• Journal of Korean Society of Water and Wastewater
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• v.32 no.5
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• pp.453-460
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• 2018

The impact of sodium hydroxide, which is one of chemicals of clean in place (CIP) for removing membrane fouling, on the PVDF membrane is reviewed with respect to physical/chemical structural change, the permeability affected therefrom. Based on the cleaning concentration applied in membrane water treatment facilities, 10% of accumulated defluorination was confirmed up to 166g.hr/L which reflects the exposure time. However, membrane resistance was confirmed to be reduced by about 10%. Through FT-IR and EDS analysis, reduction of F and change of are confirmed as factors that affect the permeability of membrane. Membrane resistance, which affects permeability, is affected by loss of additives for hydrophilicity, rather than defluorination of PVDF material. Therefore, in order to check membrane degradation degree, an accelerated test by NaOH was carried out, loss of additives was confirmed, and then PVDF inherent characteristic was observed.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2008.05a
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• pp.67-71
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• 2008

The study analyzed on fire resistance of high strength concrete followed by thickness of fireproof plaster board and change of adhesive method. In spalling characteristics after fire resistance test, all four-side covering concretes were left out of testing screens. Thus, serious spalling was happened by exposing their internal reinforcing rods. in partial testing screens, spalling was happened till the internal concrete of main reinforcing rod. Only, temperature history didn't have special differences among changes of adhesive method. However, thickness of fireproof plaster board is very important. Namely, mock member reinforcing 25mm general adhesive + Bending was 583℃ in the highest temperature of surface part and 479℃ in the highest temperature of the main reinforcing rod, which was relatively good temperature history.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.85.1-85.1
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• 2011

In this study, Grafoil$^{TM}$ which has comparable electric resistance and chemical stability but is flexible, fragile, and cheap material was adopted as bipolar plates for proton exchange membrane fuel cell(PEMFC) having only one straight line flow channel. Because of its flexibility, pressurizations of cell with various pressures showed different operating characteristics compared to ordinary graphite-used PEMFC. While performances of both cells decreased as these were pressurized, investigation of ohmic and faradaic resistance by electrochemical impedance measurement indicated different tendency of change. Ohmic resistance of graphite-used cell increased with increasing pressure, which is reversed in Grafoil$^{TM}$-used cell. It is speculated that effective chemical reaction area is decreased with increasing pressure in case of graphite-used one, but because of flexible property of Grafoil$^{TM}$, gas diffusion layer in Grafoil$^{TM}$-used cell was well-activated. Different rate of change of faradaic resistances in both cells support this supposition. However, although optimum point of pressurization is found, it is required to investigate other operating conditions because of low performance compared to graphite-used cell.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.129-134
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• 2005

The behavior of whole system is affected by a minor change of system in the hydronic radiant floor heating system. Under partial load condition, the change of system resistance causes overflow of supply water. This unexpected effect is the cause of several problems in the heating system. In this study, we find some factors were validated with several computer simulations. After validation of this result, several conceptual solutions are evaluated to prevent overflow.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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• pp.417-424
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• 2007

This paper reports fabrication and characterization of a pressure sensor using a pitch-based carbon fiber. Pitch-based carbon fibers have been shown to exhibit the piezoresistive effect, in which the electric resistance of the carbon fiber changes under mechanical deformation. The main structure of pressure sensors was built by performing backside etching on a SOI wafer and creating a suspended square membrane on the front side. An AC electric field which causes dielectrophoresis was used for the alignment and deposition of a carbon fiber across the microscale gap between two electrodes on the membrane. The fabricated pressure sensors were tested by applying static pressure to the membrane and measuring the resistance change of the carbon fiber. The resistance change of carbon fibers clearly shows linear response to the applied pressure and the calculated sensitivities of pressure sensors are $0.25{\sim}0.35 and 61.8 ${\Omega}/k{\Omega}{\cdot}bar$ for thicker and thinner membrane, respectively. All these observations demonstrated the possibilities of carbon fiber-based pressure sensors.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.5
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• pp.644-653
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• 2019

With the development of themal observatory device(TOD), thermal camouflage system has been applied not only to the weapon system but also to the combat suit for soldiers. In this paper, the characteristic of thermal radiation of human body depending on the clothing material properties was analyzed through numerical simulations. The bioheat equation with thermoregulatory model was solved to obtain the realistic surface temperature of human body and these results are combined with the emissivity of human skin and clothing in order to calculate the thermal signature from the human body. According to each thermal resistance of clothing, the optimal background radiance which makes contrast radiance intensity(CRI) be lowest is different. Also, the average CRI variation per thermal resistance change is about twice as much as the case of evaporative resistance change.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1581-1583
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• 1999

Epoxy Compound has been used as insulation material in cable accessories. During the applying voltage to cable, heat shock is induced to accessory by the temperature difference between atmosphere and conductor. In this study, crack resistance, thermal and mechanical properties were evaluated about conventional epoxy compound and rubber toughened epoxy compound. Because rubber absorbs the stress caused by heat shock, crack resistance of rubber toughened epoxy compound is high. In the case of low thermal expansion coefficient, the compound shows high crack resistance because of low volumetric change.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.267-268
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• 2009

Resistance standards from 1 ${\Omega}$ to 100 $k{\Omega}$, with calculable frequency dependencies of up to 1 MHz, have been developed for the calibration of commercial inductance-capacitance-resistance (LCR) meters and impedance analyzers. The resistors are designed on the basis of single bifilar loops. The typical resistance change from dc to 1 MHz is from 200 to $800\;{\mu}{\Omega}/{\Omega}$. According to the measurement results, the frequency dependencies of the resistors are severaltimes lower than the measurement uncertainty of commercial LCR meters.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.04a
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• pp.130-135
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• 1995

We can consider that the study on early evaluation of strength of concrete is useful to raise safety of building and utility of quality control of concrete is useful to raise safety of building and utility of quality control of concrete. In this paper, was proposed to method early to predict strength of concrete with key parameters, such as Water/Cement(W/C) ratio and Sand / Aggregate(S/A) ratio. Through a series of experiment, the obtained results are summarized as follow. $\circled1$ The ratio of resistance was decteased as the increase of W/C ratio. $\circled2$ The maximum value for the ratio of resistance and compressive strength was presented in the case of 40% S/A ratio. $\circled3$ The relationship. of the ratio of resistance and compressive strength on 28days according to the change of W/C and S/A ratio is to be: $F_{28}=-0.00104R^2 + 2.263R - 935.5$ (W/C Ratio) $F_{28} = 0.007R^2 - 10.693R - 4269.1$ (S/A Ratio)

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.1
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• pp.193-201
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• 1995

The role of thermal contact resistance between a casting and a metal mold as well as natural convection in the melt during solidification of a pure metal is numerically studied. Numerical simulation is performed for a rectangular cavity using the coordinate transformation by boundary-fitted coordinate and pure aluminum is used as the phase- change material. The influences of thermal contact resistance on the interface shape and position, solidified volume fraction, temperature field and local heat transfer are investigated.