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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]

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]

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]