• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.6
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• pp.921-927
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• 1999

In this study, the defrosting behaviors according to the surface characteristics in the fin-tube heat exchanger is experimentally examined. It is found that the draining rate of the hydrophilic and hydrophobic heat exchangers are evenly dispersed during defrosting, compared with that of the bare one. It is caused by the high density frost for the hydrophilic heat exchanger, and surface characteristic for the hydrophobic heat exchanger, respectively. The rest period of the hydrophilic and hydrophobic heat exchangers are shorter and their weight of residual water are smaller than those of the bare heat exchanger The hydrophilic and hydrophobic heat exchangers are more effective than the bare one in terms of defrosting efficiency, and the hydrophobic heat exchanger is better than the hydrophilic one.

• Journal of the Korean Geotechnical Society
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• v.39 no.5
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• pp.51-63
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• 2023

Numerical analysis was conducted to determine the effect of soil behavior by thawing and freezing of seasonal frozen soil on pile foundations. The analysis was performed using the finite element method (FEM) to simulate soil-pile interaction based on the atmosphere temperature change. Thermomechanical coupled modeling using FEM was applied with the temperature-dependent nonlinear properties of the frozen soil. The analysis model cases were applied to the MCR and HDP models to simulate the elastoplastic behavior of soil. The numerical analysis results were analyzed and compared with various conditions having different length and width sizes of the pile. The results of the numerical analysis showed t hat t he HDP model was relat ively passive, and t he aspect and magnit ude of t he bearing capacit y and displacement of the pile head were similar depending on the length and width of the pile conditions. The vertical displacement of the pile head by thawing and freezing of the ground showed a large variation in displacement for shorter length conditions. In the MCR model, the vertical displacement appeared in the maximum thaw settlement and frost heaving of 0.0387 and 0.0277 m, respectively. In the HDP model, the vertical displacement appeared in the maximum thaw settlement and frost heaving of 0.0367 and 0.0264 m, respectively. The results of the pile bearing capacity for the two elastoplastic models showed a larger difference in the width condition than the length condition of the pile, with a maximum of about 14.7% for the width L condition, a maximum of about 5.4% for M condition, and a maximum of about 5.3% for S condition. The significance of the effect on the displacement of the pile head and the bearing capacity depended on the pile-soil contact area, and the difference depended on the presence or absence of an active layer in the soil and its thickness.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.73-80
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• 2005

Both theoretical and experimental investigations were conducted to analyze defrosting behavior of a window heater operating in the low outdoor temperature($-20^{\circ}C$). To achieve this purpose, first a warm-chamber experiment($23^{\circ}C$) was performed to measure inner and outer surface temperature of the rear window(heated by the electric heater supplying 195 W) as functions of both time and position. Secondly, a cold chamber experiment was made to continuously record defrosting process of the frosted window. From the comparisons of the two experimental results, it was found that there was a similarity between the spatial distributions of both temperature and remaining frost. Thus, the temperature data from the warm-chamber experiments can be utilized to predict an expected zone covered with remaining frosts, and this approach can also be adopted in the inspection process in order to economically guarantee optimized performance of the window heater. Finally, an analytical model based on one-dimensional, steady-state heat transfer theories was proposed and successfully predicted the outer surface temperature of the rear window surrounded by cold air($-20^{\circ}C$) for the given operating conditions(heater power, inside and outside heat transfer coefficients, and surrounding air temperature, etc.).

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.1
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• pp.29-38
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• 2001

In this paper, the defrosting characteristics of a PTC heating sheet is investigated by means of a defrosting heat source for the fin-tube heat exchanger in a refrigerator The defrosting characteristics of the PTC heating sheet are examined and compared with those of a conventional electric heater experimentally. It is found that the characteristics of the water draining rate with the defrosting time show a smoothly oscillating pattern when the PTC heating sheet Is used, and the drained water is completely melted. The defrosting efficiency of the PTC heating sheet is found to be about 75%, which is about 25% higher than that of the electric heater. Also, the reduction of the defrosting time and the increment of the defrosting efficiency may be obtained by improving the arrangement of the heating elements of the healing sheet. It is shown that the defrosting time of the PTC heating sheet increases linearly with the amount of frost, whereas the defrosting efficiency is nearly constant. When applying the PTC heating sheet to the refrigerating system, one should notice the fact that the defrosting performance of the PTC heating sheet may be degraded due to the repetitive operations.

• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.3
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• pp.108-114
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• 1997

Concrete is said to have a high degree of extensibility when it is subjected to large deformations without cracking. The cracking behavior of concrete in the field may even be more complex. For example, in mass concrete compressive stresses are developed during the very early period when temperatures are rising, and the tensile stresses do not develop until at a later age when the temperature begins to decline. Actual cracking and failure depend on the combination of factors and indeed it is rarely that a single adverse factor is responsible for cracking of concrete. The importance of cracking and the minimum width at which a crack is considered significant depend on the conditions of exposure of the concrete. The ultrasonic pulse measurements can be used to detect the development of cracks in structures such as dams, and to check deterioration due to frost or chemical action. An estimate of the depth of a crack visible at the surface can be obtained by measuring the transit times across the crack for two different arrangements of the transducers placed on the surface. In this paper, the concrete cracks that artificially introduced crack width is 1 and 2mm, crack depth is 2, 4, 6, 8cm were measured by Tc-To Method In consequence, the measured depth was increased with increase of measuring distance from concrete crack. The most reliable results were shown when the introduced crack width was 1mm, and the measuring distance was 10cm from concrete crack.

• Journal of Korea Society of Digital Industry and Information Management
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• v.16 no.4
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• pp.123-132
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• 2020

With increasing social interest in health and health promotion, the government and many organizations are conducting various health campaigns for the public. The public health campaign is aimed at protecting the people from the dangers of disease and contributing to a healthy life and also help establishing a healthy attitude and changing behavior as well. In addition, many researches have been carried out in order to enhance the advertising effect of campaigns aimed at forming preventive attitudes and to verify it by applying many theories. However, as a result, there is a significant lack of research regarding analysis of differences in the effectiveness of the campaign by media. This study is to analyze the effect of health campaign by the type of media which published health campaign advertisements that can affect prevention attitude. To meet the purpose of this study, The 15 print media were to examine the impact of media characteristics and types on participation in campaigns for health campaigns. Through this, we will present the role of the media as an efficient channel to encourage the formation and participation of the health attitude of campaign advertisements, and present significant implications in the selection of optimal media and the execution of campaign budgets.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1097-1100
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• 2008

The purpose of this study to investigate the bond strength of recycled coarse aggregate concrete deteriorated by freezing and thawing. Concrete specimens with recycled coarse aggregate representing lower limit of the quality standard (water absorption : 3.0%, specific gravity : $2.5g.cm^3$) were manufactured and tested. The replacement ratio (0, 30, 60 and 100%) of recycled coarse aggregate and freezing-thawing cycles were considered in this test. From the test results, it was found that the bond strength of normal strength concrete is not affected by the replacement ratio of recycled coarse aggregate under freezing and thawing conditions. Also, the bond strength of the natural and recycled coarse aggregate concrete using AE admixtures was not decreased by frost action.

• Journal of the Korean Geosynthetics Society
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• v.21 no.4
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• pp.31-40
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• 2022

Recently, the Arctic resource development project, where undeveloped energy resources (oil, natural gas, etc.) are deposited, is actively being promoted for the perspective of diversifying the construction market and developing future energy resources. However, the frozen ground always has problems such as sinking and frost-heaving due to extreme weather. Therefore, it is necessary to analyze the thermal characteristics of the frozen soil to secure the stability of the ground structure. In this study, a series of laboratory tests were performed to evaluated the thermal characteristics of frozen soil samples in the oil sand field in Alberta, Canada. In additon, it was compared with the results of domestic(Gangwond-do) sample performed under the same conditions. As a comparison results of the experiments, it was clarified that the different frozen water content and thermal conductivity characteristics by temperature after completion of freezing could affect the frozen soil behavior.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.27-36
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• 2014

Due to the latitudinal location of Korea, the seasonally frozen ground has been focused on as research topics such as the frost heaving under the asphalt road rather than the permafrost ground. However, the recent construction of the second Korean Antarctic research station, the Jangbogo station and the participation on the development of the natural gas pipeline in Russia arouse the research interests on the behavior of the permafrost ground. At the design process of the geotechnical structures on the permafrost ground, the evaluation of the creep characteristics of the frozen soil is very crucial. Since the domestic specification on the frozen soil testing does not exist currently, it is necessary to evaluate the creep characteristics of frozen soils systematically with regard to the affecting factors. Therefore, the creep characteristics of the frozen specimens of dense Jumoonjin sand were evaluated under various loads at -5 and $-10^{\circ}C$. Based on the test results, as the load became close to the strength and the temperature became lower, the duration of the secondary creep became shorter and more distinct tertiary creep responses were observed.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.131-141
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• 2004

For geotechnical applications, engineers use data obtained from a site investigation to interpret the structure and potential behavior of the subsurface. In most cases, these data consist of samples that represent 1/100,000 or less of the total volume of soil. These samples and associated field and lab testing provide the information used to estimate soil parameter values. The resulting values are estimated ones and there exists some likelihood that actual soil conditions are significantly different from the estimates. This may be the case even if the sampling and interpretation procedures are performed in accordance with standard practice. Although these efforts have been made to characterize the uncertainty associated with geotechnical parameters, there is no commonly accepted method to evaluate quantitatively the quality of an investigation plan as a whole or the relative significance of individual sampling points or potential sampling points.