• ETRI Journal
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• 제19권2호
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• pp.59-70
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• 1997

A study on the operation of a heat pipe with two heat sources has been performed to optimize the heat distribution of satellite equipment. A numerical modeling is used to predict the temperature profile for the heat pipe assuming cylindrical two-dimensional laminar flow for the vapor, and the conduction heat transfer for the wall and wick. An experimental study using the copper-water heat pipe with the length of 0.45 m has been performed to evaluate the numerical model and to compare the temperature distribution at the outer wall for the non-uniform heat distribution. The results on temperature profiles for the heat input range from 29 W to 47 W on each heater are presented. Also the correlation between the heat input and the temperature increase is presented for the optimum distribution on two heaters. The result shows that the outer wall temperature can be controlled by redistribution of heat sources. It is also concluded that the heat source closer to the condenser can carry more heat while maintaining lower temperatures at the outer wall.

• 열처리공학회지
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• 제22권3호
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• pp.162-168
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• 2009

A horizontal tube furnace with a wide uniform-temperature zone was developed using isothermal characteristics of a heat pipe. The heat pipe heating system consists of a concentric annular shaped stainless-steel container, sodium as a working fluid and a screen mesh wick structure. The performance test of the heat pipe revealed that temperature changes along seven consecutive positions of the heat pipe outer wall were less than${\pm}0.1^{\circ}C$, thereby ensuring the high isothermal property. The isothermal property of the heat pipe-adapted tube fumace was investigated and compared to a conventional non-heat pipe type tube furnace. The temperature distribution measurement showed that the uniform temperature zone, in which temperature change is less than${\pm}$1$^{\circ}$C, of the heat pipe employed tube furnace system was about three times longer compared to the conventional tube furnace system.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1520-1532
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• 2003

An experiment was performed to obtain the local heat transfer coefficient and Nusselt number in a circular duct with a 180$^{\circ}$ bend for Re=6 x 10$^4$, 8 x 10$^4$ and 1 x 10$\^$5/ under swirling flow and non-swirling flow conditions. The test tube with a circular section was made from stainless steel having a curvature ration of 9.4. Current heat flux of 5.11 kW/㎡ was applied to the test tube by electrical power and the swirling motion of air was produced by a tangential inlet to the pipe axis at 180$^{\circ}$. Measurements of local wall temperatures and the bulk mean temperatures of air were made at four circumferential positions at 16 stations. The wall temperatures showed a reduced distribution curve at the bend for the non-swirling flow, but this effect did not appear for the swirling flow. The Nusselt number distributions for the swirling flow, which was calculated from the measured wall and the bulk temperatures, were higher than that of the non-swirling flow. The average Nusselt number of the swirling flow increased by about 90-100%, compared to that of the non-swirling flow. The Nu/Nu$\_$DB/ values at the 90$^{\circ}$ station for non-swirling flow and swirling flow were approximately 2.5 and 4.8 at Re=6x10$^4$ respectively. The values agree well with Said's results for non-swirling flow.

• 대한기계학회논문집B
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• 제22권8호
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• pp.1073-1082
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• 1998

When thermal diffusivity is measured by laser flash method, the thermal diffusivity call be calculated front the assumption of the uniformly heated whole surface of the specimen. It has been known that the approximate 5% error is made by the non-uniform energy distribution on the specimen surface of laser pulse heat source. In this study, to obtain the highly-uniformed laser beam, which has both the low non-uniform heating error from non-uniform laser beam and the energy loss, research was carried out on no transmitting loss by optical fiber and high repetitions. In addition, heating error and thermal diffusivity were measured as the measuring positions were varied and compared with the results using the uniform and the non-uniform laser beams. In addition, dole to using the uniformalized laser beam, the whole surface of the specimen was heated uniformly and as a result, it was the thought that this was very effective to reduce the variations of the errors of the thermal diffusivity as the measuring positions were varied. It can be obtained that when the thermal diffusivity of POCO-AXM-5Q1 of SRM in NBS was measured with both the uniform and the non-uniform laser beams, the dispersion error of the former was from 2 to 2.5%, which was more improved than that of the latter.

• Nuclear Engineering and Technology
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• 제34권4호
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• pp.382-395
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• 2002

An experimental study on transient critical heat flux (CHF) under flow coastdown has been performed for the water flow in a non-uniformly heated vertical annulus under low flow and a wide range of pressure conditions. The objectives of this study are to systematically investigate the effect of the flow transient on the CHF and to compare the transient CHF with steady-state CHF The transient CHF experiments have been performed for three kinds of flow transient modes based on the coastdown data of a nuclear power plant reactor coolant pump. At the same inlet subcooling, system pressure and heat flux, the effect of the initial mass flux on the critical mass flux can be negligible. However, the effect of the initial mass flux on the time-to- CHF becomes large as the heat flux decreases. The critical mass flux has the largest value for slow flow reduction rate. There is a pressure effect on the ratio of the transient CHF data to steady-state CHF data. Except under low system pressure conditions, the flow transient CHF was revealed to be conservative compared with the steady-state CHF data. Bowling CHF correlation and thermal hydraulic system code MARS show promising results for the prediction of CHF occurrence .

• 한국초전도ㆍ저온공학회논문지
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• 제14권2호
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• pp.20-23
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• 2012

With continuous development of the 2nd generation HTS conductor, the critical current of the conductor is also increasing. However, many applications require more than 2 conductors in parallel to transport large current. Applications such as HTS power cables and some HTS current leads usually need much larger transport current than that provided by a single conductor and they require more than several tens of HTS conductors. In the case of parallel connection of multiple HTS conductors, the current distribution depends on the contact resistance of each conductor at the terminals for DC operation. The non-uniform distribution of the terminal resistances results in a non-uniform distribution of the current. The resultant current non-uniformity affects on the measurement of the I-V curve and the thermal performance of the multiple conductors. This paper describes the I-V curves obtained from multiply connected HTS conductors with different terminal contact resistances to investigate the relationship between the distorted I-V curve and heat generation.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.221-226
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• 2008

A microchannel condenser as a part of a R410A residential air-conditioning system was examined experimentally and numerically in this study. The system was operated in separate environmental chambers and its performance was measured in ARI A, B, and C conditions. A numerical model for the microchannel condenser was developed and its results were compared with the experimental results. The model simulated the condenser with the assumption of the uniform air and refrigerant distribution, and with the consideration of the non-uniform air distribution at the face of the condenser and refrigerant distribution in the headers. In order to consider the non-uniform air distribution, air velocity contours were generated from the measured local air velocities at the face of the condenser. The simulation results showed that the effect of the air and refrigerant distribution was not a significant parameter in predicting the capacity of the microchannel condenser which was experimentally examined in this study. The comparison of the calculated and experimental results showed that the condenser capacity could be predicted well for every test condition. However, the prediction of refrigerant pressure drop deviated significantly from the measured values.

• 설비공학논문집
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• 제15권12호
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• pp.1043-1048
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• 2003

An experimental investigation was executed to determine the capacity degradation due to non-uniform refrigerant distribution in a multi-path evaporator. In addition, the possibility of recovering the capacity reduction by controlling the refrigerant distribution among refrigerant paths was assessed. The finned-tube evaporator, which had a three-path and three-depth-row, was tested by controlling inlet quality, exit pressure, and exit superheat for each refrigerant path. The capacity reduction due to superheat unbalance between each path was as much as 30%, even when the overall evaporator superheat was kept at a target value of 5.6$^{\circ}C$. It may indicate that the internal heat transfer within the evaporator assembly caused the partial capacity drop. For the evaporator having air mal-distributions, the maximum capacity reduction was found to be 8.7%. A 4.5% capacity recovery was obtained by controlling refrigerant distribution to obtain the target superheat at the outlet of each path.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.256-261
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• 2008

In this study, frost behavior on two dimensional fins of a heat exchanger was experimentally investigated. Temperature distribution on a 2-D fin surface and frost properties were measured in the directions perpendicular to and parallel to airflow. The results indicated that the temperature gradient in the direction perpendicular to airflow was large because of fin heat conduction, while that in the direction parallel to airflow was very small. Frost thickness in the airflow direction decreased from the leading edge towards the trailing edge of the fin due to leading edge effect. The reduction rate of frost thickness in the airflow direction, however, was very small compared with that in the direction perpendicular to the airflow, as affected by the temperature distribution.

• 대한기계학회논문집B
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• 제27권7호
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• pp.963-972
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• 2003

Performance characteristics of the planar-type solid oxide fuel cell (SOFC) are investigated by the analysis of flow fields coupled with heat and mass transfer phenomena in anode and cathode channels. For these purposes, performance analysis of the SOFC is conducted based on electrochemical reaction phenomena in electrodes and electrolyte coupled with flow fields in anode and cathode channels. In the present study, the isothermal model adopted in the previous paper prepared by the same authors is extended to the non-isothermal model by solving energy equation additionally with momentum and mass transfer equations using CFD technique. It is found that the difference between isothermal and non-isothermal models come from non-uniform temperature distribution along anode and cathode electrodes by solving energy equation in non-isothermal model. Non-uniform temperature distribution in non-isothermal model contributes to the increase of average temperature of the fuel cell and influences its performance characteristics.