• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.64-69
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• 2007

This study is to develop heat recovery system using high performance heat pipe heat exchanger for Middle-high temperature range industrial exhaust gas. The naphthalene is used as working fluid of heat pipe in this study. Single naphthalene heat pipe could transport over 2,000 watts with $0.05^{\circ}C/W$. The heat pipe heat exchanger consist of 50 naphthalene heat pipes recovered 62 kW when over $400^{\circ}C$ gas exhausted and the maximum recovered heat rate was 173 kW in this study.

• Nuclear Engineering and Technology
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• 제39권1호
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• pp.21-30
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• 2007

Current high-temperature gas-cooled reactors (HTGRs) are based on a closed Brayton cycle with helium gas as the working fluid. Thermodynamic performance of the axial-flow helium gas turbines is of critical concern as it considerably affects the overall cycle efficiency. Helium gas turbines pose some design challenges compared to steam or air turbomachinery because of the physical properties of helium and the uniqueness of the operating conditions at high pressure with low pressure ratio. This report present a review of the helium Brayton cycle experiences in Germany and in Japan. The design and availability of helium gas turbines for HTGR are also presented in this study. We have developed a new throughflow calculation code to calculate the design-point performance of helium gas turbines. Use of the method has been illustrated by applying it to the GTHTR300 reference.

• 한국전산유체공학회지
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• 제12권3호
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• pp.47-54
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• 2007

A periodic CFD approach for the performance analysis of compact high temperature heat exchangers is introduced and applied to selected benchmark problems, which are a fully developed 2D laminar heat transfer, a conjugate heat transfer between parallel plates which have exact solutions, and a heat transfer in a real high temperature heat exchanger module. The results for the 2D laminar heat transfer and the 2D conjugate heat transfer showed a very good agreement with the exact solutions. For the high temperature heat exchanger module, the pressure drops were predicted well but some difference was observed in the temperature parameters when compared to the full channel CFD analysis due to assumptions introduced into the periodic approach. Considering its assumptions and simplicities, however, the results showed that the periodic approach provides physically reasonable results and it is sufficient to predict the performance of a heat exchanger within an engineering margin and with much less CPU time than the case of a full channel analysis.

• 동력기계공학회지
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• 제18권4호
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• pp.23-28
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• 2014

In order to increase the performance of conventional hot water floor heating system, the bubble jet loop heat pipe for the system was developed. This experiment was conducted under next conditions : Working fluid was R-134a, charging ratio was 50%. A temperature of hot water, room temperature and flow rate were $60^{\circ}C$, $15^{\circ}C$ and 0.5~1.5 kg/min, respectively. The experimental results, show that bubble jet loop heat pipe had a high effective thermal conductivity of $4714kW/m^{\circ}C$ and a sufficient heat flux of $73W/m^2$ to heat the floor to $35^{\circ}C$ in case of the 1.5 kg/min of flow rate. So the bubble jet loop heat pipe has a possibility for appling of the floor heating system. Additionally, the visualization of bubble jet loop heat pipe was performed to understand the operating principle. Bubbles made by the narrow gap between inner tube and outer tube of evaporating part generate pulsation at liquid surface of working fluid. The pulsation had slug flow and wavy flow. So working fluid circulates in the bubble jet loop heat pipe as two phase flow pattern. And large amount of heat is transferred by the latent heat from evaporating part to condensing part.

• 한국표면공학회지
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• 제46권6호
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• pp.283-289
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• 2013

The experimental study for the temperature uniformity on the wafer using liquid-vapor phase heat transfer mechanism is performed. For the experiment, the heater plate which is consist of stainless steel container, working fluid and electrical heater is designed, manufactured and tested at the range of 600 to $850^{\circ}C$. The results showed that the phase change type heater plate was much more uniform and stable temperature on the heater plate surface and wafer than the uniform heat flux type heater plate at the atmospheric condition. Also, the results of 300 mm outer diameter of heater plate showed that the same temperature uniformity compared with 230 mm.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.419-424
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• 2001

TCV(Temperature control valve by pressure compensation) controls temperature constantly, when it is sending steam or high temperature water to heating device of heat exchanger. For designing TCV, the ratio of piston and hole diameters is one of the important design parameters. Numerical analysis is carried out to elucidate the flow characteristics in the TCV with different port areas of cold and hot waters, using the k-$\epsilon$ turbulence model and Cartesian cut-cell method. Numerical results show that the exit flow rate is mainly affected by pressure distribution in the piston.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1250-1254
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• 2004

To develop more compact and light generators which have high capacity, the most important thing that should be considered is the inner cooling system. Under all circumstances, the temperature of rotor and stator windings must be kept below the maximum temperature of insulation to maintain reliability and prolong durability of the machine. Therefore, the development of more effective cooling system and the exact prediction of windings are essential to produce our unique generator model which is reliable and competitive in international market. In this study, the flow of cooling air and the temperature distribution of winding is analyzed by using computational fluid dynamics. This analysis can lead to optimize the structure of cooling system and predict a local temperature rise.

• 동력기계공학회지
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• 제10권1호
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• pp.90-95
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• 2006

Pneumatic control systems have been mainly used as a high speed operating system. Therefore, state change of air in a control volume was assumed to be adiabatic change and, pneumatic control systems have been analyzed by using this assumption. Especially, when absolute value of pressure change in the control volume is small, there is a tendency to neglect effect of temperature change on pneumatic control system because temperature change owing to pressure change is small. In this study, an effect of temperature change of air on the decompression control process was analyzed by considering change of mass flow rate, and heat transfer characteristics between air in the chamber and the chamber wall. As a result, this study could confirm that a slight temperature change of the air in the pneumatic pressure control system can influence on the dynamic characteristics of pressure response, and pressure control performance.

• Nuclear Engineering and Technology
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• 제38권2호
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• pp.147-154
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• 2006

Thermal fatigue of the coolant circuits of PWR plants is a major issue for nuclear safety. The problem is especially accute in mixing zones, like T-junctions, where large differences in water temperature between the two inlets and high levels of turbulence can lead to large temperature fluctuations at the wall. Until recently, studies on the matter had been tackled at EDF using steady methods: the fluid flow was solved with a CFD code using an averaged turbulence model, which led to the knowledge of the mean temperature and temperature variance at each point of the wall. But, being based on averaged quantities, this method could not reproduce the unsteady and 3D effects of the problem, like phase lag in temperature oscillations between two points, which can generate important stresses. Benefiting from advances in computer power and turbulence modelling, a new methodology is now applied, that allows to take these effects into account. The CFD tool Code_Saturne, developped at EDF, is used to solve the fluid flow using an unsteady L.E.S. approach. It is coupled with the thermal code Syrthes, which propagates the temperature fluctuations into the wall thickness. The instantaneous temperature field inside the wall can then be extracted and used for structure mechanics computations (mainly with EDF thermomechanics tool Code_Aster). The purpose of this paper is to present the application of this methodology to the simulation of a straight T-junction mock-up, similar to the Residual Heat Remover (RHR) junction found in N4 type PWR nuclear plants, and designed to study thermal striping and cracks propagation. The results are generally in good agreement with the measurements; yet, in certain areas of the flow, progress is still needed in L.E.S. modelling and in the treatment of instantaneous heat transfer at the wall.

• 한국기계가공학회지
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• 제17권1호
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• pp.34-41
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• 2018

A flange joint is a pipe connection used to prevent the leakage of high-pressure fluids by inserting a gasket and tightening the bolts. Among several kinds of gaskets available, metal ring type joint gaskets are most widely used in conditions that require high-temperature and high-pressure fluid flow, such as oil pipelines, gas pipes, pumps, valve joints, etc. The purpose of this study is to investigate the contact pressure and stress characteristics closely related to the sealing performance of Class 900 flange joints used in high temperature and high pressure environments. The dimensions of flange joints with five different nominal pipe sizes were determined with reference to those specified in ASME 16.5. The metal ring gaskets inserted in the joints were octagonal and oval gaskets. The bolt tensile forces calculated from the tightening torques were input as the bolt pretension loads in order to determine the contact pressure and stress levels after fastening. Loading was composed of three steps, including the fastening step, and different amounts of applied pressures were used in each analysis to investigate the effect of fluid pressure on the contact force of the joints. A general-purpose software, ANSYS 17.2, was used for the analysis.