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6 results on '"vacuum flows"'

1. Cubic Fokker–Planck method for rarefied monatomic gas flow through a slit and an orifice.

Author

Jun, Eunji, Grabe, Martin, and Hannemann, Klaus

Subjects
*GAS flow, *MONTE Carlo method, *ORIFICE plates (Fluid dynamics), *FOKKER-Planck equation, *STOCHASTIC analysis
Abstract

Highlights • Rarefied monatomic gas flow through a thin slit and a thinorifice. • Access of accuracy and efficiency of DSMC/cubic FP/cubic FP-DSMC. • Translational non-equilibrium based on direction dependent temperature of cubic FP. • Investigation of breakdown of translational equilibrium on cubic FP-DSMC hybrid. Abstract The flow through a thin slit and a thin orifice is studied with the Direct Simulation Monte Carlo (DSMC), cubic Fokker–Planck (FP), and a coupled FP-DSMC hybrid method. Pressure driven monatomic gas flows through a slit and an orifice with various values of degree of rarefaction and pressure ratio are computed. The DSMC method is physically accurate for all flow regimes; however it is computationally expensive in high density, near continuum regions. An alternative stochastic particle scheme, the cubic FP kinetic model has addressed this issue by approximating the particle collisions involved in the Boltzmann collision integral with continuous stochastic processes. The ability of the cubic FP method to reproduce breakdown of translational equilibrium is discussed. In addition, a coupled FP-DSMC hybrid scheme is employed aiming at an efficient and accurate solution. The FP-DSMC hybrid scheme employs DSMC in rarefied regions and FP method in near continuum flow regions. Numerical procedures of the cubic FP method are implemented within the framework of an existing DSMC-solver, SPARTA. The FP-DSMC hybrid solution reproduces pure DSMC solution with improved computational efficiency up to a factor of eight for vacuum flow through a thin slit. [ABSTRACT FROM AUTHOR]

Published
2018
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2. Modeling of complex gas distribution systems operating under any vacuum conditions: Simulations of the ITER divertor pumping system.

Author

Vasileiadis, N., Tatsios, G., Misdanitis, S., and Valougeorgis, D.

Subjects
*GAS distribution, *VACUUM, *FUSION reactor divertors, *PUMPING machinery, *INTEGRATED software, *COMPUTER simulation, *ALGORITHMS, *ENERGY conservation
Abstract

An integrated software tool for modeling and simulation of complex gas distribution systems operating under any vacuum conditions is presented and validated. The algorithm structure includes (a) the input geometrical and operational data of the network, (b) the definition of the fundamental set of network loops and pseudoloops, (c) the formulation and solution of the mass and energy conservation equations, (d) the kinetic data base of the flow rates for channels of any length in the whole range of the Knudsen number, supporting, in an explicit manner, the solution of the conservation equations and (e) the network output data (mainly node pressures and channel flow rates/conductance). The code validity is benchmarked under rough vacuum conditions by comparison with hydrodynamic solutions in the slip regime. Then, its feasibility, effectiveness and potential are demonstrated by simulating the ITER torus vacuum system with the six direct pumps based on the 2012 design of the ITER divertor. Detailed results of the flow patterns and paths in the cassettes, in the gaps between the cassettes and along the divertor ring, as well as of the total throughput for various pumping scenarios and dome pressures are provided. A comparison with previous results available in the literature is included. [ABSTRACT FROM AUTHOR]

Published
2016
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3. Unsteady vacuum gas flow in cylindrical tubes

Author

Lihnaropoulos, John and Valougeorgis, Dimitris

Subjects
*GAS flow, *VACUUM, *TUBES, *NUMERICAL analysis, *NUMERICAL solutions to equations, *BOUNDARY value problems
Abstract

Abstract: The starting gas flow in a cylindrical channel is investigated in the whole range of the Knudsen number by numerically solving the governing time dependent kinetic equations in a fully deterministic manner. The gas is initially at rest and then due to a suddenly imposed uniform pressure gradient, is starting to flow. The motion is time dependent up to the point where the steady-state flow conditions are recovered. The flow field is modeled by the linearized unsteady BGK equation subject to Maxwell purely diffuse boundary conditions. The solution provides a detailed description of the evolution of the flow field with regard to time from the starting point, where the gas is at rest up to a certain time where almost steady-state conditions are recovered. Based on the results some insight of how rapidly a vacuum flow will respond to a sudden change, related to an externally imposed pressure gradient coming from a vacuum pump or a valve, is obtained. The total time to recover the stationary solution in terms of the rarefaction parameter exhibits a minimum close to the well known Knudsen minimum. [Copyright &y& Elsevier]

Published
2011
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4. Experimental and numerical investigation in flow configurations related to the vacuum systems of fusion reactors

Author

Varoutis, S., Hauer, V., Day, C., Pantazis, S., and Valougeorgis, D.

Subjects
*FUSION reactors, *VACUUM, *HYDRAULIC engineering, *DIFFERENTIABLE dynamical systems, *NUCLEAR reactors, *NUMERICAL calculations
Abstract

Abstract: Vacuum flows in various configurations, which are related to fusion reactors are simulated using linear kinetic theory and the direct simulation Monte Carlo method (DSMC), in the whole range of the Knudsen number. In the case of flows through channels of infinite length, even for large pressure differences, the flow is linear (fully developed) and linearized kinetic theory has been applied with considerable success. In the case of flows through channels of finite length, the flow is strongly non-equilibrium and has to be tackled by the DSMC method. In the present work we present a comparative study between experimental and computational results for the case of circular channels of finite length. Experimental data and corresponding computational results are provided for the conductance of channels with different lengths and several downstream to upstream pressure ratios, covering a wide range of the Knudsen number. In addition, a brief review of some recent work related to the case of long channels is presented and general remarks related to the overall flow conditions and characteristics for flows through channels of various lengths and cross sections are stated. [ABSTRACT FROM AUTHOR]

Published
2010
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5. Self-consistent coupling of DSMC method and SOLPS code for modeling tokamak particle exhaust

Author

Alexander Lukin, Stefan Matejcik, Soare Sorin, Francesco Romanelli, Bohdan Bieg, Stylianos Varoutis, Christian Day, Vladislav Plyusnin, José Vicente, Alberto Loarte, Axel Jardin, Rajnikant Makwana, CHIARA MARCHETTO, Marco Wischmeier, William Tang, Choong-Seock Chang, Manuel Garcia-munoz, and JET Contributors

Subjects
Physics, Work (thermodynamics), Jet (fluid), divertor gas flows, DSMC, SOLPS, vacuum flows, Nuclear and High Energy Physics, Condensed Matter Physics, Tokamak, Number density, Flow (psychology), Cryopump, Mechanics, Plasma, 01 natural sciences, 010305 fluids & plasmas, law.invention, Physics::Fluid Dynamics, Physics::Plasma Physics, law, 0103 physical sciences, Direct simulation Monte Carlo, 010306 general physics
Abstract

In this work, an investigation of the neutral gas flow in the JET sub-divertor area is presented, with respect to the interaction between the plasma side and the pumping side. The edge plasma side is simulated with the SOLPS code, while the sub-divertor area is modeled by means of the direct simulation Monte Carlo (DSMC) method, which in the last few years has proved well able to describe rarefied, collisional flows in tokamak sub-divertor structures. Four different plasma scenarios have been selected, and for each of them a user-defined, iterative procedure between SOLPS and DSMC has been established, using the neutral flux as the key communication term between the two codes. The goal is to understand and quantify the mutual influence between the two regions in a self-consistent manner, that is to say, how the particle exhaust pumping system controls the upstream plasma conditions. Parametric studies of the flow conditions in the sub-divertor, including additional flow outlets and variations of the cryopump capture coefficient, have been performed as well, in order to understand their overall impact on the flow field. The DSMC analyses resulted in the calculation of both the macroscopic quantities—i.e. temperature, number density and pressure—and the recirculation fluxes towards the plasma chamber. The consistent values for the recirculation rates were found to be smaller than those according to the initial standard assumption made by SOLPS.

Published
2017

6. Self-consistent coupling of DSMC method and SOLPS code for modeling tokamak particle exhaust

Author

Bonelli, F., Andersson Sundén, Erik, Binda, Federico, Cecconello, Marco, Conroy, Sean, Dzysiuk, Natalia, Ericsson, Göran, Eriksson, Jacob, Hellesen, Carl, Hjalmarsson, Anders, Possnert, Göran, Sjöstrand, Henrik, Skiba, Mateusz, Weiszflog, Matthias, Zychor, I., Bonelli, F., Andersson Sundén, Erik, Binda, Federico, Cecconello, Marco, Conroy, Sean, Dzysiuk, Natalia, Ericsson, Göran, Eriksson, Jacob, Hellesen, Carl, Hjalmarsson, Anders, Possnert, Göran, Sjöstrand, Henrik, Skiba, Mateusz, Weiszflog, Matthias, and Zychor, I.

Abstract

In this work, an investigation of the neutral gas flow in the JET sub-divertor area is presented, with respect to the interaction between the plasma side and the pumping side. The edge plasma side is simulated with the SOLPS code, while the sub-divertor area is modeled by means of the direct simulation Monte Carlo (DSMC) method, which in the last few years has proved well able to describe rarefied, collisional flows in tokamak sub-divertor structures. Four different plasma scenarios have been selected, and for each of them a user-defined, iterative procedure between SOLPS and DSMC has been established, using the neutral flux as the key communication term between the two codes. The goal is to understand and quantify the mutual influence between the two regions in a self-consistent manner, that is to say, how the particle exhaust pumping system controls the upstream plasma conditions. Parametric studies of the flow conditions in the sub-divertor, including additional flow outlets and variations of the cryopump capture coefficient, have been performed as well, in order to understand their overall impact on the flow field. The DSMC analyses resulted in the calculation of both the macroscopic quantities-i.e. temperature, number density and pressure-and the recirculation fluxes towards the plasma chamber. The consistent values for the recirculation rates were found to be smaller than those according to the initial standard assumption made by SOLPS., For complete list of authors see http://dx.doi.org/10.1088/1741-4326/aa686f

Published
2017
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