평관에서도 실험적인 연구를 하였다. 작동유체는 증류수와 CFC-30을 사용하였다. 열사이폰의 경사각과 자동온도를 변화시키면서 실험한 결과 경사각의 변화에 따라 열사이폰의 열전달 성능은 큰 변화를 나타내었다. 그리고 평관으로 제작한 열사이폰보다 관 외벽에 낮은 핀관을 가진 동관으로 제작한 열사이폰의 열전달 성능이 높게 나타났다. 그리고 열사이폰의 경사각이 $20{\sim}50^{\circ}$ 범위에서 열전달 성능이 높게 나타났다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.2
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• pp.202-209
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• 2005

This study concerns the performance of boiling heat transfer in inclined thermosyphons with internal grooves. A study was carried out with the performance of the heat transfer of the inclined thermosyphon having 60 internal grooves in which boiling and condensation occur. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphon is also tested for comparison. Distilled water, methanol and ethanol have been used as the working fluid. The inclination angle, three working fluids, heat flux and the boiling heat transfer coefficient at the evaporator zone are estimated from the experimental results. The experimental results have been assessed and compared with existing correlations. Imura's and Kusuda's correlation for boiling showed in good agreement with experimental results within ${\pm}20%$ in plain thermosyphon. The high heat transfer coefficient was found between $25^{\circ}$ and $30^{\circ}$ of inclination angle for water and between $20^{\circ}$ and $25^{\circ}$ for methanol and ethanol. The relatively high rates of heat transfer have been achieved in the thermosyphon with internal micro grooves.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.971-980
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• 1990

본 연구에서는 실험적으로 2상 밀폐 직사각형 열사이폰 루프에 대하여 안정성 에 주된 영향을 줄수 있는 변수들, 즉 루프 경사각도, 작동유체의 유동현상을 관찰하 고 작동유체의 온도변동과 류프의 전열성능을 측정하여 열사이폰이 안정하게 작동하는 범위를 종합적으로 조사해 보았다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.960-970
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• 1990

본 연구에서는 단상 밀폐 사각형 열사이폰 루프에서 가열부는 일정 열유속으 로 가열되고 냉각부는 일정온도로 냉각될 경우에 대해 루프 경사각도, 종횡비, 작동유 체 종류 및 관 직경변화에 대한 유동 및 온도변동 특성과 이에따른 전열성능 및 안정 작동범위를 실험적으로 조사하였다.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.5
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• pp.38-44
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• 2002

An experimental investigation was performed to observe the cooling performance of cutting oil and the effect of inclination angle on the transport behaviour of a inclined thermosyphons with low integral-fins. Relatively high rates of heat transfer have been achieved by operating this manner. Water has been used as the working fluid. The inclimation angle of thermoryphon and the ratio of Reynolds number of cooling to hot fluid have been used as the experimental parameters. Heat transfer coefficients at the condenser and the evaporator are estimated from experimental results. The experimental results have been assessed and compared with existing theory. Good agreement with the theory of Yiwei has been found. The maximum heat flow rate in the thermosyphon proved to depend upon the inclination angle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.9
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• pp.725-733
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• 2002

In this study, the heat transport limitations of a two-phase closed thermosyphon were investigated. For the test, a two-phase closed thermosyphon ($L_t/: 600 mm,\;L_e:105mm,\;L_a:75mm,\;L_c:420mm,\;D_o:22.2mm,$ container: copper (inner grooved surface), working fluid: PFC ($C_6F_14$) was fabricated with a reservoir that can change the fill charge ratio. The following was imposed as the factors on the heat transport limitations of a two-phase closed thermosyphon. 1) Fill charge ratio of the working fluid. 2) Tilt angle of the longitudinal axis. From tile experimental data, some results were obtained as follows. When the fill charge ratio was relatively small ($\psi$20%), the heat transport limitation occurred about 100W by dry-out limitation. However over 40%, it shelved nearly constant value (500 W) by flooding limitation. The heat transport limitation according to the tilt angle increased smoothly until the tilt angle was $60^{\circ}$,/TEX>, after then decreased slowly.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.1-12
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• 1996

In lots of application to heat exchanger systems, closed two-phase thermosyphons are tilted from a horizontal. If the tilt angle, especially, is less than 30$^{\circ}$, the operational performances of thermosyphon are highly dependent on tilt angle. The present study was conducted to better understand such operational behaviors as mech-anni는 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 19mm and a length 1500mm. 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㎾/$m^2$. 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 dry patch in the top end zone of the evaporator, with a values of temperature 20~4$0^{\circ}C$ higher than the wetted surface for a moderate heat flux q≒20㎾/$m^2$. Inspite of the presence of hot dry patch, however, the mean values of boiling 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%.

• Journal of Energy Engineering
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• v.7 no.2
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• pp.194-201
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• 1998

In electric commuter trains using AC motors, lots of GTO thyristors and diodes are needed for power controls. These semiconductors generate heat about 1~2 kW, and for cooling which perfluorocarbon(PFC) heat pipes have been in use for the last two decades. The present study was investigated on the effects of such important design parameters as structure of internal surface (grooved or smooth), fill charge ratio, and inclinating angle from a vertical on heat transfer coefficients at both evaporators and condensers. To obtain experimental data, several heat pipes of the same geometry of 520 mm long and diameter of 15.88 mm but different in fill charge ratio and internal surface structure were designed and fabricated. For prediction of the heat transfer coefficients, related expressions were examined and the results of calculations were compared with experimental data. Performance tests were conducted while heat pipes operated at mode of thermosyphons. High enhancements of heat transfer coefficient were obtained internal grooves. In these cases, the evaporating heat transfer coefficients distributed in the range of 2~5.5 kW/$m^2$K, with an increase of heat flux from 15~45 kW/$m^2$. These experimental data were in good agreement with Rohsenow's expression based on nucleate boiling when correction factor $C_R$=1.3 was encountered. In addition, the condensation heat transfer coefficients were distributed from 1.5 to 3.5 kW/$m^2$K, and the data were in good agreements with Nusselt's correlation, based on filmwise condensation on vertical plate, when choosing a correction factor $C_N=4$. A fill charge ratio of 40~100% were recommended, and the in clination angle effects were negligible when the angle was higher then 30$^{\circ}$.