• 설비공학논문집
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• 제12권1호
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• pp.83-94
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• 2000

The performance of a turbomolecular pump(TMP) in both molecular and transition flow regions is predicted by the numerical solutions of the Boltzmann equation obtained by the direct simulation Monte Carlo method. The compression characteristics of the TMP are investigated for a wide range of the Knudsen number( Kn ). The maximum compression ratios strongly depend on Kn in transition region, while do they weakly on Kn in free molecular flow region. The present numerical results of the single blade row in both molecular and transition regions are used to predict the overall performance of a TMP, which has three kinds of blade with 24-rows.

• Coupled systems mechanics
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• 제12권1호
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• pp.21-40
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• 2023

In thisstudy, the vibration problem ofthermo elastic carbon nanotubes conveying pulsating viscous nano fluid subjected to a longitudinal magnetic field is investigated via Euler-Bernoulli beam model. The controlling partial differential equation of motion is arrived by adopting Eringen's non local theory. The instability domain and pulsation frequency of the CNT is obtained through the Galerkin's method. The numerical evaluation of thisstudy is devised by Haar wavelet method (HWM). Then, the proposed model is validated by analyzing the critical buckling load computed in presentstudy with the literature. Finally, the numerical calculation ofsystem parameters are shown as dispersion graphs and tables over non local parameter, magnetic flux, temperature difference, Knudsen number and viscous parameter.

• 한국세라믹학회지
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• 제33권1호
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• pp.110-118
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• 1996

• 한국수소및신에너지학회논문집
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• 제10권1호
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• pp.9-17
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• 1999

기계적인 합금처리된 여러 Mg-Ni 혼합물 중에서 가장 우수한 수소저장 성질을 가지고 있는 Mg-25wt.%Ni 혼합물의 수소화물 형성 및 분해 반응에 대한 반응속도론적 연구를 하였다. 수소화물 형성 및 분해 속도를 측정하여 이론적인 반응 속도식과 비교함으로써 율속 단계를 결정하였다. Mg-25wt.%Ni의 수소화물 형성의 율속단계는 $H_a$ = 4.0 미만의 여러 $H_a$ 범위에서는 입자간 통로 (interparticle channel), 입자의 갈라진 틈(crack) 등을 통한 수소 분자의 이동 단계인 Knudsen 유동과 보통의 기체 확산이고, 4.0 < $H_a{\leq}4.25$ 범위에서는 성장하는 수소화물 층을 통한 수소 원자의 확산으로 생각된다. Mg-25wt.%Ni의 수소화물 분해의 율속 단계는 전 $H_d$ 범위에 걸쳐 수소 분자의 이동 단계인 Knusden 유동과 보통의 기체 확산이다.

• 공업화학
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• 제10권2호
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• pp.212-217
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• 1999

기체투과 특성을 관찰하기 위해 양극산화에 의해 세공직경의 크기가 서로 다른 상부층과 하부층으로 이루어진 이중기하구조의 다공성 알루미나막을 제조하였다. 양극산화는 황산 전해질 하에서 직류에 의한 정전류법으로 행하였으며, 양질의 막을 얻기 위해 열산화, 화학연마, 전해연마 등의 전처리를 한 후 양극산화를 행하였다. 양극산화에 의한 알루미나 막의 제조에서 세공직경은 전해질의 종류 및 농도, 전해 온도, 전류밀도 등에 의존하는데, 전류밀도를 극도로 낮추어 세공직경이 20 nm 이하인 상부층을 제조하고 전류밀도를 높여서 세공직경이 36 nm인 하부층을 제조하였다. 막의 두께는 전기량에 의해 조절되어 상부층의 두께는 약 $6{\mu}m$이었으며 하부층을 포함하는 막의 총 두께는 약 $80{\sim}90{\mu}m$로 제조되었다. 제조된 막은 가압법에 의한 기체투과 실험을 행하였다. 제조된 막의 기체투과 기구는 Knudsen 흐름을 따르는 것을 확인하였다.

• The Plant Pathology Journal
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• 제17권6호
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• pp.365.5-366
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• 2001

• 한국식물병리학회:학술대회논문집
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• 한국식물병리학회 2000년도 추계 학술발표회
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• pp.41.1-41
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• 2000

• 한국막학회:학술대회논문집
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• 한국막학회 1996년도 춘계 총회 및 학술발표회
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• pp.16-19
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• 1996

Separation with synthetic membrane have become increasingly important processes in many fields. In the most application of membrane process, polymer membrane is used. the main advantage of polymers as a material for membrane preparation is the relative simplicity of this film formation which enables one to obtain rather high permeability rates. However, polymeric membranes have several limitations, such as high temperature instability, swelling and decomposition in organic solvent, et. al.. These limitations can be overcome by inorganic membrane. At the present time, commercially available inorganic membranes have pore diameters ranging 5nm to 50mm, and the predominant flow regime in such membrane is Knudsen diffusion. Since the Knudsen permeability is directly proportional to the molecular velocity, gases can be separated due to their molecular masses. However, this separation mechanism is only of important for light gases such as H2 and He. Other separation mechanisms like surface diffusion, active diffusion can play an important role only with very small pore diameters(2nm) and give rise to large permselectivities. Therefore, preparation of inorganic membrane with nano-sized pore have been attracting more and more attention.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.137-142
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• 2002

The fluid mechanics and operating conditions of gas-lubricated proceeding bearings in micro rotating machinery such as micro polarization modulator and micro gas turbine are different from their larger size ones. Due to non-continuum effects, there is a slip of gas at the walls. Thus in this paper, the slip flow effect is considered to estimate the pressure distribution and load-carrying capacity of micro gas-lubricated proceeding bearings as the local Knudsen number at the minimum film thickness is greater than 0.01. Based on the compressible Reynolds equation with slip flow, the static characteristics of micro gas-lubricated proceeding bearings are obtained. Numerical predictions compare the pressure distribution and load capacity considering slip flow with the performance of micro proceeding bearings without slip f]ow for a range of bearing numbers and eccentricities. The results clearly show that the slip flow effect on the static characteristics is considerable and becomes more significant as temperature increases.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1572-1577
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• 2003

High-power pulsed laser ablation under atmospheric pressure is studied utilizing numerical and experimental methods with emphasis on recondensation ratio, and the dynamics of the laser induced vapor flow. In the numerical calculation, the temperature pressure, density and vaporization flux on a solid substrate are first obtained by a heat-transfer computation code based on the enthalpy method, and then the plume dynamics is calculated by using a commercial CFD package. To confirm the computation results, the probe beam deflection technique was utilized for measuring the propagation of a laser induced shock wave. Discontinuities of properties and velocity over the Knudsen layer were investigated. Related with the analysis of the jump condition, the effect of the recondesation ratio on the plume dynamics was examined by comparing the pressure, density, and mass fraction of ablated aluminum vapor. To consider the effect of mass transfer between the ablation plume and air, unlike the most previous investigations, the equation of species conservation is simultaneously solved with the Euler equations. Therefore the numerical model computes not only the propagation of the shock front but also the distribution of the aluminum vapor. To our knowledge, this is the first work that employed a commercial CFD code in the calculation of pulsed ablation phenomena.