• Title/Summary/Keyword: Gas dynamics

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Modeling and Simulation for PIG with Bypass Flow Control in Natural Gas Pipeline

  • Nguyen, Tan-Tien;Kim, Sang-Bong;Yoo, Hui-Ryong;Park, Yong-Woo
    • Journal of Mechanical Science and Technology
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    • v.15 no.9
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    • pp.1302-1310
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    • 2001
  • This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

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Analysis of PIG Dynamics through Curved Section in Natural Gas Pipeline (천연가스 배관 곡관부에서의 피그 동적 거동 해석)

  • Kim D. K.;Nguyen T. T.;Yoo H. R.;Rho Y. W.;Kho Y.T.;Kim S. B.
    • Journal of the Korean Institute of Gas
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    • v.6 no.1 s.17
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    • pp.1-9
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    • 2002
  • This paper presents simple models for flow and the PIG dynamics when it passes through a $90^{\circ}$ curved section of pipeline. The simulation has been done with two different operational boundary conditions. The solution fur non-linear hyperbolic partial equations for flow is given by using MOC. The Runge-Kuta method is used to solve the initial condition equation fur flow and the PIG dynamics equation. The simulation results show that the proposed model and solution can be used fur estimating the PIG dynamics when the pig runs in the pipeline including curved section. In this paper, dynamic modeling and its analysis for the PIG flow through $90^{\circ}$ curved pipe with compressible and unsteady flow are studied. The PIG dynamics model is derived by using Lagrange equation under assumption that it passes through 3 different sections in the curved pipeline such that it moves into, inside and out of the curved section. The downstream and up stream flow dynamics including the curved sections are solved using MOC. The effectiveness of the derived mathematical models is estimated by simulation results fur a low pressure natural gas pipeline including downward and upward curved sections. The simulation results show that the proposed model and solution can be used for estimating the PIG dynamics when we pig the pipeline including curved section.

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Molecular Dynamics Study for Improving the Adhesion of Paint (도료의 부착성 개선을 위한 분자동역학적 연구)

  • Yang, Young-Joon;Lee, Chi-Woo
    • Journal of Advanced Marine Engineering and Technology
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    • v.31 no.8
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    • pp.932-938
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    • 2007
  • The interaction between adherent molecules and gas molecules was modeled in molecular scale and simulated by the molecular dynamics method in order to understand the evaporation and removal processes of adherent molecules on metallic surface using high temperature gas flow. Methanol molecules were chosen as adherent molecules to investigate effects of adhesion quantify and gas molecular collisions because the industrial oil has too complex structures of fatty acid. The effects of adherent quantify, gas temperature and surface temperature for the evaporation rate of adherent molecules and the molecular removal mechanism were investigated and discussed in the present study. Evaporation and removal rates of adherent molecules from metallic surface calculated by the molecular dynamics method showed the similar dependence on surface temperature shown in the experimental results.

Development of a Software System for Measurements of Combustion Dynamics of a Dry Low NOx Gas Turbine (건식 저 NOx 가스터빈의 연소동압 측정용 소프트웨어 시스템 개발)

  • Jang, Wook;Seo, Seok-Bin;Jung, Jae-Hwa;An, Dal-Hong;Kim, Jong-Jin;Cha, Dong-Jin
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.14 no.11
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    • pp.931-938
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    • 2002
  • Combustion dynamics of a dry low NOx gas turbine have been measured by utilizing a dynamic pressure measurement system. The software part of the measurement system, implemented with a commercial general-purpose DASYLab version 5.6 code, basically acquires combustion dynamics signals, performs the FFT analysis, and displays the results. The gas turbine often experiences momentary combustion instability, especially when its combustion mode changes. It is found that the measurement system developed in the study may outperform the other commercial dynamic pressure measurement system. The developed system currently serves to monitor the combustion dynamics of the gas turbine.

Synthesis of Highly Selective Polyimide Material and Comparison of Gas Permeability by Molecular Dynamics Study (고선택성 폴리이미드 소재의 합성 및 분자동력학 연구를 통한 기체투과도의 비교)

  • Lee, Jung Moo;Kim, Deuk Ju;Jeong, Moon Ki;Lee, Myung Gun;Park, Chi Hoon;Nam, Sang Yong
    • Membrane Journal
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    • v.25 no.2
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    • pp.162-170
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    • 2015
  • In this study, gas permeability of polyimide materials having a various amine group was measured and molecular dynamics was used to analyze the dynamic characteristics of the gas molecules in the polyimide by calculating the position and velocity of the gas molecules with change of the time. The gas permeability of polyimide membrane having substitution site which increase free volume in the polymer was increased. However, polyimide with rigid structure showed decreased gas permeability. As a result of analyzing the change in the gas permeation behavior using molecular dynamics simulations, we confirmed that the results show the same tendency with actual measurements of the gas permeability.

Investigation of the gas Dynamics in an Upflow OMVPE Reactor by Raman Spectroscopy

  • Park, Chinho;Timoghy J. Anderson
    • Proceedings of the Korea Association of Crystal Growth Conference
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    • 1997.06a
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    • pp.223-228
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    • 1997
  • The gas dynamics in a stagnation point upflow OMVPE reactor were studied by Raman spectroscopy. The gas temperature was measured as a function of inlet gas velocity and aspect ratio for both H$_2$ and N$_2$ carrier gases. The centerline temperature gradient was latger at higher inlet velocities and with the use of N$_2$, and only weakly dependent on the aspect ratio. a tracer molecule, CH$_4$, was used to investigate the steady state behavior of reactants in the reactor, and the use of a sweeping flow was found to be a suitable method for preventing wall deposition. The transient switching response of the gas manifold was also investigated. Under certain conditions (low velocities, unmatched flows) recirculation flows were apparent. Numerical calculations of the reactor gas dynamics gave reasonable agreement with experimental results when detailed thermal boundary conditions were included.

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MOLECULAR SCALE MECHANISM ON EVAPORATION AND REMOVAL PROCESS OF ADHERENT MOLECULES ON SURFACE BY BURNT GAS

  • Yang, Y.J.;Lee, C.W.;Kadosaka, O.;Shibahara, M.;Katsuki, M.;Kim, S.P.
    • International Journal of Automotive Technology
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    • v.7 no.2
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    • pp.121-128
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    • 2006
  • The interaction between adherent molecules and gas molecules was modeled in the molecular scale and simulated by the molecular dynamics method in order to understand evaporation and removal processes of adherent molecules on metallic surface using high temperature gas flow. Methanol molecules were chosen as adherent molecules to investigate effects of adhesion quantity and gas molecular collisions because the industrial oil has too complex structures of fatty acid. Effects of adherent quantity, gas temperature, surface temperature and adhesion strength for the evaporation rate of adherent molecules and the molecular removal mechanism were investigated and discussed in the present study. Evaporation and removal rates of adherent molecules from metallic surface calculated by the molecular dynamics method showed the similar dependence on the surface temperature shown in the experimental results.

Dynamic Modeling of PIG Flow in Natural Gas Pipelines (천연가스배관내 피그흐름의 동적모델링)

  • Kim, Sang-Bong;Nguyen, Tan Tien;Yoo, Hui-Ryong;Rho, Yong-Woo
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.241-246
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    • 2001
  • This paper introduces modeling and solution for the dynamics of pipeline inspection gauge (PIG) flow in natural gas pipeline. Without of bypass flow, the dynamic behavior of the PIG depends on the different pressure between the rear and nose parts, which is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. With bypass flow, the PIG dynamics also depends on the amount of bypass flow across its body. The mathematical model are derived for unsteady compressible flow of the PIG driving and expelled gas, and for dynamics of the PIG. The bypass flow is assumed to be incompressible with the condition of its Mach number smaller than 0.45. The method of characteristic (MOC) and the Runge-Kutta method are used to solve the system governing equations. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show that the derived mathematical model and the proposed solution are effective for estimation the dynamics of the PIG with and without bypass flow under given operational condition.

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Modeling of hollow formation and its dynamics in liquid gas assisted injection molding process

  • Kim, Dong-Hak;Ahn, Kyung-Hyun
    • Korea-Australia Rheology Journal
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    • v.16 no.1
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    • pp.27-33
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    • 2004
  • Application of gas assisted injection molding has been expanded during last two decades because of many advantages such as design flexibility, dimensional stability, reduction of machine tonnages, and so on. However, the surface defects including hesitation mark and gloss difference are observed for thick parts. Difficulties in lay-out of the gas channel and processing condition are another disadvantages. Liquid gas assisted injection molding(LGAIM), in which a liquid with a boiling point lower than the temperature of the polymer melt is injected into the melt stream, and travels with the melt into the mold where it vaporizes and pushes the melt downstream and against the cavity walls to create hollow channels within the part, is a good alternative of the conventional gas assisted injection molding especially in manufacturing simple and very thick parts. Though this is a new frontier of the innovation in the injection molding industry, there is no guideline for the design and processing conditions. In this paper, theoretical analysis has been made to describe the hollow formation dynamics in LGAIM. This model provides an insight into LGAIM process: explains why LGAIM has advantages over conventional gas assisted injection molding, and gives a guideline for the design and processing conditions.

A Study on the Velocity Distribution of Gas Molecules by the Molecular Dynamics Method (분자동역학법에 의한 기체분자의 속도분포에 관한 연구)

  • 최순호
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.3
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    • pp.441-450
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    • 2004
  • The velocity distribution of gas molecules from the experimental results was confirmed as the same with the Maxwell-Boltzmann's theoretical results within the experimental error. This study is on the realization of the Maxwell-Boltzmann's velocity distribution of gas molecules by the molecular dynamics(MD) method. The Maxwell-Boltzmann's velocity distribution of gas molecules is extremely important to confirm the equilibrium state because the properties of a thermodynamic system shall be obtained from the system's equilibrium configuration in the MD method. This study is the first trial in the successive researches to calculate the properties of a thermodynamic system by the computer simulations. We confirmed that the maxwell-boltzmann's velocity distribution is developed in some transient time after starting a simulation and dependent on the size of a system. Also it is found that the velocity distribution has no relation with an initial configuration of gas molecules.