• Corrosion Science and Technology
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• 제6권4호
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• pp.186-192
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• 2007

Carbonation is one of the most important factors causing the corrosion of reinforcement concrete. Nevertheless, experimental studies on the concrete carbonation have not been carried out sufficiently because of the slow process of carbonation process. Therefore, this study adopts an experimental system exploiting a vacuum instrument that has been recently developed to accelerate carbonation instead of existing experimental system to conduct rapid carbonation tests on Portland cement and fly-ash cement concretes. Test results revealed that, compared to water-cement ratio of 40%, the carbonation depth increases from 103% to 138% for an increase of water-cement ratio from 45% to 60%. These results are larger than the carbonation depths obtained by mathematical model, and such difference is increasing with larger water-cement ratios. The results also indicated that larger fly-ash contents lead to sharp increase of the carbonation depth, which is in agreement with previous experimental researches. The adoption of the new accelerated carbonation test system enabled to shorten effectively the time required to produce experimental data compared to the existing carbonation test method. The experimental data obtained in this study together with ongoing acquisition of data using the new carbonation test method are expected to contribute in the understanding of the carbonation process of concrete structures in Korea.

• 한국전산유체공학회지
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• 제8권2호
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• pp.16-23
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• 2003

A numerical study of the mixing of two fluids(pure water and a solution of glycerol in water) in a microchannel was carried out. By varying the glycerol content of the glycerol/water solution, the variation in mixing behavior with changes in the difference of the properties of the two fluids(e.g., viscosity, density, diffusivity) was investigated. The mixing phenomena were tested for three micromixers: a square mixer, a three-dimensional serpentine mixer, and a staggered herringbone mixer. The governing equations of continuity, momentum and solute mass fraction were solved numerically. To evaluate mixing performance, a criterion index of mixing of mixing uniformity was proposed. In the systems considered, the Reynolds numbers based on averaged properties were 1 and 10. For low Reynolds number (Re = 1), the mixing performance varied inversely with mass fraction of glycerol due to the dominance of molecular diffusion. The mixing performance by diffusion deteriorated due to a significant reduction in the residence time of the fluid inside the mixers.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.676-683
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• 2003

A laboratory experiment using artificial fracture rocks was used to understand the 3-dimensional dispersion of a tracer and the mixing process in a fractured network. In this experiment, 12cm polystyrene foam cubes with two electrodes for monitoring electric conductivity (EC) were used as artificial fractured rocks. Distilled water with 0.5mS/m was used as a tracer in water with 35mS/m and the difference of EC between the tracer and the water was monitored by a multipoint simultaneous measurement system of electrical resistance. The results showed that even if the fracture arrangement pattern was not straight in the direction of the flow, the tracer did not diffuse along individual fractures and an oval tracer plume, which was the distribution of tracer concentrations, tended to be form in the direction of the flow. The vertical cross section of the tracer distribution showed small diffusivity in the vertical direction. The calculated total tracer volume passing through each measurement point in the horizontal cross section showed while that the solute passed through measurement points near the direction of hydraulic gradient and in other directions, the passed tracer volumes were small. Using Peclet number as a criterion, it was found that the mass distribution at the fracture intersection was controlled in the stage of transition between the complete mixing model and the streamline routing model.

• 대한토목학회논문집
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• 제13권2호
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• pp.191-199
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• 1993

정상 2차원 이송확산(移送擴散) 방정식의 수치해석에 의하여 난류전단(亂流剪斷) 흐름에서의 정상(定常) 수평(水平) 선오염원(線汚染源)의 확산(擴散)을 모의하였다. 유속과 난류확산계수(亂流擴散係數)의 수심에 따른 변화가 없을 경우에 대한 해석해와 비교한 결과, 일정 유속 및 난류확산계수(亂流擴散係數)를 가정할 경우 수심방향 확산(擴散)을 과대평가하는 것으로 나타났다. 무차원화된 지배방정식에 따르면 수심방향 확산(擴散)을 지배하는 물리적 변수는 마찰계수(摩擦係數)뿐이다. 마찰계수(摩擦係數)에 대한 확산과정의 민감도(敏感度) 분석(分析)으로부터 수심방향 확산속도(擴散速度)는 대략 마찰계수(摩擦係數)의 제곱근에 비례함을 알 수 있었다. 오염원(汚染源)의 초기 방류위치에 따른 민감도(敏感度) 분석(分析) 결과, 가장 신속한 수심 방향 확산(擴散)을 가져오는 최적의 방류위치는 수심의 중간정보다 위쪽이며, 마찰계수(摩擦係數)가 커질수록 그 위치가 수면쪽에 가까와지는 것으로 나타났다.

• 콘크리트학회논문집
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• 제25권2호
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• pp.145-153
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• 2013

촉진 염화물 확산계수는 최근들어 염화물 거동 평가를 위하여 많이 사용되고 있다. 촉진 염화물 확산계수는 겉보기 확산계수와 마찬가지로 재령에 따라 감소하는데, 이 연구에서는 공극률을 이용하여 촉진확산계수의 감소를 구현하였다. DUCOM 프로그램을 이용하여 15 배합에 대한 공극률을 도출하였으며, 이를 회귀분석하여 재령 270일 동안 감소하는 염화물 확산계수를 모델링하였다. 또한 자유염화물과 구속염화물간의 관계인 비선형 구속능을 고려하여, 고성능 콘크리트내의 염화물 거동을 평가하였다. 기존의 실험자료인 180일간 염화물에 침지되어 있는 시편을 이용하여, 이 연구에서 제안한 기법의 검증을 수행하였다. 제안된 기법은 다양한 물-시멘트비 및 혼화재(고로슬래그 미분말 및 플라이애쉬)를 가진 고성능 콘크리트의 염화물 거동을 적절하게 평가하였다. 또한 혼화재료를 사용한 콘크리트의 경우, 확산계수의 시간의존성이 뚜렷하므로 염화물 거동 해석시 재령에 따른 염화물 확산계수의 감소를 반드시 구현해야 함을 알 수 있었다.

• 한국환경과학회지
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• 제23권4호
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• pp.661-672
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• 2014

Due to tidal force, it is very difficult to estimate the hydraulic parameters of high permeable aquifer near coastal area in Jeju Island. Therefore, to eliminate the impact of tidal force from groundwater level and estimate the hydraulic properties, tidal response technique has been mainly studied. In this study we have extracted 38 tidal constituents from groundwater level and harmonic constants including frequency, amplitude, and phase of each constituent using T_TIDE subroutine which is used to estimate oceanic tidal constituents, and then we have estimated hydraulic diffusivity associated with amplitude attenuation factor(that is the ratio of groundwater level amplitude to sea level amplitude for each tidal constituent) and phase lag(that is phase difference between groundwater level and sea level for each constituent). Also using harmonic constants for each constituent, we made the sinusoidal wave and then we constructed the synthesized wave which linearly combined sinusoidal wave. Finally, we could get residuals(net groundwater level) which was excluded most of tidal influences by eliminating synthesized wave from raw groundwater level. As a result of comparing statistics for synthesized level and net groundwater level, we found that the statistics for net groundwater level was more insignificant than those of synthesized wave. Moreover, in case of coastal aquifer which the impact of tidal force is even more than those of other environmental factors such as rainfall and groundwater yield, it is possible to predict groundwater level using synthesized wave and regression analysis of residuals.

• 한국전기전자재료학회논문지
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• 제32권6호
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• pp.490-495
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• 2019

This study performs the thermal aging of chlorosulfonated polyethylene (CSPE) for 807.36 and 1,614.48 hours at $110^{\circ}C$, which is equivalent to 40 and 80 years of aging at $50^{\circ}C$ in nuclear power plants, respectively. Flat-type CSPEs were soaked in seawater for five days and then dried for five days at room temperature. Furthermore, the soaked CSPEs were cleaned for 5 days with fresh water and dried for 1,100 days at room temperature. Through this process, the log IV of the CSPEs decreases, whereas the dissipation factor of the CSPEs increases as thermally accelerated aged years increase at the measured frequency. Although the phase degree of the response voltage versus excitation voltage of the CSPEs increases, that of the response current versus excitation voltage decreases with the thermally accelerated aging. The thermal conductivity of the CSPEs increases slightly, but the thermal diffusivity does not vary with the thermally accelerated aged year increase. The displacement of the compressive strength of the CSPEs decreases gradually as the thermally accelerated aged years increase.

• Journal of Biosystems Engineering
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• 제43권3호
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• pp.237-246
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• 2018

Purpose: This study (a) investigated the effect of microwave power intensity and sample thickness on microwave drying characteristics of radish strips, and (b) determined the best-fit drying model for describing experimental drying data, effective moisture diffusivity ($D_{eff}$), and activation energy ($E_a$) for all drying conditions. Methods: A domestic microwave oven was modified for microwave drying and equipped with a small fan installed on the left upper side for removing water vapor during the drying process. Radishes were cut into two fixed-size strip shapes (6 and 9 mm in thickness). For drying experiments, the applied microwave power intensities ranged from 180 to 630 W at intervals of 90 W. Six drying models were evaluated to delineate the experimental drying curves of both radish strip samples. The effective moisture diffusivity ($D_{eff}$) was determined from Fick's diffusion method, and the Arrhenius equation was applied to calculate the activation energy ($E_a$). Results: The drying time was profoundly decreased as the microwave power intensity was increased regardless of the thickness of the radish strips; however, the drying rate of thicker strips was faster than that of the thinner strips up to a certain moisture content of the strip samples. The majority of the applied drying models were suitable to describe the drying characteristics of the radish strips for all drying conditions. Among the drying models, based on the model indices, the best model was the Page model. The range of estimated $D_{eff}$ for both strip samples was from $2.907{\times}10^{-9}$ to $1.215{\times}10^{-8}m^2/s$. $E_a$ for the 6- and 9-mm strips was 3.537 and 3.179 W/g, respectively. Conclusions: The microwave drying characteristics varied depending on the microwave power intensity and the thickness of the strips. In order to produce high-quality dried radish strips, the microwave power intensity should be lower than 180 W.

• 유기물자원화
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• 제27권3호
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• pp.75-80
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• 2019

본 연구는 난류로 흐르는 물에서 미세먼지 전구체 중 하나인 암모니아가 흡수되는 거동을 해석하였다. 물의 흐름이 층류보다 난류인 조건에서 암모니아의 침투 깊이가 더 깊으므로 레이놀즈 수가 $10^4$보다 큰 난류 조건이 고려된다. 거동 해석을 위하여, 무차원 물질전달 지배방정식과 상온 기준의 일정한 물성치들이 사용되었다. 물에서의 암모니아 확산계수와 물의 동점도계수는 각각 $2.45{\times}10^{-9}m^2/s$와 $1{\times}10^{-6}m^2/s$이었다. 물에서의 암모니아 농도 분포는 암모니아에 노출되기 시작하는 지점으로부터의 위치에 대하여 산출되었다. 혼합 깊이에 따른 정량적인 분포 또한 도출되었다. 이와 같은 정량적인 해석은 난류로 흐르는 물이 층류로 흐르는 것과 비교하여 얼마나 더욱 효율적으로 암모니아를 제거할 수 있는지에 대한 통찰력을 제시할 수 있다.

• 한국식품영양과학회지
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• 제22권2호
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• pp.222-225
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• 1993

축육제품의 실제 열처리 온도범위에서 적용가능한 열확산도 추정식을 제시하고자, 식염 1.5%, 중합인산염 0.2%, lard 및 대두단백질을 임의의 농도로 혼합한 돼지고기를 사용하여 열전달실험을 행하고 열확산도 추정식을 구하였다. 수분함량 49.01~77.55%, 가열온도 80.76~121.03$^{\circ}C$의 범위에서 열확산도는 동일온도에서는 수분함량의 증가에 따라, 동일 수분함량에서는 가열온도가 높아짐에 따라 커졌으며, 각 온도에서의 실측 열확산도는 다음의 식들로 나타낼 수 있었다. $\alpha$p,(80.76$\pm$0.3$^{\circ}C$) =0.0869.$10^{-6}$ .Xw+0.0720.$10^{-6}$ ,(m$^2$.s$^{-1}$, r=0.9230) $\alpha$p, (98.59$\pm$0.3$^{\circ}C$) =0.0849.$10^{-6}$ .Xw+0.0818.$10^{-6}$ , (m$^2$.s$^{-1}$, r=0.9264) $\alpha$p, (121.03$\pm$0.5$^{\circ}C$) =0.0909.$10^{-6}$ .Xw+0.0893.$10^{-6}$ , (m$^2$.s$^{-1}$, r=0.9507)이 식들을 종합한, 임의의 온도에서의 열확산도 추정식은 다음과 같았으며 이로부터 구한 열확산도와 실측치의 차이는 실측치를 기준으로 $\pm$1.7% 이내였다. $\alpha$p=(2.1394+0.5.Xw).$\alpha$w+0.0035.$10^{-6}$ .Xw-0.2785.$10^{-6}$ , (m$^2$.s$^{-1}$).