• Journal of Hydrogen and New Energy
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• v.30 no.1
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• pp.58-66
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• 2019

Static compound parabolic collectors (CPCs) have advantages such as ease for fabrication and lower cost compared with other concentrating collectors. In this study, thermal performance analysis of CPC employing heat storage tank was carried out. The clearness index and capacity of heat storage tank are taken as the main parameters for numerical simulation. The effects of the parameters on the hourly and daily system performances ncluding the useful energy, heat loss, and collector efficiency were numerically investigated. Results showed that the system has a potential for efficient recovery of solar thermal energy.

• Nuclear Engineering and Technology
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• v.51 no.6
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• pp.1504-1513
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• 2019

Recently, ocean nuclear reactors have received attention due to enhanced safety features. The movable and transportable characteristics distinguish ocean nuclear reactors from land-based nuclear reactors. Therefore, for safety/design analysis of the ocean reactor, the thermos-hydraulics must be investigated in the moving system. However, there are no studies reporting the general two-fluid equations that can be used for multi-dimensional simulations of two-phase flows in moving systems. This study is to systematically formulate the multi-dimensional two-fluid equations in the non-inertial frame of reference. To demonstrate the applicability of the formulated equations, we perform a total of six different simulations in 2D tanks with translational and/or rotational motions.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.261-265
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• 2002

In the machining tool avoid vibration problem have an effect on high precision as well as statical and thermal characteristics. Therefore overcome this problem is essential to advance of machine tool and machining skill. Even though vibration arises owing to a variety of causes, in this paper vibration analysis of column as a major part of machine tool structures is presented. At this procedure vibration analysis applied to mode synthesis method using a attachment mode .

• Current Optics and Photonics
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• v.1 no.4
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• pp.263-270
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• 2017

Solar radiation data measured by pyranometers is of fundamental use in various fields. In the field of atmospheric optics, the measurement of solar energy must be precise, and the equipment needs to be maintained frequently. However, there seem to be many errors with the existing type of pyranometer, which is an element of the solar-energy observation apparatus. In particular, the error caused by the thermal dome effect occurs because of the thermal offset generated from a temperature difference between outer dome and inner casing. To resolve the thermal dome effect, intensive observation was conducted using the method and instrument designed by Ji and Tsay. The characteristics of the observed global solar radiation were analyzed by classifying the observation period into clear, cloudy, and rainy cases. For the clear-weather case, the temperature difference between the pyranometer's case and dome was highest, and the thermal dome effect was $0.88MJ\;m^{-2}\;day^{-1}$. Meanwhile, the thermal dome effect in the cloudy case was $0.69MJ\;m^{-2}\;day^{-1}$, because the reduced global solar radiation thus reduced the temperature difference between case and dome. In addition, the rainy case had the smallest temperature difference of $0.21MJ\;m^{-2}\;day^{-1}$. The quantification of this thermal dome effect with respect to the daily accumulated global solar radiation gives calculated errors in the cloudy, rainy, and clear cases of 6.53%, 6.38%, and 5.41% respectively.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.1
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• pp.63-70
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• 2023

Today, the importance of power semiconductors continues to increase due to serious environmental pollution and the importance of energy. Particularly, SiC-MOSFET, which is one of the wide bandgap (WBG) devices, has excellent high voltage characteristics and is very important. However, since the electrical properties of SiC-MOSFET are heatsensitive, thermal management through a package is necessary. In this paper, we propose an insulated metal substrate (IMS) method rather than a direct bonded copper (DBC) substrate method used in conventional power semiconductors. IMS is easier to process than DBC and has a high coefficient of thermal expansion (CTE), which is excellent in terms of cost and reliability. Although the thermal conductivity of the dielectric film, which is an insulating layer of IMS, is low, the low thermal conductivity can be sufficiently overcome by allowing a process to be very thin. Electric-thermal co-simulation was carried out in this study to confirm this, and DBC substrate and IMS were manufactured and experimented for verification.

• Tunnel and Underground Space
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• v.24 no.4
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• pp.297-307
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• 2014

Cavern Thermal Energy Storage system stores thermal energy in caverns to recover industrial waste heat or avoid the sporadic characteristics of renewable-energy resources, and its advantages include high injection-and-extraction powers and the flexibility in selecting a storage medium. In the present study, the structural stability of rock mass pillar between these silo-type storage caverns was assessed using a coupled thermal-mechanical model in $FLAC^{3D}$. The results of numerical simulations showed that thermal stresses due to long-term storage depended on pillar width and had significant effect on the pillar stability. A sensitivity analysis of main factors indicated that the influence on the pillar stability increased in the order cavern depth < pillar width < in situ condition. It was suggested that two identical caverns should be separated by at least one diameter of the cavern and small-diameter shaft neighboring the cavern should be separated by more than half of the cavern diameter. Meanwhile, when the line of centers of two caverns was parallel to the direction of maximum horizontal principal stress, the shielding effect of the caverns could minimize an adverse effect caused by a large horizontal stress.

• Journal of the Korean Association of Geographic Information Studies
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• v.16 no.4
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• pp.153-170
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• 2013

This study was conducted to analyze the thermal comfort in the urban neighborhood park and to obtain a plan for improvement of the thermal environment. First, in the result of the analysis of the distribution characteristics of the park's main thermal environment factors and differences among types of space, temperature, relative humidity, and wind speed did not show a clear difference spatially. However, the median radiant temperature showed great differences according to the openness of the space and the covering material. According to the evaluation of thermal comfort by types of space based on derived thermal environmental factors, the PMV value of the square was the highest at 4.39, the paths showed 2.58, greenery 1.90, and resting spaces 0.42. In the result of the PMV regression model established for the evaluation of the significance of these thermal environment factors that decide thermal comfort, it showed that the relative significance to the PMV was as follows in decreasing order: median radiant temperature(1.084), wind speed(-0.280), temperature(0.013), and relative humidity(-0.009). When conducting a scenario analysis on the areas with need for improvement in thermal environment, it was found that through reflectivity, color and the change in the physical properties of packing materials the thermal comfort felt by the body could be improved, and it is believed that through this the improvement plan can be established.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.10
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• pp.2509-2515
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• 2014

In this paper, the conventional vertical structure for VLSI circuits CMOS intend to improve the stress effects of active region and built-in threshold voltage. For these improvement, the proposed structure is shallow trench isolation of moat shape. We want to analysis the electron concentration distribution, gate bias vs energy band, thermal stress and dielectric enhanced field of thermal damage between vertical structure and proposed moat shape. Physically based models are the ambient and stress bias conditions of TCAD tool. As an analysis results, shallow trench structure were intended to be electric functions of passive as device dimensions shrink, the electrical characteristics influence of proposed STI structures on the transistor applications become stronger the potential difference electric field and saturation threshold voltage, are decreased the stress effects of active region. The fabricated device of based on analysis results data were the almost same characteristics of simulation results data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.53-61
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• 2021

This paper is a preliminary study for the development of a drone for inspection inside a boiler in a thermal power plant, which is a high-temperature environment, and validated whether the drone can fly normally through a high-temperature environment simulation using AirSim. In a high-temperature flight environment, the aerodynamic characteristics of the air density and viscosity are different from room temperature, and the flight performance of the drone is also changed accordingly. Therefore, in order to confirm the change of the aerodynamic characteristics of the propeller according to the temperature change, the propeller analysis and thrust test through JBLADE, and the operation characteristics prediction through the electric propulsion system performance prediction model were performed. In addition, the analysis and performance prediction results were applied to AirSim for simulation, and the aircraft redesigned through the analysis of the results. As a result of the redesign, it was confirmed that about 65% of the maximum power used before the redesign was reduced to 52% to obtain the necessary thrust when hovering in an environment of 80℃.

• Journal of the Korean Institute of Landscape Architecture
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• v.30 no.4
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• pp.28-36
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• 2002

The main purpose of this study was to estimate a new regression model to explain the relationship between urban forest and air temperature in summer, 2001. This study consists of two parts: correlation coefficient analysis and regression analysis. According to correlation coefficient analysis, thermal infra-red radiations of the major land use categories found significant difference in each category. However there were no significant relationship between the data (thermal infra-red radiation and NDVI) derived from Landsat-7 ETM+ image and air temperature at Automatic Weather Stations(AWSs). After estimating various regression models for summer air temperature, the final models were chosen. The final regression models consisted of two variables such as forest m and traffic facilities area. The regression models explained over 78% of the variability in air temperatures. The regression models with variables of forest area and traffic facilities area showed that the coefficient of the first variable was even more significant than the second one. However, the negative impact of the traffic facilities area was slightly greater than the positive impact of the forest area. Consequently, the effects of forest area and traffic facilities area were apparent to explain summer air temperature in Seoul. Therefore two policies have the most important implications to mitigate the summer air temperature in Seoul: to expand and to conserve the urban forest; and to change the Oafnc facilities'characteristics. The results from this study are expected to be useful not merely in informing the public that urban forest mitigates summer air temperahne, but in urging the necessity of budgets for trees and managing urban forests. It is recommended that field swey of summer air temperature be Performed for the vadidation of the models. The main purpose of this study was to estimate a new regression model to explain the relationship between urban forest and air temperature in summer, 2001. This study consists of two parts: correlation coefficient analysis and regression analysis. According to correlation coefficient analysis, thermal infra-red radiations of the major land use categories found significant difference in each category. However there were no significant relationship between the data (thermal infra-red radiation and NDVI) derived from Landsat-7 ETM+ image and air temperature at Automatic Weather Stations(AWSs). After estimating various regression models for summer air temperature, the final models were chosen. The final regression models consisted of two variables such as forest m and traffic facilities area. The regression models explained over 78% of the variability in air temperatures. The regression models with variables of forest area and traffic facilities area showed that the coefficient of the first variable was even more significant than the second one. However, the negative impact of the traffic facilities area was slightly greater than the positive impact of the forest area. Consequently, the effects of forest area and traffic facilities area were apparent to explain summer air temperature in Seoul. Therefore two policies have the most important implications to mitigate the summer air temperature in Seoul: to expand and to conserve the urban forest; and to change the traffic facilities'characteristics. The results from this study are expected to be useful not merely in informing the public that urban forest mitigates summer air temperature, but in urging the necessity of budgets for trees and managing urban forests. It is recommended that field survey of summer air temperature be Performed for the vadidation of the models.