• Fire Science and Engineering
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• v.17 no.3
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• pp.7-12
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• 2003

A 50 kW polyurethane fire in a compartment of 4 m ${\times}$ 1 m ${\times}$ 1.5m with large openings similar to a subway station was simulated by a large eddy simulation to investigate the fire and smoke control. The NIST FDS, which employed a mixture fraction combustion model and a finite volume method for radiation, was utilized. Distribution of temperature and smoke particles was compared with in the lower and upper corridors for three different smoke control systems, ventilation, purge, and extraction, starting in 5 sec from the ignition of the fire. For the given geometries, the ventilation system showed the best smoke removal rate and lowest temperature distribution in the both corridors. It was confirmed that the purge system is not recommended for a subway station since the smoke removal rate of the purge system was worse than that without a smoke control system.

• Solar Energy
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• v.12 no.3
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• pp.47-59
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• 1992

In the concentric tube type recuperator, which is the most typical type of radiation recuperator, installed on the exhaust-secion of industrial furnace, air flows between the adiabatic outer tube and the inner tube in which exhausted gas flows with high temperature. The waste heat of the exhausted gas is transferred to the inner tube, and transferred from the inner tube to the flowing air. The heat transfer by radiation In the concentric tube type recuperator is modeled using spherical harmonics approximation, namely, P-N method and numerically analyzed considering the effect of dynamic flow field. The results are compared with the existing empirical data. In addition, a theoretical method is presented for the analysis of the heat transfer characteristics of a recuperator with a reradiator installed in the inner tube, which causes re-radiant in the inner tube, and the characteristics of the recuperator is analyszed and defined.

• Journal of the Korea Concrete Institute
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• v.14 no.3
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• pp.275-282
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• 2002

High fluidity concrete needs high dosage of superplasticizer to acquire sufficient fluidity and high contents of fine powder and viscosity agents to prevent segregation. But it requires high manufacturing cost and has difficult in quality control. Therefore, in this paper, determination of optimal mixture proportion of segregation type superplasticizer for high fluidity concrete and manufacturing high fluidity concrete by applying developed segregation reducing type superplasticizer are discussed using flowing concrete method. According to test results, as dosage of superplasticizer increases, it shows that fluidity and bleeding increase, while air contents and ratio of segregation resistance decrease. It also shows that adding viscosity agent into it reduce bleeding and improve segregation resistance. Dosage of AE agent into it containing viscosity agent recovers loss of air contents during flowing procedure. Combination of proper contents of superplasticizer, viscosity agent and AE agent make possible to develope segregation reducing type superplasticizer Compressive strength of high fluidity concrete applying flowing method with it is higher than that of base concrete. No differences of compressive strength between compacting methods are found.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.589-596
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• 2002

In this paper, setting and strength performances of concrete containing saccharic type super retarding agents are investigated under various kinds and contents of super retarding agents. According to test results, as super retarding agents contents increase, slump shows to be increased, while air contents decrease about 1∼2％. Setting time shows to be retarded considerably with increase of super retarding agents. It takes 20 days after mixing to reach final setting in case of concrete containing gluconic acid more than 0.3％. And 10 days after mixing in case of enhancing sucrose, white and brown sugar. Compressive strength of concrete containing super retarding agents is lower than that of plain concrete at early age. However, it keeps up with and exceeds the compressive strength of plain concrete at later age. White sugar md brown sugar shows positive performances in delaying setting time and strength compared to existing super retarding agents. n further investigations on durability are conducted, it is thought that application of white sugar as super retarding agent is available.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.733-736
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• 2008

This study, with the purpose for early quality improvement of concrete which used large quantity of fly ash, changed various admixture material type and reviewed the basic characteristics. First off, the flow overall was highest when polycarb onic Acid high early strength AE water reducing agent was displaced, while air amount satisfied target level only in the case of plain, and setting time was shown best by getting 30 more minutes than plain and about 3 more hours than conventional when KOH is displaced. Compressive strength was shown best at age 1 day and 3 days when KOH was displaced, and at age 28 days when fine particle cement was displaced. By and large, this study concludes that concrete quality improvement admixture material that used large amount of fly ash showed worse effects than plain, therefore it is determined that there need be more study for development of concrete early quality improvement admixture material that used large amount of fly ash.

• Journal of the Korean earth science society
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• v.24 no.4
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• pp.325-336
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• 2003

The onset time of sea breeze at Haeundae is faster than that at Suyoung in spite of the observation site at Suyoung being 5m and that of Haeundae being 1 km away from the coastline. We therefore simulate the effects of terrain on the onset time of sea breeze at Suyoung and Haeundae districts by using the LCM(Local Circulation Model). This phenomenon is due to the nighttime density flow, which is created by nighttime radiative cooling. It follows the slope of the highlands surrounding the urban area, gathers at a central area of Busan, and then flows out to a lower area like Suyoung river. This process continues after sunrise. In researching the AWS wind speed, we find an important thing. That is to say, the nighttime mean wind speed at Suyoung is three times greater than that at Haeundae. This property shows that Suyoung is an outflow channel of nighttime air mass. The above observed data shows that terrain effect has a important role on the onset of sea breeze.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.737-740
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• 2008

This study, with the purpose for early quality improvement of concrete which used large quantity of fly ash, changed various admixture material type and reviewed the basic characteristics. First off, the flow overall was highest when polycarb onic Acid high early strength AE water reducing agent was displaced, while air amount satisfied target level only in the case of plain, and setting time was shown best by getting 30 more minutes than plain and about 3 more hours than conventional when KOH is displaced. Compressive strength was shown best at age 1 day and 3 days when KOH was displaced, and at age 28 days when fine particle cement was displaced. By and large, this study concludes that concrete quality improvement admixture material that used large amount of fly ash showed worse effects than plain, therefore it is determined that there need be more study for development of concrete early quality improvement admixture material that used large amount of fly ash.

• Journal of the Korean Chemical Society
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• v.54 no.5
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• pp.611-620
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• 2010

The purpose of this study was to explore the structure and content of chemistry teacher's explanations from the perspective of 'persuasion'. Especially, this study was to explore how the argument structure and the conceptual change constructs in chemistry teachers' explanations were established and interacted. Data were collected from chemistryI classes considering the gas unit which includes kinetic theory of gas, Graham's law, Boyle's law, and Charles' law. The classes were vediotaped and transcribed. The transcriptions were analyzed with Toulmin's argument frame and the two constructs of conceptual change model; the conceptual ecology and the status of a conception to interpret the persuasive structure and content of the teacher's explanations. As the results of this study, four explanatory discourses which show various persuasive explanations in chemistry classes. Based on this results, discussion and implications for effective teachers' explanations in chemistry classes were presented.

• Culinary science and hospitality research
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• v.16 no.4
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• pp.220-229
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• 2010

Brewing tea with regular teapots can cause a problem in keeping the temperature of the tea. Cold weather, a cold teapot, and/or the temperature of tea leaves make tea cold, lowering the temperature of the tea leaves that can also make the flavor of the tea leaves worse. This experiment shows both the problem and the solution to the temperature problem of tea leaves. To maintain the appropriate temperature and reduce the problem, we researched and developed a special straw for tea leaves as a result of this experiment The straw consists of various filtering holes(diameter 1~2 mm) with the height of 5 mm from the very bottom of the straw. Using the straw is better to keep higher temperature, better flavor, and the smell of tea. Also, the sensory evaluation shows that the overall taste of tea is improved(p<0.05).

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.62-68
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• 2009

This research examined engineering properties of high performance concrete, when substitution rate of BS increases. A summary of the test result is as follows. The fluidity of unset concrete increases as the substitution rate of BS increases. The amount of air is reduced more or less, but it seems that enough amount of air can be secured by using more air-entraining agent. Setting time is dramatically delayed as the substitution rate of BS increases. The compressive strength of hardening concrete was weaker than OPC before 28 days passes, due to latent hydraulic property of BS. However, after 28 days, it shows same or better property, which is exceptional for the practical uses of hyper strength concrete. Changes in drying shrinkage rate is quite much, because when hydration happens, the amount of free water in concrete increased as W/B gets larger. The amount of drying shrinkage increases as BS substitution rate increases, but every composition shows less than $-500{\times}10^{-6}$, which is relatively fine.