• 설비공학논문집
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• 제6권3호
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• pp.182-192
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• 1994

This paper focuses on the investigation of the heat transfer phenomena that occur inside the cylindrical tube. The inclination of the tube is adopted as a principal parameter varying from vertical to horizontal. The phase change material employed in this experiment is 99 percent pure n-docosane paraffin($C_{22}$ $H_{46}$). It is found that the amount of solidified mass during a prescribed solidifying period is not sensitive to the inclination of the tube but to the local layer thickness. It is studied that the latent energy is the largest contributor to the total extracted energy. The sensible energy($E_{s1}$, $E_{s2}$, $E_{s3}$) may not be negligible at the large wall-subcooling and initial-liquid-superheating, also at the first step of solidifying.

• 한국안전학회지
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• 제11권2호
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• pp.33-41
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• 1996

Experiments were performed to study solidification of phase change material on a finned vertical tube when either conduction In the solid or natural convection in a liquid controls the heat transfer. The liquid was housed in a cylindrical containment vessel whose surface was maintained at a uniform, time-invariment temperature during a data run, and the solidification occurred at a finned and unfinned vertical tube positioned along the axis of the vassel. The phase change material(PCM) employed in this experiment is 99 percent pure n-Octacosan paraffin($C -{28}H_{58}/$). For conduction-controlled and convection-controlled solidification, the enhancement of the solidified mass rate due to finning is great when the solidified layer is thin and decreases as the layer grows thicker. It is studied that the latent energy($E_{\lambda}$) is the largest contributor to the total extracted energy($E_{\lambda} ＋ E_{sl}＋E_{s2}$) and the total extracted energy rate at a finned vertical tube is greater than that at a unfinned vertical tube.

• 대한기계학회논문집A
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• 제30권4호
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• pp.428-434
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• 2006

Pulse laser welding of AISI 304 stainless steel plate was simulated to find optimal welding conditions by using commercial finite element code MARC. Due to geometric symmetry, a half model of AISI 304 stainless steel plate was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat, mass density and latent heat were given as a function of temperature. A moving heat source was designed on the basis of experimental data. As a result, Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

• 설비공학논문집
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• 제13권12호
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• pp.1275-1281
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• 2001

Aqueous polymer solutions are known to have small pressure reduction. Paraffin slurries are known to have high thermal capacity. Paraffin particles are mixed into an aqueous polymer solution to make a new heat transfer fluid having high thermal capacity but low pressure reduction. The heat transfer characteristics of the new slurry was tested in a circular tube having a constant heat transfer boundary condition. The new slurry was found to have high Nusselt numbers as well as high thermal capacity and low pressure reduction in the laminar flow. The trends of the Nusselt numbers along the heating test section were studied for various heating conditions.

• 한국포장학회지
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• 제29권1호
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• pp.27-33
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• 2023

본 연구에서는 저온물류 시스템의 단열용기의 온도유지 성능에 대하여 5℃급 저온 LHM을 배치하였을 때 배치구성 조건에 따른 온도특성을 확인하였다. LHM을 단열용기 내부에 배치하였을 때 6면과 5면에 상/하부 배치 비중에 차이를 두고 외기부하에 따른 내부 공기 온도균일도 및 목표 온도 유지시간을 분석하였다. 단열용기 내부 공기는 상부의 상승온도와 이때 발생하는 밀도차에 의한 공기 대류현상이 온도 성층화를 발생시키고, 균일도를 확보하기 위해 LHM의 상부 배치 비중이 하부보다 컸을 때 균일성이 높고 유지 시간이 오래 지속되는 것을 확인하였다. 다만, 상부 배치 비중을 높이기 위해 하부 배치를 제외한 조건에서 높은 균일성을 보이지만 짧은 유지 시간으로 보여 적정조건으로 알맞지 않다. 결과적으로 단열용기의 단열재 대칭구성과 LHM의 동일한 중량을 배치하여 보냉용기를 제작할 경우, LHM의 전면 배치를 바탕으로 하부에 비해 상부 배치 비중을 늘렸을 때 내부 공기 온도의 분포 균일도와 유지시간 성능을 높이는데 효율적인 방안이라고 판단된다. 저온물류 보냉용기 성능분석에 있어, 본 연구를 기반으로 다른 조건의 상변화 온도와 잠열량을 갖는 다양한 저온영역대의 LHM을 적용한 수치해석을 수행하여 성능 예측 결과를 확보할 수 있고 온도 균일도를 위한 단열 및 잠열 복합 구성 이송 용기의 최적 설계조건 수립에 기여할 것으로 기대된다.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1277-1284
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• 2000

To enhance heat transfer characteristics of water, micro-encapsulated octadecane of about $10{\mu}m$ diameter was added to water. Viscosity of the slurry was measured by using a capillary tube viscometer. The measured viscosity decreased as the temperature of the slurry increased, and it increased as the fraction of the capsules in the slurry increased. Thermal characteristics of the octadecane were studied by using a differential scanning calorimeter. The melting temperature and the melting energy of the octadecane were found to be $28.6^{\circ}$ and 34.4kcal/kg, respectively. The convective heat transfer characteristics of the slurry were investigated in a flow loop with a constant heat flux test section. Friction factor of the slurry flow was found to be similar to the expected curve by Petukhov. The Nusselt number of the slurry flow was highest when the octadecane melted. Effective thermal capacity of the 14.2% slurry was found to have 1.67 times of the thermal capacity of water.

• 한국항공우주학회지
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• 제50권10호
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• pp.729-737
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• 2022

하반기에 발사 예정인 차세대소형위성2호(NEXTSat-2)에 탑재된 고상-액상 상변화물질 열제어장치(Phase Change Material Thermal Control Unit, PCMTCU)의 비행모델에 대한 위성 차원 열진공시험 결과로부터 융해-응고에 따른 작동과정을 분석하였다. 시험결과 PCM의 상변화는 발열부품의 온도 안정화에 기여함을 확인하였다. 시험에서 계측된 온도변화를 이용하여 타당한 정도의 정확도를 갖도록 PCMTCU의 열해석모델에 대한 보정을 수행하였다. 보정된 열해석모델로써 임무궤도의 정상 작동에 따른 PCMTCU의 주기적 온도변화를 예측하였으며, PCM의 액상분율로써 정량적 기여도를 평가하였다. 향후 임무궤도에서의 비행자료를 수신하여 PCMTCU의 우주 환경 검증을 완료할 예정이다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.137-146
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• 2008

Nd:YAG pulse laser welding of stainless steel plate was simulated to find welding condition by using commercial finite element code MARC. Due to geometric symmetry, a half model of AISI 304 stainless steel plate was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat, mass density and latent heat were given as a function of temperature. As results, Three dimensional heat source model for pulse laser beam conditions of butt welding has been designed by the comparison between the finite element analysis results and experimental data on AISI 304 stainless steel plate. Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

• 대한기계학회논문집A
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• 제31권8호
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• pp.839-846
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• 2007

Nd:YAG pulse laser fillet welding of stainless steel plate was simulated to find welding condition by using commercial finite element code MARC. Full model of AISI 304 stainless steel plate was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat, mass density and latent heat were given as a function of temperature. As results, Three dimensional heat source model for pulse laser beam conditions of fillet welding has been designed by the comparison between the finite element analysis results and experimental data on AISI 304 stainless steel plate. Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

• 에너지공학
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• 제5권2호
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• pp.115-122
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• 1996

망초를 이용한 저온 잠열축열시스템에서 핀을 설치한 전열관에서 방열과정중의 열전달 특성을 살펴보았다. 잠열물질의 과냉각과 상분리를 방지하기위해 3.0 wt% $Na_2$B$_4$O$_{7}$10$H_2O$와 2.2 wt% acrylic acid sodium sulfate가 조핵제 및 증점제로 사용되었다. 축열조는 높이가 530 mm, 직경이 74 mm이고 열전달관은 높이가 480 mm, 직경이 13.5 mm인 이중관으로 되어있으며 열전달 유체로는 물을 사용하였다. 축열재로부터 열을 치수하는 방열과정에서 열회수율은 열전달 유체의 유입온도와 유량에 크게 의존하였다. 핀이 설치되지 않은 전열관과의 비교실험을 통하여 핀에 의한 열전달 촉진은 얇은 핀의 경우에는 열전달계수의 증가가 미미하였지만 두꺼운 핀을 사용한 경우에는 같은 조업조건에서 열전달계수가 약 60% 정도 증가하였다. 실험적으로 결정된 총괄 열전달계수는 핀이 없는 경우에는 약 150-260 w/$m^2$K이었고 두꺼운 핀을 사용한 전열관에서는 230-530 W/$m^2$K정도였다. 총괄 열전달계수의 크기와 핀에 의한 전열면적을 기준으로 한 핀의 효율은 두꺼운 핀의 경우에는 약 0.26, 얇은 핀의 경우에는 0.05 정도로 계산되었다.다.