• 대한기계학회논문집
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• 제19권4호
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• pp.1095-1101
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• 1995

Numerical analysis of vertical solidification process allowing solid-liquid density change is performed by a hybrid method between a winite volume method (FVM) and a finite element method (FEM). The investigation focuses on the influence of solid-liquid density change and cooling rates on the motion of solid-liquid interface, solidified mass fraction, temperatures and thermal stresses in the solid region. Due to the density change of pure aluminium, solid-liquid interface moves more slowly but the solidified mass fraction is larger. The cooling rate of the wall is shown to have a significant influence on the phase change heat transfer and thermal stresses, while the density change has a small influence on the motion of the interface, solidified mass fraction, temperature distributions and thermal stresses. As the cooling rate increases, the thermal stresses become higher at the early stage of a solidification process, but it has small influence on the final stresses as the steady state is reached.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 추계 학술논문 발표대회
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• pp.66-67
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• 2019

Insulated buildings are exposed to the external environment due to aging and construction problems, resulting in a decrease in building energy efficiency. Therefore, the purpose of this paper is to provide a material for the change in thermal conductivity of the insulation when it is exposed to various external environments. In the experiment, five types of heat insulating materials were selected, stored under different environmental conditions, and the thermal conductivity was measured periodically to confirm the change in thermal conductivity. As a result, the thermal conductivity of all the insulating materials except the PF board increased with the passage of time. This is because thermal insulation absorbs atmospheric moisture under all environmental conditions and the thermal conductivity increases, and in the case of thermal insulation stored indoors in environmental conditions, the temperature differs from the thermal insulation stored outside. It is considered that there is little evaporation of moisture absorbed constantly, and the change in thermal conductivity is large.

• 한국군사과학기술학회지
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• 제23권3호
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• pp.237-245
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• 2020

In this paper, I introduce Phase-Change Cooling for thermal management of high power devices that can be applied to High Power Laser and Electric Propulsion Systems which are composed of multiple distributed superheat sources. Phase-Change Cooling can be good used to efficient cooling of their heat sources. Phase-Change Cooling has extremely high efficiency of two-phase heat transport by utilizing heat of vaporization, relatively low flow rates and reduced pumps power. And I suggest TPI(Thermal Performance Index) which is a quantitative performance index of Phase-Change Cooling for thermal management. I quantify the performance of Phase-Change Cooling by introducing TPI. I present the test results of TPI's changing refrigerant, heat sink and flow rate of the Phase-Change Cooling system through the experiments and analyze these results.

• Bulletin of the Korean Chemical Society
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• 제21권6호
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• pp.628-634
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• 2000

Crosslink is the most important chemistry in a rubber vulcanizate. Degree and type of crosslinks of the vulcanizate determine its physical properties. Change of crosslink density and deformation of a rubber vulcanizate by thermal aging were studied using natural rubber (NR) vulcanizates with various cure systems (conventional, semi-EV, and EV) and different cure times (under-, optimum-, and overture). All the NR vulcanizates were deformed by the thermal aging at 60-100 $^{\circ}C.$ The higher the aging temperature is, the more degree of the deformation is. The undercured NR vulcanizates after the thermal aging were deformed more than the optimumand overcured ones. The NR vulcanizates with the EV cure system were less deformed than those with the conventional and semi-EV cure systems. The deformation of the NR vulcanizates was found to be due to change of the crosslink density of the vulcanizates. The crosslink densities of all the vulcanizates after the extraction of organic materials were also changed by the thermal ging. The sources to change the crosslink densities of the vulcanizates by the thermal aging were found to be dissociation of the existing sulfur crosslink and the formation of new crosslinks by free sulfur, reaction products of curing agents, and pendent sulfide groups.

• 한국가시화정보학회지
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• 제21권2호
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• pp.63-71
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• 2023

Energy storage and distribution technologies are emerging as important factors as research on renewable energy continues. Analyzing the thermal flow of phase change material inside a latent heat storage device and to predict the phase change time is an important part for improvement of thermal performance. However, most of the current research is based on the trial-and-error experimental investigation to measure the phase change time. Therefore, in this study, a can-type phase change material container was designed, and the numerical method for analyzing the thermal flow of phase change material was established and validated. The error rate of the phase change time between the numerical and experimental results was within 5%, which proves its reliability. As a result, the phase change finishing times were found to be 78 minutes with inlet fluid temperature of 80℃ during charging process, and 126 minutes with inlet fluid temperature of 9℃ during discharging process.

• 설비공학논문집
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• 제25권12호
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• pp.647-653
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• 2013

TABS (Thermally Activated Building System) has recently applied by huge commercial buildings, airports, and convention centers in Europe. TABS provides night-time thermal storage by heating or cooling. The embedded water-based heating and cooling system uses the high thermal inertia of concrete in the building construction, in which a heating or cooling pipe is embedded. The aim of this study is to analyze the thermal storage and thermal output of TABS applied with PCM (Phase Change Material). To achieve this, prototypes of TABS and the thermal properties of various PCMs were investigated. By using the simulation program Physibel Voltra 6.0 W, the thermal storage and thermal output were evaluated according to a heating and cooling operation schedule.

• Geomechanics and Engineering
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• 제23권6호
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• pp.561-573
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• 2020

The creep and consolidation behaviors of clays subjected to thermal cycles are of fundamental importance in the application of energy geostructures. This study aims to numerically investigate the physical mechanisms for the temperature-triggered volume change of saturated clays. A recently developed thermodynamic framework is used to derive the thermo-mechanical constitutive model for clays. Based on the model, a fully coupled thermo-hydro-mechanical (THM) finite element (FE) code is developed. Comparison with experimental observations shows that the proposed FE code can well reproduce the irreversible thermal contraction of normally consolidated and lightly overconsolidated clays, as well as the thermal expansion of heavily overconsolidated clays under drained heating. Simulations reveal that excess pore pressure may accumulate in clay samples under triaxial drained conditions due to low permeability and high heating rate, resulting in thermally induced primary consolidation. Results show that four major mechanisms contribute to the thermal volume change of clays: (i) the principle of thermal expansion, (ii) the decrease of effective stress due to the accumulation of excess pore pressure, (iii) the thermal creep, and (iv) the thermally induced primary consolidation. The former two mechanisms mainly contribute to the thermal expansion of heavily overconsolidated clays, whereas the latter two contribute to the noticeable thermal contraction of normally consolidated and lightly overconsolidated clays. Consideration of the four physical mechanisms is important for the settlement prediction of energy geostructures, especially in soft soils.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.23-28
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• 2007

In most existing research, it is difficult to evaluate thermal comfort exactly because of reflecting individual ideal or psychological response by subjective questions. Physiological variable was selected in this study to evaluate objectively thermal comfort. MST was appeared very sensitively in indoor temperature and can express correctly thermal comfort of human body. The results of CSV are different each individual feeling sensation, so is difficult to evaluate detailedly thermal comfort unlike TSV. But the results of PP, AIx, ED, SEVR are greatly related to temperature change. So thermal comfort is evaluated more objectively by using PP, AIx, ED, SEVR on behalf of TSV, CSV. Human body was presented physiological feedback by temperature impetus and specially, tendency of heart rate agree with temperature change. Physiological reaction was showed sufficient possibility availing evaluation index of thermal comfort. In the future another one needs to review beside the selected physiological variable.

• 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.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 추계학술대회 논문집
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• pp.205-208
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• 2002

Thermal design is required with considering thermal stability to verify the reliability of electric power device with using IGBT. Numerical analysis is performed to analyzed the change in thermal resistance with respect to the various thermal density of heating element. Correlations between thermal resistance and heat generation density are established. With using these correlations, performance curve is composed with respect to the change in thermal resistance of cooling conditions for natural convection and forced convection. Thermal fatigue is occurred at the Inside and outside of IGBT by repeated heat load. The crack is occurred between base plate and ceramic substrate for the inside. When the crack length is 4mm, the failure is occurred. Therefore, Thermal design method considering thermal density, thermal fatigue resistance is presented on this study and it is expected to thermal design with considering life prediction.