• Journal of the Korean Solar Energy Society
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• v.31 no.4
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• pp.87-94
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• 2011

To develop the solar air heater, prototype of solar heater with test room set up on the roof of test chamber and operation characteristics were examined with solar radiation. Air induced from outside was supplied by a blower and also heated air was supplied to the test chamber(size of 1,000mm(inwidth)*2,000mm(in length)*2,000mm(in depth)) established already for performance. It was clear that almost 30% of solar radiation was converted into effective heating energy at maximum and the highest air temperature was $46^{\circ}C$, and thus solar air heater in winter could be used as an possible alternative heating system in building. Furthermore, heat energy obtained from solar air heater can be applied to regenerate absorber in the solar desiccant cooling system.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.832-837
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• 2006

This study describes thermal performance of heating and cooling demonstration system using ETSC(Evacuated tubular solar collector) installed at Seo-gu art center of Kwangju. For demonstration study, a reading room with about $331m^2$ was heated and cooled using that system. The demonstration system was consisted of ETSCs, storage tank, hot water supply tank, subsidiary boiler, and subsidiary tank. From January to March in 2006, demonstration test were performed with 4 control mode to find the optimum control condition for solar thermal system. After experiments and analysis, this study found that solar thermal system of control mode IV was corresponded to 78% for the hot water supply and 49% for space heating.

• Advances in concrete construction
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• v.7 no.4
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• pp.263-275
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• 2019

In the present work, Granulated Blast Furnace Slag (GBFS) and Fly ash (FA) were used as partial replacement of Natural Sand (NS) and Ordinary Portland Cement (OPC) by weight. One control mix, one with GBFS, three with FA and three with GBFS-FA combined mixes were prepared. Replacements were 50% GBFS with NS and 20%, 30% and 40% FA with OPC. Preliminary investigation on development of compressive strength was carried out at 7, 28 and 90 days to ensure sustainability of waste materials in concrete matrix at room temperature. After 90days, thermo-mechanical study was performed on the specimen for a temperature regime of $200^{\circ}-1000^{\circ}C$ followed by furnace cooling. Weight loss, visual inspection along with colour change, residual compressive strength and microstructure analysis were performed to investigate the effect of replacement of GBFS and FA. Although adding waste mineral by-products enhanced the weight loss, their pozzolanicity and formation history at high temperature played a significant role in retaining higher residual compressive strength even up to $800^{\circ}C$. On detail microstructural study, it has been found that addition of FA and GBFS in concrete mix improved the density of concrete by development of extra calcium silicate gel before fire and restricts the development of micro-cracks at high temperature as well. In general, the authors are in favour of combined replacement mix in view of high volume mineral by-products utilization as fire protection.

• Design & Manufacturing
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• v.15 no.3
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• pp.7-12
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• 2021

Plastic injection molds used for rapid heating and cooling must minimize surface damage due to friction and maintain excellent thermal and low electrical conductivity. Accordingly, various surface treatments are being applied. The properties of Al₂O₃ coating and DLC coating were compared to find the optimal surface treatment method. Al₂O₃ coating was deposited by thermal spray method. DLC films were deposited by sputtering process in room temperature and high temperature PECVD (Plasma enhanced chemical vapor deposition) process in 723 K temperature. For the evaluation of physical properties, the electrical and thermal conductivity including surface hardness, adhesion and wear resistance were analyzed. The electrical resistance of the all coated samples was showed insulation properties of 24 MΩ/sq or more. Especially, the friction coefficient of high temp. DLC coating was the lowest at 0.134.

• Korean Journal of Metals and Materials
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• v.48 no.3
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• pp.187-193
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• 2010

The solute carbon content in ferrite is one of the important factors to obtain good formability in low carbon steels. Although most of the carbons are consumed by the formation of grain boundary cementite during coiling after hot-rolling, the carbon content after coiling is normally observed much more than that of equilibrium. In this study, a classical nucleation and growth model is used to simulate the precipitation kinetics of the grain boundary cementite from coiling temperature (CT) to room temperature (RT). The predicted precipitation behaviors depending on the initial carbon content and the cooling rate are compared with the reported. As a result, the lateral growth of thickening of cementite is a major factor for the sluggish reaction of grain boundary cementite. The reduction of solute carbon content after coiling is divided into three regions: a) increase due to no cementite precipitation, b) decrease due to the fast length-wise growth of cementite, c) increase due to the slow thickness-wise growth of cementite.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.819-830
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• 2021

To evaluate the performance of concrete load bearing walls in a structure under horizontal loads after being exposed to real fire, two steps were followed. In the first step, an experimental study was performed on the thermo-mechanical properties of concrete after heating to temperatures of 200-1000℃ with the purpose of determining the residual mechanical properties after cooling. The temperature was increased in line with natural fire curve in an electric furnace. The peak temperature was maintained for a period of 1.5 hour and then allowed to cool gradually in air at room temperature. All specimens were made from calcareous aggregate to be used for determining the residual properties: compressive strength, static and dynamic elasticity modulus by means of UPV test, including the mass loss. The concrete residual compressive strength and elastic modulus values were compared with those calculated from Eurocode and other analytical models from other studies, and were found to be satisfactory. In the second step, experimental analysis results were then implemented into structural numerical analysis to predict the post-fire load-bearing capacity response of the walls under vertical and horizontal loads. The parameters considered in this analysis were the effective height, the thickness of the wall, various support conditions and the residual strength of concrete. The results indicate that fire damage does not significantly affect the lateral capacity and stiffness of reinforced walls for temperature fires up to 400℃.

• Journal of the Korean Institute of Rural Architecture
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• v.24 no.3
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• pp.23-30
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• 2022

In this study, in order to grasp the current situation of indoor environmental pollution and indoor ventilation in one-room around the university in the post-corona era, we analyzed the experimental data and conducted a questionnaire survey on university students. By analyzing the content, the effects of formaldehyde, dust and other pollution on the human body, which are usually not easily detectable, are digitized and more easily taken into account. Among the experimental results, the concentration of VOC and HCHO, gas pollutants among indoor pollutants, exceeded the recommended criteria of the Ministry of Environment in most studio apartments. Overall, the average CO₂ concentration was lower than the Ministry of Environment's maintenance standard (1000ppm), but it was relatively high in summer and winter, and it is believed to be caused by cooling and heating in an enclosed space. The levels of PM2.5 and PM10, particulate pollutants, increased in November and December, and it is believed that ventilation defects due to degradation in external temperature. There was no clear difference between the two types, and there was a very high correlation between PM2.5 and PM10, HCHO and VOC. It was found that temperature was closely correlated with all sources except CO₂, and humidity was closely correlated with all sources except PM2.5 and PM10. Health risk assessment was conducted for formaldehyde. The average ECR of studio R2 in May was 3.91E^-4, and the ECR figure in September was 3.65E^-4, which was very high compared to other residential spaces. The R2 level was calculated as 4 people per 10,000 people in the lifetime risk of cancer of residents, exceeding the allowable risk. R8 also showed higher ECR results than other spaces after R2, especially in October, 2.01E^-4, six times higher than R7 measured in October, and 1.87E^-4 in July, four times higher than R9.

• Economic and Environmental Geology
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• v.38 no.6 s.175
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• pp.717-729
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• 2005

Peak cooling load of large buildings is generally greater than their peak heating load. Internal and solar heat gains are used fur selection of adquate equipment in large building in cold winter climate like Canada and even Korea. The cost of geothermal heat exchanger to meet the cooling loads can increase the initial cost of ground source heat pump system to the extend less costly conventional system often chosen. Thermal ice storage system has been used for many years in Korea to reduce chiller capacity and shift Peak electrical time and demand. A distribution system designed to take advantage of heat extracted from the ice, and use of geothermal loop (geothermal heat exchanger) to heat as an alternate heat source and sink is well known to provide many benifits. The use of thermal energy storage (TES) reduces the heat pump capacity and peak cooling load needed in large building by as much as 40 to $60\%$ with less mechanical equipment and less space for mechanical room. Additionally TES can reduce the size and cost of the geothermal loop by 1/3 to 1/4 compared to ground coupled heat pump system that is designed to meet the peak heating and cooling load and also can eliminate difficuties of geothermal loop installation such as space requirements and thermal conditions of soil and rock at the urban area.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.42 no.1
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• pp.95-103
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• 1997

This experiment was carried out to obtain the basic information necessary to establish suitable postharvest handling techniques and to keep high quality of the sweet(Danok 2), supersweet(Cooktail 86) and waxy(Chalok 1) corn which are mainly consumed as vegetable in Korea. Vegetable corns were cooled with ice fragments in the insulation box immediately after harvest and stored in low temperature warehouse at 0 to 2$^{\circ}C$. During the 15 days short-term storage, changes of chemical components were compared with those of uncooled corns. The losses of moisture in kernels were as high as 7.4 to 24.4％ in uncooled corns while those of ice cooled corns increased 0.4 to 0.5％ of their weight. The ratio of pericarp and alcohol insoluble solid(AIS) content increased as the storage days prolonged in all treatments but increasing rates were much higher in uncooled samples. On the other hand, the total sugar loss during storage was the least in supersweet corn when they were cooled with ice fragments in insulation box. After 5 days storage, the ice cooled samples showed the highest free amino acid contents compare to those of uncooled and stored at room temperature (25 to 3$0^{\circ}C$) or low temperature warehouse, and ${\gamma}$-aminobutylic acid (GABA) which was known as a fuctional amino acid was detected in all three kinds of vegetable corns.

• Journal of the Mineralogical Society of Korea
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• v.26 no.1
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• pp.19-25
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• 2013

Recent progress in Martian exploration identified hematite as the major candidate for the strong magnetic anomalies observed in Martian lithosphere. In the present study, grain-size dependence of thermoremanent magnetization and low-temperature stability of room-temperature saturation isothermal remanent magnetization (RTSIRM) were monitored using synthetic hematites. For hematite, the antiferromagnetic spin configuration is re-arranged from being perpendicular to the c-axis to be parallel to the c-axis below the Morin transition ($=T_M$). A large fraction of RTSIRM is demagnetized at $T_M$ (= 260 K) during zero-field cooling from 300 K to 10 K. About 37% of the initial RTSIRM is recovered on warming from 10 K to 300 K. Shallow Martian subsurface at 1~2 km depth would experience low-temperature cooling-warming of $T_M$ because average Martian surficial temperature is about 220 K. However in most Martian lithosphere whose temperatures are higher than 260 K, the very stable magnetic memory of hematite could be a contributor to Martian magnetic anomalies.