• 한국방재학회 논문집
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• 제7권2호통권25호
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• pp.1-6
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• 2007

콘크리트내의 수량이 증가하면 내구성저하등에 다양한 문제점이 발생한다. 이러한 이유로 단위수량의 측정방법인 정전용량법, 고주파가열법, 단위용적질량법을 이용하여 단위수량의 변동을 관리하고 있다. 특히 일본에서는 단위수량 변동$({\pm}10,\;15,\;20kg/m^3$ 등)에 대한 관리지침을 규정하고 있다. 그러나 일본의 지침은 내구성 저하를 고려하지 않고 있으며, 제조오차와 측정오차를 확률적으로 고려하여 합부 판정기준 값을 정하고 있다. 이에 본 연구에서는 관리오차에 의한 가수 및 인위적인 가수 등에 의한 콘크리트 내의 수량 변화가 콘크리트의 내구성저하에 미치는 영향을 검토하고자 하였다.

• The Journal of Advanced Prosthodontics
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• 제1권1호
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• pp.1-5
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• 2009

STATEMENT OF PROBLEM. Poor wettability of denture relining materials may lead to retention problems and patient discomfort. PURPOSE. Purpose of this study is to compare and evaluate wettability of nine denture relining materials using contact angle measurements under air and water storage over time. MATERIAL AND METHODS. Nine denture relining materials were investigated in this study. Two heat-curing polymethyl-methacrylate(PMMA) denture base materials: Vertex RS, Lang, one self-curing polyethyl-methacrylate(PEMA) chairside reline resin: Rebase II, six silicone relining materials: Mucopren soft, Mucosoft, $Mollosil^{{R}}$ plus, Sofreliner Touch, GC $Reline^{TM}$ Ultrasoft, Silagum automix comfort were used in this experiment. Contact angles were measured using high-resolution drop shape analysis system(DSA 10-MK2, KRUESS, Germany) under three conditions(in air after setting, 1 hour water storage, and 24 hours water storage). Nine materials were classified into three groups according to material composition(Group 1: PMMA, Group 2: PEMA, Group 3: Silicone). Mean values of contact angles were compared using independent samples t-test and one-way ANOVA, followed by a Scheffe's post hoc analysis($\alpha$=0.01). RESULTS. Contact angles of materials tested after air and water storage increased in the following order: Group 1(PMMA), Group 2(PEMA), Group 3(Silicone). Heat-cured acrylic denture base resins had more wettability than silicone relining materials. Lang had the highest wettability after 24 hours of water storage. Silicone relining materials had lower wettability due to their hydrophobicity. Wettability of all denture relining materials, except Rebase II and $Mollosil^{{R}}$ plus, increased after 24 hours of water storage. CONCLUSIONS. Conventional heat-cured resin showed the highest wettability, therefore, it can be suggested that heat-cured acrylic resin is material of choice for denture relining materials.

• 한국안전학회지
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• 제27권5호
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• pp.135-140
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• 2012

In this study, the behavior of pollutant was calculated at Paldang reservior according to several scenarios of the accidental water pollution by means of the numerical models for forecasting water quality. Also managemental plans for situation of the accidental water pollution happening at Paldang watershed were simulated. According to the simulating results, a plan of increase of discharge at Cheongpyeong dam reduced the peak concentration of pollutants, whereas extended the time for stopping water intake. Another plan, drop of water elevation at Paldang dam, decreased seriously the time for stopping water intake although there were a little effect to decrease the peak concentration. Thus it was concluded that appropriate combinations of the plans for the increase discharge and the dropping water elevation should be used to deal with the accidental water pollution at Paldang watershed.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1332-1336
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• 2009

If water-chillers are arranged in series-series counterflow, compressor lift of each chiller will be decreased in comparison with water-chillers in parallel. That means that compressor power of the chillers in series will be lower than that of chillers in parallel. However, the pressure drop of the water flow through the chillers in series will increase, and thus increase the power of water pumps. This disadvantage will be made good by increasing the temperature difference of water flow through evaporator and condenser, but the water flow rates will decrease. This paper explores the optimal parameters in system of series-series counterflow for central chilled water plants such as the leaving chilled water temperature, the leaving condenser water temperature, condenser water flow rate and number of chillers in series.

• 펄프종이기술
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• 제34권5호
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• pp.39-48
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• 2002

The water retention of coating colors can be accurately measured by devices such as an AA-GWR water retention meter whose principle of measurement Is based on pressure filtration of coatings under an externally applied air pressure over a certain period of time. It was hypothesized that such devices could be also used to determine the immobilization solids (IMS) of coating colors by determining a sudden drop in the rate of dewatering, that is, a sudden change in the drainage curves. To test this hypothesis, the immobilization solids of coating colors containing various thickeners and water retention additives at different levels were first accurately measured by a modified immobilization tester based on the well-known gloss drop method, and then their values were compared with those obtained by an AA-GWR water retention tester. They agreed very well and showed that the standard deviation is only 0.14% in the IMS points between both methods. This good agreement was not surprising because both test methods are based on the same end-point, that is, the immobilization solids point at which menisci begin to form at the coating surface. Theoretical considerations supporting this new method for measuring the immobilization solids of coating colors are presented and some recommendations for the test method are discussed. Also, the effect of various thickeners and water retention additives on the properties and printability of coated papers is discussed.

• 한국산업융합학회 논문집
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• 제23권6_2호
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• pp.1093-1101
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• 2020

This study was carried out numerically to investigate the air flow and thermal performance around single and parallel fin-tube heat exchangers and the cooling performance of the fluid inside the heat exchangers. In this study, the air velocity(1~7m/s), the pitch of fin(4, 6.1, 8, 11.3, 18.3, 44mm) and the diameter of fin(31, 33, 35, 37, 39mm) were varied. The flow rate of the water at the fin-tube heat exchanger inlet is 89cc/min and the water temperature is 353K. The air temperature at the upstream region of the heat exchanger is 300K. flow rate of the water at the fin-tube heat exchanger inlet is 80cc/min and the water temperature is 353K. It was found that the air pressure drop around single and parallel fin-tube heat exchangers was highly dependent on the air velocity and the fin pitch, but was independent of the fin diameter. Also, it was shown that pressure drop increased more the parallel arrangements than in single heat exchanger. The temperature difference of water at the inlet and outlet of the heat exchanger depended on the air velocity, the fin pitch and the fin diameter, and it was found that the parallel arrangement method further reduced the temperature of water. It was shown that the Nusselt number increased as the Reynolds number and the fin pitch increased, and decreased as the fin diameter increased.

• Korean Chemical Engineering Research
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• 제47권4호
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• pp.512-517
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• 2009

순산소 연소에서 $SO_2$ 농도는 배가스의 재순환으로 인해 기존의 공기연소에 비해 3배 이상 높게 나타나고, $CO_2$ 농도와 $SO_2$ 농도가 높기 때문에 탈황현상이 기존의 공기 연소와는 다르게 나타난다. 본 연구에서는 순산소 연소조건에서 로내탈황 특성을 알아보기 위해 Drop Tube Furnace(DTF)를 이용하여, 반응온도, 유입 $SO_2$ 농도 그리고 Ca/S 비 등의 운전변수에 따른 $SO_2$ 제거효율을 측정하였으며 수분의 영향에 대해서도 알아보았다. 반응온도, 유입 $SO_2$ 농도 그리고 Ca/S 비가 증가함에 따라 $SO_2$ 제거효율은 증가하였고 유입가스 내 수분이 존재할 경우 $SO_2$ 제거효율은 약 4~6% 증가하는 것으로 나타났다.

• 한국광학회지
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• 제23권5호
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• pp.179-188
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• 2012

어안렌즈(fisheye lens)란 통상 초 광각의 시야각을 가지는 렌즈를 일컫는다. 초 광각의 시야각을 가지는 렌즈에서는 주변부시야각으로 갈수록 상의 조도가 급격히 저하하게 되는데, 본 논문에서는 이의 원인과 개선방안에 관해 논의한다. 왜냐하면 어안렌즈와 같은 초 광각의 렌즈에서는 기하광학적인 수차특성보다 오히려 시야각의 안정적인 확보가 광학적인 성능을 훨씬 더 좌우할 수 있기 때문이다. 그러므로 이를 위해, 먼저, 방향코사인벡터의 부호규약과 곡면 상에서의 법선벡터의 방향을 해석기하학적으로 다룬다. 이어서 해석기하학적인 논의를 바탕으로 조도저하의 다양한 원인들에 대해 수치 및 원리적인 분석을 실시하고, 개선에 대한 방안들을 제시한다.

• 한국입자에어로졸학회지
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• 제5권2호
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• pp.37-43
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• 2009

Particulate matter (PM) is one of the major indoor air pollutants especially in the subway station in Korea. In order to remove PM in the subway station, several kinds of PM removal system such as roll-filter, auto-washable air filter, demister, and electrostatic precipitator are used in the air handling unit (AHU) of subway stations. However, those systems are prone to operation and maintenance problems since the filter-regeneration unit consisting of electrical or water jet parts might malfunction due to the high load of particulates unless the filter medium is periodically replaced. In this study, the use of axial-flow cyclone was proposed for particulate filter unit in the AHU for its low operation and maintenance cost. Novel shape of axial-flow cyclone was designed by using computational fluid dynamics (CFD). The shape of vortex vane was optimized in terms of pressure drop and tangential velocity. In addition, CFD analysis was validated experimentally through the pressure drop measurement of mock-up model. We found that pressure drop and tangential velocity of fluid through the axia-flow cyclone was significantly affected by the rotating degree of vortex vane and the numerical prediction of pressure drop agreed well with experimental measurement.

• Journal of Mechanical Science and Technology
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• 제18권12호
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• pp.2284-2293
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• 2004

The evaporation heat transfer coefficient h$\_$r/ and frictional pressure drop Δp$\_$f/ of refrigerant R-134a flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the oblong shell and plate heat exchanger by four plates of geometry with a corrugated sinusoid shape of a 45 chevron angle. Upflow of refrigerant R-134a boils in two channels receiving heat from downflow of hot water in other channels. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation temperature and vapor quality of R-134a were explored in detail. Similar to the case of a plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. The results indicate that the evaporation heat transfer coefficient h$\_$r/ and pressure drop Δp$\_$f/ increase with the vapor quality. A rise in the refrigerant mass flux causes an increase in the h$\_$r/ and Δp$\_$f/. But the effect of the average heat flux does not show significant effect on the h$\_$r/ and Δp$\_$f/. Finally, at a higher saturation temperature, both the h$\_$r/ and Δp$\_$f/ are found to be lower. The empirical correlations are also provided for the measured heat transfer coefficient and pressure drop in terms of the Nusselt number and friction factor.