• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.285-290
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• 2000

The present study was conducted to determine flooding heat transfer limitation of a two-phase closed thermosyphon using PFC as working fluid. The variables such as pipe inner diameter, working fluid property, operating temperature were examined by way of analytic method. Comparison of experimental data on flooding heat transfer limitation shows a fairly good agreement with the analytic results. An expression fur flooding maximum heat transfer rate was formulated as a function of Bond number and saturation pressure and written as follows ; $Q_{max} =0.989{\cdot}P_s^{0.286}{\cdot}Bo^{1.74}$.

• 태양에너지
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• 제8권1호
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• pp.5-12
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• 1988

One of the effective means to transfer the heat into and from the energy storage medium is thermosyphon. In this study, a two-phase closed thermosyphon with circular fins was used to extract the thermal energy stored in paraffin wax (Sunoco p-116). Heat transfer characteristics along the heat flow path were investigated as well as the overall performance. Some of the important results are as follows: (1) The temperature distribution of the wax in the radial direction was always maintained fairly uniformly; (2) Compared with bare thermosyphon, the heat transfer rate was vastly improved in the early stage of the experiment; and (3) Heat transfer coefficient between the wax and evaporating section of thermosyphon remained nearly constant during the experiment.

• 대한기계학회논문집B
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• 제26권12호
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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.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1102-1111
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• 2002

The study focuses on the heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal grooves. Three different working fluids(distilled water, methanol, ethanol) are used with various volumetric liquid fill charge ratio from 10 to 40%. Additional experimental parameters such as operating temperature and inclination angle of zero to 90 degrees are used for the comparison of heat transfer performance of the thermosyphon. Condensation and boiling heat transfer coefficients, heat flux are obtained using experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, liquid fill charge ratio, number of grooves and inclination angle are very important factors for the operation of thermosyphons. The relatively high rate of heat transfer is achieved when the thermosyphon with internal grooves is used compared to that with plain tube. The optimum liquid fill charge ratio for the best heat transfer performance lies between 25% and 30%. The range of the optimum inclination angle for this study is 20$^{\circ}$～30$^{\circ}$ from the horizontal position.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.239-244
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• 2003

This study concerns the performance of condensing heat transfer in two-phase closed thermosyphons with various helical grooves. Distilled water, methanol, ethanol have been used as the working fluid. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A experimental study was carried out for analyzing the performances of having 50, 60, 70, 80, 90 helical grooves. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphons is also tested for the comparison. The type of working fluid and the numbers of grooves of the thermosyphons with various helical grooves have been used as the experimental parameters. The experimental results have been assessed and compared with existing theories. The results show that the type of working fluids are very important factors for the operation of thermosyphons. And the maximum enhancement (i.e. the ratio of the heat transfer coefficients the helical thermosyphons to plain thermosyphons) is $1.5{\sim}2$ for condensation.

• 설비공학논문집
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• 제17권2호
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• pp.131-139
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• 2005

This study concerns the performance of boiling heat transfer in two-phase closed thermosyphons with various helical grooves. Distilled water, methanol, ethanol have been used as the working fluids. In the present work, a copper tube of the length of 1200 mm and 14.28 mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550 mm, while the remaining part of the thermosyphon tube is adiabatic section. A experimental study was carried out for analyzing the Performances of having 50, 60, 70, 80 and 50 helical grooves. A Plain thermosyphon having the same inner and outer diameter as the grooved thermosyphons is also tested for comparison. The type of working fluid and the numbers of grooves of the thermosyphons with various helical grooves have been used as the experimental parameters. The experimental results have been assessed and compared with existing theories. The results show that the number of grooves and the type of working fluids are very important factors for the operation of thermosyphons. The helical grooved thermosyphons having 50 to 60 grooves in water, 60 to 70 grooves in methanol and ethanol shows the best heat boiling heat transfer coefficient.

• 대한기계학회논문집B
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• 제29권1호
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• pp.116-122
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• 2005

This study concerns the performance of condensing heat transfer in two-phase closed thermosyphons with various helical grooves. Distilled water, methanol, ethanol have been used as the working fluid. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A experimental study was carried out for analyzing the performances of having 50, 60, 70, 80, 90 helical grooves. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphons is also tested for the comparison. The type of working fluid and the numbers of grooves of the thermosyphons with various helical grooves have been used as the experimental parameters. The experimental results have been assessed and compared with existing theories. The results show that the type of working fluids are very important factors for the operation of thermosyphons. And the maximum enhancement (i.e. the ratio of the heat transfer coefficients the helical thermosyphons to plain thermosyphons) is $1.5{\sim}2$ for condensation.

• 수산해양교육연구
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• 제16권2호
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• pp.257-270
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• 2004

The two-phase closed thermosyphon is a heat transfer device capable of transfer large quantities of heat from a source to a sink by taking advantage of the high heat transfer rates associated with the evaporation and condensation of a working fluid within the device. A study was carried out with the performance of the heat transfer of the thermosyphon having 50, 60, 70, 80, 90 internal micro 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. Water, methanol and ethanol have been used as the working fluids. The liquid filling as the ratio of working fluid volume to total volume of thermosyphon, the inclination angle, micro grooves and operating temperature have been used as the experimental parameters. The heat flux and the boiling and the condensation heat transfer coefficient and overall heat transfer coefficient at the condenser and 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 maximum heat transfer rate was obtained when the liquid fill ratio was about 25%. The high heat transfer coefficient was found between 25o and 30o of inclination angle for water and between 20o and 25o for methanol and ethanol. The relatively high rates of heat transfer have been achieved in the thermosyphon with internal micro grooves. The micro grooved thermosyphon having 60 grooves shows the best heat transfer coefficient in both condensation and boiling. The maximum enhancement (i.e. the ratio of the heat transfer coefficients of the micro grooved thermosyphon to plain thermosyphon) is 2.5 for condensation and 2.3 for boiling.

• Journal of Mechanical Science and Technology
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• 제19권8호
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• pp.1662-1669
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• 2005

Boiling heat transfer characteristics of a two-phase closed thermosyphons with various helical grooves are studied experimentally and a mathematical correlation is developed to predict the performance of such thermosyphons. The study focuses on the boiling heat transfer characteristics of two-phase closed thermosyphons with copper tubes having 50, 60, 70, 80, 90 internal helical grooves. A two-phase closed thermosyphon with plain copper tube having the same inner and outer diameter as those of grooved tubes is also tested for comparison. Water, methanol and ethanol are used as working fluid. The effects of the number of grooves, various working fluids, operating temperature and heat flux are investigated experimentally. From these experimental results, a mathematical model is developed. In the present model, boiling of liquid pool in the evaporator is considered for the heat transfer mechanism of the thermosyphons. And also the effects of the number of grooves, the various working fluids, the operating temperature and the heat flux are brought into consideration. A good agreement between the boiling heat transfer coefficient of the thermosyphon estimated from experimental results and the predictions from the present mathematical correlation is obtained. The experimental results show that the number of grooves, the amount of the working fluid and the various working fluids are very important factors for the operation of thermosyphons. Also, the thermosyphons with internal helical grooves can be used to achieve some inexpensive and compact heat exchangers in low temperature.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권4호
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• pp.184-191
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• 2002

This study concerns the performance of the condensing heat transfer performance of two-phase closed thermosyphons with plain copper tube and tubes having 50, 60, 70, 80, 90 internal micro grooves. Distilled water, methanol, ethanol have been used as the working fluid. The numbers of grooves and operating temperature have been investigated as the experimental parameters. Condensing heat transfer coefficients and heat flux are obtained from experimental data for each case of specific parameter. The experimental results are assessed and compared with existing correlations. The results show that working fluids, numbers of grooves are very important factors for the operation of thermosyphons. The working fluid with high latent heat such as water has a good heat transfer rate compared to methanol and ethanol. The relatively high rate of heat transfer is achieved when the thermosyphon with internal micro grooves is used compared to that with plain tube. Condensing heat transfer coefficient of grooved thermosyphon is 1.5∼2 times higher in methanol and 1.3∼l.5 times higher in ethanol compared to plain tube. The best condensation heat transfer performance is obtained for 60 grooves, and the maximum value of this case is 2.5 times higher than that of the plain tube.