• Journal of Energy Engineering
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• v.4 no.2
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• pp.261-269
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• 1995

본 연구에서는 밀폐형 2상 열사이폰의 액체 Pool에서 발생하는 핵비등현상과 유동영역에 대해 가시화 방법으로 연구하였다. 실험용 열사이폰은 스텐레스와 유리관을 이용하여 제작하였으며, 열공급은 증발부 주위에 설치된 유도 가열용 코일에 고주파를 가함으로써 스텐레스 외면에 발열이 일어나도록 하였다. 이에 따른 결과는 다음과 같다. 실험용 열사이폰은 고주파 가열등 열사이폰의 작동성능을 저해하는 여러 요인들이 포함되어 있었으나, 실험결과 이러한 문제는 실험 내용에 영향을 미칠만큼 크게 나타나지 않았다. 열속과 상당압력의 범위는 각각2$m^2$, 0.1

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.12
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• pp.1646-1654
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• 2002

A two-phase closed thermosyphon was one of the most effective devices in the removing heat because of its simple structure, thermal diode characteristics, wide operating temperature range and so on. In this study, a two-phase closed thermosyphon(working fluid PFC(C6F14), container copper(inner grooved surface)) was fabricated with a reservoir which can change the fill charge ratio. The experiments were performed in the range of 50~600W heat flow rate and 10~70% fill charge ratio. The results were compared with some correlations that were presented by Rohsenow and Immura et al. in the evaporator, by Nusselt, Gross and Uehara et al. in the condenser and by Cohen and Bayley, Wallis, Kutateladze and Faghri et al. in heat transfer limitation etc.. The heat transfer coefficient at the evaporator increased with the input power. However the effect of the fill charge ratio was nearly negligible. At the condenser, it showed an opposite trend to the evaporator and with increase of the fill charge ratio, showed some enhancement of heat transfer. The heat transport limitation was occurred by the dry-out limitation for small fill charge ratio(10%) and presented about 100W. For the case of large fill charge ratio(Ψ$\geq$40%), it was occurred by the flooding limitation at about 500W.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.10
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• pp.1254-1261
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• 1997

Pulse boiling, the unsteady periodic boiling phenomenon appearing in the evaporator of thermosyphons was investigated by many researchers. In the present study investigations were conducted to examine the evolution of flow patterns at the evaporator, and changes in thermodynamic state that each of liquid pool and vapor experiences through 1 cycle of pulse boiling process. For wall and liquid pool the degree of superheat for the onset of nucleation was examined. It revealed that the degree of superheat increased with the increase of pulse period, reaching to 16.5 deg.C and 23 deg.C for liquid pool and evaporator wall respectively at .tau.=80 sec. The data on flow patterns obtained through series of operation tests were plotted in the coordinates of heat flux and vapor pressure to get a regime map. Further this map could be used to figure out the conditions of pulse boiling for a thermosyphon.

• 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 the Korean Society of Industry Convergence
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• v.5 no.3
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• pp.165-171
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• 2002

The thermosyphon has been used as a heat transmission device in the heat recovery of low level energy and cooling for heat generating equipments. Many studies on the working fluids and wicks have been reported to improve the heat transfer efficiency of the thermosyphon. A low temperature heat pipe with acetone is chosen in the present study to compare the heat transfer characteristics due to pouring amount of working fluid, magnitude of power supplied and tilt angles. The thermosyphon made ⵁ$15.88{\times}0.8t{\times}600mm$ of copper, evaporation section 200mm, insulation section 25mm, condensation 375mm. Heat transfer rate of the thermosyphon increase as magnitude of power supplied increase and observe dry out phenomenon at 5~10% of pouring amount of working fluid. So thermosyphon at the 150kJ/s judged to need 12% or more. Heat transfer rate of the thermosyphon have nothing to do with tilt angles. Dry out phenomenon of the thermo syphon makes it possible that a low temperature thermosyphon may be used to control temperature and heat transfer of a system when the critical quantity of a working fluid is supplied in the thermosyphon.