• Current Optics and Photonics
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• 제1권1호
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• pp.7-11
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• 2017

In this study, multilayered graphene was easily transferred to the target substrate in one step using thermal release tape. The transmittance of the transferred graphene according to the number of layers was measured using a spectrophotometer. The sheet resistance was measured using a four-point probe system. Graphene formed using this transfer method showed almost the same electrical and optical properties as that formed using the conventional poly (methyl methacrylate) transfer method. This method is suitable for the mass production of graphene because of the short process time and easy large-area transfer. In addition, multilayered graphene can be transferred on various substrates without wetting problem using the one-step dry transfer method. In this work, this easy transfer method was used for dielectric substrates such as glass, paper and polyethylene terephthalate, and a sheet resistance of ~240 ohm/sq was obtained with three-layer graphene. By fabricating organic solar cells, we verified the feasibility of using this method for optoelectronic devices.

• 한국생산제조학회지
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• 제26권2호
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• pp.243-250
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• 2017

A numerical study was conducted to calculate the cooling capacity variation of a power plant ACC (air-cooled condenser) caused by changes in operating conditions. A numerical model was developed using the ${\varepsilon}-NTU$ and finite volume method, containing 100 elements for a single low fin tube. The model was validated through a comparison of cooling capacity between the simulated values and manufacturer's data. Even though simple assumptions and previously presented heat transfer correlations were applied to the model, the prediction error was 1.9%. The simulated variables of the operating conditions were air velocity, air temperature, and mass flux. The analysis on the variation of thermal resistance along the tube showed that the water side thermal resistance was higher than the air side thermal resistance at the downstream end of the tube, indicating that the ACC capacity could be increased by applying technology to enhance in-tube flow condensation heat transfer.

• 대한기계학회논문집
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• 제16권6호
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• pp.1205-1215
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• 1992

본 연구에서는 1차원 상변화문제를 확장하여 사각형 주형내에서의 접촉열저항 을 고려한 2차원 상변화문제를 해석하고자 한다.즉 고상/액상 경계면인 상변화면을 추적하기 위하여 온도수식법(temperature formulation method)을 적용시 나타나는 복 잡성을 극복하기 위하여 제시된 엔탈피법을 이용하여 순수물질의 경우 뿐만 아니라 2상영역이 존재하는 합금에서의 온도분포, 상변화면의 이동속도 및 총응고에 소요되는 시간등의 열적특성을 해석하며, 또한 이러한 열적특성에 영향을 미치는 매개변수를 도출하고자 주형의 형상, 주형 외벽에서의 열전달계수, 접촉 열전달계수, 주형의 열전 도계수 및 주물의 초기온도등의 변화에 따른 효과를 고찰한다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.135-144
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• 2009

In this study, the heat transfer and fluid flow characteristics of a condenser for a refrigerator are analyzed with the numerical method. The main objective of the study is to obtain basic data in order to develop a new type of condenser focused on an influence of thermal resistance of air side and thermal contact resistance on the heat transfer performance. The CFD technique was used for whole study, and experiments were performed in order to verify the reliability of the numerical analysis and predict the thermal contact resistance. In this study, a heat exchanger sample was made of a part of condenser to make the experimental and numerical analysis simple and efficient. Water was used for the inner working fluid of the heat exchanger, and an experimental apparatus was composed concisely. A heat exchanger sample of tube type was used to verify the reliability of numerical analysis, and a heat exchanger of fin and tube type was used to predict the ratio of thermal contact resistance to the overall thermal resistance.

• 한국전산유체공학회지
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• 제15권1호
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• pp.46-55
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• 2010

In this study, the heat transfer and fluid flow characteristics of a condenser for a refrigerator are analyzed with the numerical method. The main objective of the study is to obtain basic data in order to develop a new type of condenser focused on an influence of thermal resistance of air side and thermal contact resistance on the heat transfer performance. The CFD technique was used for whole study, and experiments were performed in order to verify the reliability of the numerical analysis and predict the thermal contact resistance. In this study, a heat exchanger sample was made of a part of condenser to make the experimental and numerical analysis simple and efficient. Water was used for the inner working fluid of the heat exchanger, and an experimental apparatus was composed concisely. A heat exchanger sample of tube type was used to verify the reliability of numerical analysis, and a heat exchanger of fin and tube type was used to predict the ratio of thermal contact resistance to the overall thermal resistance.

• 한국화재소방학회논문지
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• 제25권2호
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• pp.80-87
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• 2011

합성보의 내화성능을 확인하기 위한 재하가열시험 결과, 내화성능이 부족한 경우 단면의 변경을 통하여 그 성능을 향상시킬 수 있다. 하지만 변경조건이 다양하다면 다수의 실험을 실시해야 하기 때문에 많은 시간 및 비용이 필요하다. 본 연구에서는 비대칭 H형강 합성보 단면에서 내화성능에 가장 큰 영향을 미치는 부분을 열전달해석을 수행하여 확인하고, 이후 단면변경을 통한 내화성능 향상 추세를 열전달해석 및 비선형구조해석으로 확인하여 1시간 내화성능을 가질 수 있는 변경된 단면을 제시하였다.

• 대한기계학회논문집B
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• 제20권2호
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• pp.720-729
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• 1996

An analysis of convective boiling heat transfer for refrigerant mixtures is performed for an annular flow to investigate the degradation of the heat transfer rate. Annular flow is selected in this study because a great portion of the evaporator in the refrigeration and air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor is included in this analysis, which is considered to be one of driving forces for the mass transfer at the interface. Due to the concentration gradient at the interface the mass transfer is interfered, so is the evaporative heat transfer at the interface. The mass transfer resistance makes the interface temperature slightly higher and, as a result, the heat transfer coefficients decrease compared with those without mass transfer effects. The degradatioin of the heat transfer rate reaches its maximum at a certain composition. The composition difference between vapor core and vapor at the interface has a direct effect on the temperature difference between the vapor core and the interface and the degradation of the heat transfer rate. Correction factor $C_{F}$ for the mixture effects is added to the correlation for pure substances and the flow boiling heat transfer coefficients can be calculated using the modified equation.n.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.173-181
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• 2017

In this paper, the bifurcation criteria for inductive power transfer (IPT) systems is suggested considering the inductive power pad losses. The bifurcation criteria for series-series (SS) and series-parallel (SP) topologies are derived in terms of the main parameters of the IPT system. For deriving precise criteria, power pad resistance is obtained by copper loss calculation and core loss analysis. Utilizing the suggested criteria, possibility of bifurcation occurrence can be predicted in the design process. In order to verify the proposed criteria, 50 W IPT laboratory prototype is fabricated and the feasibilities of the switching frequency and AC load resistance shift to escape from bifurcation are identified.

• 설비공학논문집
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• 제6권2호
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• pp.78-92
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• 1994

Thermal performance of pipe network of continuous heating system controlled by thermostat and flow control valve was simulated in consideration of radiation heat transfer and solved by linear analysis method. Thermal performance of real apartment building with radiant floor heating system was simulated by equivalence heat resistance-capacity method. This method enables to simulate the unsteady variation of temperature or each element of building. Heat transfer characteristics of each element were also investigated.

• 소성∙가공
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• 제20권1호
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• pp.29-35
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• 2011

In the design of the injection molding process, various parameters including mold design parameters and molding conditions should be investigated to improve part quality. The mold temperature is one of important processing parameters that affect the flow characteristics, surface appearance, part deformation, mechanical properties, etc. Numerical analyses have been used to predict the temperature distribution of the mold under the given cooling or heating conditions. However, conventional analyses have been performed by assuming that the mold material is a single solid even though a number of plates are assembled to construct an injection mold. In the present study, a numerical approach considering the thermal contact resistance is proposed to provide more reliable prediction of the mold temperature distribution by reflecting the heat-resistance between assembled mold plates.