• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.6
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• pp.50-59
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• 2022

The design of the substrate significantly affects the thermal history and the residual stress formation in the vicinity of a repaired region by a directed energy deposition (DED) process. The occurrence of defects in the repaired region depends on the thermal history and residual stress formation. The objective of this study was to investigate the influence of the inclined angle and depth of the substrate on the thermal and residual stress characteristics in the vicinity of a repaired region by a DED process through two-dimensional finite element analyses (FEAs). The temperature and residual stress distributions in the vicinity of the repaired region were predicted according to the combination of the inclined angle and depth of the substrate. The effects of the inclined angle and depth on the depth of the heat affected zone and the maximum value of the residual stress were examined. A proper combination of the inclined angle and depth of the substrate was estimated to decrease the residual stress in the vicinity of the repaired region.

• Journal of the Korean Solar Energy Society
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• v.27 no.3
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• pp.7-13
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• 2007

A Dish type solar concentrating system consists of a parabolic concentrator and a cavity receiver. In order to achieve high temperatures from solar energy, it is essential to efficiently reflect the solar rays in the concentrator and to minimize thermal losses in the cavity receiver. Improving the economical efficiency of a solar power system required the stirling unit to be operated continuously. For continuous operation of the stilting unit, the receiver must be continuously provided with thermal energy from solar as well as additional combustion heat. It is possible for a hybrid solar receiver system equipped with an additional combustion to be operated 24 hrs/day. A hybrid solar receiver was designed and manufactured for a total thermal load of 35 kW in the operating temperature range $700^{\circ}C$ to $800^{\circ}C$. The hybrid receiver system was tested in gas-only mode by gas-fired heat to investigate thermal characteristics at inclination angle varying from 0 deg to 30 deg(cavity facing down) and the aperture to cavity diameter ratios of 0(closed cavity) and 1.0(open cavity). This paper has been conducted to measure temperature distribution in cavity surface and to analyze thermal resistances, and the evaporation and condensation heat transfer coefficient in all cases(open and closed cavity).

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.12
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• pp.1668-1677
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• 2013

This paper deals with the power loss and thermal characteristics of induction motor for machine tools according to the rated power and speed. To reduce the fabrication error by thermal strain in rotational machine tools, we calculated the power loss and thermal behavior of induction motors. Firstly, the inverse design of general induction motors for machine tool spindle has been performed. The inverse design results are compared with the torque-speed characteristic curve in motor's catalog. The power loss are calculated by finite element method(FEM) at rated condition. Secondary, the transient thermal characteristics of induction motors are calculated by equivalent thermal resistance model from Motor-CAD S/W. The inverse design, power loss and thermal behavior calculation for induction motors with various rated power and speed has been performed. Finally, to verify the design and calculation process of induction motor, we implemented the experimental set with 0.4kW 1710rpm class industrial induction motor model. The obtained thermal characteristics of experimental model confirmed that the design and power loss calculation processes are appropriate to the prediction of thermal strain in rotational machine tools.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.189-194
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• 2008

Measurements with a Langmuir probe, which are the most often used procedures of plasma diagnostics, can disturb plasma flows and change its characteristics quite a little because the probe should be inserted into thermal flowing plasmas. In this study, we calculated the characteristics of thermal plasmas with and without the probe into an atmospheric argon free-burning arc numerically, and investigated aerodynamic and thermal disturbances with temperature and axial velocity distributions. For the modelling of thermal plasmas, we have made two governing equations, which are on the thermal-flow and electromagnetic fields, coupled together with a commercial CFD package and user-coded subroutines. It was found that thermal disturbances happened to both sides of the probe, before and behind, seriously. Due to the aerodynamic disturbance, we could find that there were the stagnation point in front of the probe and the wake behind it. Therefore, aerodynamic and thermal disturbances caused by the probe insertion should be considered to increase the reliability of the probe diagnostics.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.11
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• pp.739-745
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• 2008

This paper presents the measurement of ground thermal conductivity and the characteristics of ground thermal diffusion by a ground heat exchanger(GHE). A borehole is installed to a depth of 175 m with a diameter of 150 mm. To analyze the thermal diffusion property of the GHE, thermocouples are installed under the ground near the GHE. The outdoor temperature, the ground temperature, and the water temperature of the GHE are monitored for evaluating the characteristics of ground thermal diffusion. The ground thermal conductivity is evaluated by the in-situ thermal response tester and the line source model. It is found to be 3.08 W/$m^{\circ}C$ in this study. The ground temperature is greatly dependent on the outdoor temperature from the ground surface to 2.5 m in depth and is stable below 10 m in depth. The surface temperature of the GHE varies as a function of the temperature of circulating water. But the ground temperature at 1.5 m far from the GHE is not changed in accordance with the temperature of circulating water.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.357-358
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• 2016

This paper presents a dynamic, electric-thermal model for a photovoltaic (PV) cell that combines electrical and thermal parameters. In this model, the irradiance and ambient temperature are used to calculate the PV cell temperature based on a five-layer thermal model. The cell temperature is then used in the electrical model to accurately adjust the PV cell output electrical characteristics and power. A custom experimental setup was built to test and verify the electrical and thermal characteristics of the PV cell and its surrounding layers. The electric-thermal model is validated using experimental data in realistic scenarios. This PV model can be scaled up and used to simulate PV systems in wide variety of applications, extreme environmental conditions, and fault conditions in real-time.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.1
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• pp.15-21
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• 2015

The purpose of this paper is to analyze thermal characteristics of the heat sinks to maximize the thermal diffusivity for LED floodlight. The 2 kind of samples were prepared by vapor chamber manufacturing technology using the heat pipe principle. It was analyzed the maximum temperature reduction effect and the thermal diffusion from the heat source depending on the types of chambers with 3 kind of working fluids. As a result, it was confirmed that thermal conductivity 23% increased, GVC-R type than IVC-R type.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.765-771
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• 2002

This Paper presents numerical solutions of two-dimensional Euler equations for supersonic steady and unsteady flows with heat addition in a convergent-divergent duct, The Van Leer FVS (flux vector splitting) method in generalized coordinates is employed in order to calculate the inviscid strong shock waves caused by thermal choking. We discuss on transient characteristics, start and unstart phenomena caused by thermal choking, limit of equivalence ratio to avoid thermal choking and fluctuation of specific thrust caused by thermal choking. We prove that thermal choking is a serious problem in view of engine performance.

• 한국신재생에너지학회:학술대회논문집
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• 2005.11a
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• pp.587-590
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• 2005

A detailed geothermal characteristics survey with numerical simulations of the heat transfer in a site for ground source heat pump system is necessary for deploying a shallow geothermal utilization system. Density, specific heat, thermal diffusivity, and thermal conductivity are measured on 91 core samples from a 300 m deep borehole in KIGAM(Korea Institute of Geoscience and Mineral Resources). The heat flow is estimated from the thermal gradient and average thermal conductivity and the correlation between fracture system and hydraulic conductivity is analyzed. From the obtained ground information of the study site the performance of the ground heat pump system can be analyzed with some detailed numerical simulations for seasonal heat pump operation skill and optimal system design techniques.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.7
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• pp.542-548
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• 2008

A thermal mass air flow sensor (MAFS), which consists of a micro-heater and thermo-resistive sensors on the silicon-nitride ($Si_3N_4$) thin membrane structure, is micro-fabricated by MEMS processes. Two thermo-resistive temperature sensors are located at $100{\mu}m$ upstream and downstream from the micro-heater respectively. The thermal characteristics are measured to find the best measurement indicator. The micro-heater is operated under constant power condition, and four flow indicators are investigated. The normalized temperature indicator shows good physical meaning and is easy to use in practice. It is found that the configurations and heating power of thermal-resistive elements are the dominant factors to determine the range of the flow measurement in the MAFS with higher sensitivity and accuracy.