• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.8-18
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• 2001

The direct simulation Monte Carlo Method is applied to investigate the two-dimensional flow fields of a turbomolecular pump(TMP) in both molecular and transition flow regions. The pumping characteristics of the TMP are investigated for a wide range of the Knudsen number. The maximum of compression ratio and of pumping speed strongly depend on the Knudsen number in transition region, while they weakly depend on the Knudsen number in free molecular flow region. The present numerical results show good agreement with the previously known experimental data. Finally. the 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.

• 한국공작기계학회논문집
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• 제17권2호
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• pp.45-50
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• 2008

Molecular flows inside a guide block in the OLED(organic luminescent emitting device) deposition process have been simulated using DSMC(direct simulation Monte Carlo) method. Because the organic materials are evaporated under vacuum, molecules flow at a high Knudsen number of the free molecular regime, where the continuum mechanics is not valid. A guide block is designed as a part of the linear cell source to transport the evaporated materials to a deposition chamber, When solving the flows, the inlet boundary condition is proved to affect significantly the whole flow pattern. Thus, it is proposed that the pressure should be specified at the inlet. From the analysis of the density distributions at the nozzle exit of the guide block, it is shown that the longer nozzle can emit molecules more straightly. Finally, a nondimensionalized mass flow profile is obtained by numerical experiments, where various nozzle widths and inlet pressures are tested.

• Korea-Australia Rheology Journal
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• 제20권2호
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• pp.89-94
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• 2008

To satisfy good mechanical and optical properties of polymer-coated film products, it will be indispensable to elucidate the molecular orientation of polymer chains within coating liquids in coating flows. Using hybridized numerical method between computational fluid dynamics (CFD) and Brownian dynamics (BD) simulations can provide the useful information for the better quality control of coated films. Flexible polymer chains, e.g., ${\lambda}$-DNA molecules here, change their conformation according to the flow strength and the flow type. The molecular conformation within the coated film on the web or substrate is quite different, because the polymer chains experience the complicated flow strength and flow types in flow field. Especially in the slot coating flow, these chains are more extended by the extension-like flow field generated in the free surface curvature just beyond the downstream die region. Also, the polymer chain extension beneath the free surface can be affected by the die geometry, e.g., the coating gap, changing flow field.

• 설비공학논문집
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• 제8권2호
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• pp.219-229
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• 1996

In the free molecular flow range, the pumping performance of a turbomolecular pump has been predicted by calculation of the transmission probability employing the integral method and the test particle Monte-Carlo method. The velocities of molecules incident upon a moving blade are given by the random numbers, which are sampled from the Maxwell molecular velocity distribution function. The present results agree quantitatively with the previous known numerical results. For a multi-stage pump, the velocity profile of molecules between two blade rows is not Maxwell distribution. In this case, the Monte-Carlo method is employed to calculate the overall transmission probability for the entire set of blade rows. When the results of the approximate method combining the single stage solutions are compared with those of the Monte-Carlo method for the pump having six rows at C=0.6, the approximate method overestimates as much as 36% in the maximum compression ratio and 19% in the maximum pumping speed than does the Mote-Carlo method.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2725-2730
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• 2007

Turbo-type molecular drag pumps ( MDPs ) are used in the liquid crystal display ( LCD ), semiconductor and other thin film industries. Siegbahn ( disk-type ) molecular drag pumps are used as high-pressure stages in the hybrid-type turbomolecular pumps, where they can operate in the viscous, the transition and the free molecular flow regime. In this study is performed to investigate the pumping characteristics of three-stage disk-type molecular drag pump ( DTDP ) in the molecular transition flow region. The experiments are measured using five vacuum pressure gauges in the positions for rotors of DTDP. The test is performed with nitrogen gas ( $N_2$ ).

• 대한기계학회논문집B
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• 제20권11호
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• pp.3620-3629
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• 1996

In the free molecular flow range, the pumping performance of a turbomolecular pump has been predicted by calculation of the transmission probability which employs the integral method and the test particle Monte-Carlo method. Also, new approximate method combining the double stage solutions, so called double-approximation, is presented here. The calculated values of transmission probability for the single stage agree quantitatively with the previous known numerical results. For a six-stage pump, the Monte-Carlo method is employed to calculate the overall transmission probability for the entire set of blade rows. When the results of the approximate method combining the single stage solutions are compared with those of the Monte-Carlo method at dimensionless blade velocity ratio C=0.4, the previous known approximate method overestimates as much as 34% than does the Monte-Carlo method. But, the new approximate method gives more accurate results, whose relative error is 10% compared to the Monte-Carlo method, than does the previous approximate method.

• BMB Reports
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• 제39권2호
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• pp.145-149
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• 2006

To analyze the effect of Maltol on the apoptosis of Human Neuroblastoma Cells (SH-SY5Y) treated by free radical which was generated from Hydrogen Peroxide ($H_2O_2$), flow cytometry analysis on Phosphatidylserine (PS) inverting percentage was applied to determine the apoptosis. MTT (3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl-tetrazolium bromide) assay was employed to analyze the cell viability. DNA electrophoresis was used to detect DNA fragmentation. Moreover intracellular calcium of concentration ($[Ca^{2+}]_i$) was measured by fluorescence emission. Flow cytometry analysis on the function of mitochondria and Western blto analysis of NF-${\kappa}B$. The results showed that the pretreatment with maltol for 2 hours could prevent the $H_2O_2$-induced apoptosis. Maltol could reduce the inverting percentage of PS, DNA fragmentation and $[Ca^{2+}]_i$, and enhance the cellular function of mitochondria. NF-${\kappa}B$ activated by $H_2O_2$ is reduced. The experiments suggest that maltol could effectively inhibit the apoptosis induced by $H_2O_2$. As a novel anti-oxidant, maltol is a new promising drug in protecting the neurological cells from the damage by free radical.

• Elastomers and Composites
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• 제44권2호
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• pp.156-163
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• 2009

사출성형 시 흐름자국이 생기지 않는 흐름성이 향상된 PP(Polypropylene) 복합재료를 제조하기 위한 연구를 진행하였다. PP는 분자량 분포와 용융지수(MI)가 다른 4종류의 PP를 사용하였으며, PP, 탈크, 고무와 약간의 첨가제로 구성된 PP컴파운드의 유변학적 특성은 Spiral Flow(SF), MI, 전단점도를 측정함으로써 평가하였다. 분자량 분포가 넓은 PP를 사용한 경우 MI가 상대적으로 낮다 하더라도 SF는 MI가 높은 PP보다 높게 관찰되는 경우도 있었다. 사출성형시 표면에 흐름자국이 발생하지 않도록 하기 위해서는 분자량 분포가 넓은 PP를 사용하는 것이 바람직 함을 확인하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.77-80
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• 2006

Graft copolymerized polycarboxylate(PC)-type superplasticizers(PCs) which have carboxylic acid with $\pi$ bond among the molecular structure and polyethyleneglycol methyl ether methacrylate(PMEM) were synthesized by free radical reaction and investigated the chemical structure, polymerization condition, and physical and chemical properties. Also, the effects of PCs in the dispersion, adsorption and hydration of cement were evaluated. As the molecular weight of graft chain decreases, the adsorption amount on cement particles increased. It was advantageous for the flow to reduce molar ratio, the lower the side bone molecular weight, and increase the molar ratio, the larger the side bone molecular weight. The hydration reaction speed was highly delayed at day 1, due to increase in molar ratio and reduction in side bone molecular weight, but it was recovered in the days after.