• Membrane and Water Treatment
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• 제2권3호
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• pp.159-173
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• 2011

The air gap membrane distillation (AGMD) process was applied for water desalination. The main objective of the present work was to study the heat and mass transfer mechanism of the process. The experiments were performed on a flat sheet module using aqueous NaCl solutions as a feed. The membrane employed was hydrophobic PTFE of pore size 0.22 ${\mu}m$. A mathematical model is proposed to evaluate the membrane mass transfer coefficient, thermal boundary layers' heat transfer coefficients, membrane / liquid interface temperatures and the temperature polarization coefficients. The mass transfer model was validated by the experimentally and fitted well with the combined Knudsen and molecular diffusion mechanism. The mass transfer coefficient increased with an increase in feed bulk temperature. The experimental parameters such as, feed temperature, 313 to 333 K, feed velocity, 0.8 to 1.8 m/s (turbulent flow region) were analyzed. The permeation fluxes increased with feed temperature and velocity. The effect of feed bulk temperature on the boundary layers' heat transfer coefficients was shown and fairly discussed. The temperature polarization coefficient increased with feed velocity and decreased with temperature. The values obtained were 0.56 to 0.82, indicating the effective heat transfer of the system. The fouling was observed during the 90 h experimental run in the application of natural ground water and seawater. The time dependent fouling resistance can be added in the total transport resistance.

• Journal of Biosystems Engineering
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• 제24권6호
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• pp.501-512
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• 1999

In this study, the coefficient of performance of a vapour compression heat pump system was analyzed for the evaluation of the heat pump performance. A water-to-air heat pump was assembled and tested by changing the level of the compressor driving speed and the air mass flow rate during air heating process. The coefficient of performance for air heating was 2.6~3.8 and that for water cooling was 1.0~1.4. The coefficient of performance was not depending on the levels of the compressor driving speed or levels of the air mass flow rate, but on the temperature of the air and water. The coefficient of performance for air heating increased by about 0.2 with the water temperature increasing by 1$^{\circ}C$.

• 한국안전학회지
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• 제18권1호
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• pp.19-27
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• 2003

This paper presented an experimental modal analysis of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the Rayleigh-Ritz method and compared with the experimental results. Good agreement was obtained between the analytical solution and experimental result. The experimental results in water showed that the mode shapes are not sensitive to the depth of submergence. The natural frequencies were shown to decrease drastically once the perforated plates come in contact with water. However, the natural frequencies decrease with the depth of submergence until a certain depth is reached, and become the asymptotic values beyond this depth of submergence. The depth of submergence did not affect the damping ratio greatly.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1766-1775
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• 2001

A theoretical analysis on the heat and mass transfer in an evaporative cooler is presented in this work. The evaporative cooler is modeled as a channel filled with porous media the interstitial surface of which is covered by thin water film. Assuming that the Lewis number is unity and the water vapor saturation curve is linear, exact solutions to the energy and vapor concentration equations are obtained. Based on the exact solutions, the characteristics of the heat and mass transfer in the evaporative cooler are investigated. The comparison of the cooling performance between the evaporative cooler and the usual sensible heat exchanger is also carried out. Obviously, the evaporative heat exchanger shows better cooling performance than the sensible heat exchanger. This is due to the latent heat of water vaporization, which results in apparent increases both in the interstitial heat transfer coefficient and the specific heat of the air stream in the evaporative cooler.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2005년도 학술발표논문집
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• pp.97-101
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• 2005

High strength concretes utilizing EVA with micro particles were prepared by varying polymer/binder mass ratio and curing conditions with a constant water/binder mass ratio of 0.3. The EVA modified concretes on the compressive and flexural strength, microstructure, ultrapulse modulus in curing condition(dry and water curing) were studied. Also, scanning electron microscope analysis(SEM) was performed to reveal the presence of polymer film and cement hydrates in the concrete. The compressive strength of the EVA modified concretes cured at water conditions ere higher than that of the EVA modified concretes cured at dry conditions. But, the flexural strength of the specimens cured at dry conditions were higher than that of the specimens cured at water conditions. Due to the interaction of the cement hydrates and polymer film, an interpenetrating network originated in which the aggregates were embedded. The curing of the polymer modified concrete involves two step of cement hydrates and polymer modification, and cement hydrates was promoted in water conditions and polymer film formation take place when water evaporates and was thereby was favored in dry conditions. By SEM analysis, influences of polymer modification was strengthening of the transition zone between the aggregate and the paste, and the porosity of transition zone decreases. By spring analysis, it could known that polymer film affects in porosity decrease and strengthening of transition zone.

• Mass Spectrometry Letters
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• 제2권1호
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• pp.12-15
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• 2011

The Korean government has regulated emission of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in waste water of manufacturing facilities producing chlorinated compounds since 2009. As this regulation is expected to be reinforced in 2013 to 50 pg I-TEQ/L, a large sample volume is required for the analysis of trace amounts of PCDD/Fs in waste water. Liquid-liquid extraction (LLE) is used to extract PCDD/Fs from aqueous samples; however, its low efficiency makes it inadequate for analyzing large sample volumes. Herein, we present a disk-type solid-phase extraction (SPE) method for the analysis of dioxin at a part per quadrillion level in waste water. This SPE system contains airtight glass covers with a decompression pump, which enables continuous semi-automated extraction. Small (0.5 L) and large (7 L) samples were extracted using LLE and SPE methods, respectively. The method detection limits (MDLs) were 0.001.0.25 and 0.015.4.1 pg I-TEQ/L for the SPE and LLE methods, respectively. The concentrations of detected congeners with both methods were similar. However, the concentrations of several congeners that were not detected with the LLE method were quantified using the SPE method.

• Smart Structures and Systems
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• 제23권6호
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• pp.627-639
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• 2019

Passive control may not provide enough damping for a stay cable since the control devices are often restricted to a low location level. In order to enhance control performance of conventional passive dampers, a new type of damper integrated with a rotary electromagnetic damper providing variable damping force and a flywheel serving as an inertial mass, called the rotary electromagnetic inertial mass damper (REIMD), is presented for suppressing the cable vibrations in this paper. The mechanical model of the REIMD is theoretically derived according to generation mechanisms of the damping force and the inertial force, and further validated by performance tests. General dynamic characteristics of an idealized taut cable with a REIMD installed close to the cable end are theoretically investigated, and parametric analysis are then conducted to investigate the effects of inertial mass and damping coefficient on vibration control performance. Finally, vibration control tests on a scaled cable model with a REIMD are performed to further verify mitigation performance through the first two modal additional damping ratios of the cable. Both the theoretical and experimental results show that control performance of the cable with the REIMD are much better than those of conventional passive viscous dampers, which mainly attributes to the increment of the damper displacement due to the inertial mass induced negative stiffness effects of the REIMD. Moreover, it is concluded that both inertial mass and damping coefficient of an optimum REIMD will decrease with the increase of the mode order of the cable, and oversize inertial mass may lead to negative effect on the control performance.

• 방사성폐기물학회지
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• 제21권1호
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• pp.23-41
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• 2023

Coupled thermo-hydraulic-mechanical (THM) processes are essential for the long-term performance of deep geological disposal of high-level radioactive waste. In this study, a numerical sensitivity analysis was performed to analyze the effect of rock properties on THM responses after the execution of the heater test at the Kamaishi mine in Japan. The TOUGH-FLAC simulator was applied for the numerical simulation assuming a continuum model for coupled THM analysis. The rock properties included in the sensitivity study were the Young's modulus, permeability, thermal conductivity, and thermal expansion coefficients of crystalline rock, rock salt, and clay. The responses, i.e., temperature, water content, displacement, and stress, were measured at monitoring points in the buffer and near-field rock mass during the simulations. The thermal conductivity had an overarching impact on THM responses. The influence of Young's modulus was evident in the mechanical behavior, whereas that of permeability was noticed through the change in the temperature and water content. The difference in the THM responses of the three rock type models implies the importance of the appropriate characterization of rock mass properties with regard to the performance assessment of the deep geological disposal of high-level radioactive waste.

• Journal of Biosystems Engineering
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• 제19권1호
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• pp.62-69
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• 1994

This study was designed to seek information on the heat charging and discharging characteristics of a multi-capsule type LTES(Latent Heat of Fusion Thermal Energy Storage) system, and especially prediction equation of outlet water temperature from the system. During heat charging process, the water temperature in the LTES tank increased very slowly in comparison with a predicted one and was kept near the melting point of the PCM for about 25 minutes. During heat discharging process, the latent heat discharging period of the outlet water temperature became longer as the inlet water temperature became higher and/or mass flow rate became lower. The dimensionless temperature of the outlet water was predicted by linking three equations of ${\theta}=1.1Exp(-{\tau}/0.82)$, ${\theta}=-0.06{\tau}+0.3$, ${\theta}=0.8Exp(-{\tau}/1.4)$ ($r^2{\leq}0.88$) depending on discharging period regardless of mass flow rates on the case of the inlet water temperature at $21.5^{\circ}C$.

• 해양환경안전학회지
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• 제22권7호
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• pp.836-845
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• 2016

본 연구에서는 하계 한국 남동해 간절곶 주변해역의 냉수대 구조와 변동을 CTD 관측과 수층별 수온 장기 연속 모니터링 자료를 이용하여 분석하였다. 냉수대의 표층수온은 냉수기 이전과 $-12^{\circ}C$의 차이를 보였으며 해저지형 효과로 간절곶에서 냉수대 세력이 가장 컸다. 남북해역 간 등온선의 시계열분포에 간절곶을 경계로 공간변화가 발생해 간절곶 주변 해저지형이 언덕(hill)역할을 하고 있음이 추정되었다. 냉수대는 해안에 평행한 풍속이 양(+)의 값일 때 출현하는 연안용승반응을 나타냈고, 수온의 감소와 상승은 풍향이 바뀐 후 하루 이내에 반응하였다. 간절곶 주변은 얕은 수심 주위에서 발생하는 와류효과가 결합하여 바람에 의한 용승효과가 강화되었다. 수온변화는 2~6일 주기의 바람변동에 민감하였으며, 수온감소는 12~36시간의 위상차를 나타냈다. 냉수대가 출현한 7월은 2~3일 주기, 8월은 3~8일 주기에서 바람-수온변화의 상관성이 컸다.