• 멤브레인
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• 제15권2호
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• pp.105-113
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• 2005

표면 개질한 다공성 금속 지지체에 초음파 분무 열분해법을 이용하여 silica막을 합성하고, 고온 기체 선택 투과 분리 특성을 조사하였다. Tetraethyl orthosilicate (TEOS)를 전구체로 하여 지지체 세공을 통한 감압 진공을 하면서 873K에서 표면에 defect 없이 균일한 양질의 silica막이 형성되었다. 투과 온도 523 K에서 silica막의 수th/질소 및 수증기/메탄을 분리 계수가 각각 17 및 16 정도의 우수한 선택 투과 성능을 나타냈다. 다공성 금속 지지체의 불균일한 기공에 silica 분체 및 $\gamma-alumina$층을 중간층으로 도입하고, 그 위에 열분해법에 의한 silica를 합성한 결과, Knudsen 확산에 의한 투과 영역의 세공이 완전히 제거되어 높은 수소 및 수증기 선택성을 가지는 복합 막이 형성되었다.

• 한국추진공학회지
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• 제17권5호
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• pp.54-59
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• 2013

현재 Micro Shock Tube는 다양한 공학응용분야에 적용되고 있으며, 특히 우주항공 및 연소기술 그리고 약물전달 등의 분야에서 광범위한 잠재력을 가진 장치 중 하나이다. 그러나 Micro Shock Tube에서의 유동 특성은 작은 직경으로 인해 형성되는 매우 낮은 Reynolds Number와 높은 Knudsen Number의 영향으로 일반적으로 잘 알려진 Macro Shock Tube의 유동 특성과 상이하게 나타난다. 본 연구에서는 이러한 Micro Shock Tube의 유동 특성을 상세히 연구하기 위해 직경이 다른 두 가지 Micro Shock Tube의 실험을 수행하였다. 충격파 전파를 측정하기 위해 고압관의 파막압력 그리고 저압관의 세 지점에 센서를 설치하여 압력을 측정하고 분석하였다. 본 연구로부터, 동일한 파막압력에서 Micro Shock Tube 직경의 증가에 따라 충격파 전파속도가 증가하였고, 반사파의 영향도 더 크게 받았다.

• 멤브레인
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• 제11권3호
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• pp.124-132
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• 2001

고온에서 수소 분리 회수를 목적으로 silica/alumina 복합 막을 합성하였다. 막의 선택 투과 성능을 향상시키기 위해, sol-gel법에 의한 silica 및 alumina층을 중간층으로 도입하고, 그 위에 강제유동 CVD법에 의한 silica를 합성하였다. Sol-gel법에 의해 ${\alpha}$-alumina tube에 합성한 ${\gamma}$-alumina 및 silica 막은 Knudsen 확산 영역의 많은 mesopore를 포함하고 있어서 수소 선택 분리 막으로는 적합하지 못했다. 하지만, sol-gel법에 의해 합성한 silica/${\gamma}$-alumina층에 강제유동 CVD법으로 silica를 합성한 결과, 질소 투과 영역의 세공이 완전히 제거되어, 높은 수소 선택성을 가지는 복합 막이 형성되었다. 그 막은 온도에 따라 수소 투과 속도가 증가하여 $450^{\circ}C$에서 $5.57{\times}10^{-8}molm^2s^LPa^1$의 수소 투과 속도와, 9.52 kJ/mol의 활성화 에너지를 나타냈다. 분자체 효과에 의해 질소 투과가 완전히 배제되고, 수소만 선택적으로 투과되는 silica/alumina 복합막이 성공적으로 합성된다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.71-77
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• 1998

In this study we calculated the flowfields around the axisymmetric bodies in the rarefied gas regime by using the DSMC. A flat-ended cylinder was selected as a representative axisymmetric body and the gas used for all calculations was nitrogen. With zero angle of attack, an increasingly rapid rise in density and the effect of shock waves near the flat-ended face were examined. And on the cylinder surface velocity slips and boundary layers could be observed in the results. Larsen-Borgnakke model was used for the energy redistribution in inelastic collisions. And by considering all internal energy modes, the distributions of translational, rotational and vibrational temperatures were plotted. The calculations were peformed for various Knudsen numbers, Especially the rotational temperatures calculated for a case were compared with the experimental results. And the simulation results show good agreements with the experimental ones.

• Mycobiology
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• 제29권1호
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• pp.54-57
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• 2001

Field studies were conducted over two seasons during the summers of 1997 and 1998 to investigate the effects of different spatial arrangements(random or highly aggregated) of sclerotia of Sclerotinia sclerotiorum and alginate pellet types(bran or polyethylene glycol) on colonization of sclerotia by Trichoderma spp. Treatment with alginate pellets increased the mean percentages of sclerotia colonized by Trichoderma spp. in both years. Distribution patterns of sclerotia affected the mean percentage of sclerotia colonized by Trichoderma spp. in both years, indicating that a highly aggregated distribution of sclerotia was more favorable to colonization by Trichoderma spp. The effects of the different pellet types(bran or PEG) were not siginificant in both years(P>0.05). The application of higher densities(200 pellets per 1 $m^2$) of alginate pellets resulted in higher mean percentages of sclerotia colonized by Trichoderma spp. in 1998(P<0.05), but did not in 1997.

• Tribology and Lubricants
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• 제17권6호
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• pp.441-446
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• 2001

In this paper the effect of bump compliance, load, and the number of pad on the lift-off speed is studied. When the load is greater and bump compliance lower, the shaft is lifted off at higher rotating speed. And when the load is applied near the center of pad, lift-off speed is lower. When the number of pad increases, the lift-off speed is higher. The lift-off characteristics can be used to lengthen the lift time of the coating and design the rotating machinery supported by bump bearings.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.309-317
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• 2012

Recent years have witnessed the use of micro shock tube in various engineering applications like micro combustion, micro propulsion, particle delivery systems etc. The flow characteristics occurring in the micro shock tube shows a considerable deviation from that of well established conventional macro shock tube due to very low Reynolds number and high Knudsen number effects. Also the diaphragm rupture process, which is considered to be instantaneous process in many of the conventional shock tubes, will be crucial for micro shock tubes in determining the near diaphragm flow field and shock formation. In the present study, an axi-symmetric CFD method has been applied to simulate the micro shock tube, with Maxwell's slip velocity and temperature jump boundary conditions. The effects of finite diaphragm rupture process on the flow field and the shock formation was investigated, in detail. The results show that the shock strength attenuates rapidly as it propagates through micro shock tubes.

• 대한기계학회논문집B
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• 제30권1호
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• pp.1-7
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• 2006

The characteristics of micro gaseous flows in microchannels have been analyzed in view of flow resistance using the direct simulation Monte Carlo (DSMC) method which is a molecule-based numerical modeling technique. For this purpose, a DSMC code where the pressure boundary condition was specified at the inlet and outlet, has been developed and the results of simulations showed satisfactory agreements with the analytic solution in the slip flow regime. (0.01 < Kn < 0.1) By varying the height and length of the microchannel, the effect of pressure difference between the inlet and outlet was examined. The present computation indicates that the curvature in pressure distribution along the channel increases due to the effect of compressibility when the pressure difference increases. To obtain the flow resistance regardless of the channel dimensions, a standard curve is devised in the present study by introducing the concept of unit mass flowrate and unit driving pressure force. From this curve, it is shown that in micro flows, a significant deviation from the laminar incompressible flow occurs by reducing the flow resistance.

• 공업화학
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• 제8권3호
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• pp.374-381
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• 1997

유리를 원료로 주형법에 의해 세라믹막을 제조하고, sodiumate, $S_3$-Al, $S_3$등의 실리콘 화합물을 침적시켜 세라믹-실리콘 복합막을 제조하여 이에 따른 기체 투과특성에 대해 연구하였다. 제조된 세라믹막과 세라믹-sodiumate 복합막은 다공성 구조임을 알수 있었고, 세라믹-$S_3$-Al과 세라믹-$S_3$ 복합막은 실리콘 화합물의 공극도입에 의한 치밀한 공극구조가 확인되었다. 세라믹막과 세라믹-sodiumate막의 경우 온도가 증가함에 따라 투과속도가 감소하고 압력에 따라 선형적으로 투과속도가 증가하였으며, 세라믹-$S_3$-Al과 세라믹-$S_3$ 복합막은 온도가 증가함에 따라 투과속도가 증가하는 경향을 보였으며, 상대적으로 투과속도에 미치는 압력의 영향이 적었다. 투과속도는 세라믹막이 가장 빠르게 나타났고, 세라믹-sodiumate, 세라믹-$S_3$-Al, 세라믹-$S_3$ 복합막 순서였으며, 선택도는 이와 반대 경향을 보였다. 또한 침적을 통한 투과속도를 구하여 실제 복합막의 투과속도와 비교한 결과, $S_3$가 가장 큰 영향이 있음을 확인하였다. 투과 메카니즘의 변화에서 세라믹막과 세라믹-sodiumate 복합막은 온도에 따라 투과기체의 투과도가 감소하는 Knudsen영역의 투과특성을 보였으나, 세라믹닉-$S_3$-Al과 세라믹-$S_3$ 복합막은 이와 반대로 온도에 따라 투과도가 증가하는 activated 확산 메카니즘을 따르는 특성을 보였다.

• 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.