Computation of the effective area and associated uncertainties of non-rotating piston gauges FPG and FRS

The effective areas of three force-balanced piston gauges (FPGs) and two Furness Rosenberg standards (FRS) in the operating pressure range of each device varying for 1 Pa–15 kPa have been accurately computed both in the gauge and absolute modes. Geometrical data for the non-rotating piston-cylinder assemblies (PCAs) have been provided by the National Metrology Institutes (NMIs) of PTB, RISE, INRiM and CMI. Since the flow is in a wide range of the Knudsen number, simulations have been based on the Batnagar–Gross–Krook (BGK) kinetic model equation, while the typical Dadson and CFD approaches have been complimentary applied only in the viscous regime. Furthermore, an uncertainty analysis has been performed. The effective area is strongly affected by the PCA geometry and the flow conditions, while its dependency on pressure may be different even for devices of the same type. The main source of uncertainty is the dimensional measurements of the piston and the cylinder, followed by the accommodation coefficient characterizing the gas-surface interaction, while the effect of other flow and modeling parameters is negligible. The total relative standard uncertainty of the effective area has been always found to be less than 1 · 10−5 indicating that pressure measurements of high accuracy can be ensured. Since the effective area is estimated based solely on computations the FPG and the FRS assemblies may be characterized as primary pressure standards

Uncertainty propagation analysis of the computed ITER torus effective pumping speed during the dwell phase

At the University of Thessaly the ARIADNE code for modeling complex gas distribution systems operating under any vacuum conditions has been developed by integrating a kinetic database to a typical gas network solver. The ARIADNE code has been successfully implemented to model the ITER primary pumping system providing the torus effective pumping speed, as well as the pressure evolution during the dwell phase. However, the computed results are subject to the input data, which include the pipe network geometry, approximating the real geometry of the ITER primary pumping system and the operating data, such as the torus pressure, gas temperature and cryopump pumping speed. The effect of the aforementioned input quantity uncertainties to the torus effective pumping speed is investigated via an uncertainty propagation analysis by coupling the Monte Carlo method (MCM) with the ARIADNE code. Documenting the propagation of each input parameter uncertainty to the torus effective pumping speed uncertainty is beneficial for judging the accuracy of the modeling and simulation results, as well as for identifying the most important sources of uncertainty. Furthermore, the presented methodology can be used to investigate the uncertainty propagation of any input quantity to any output quantity for vacuum systems of arbitrary complexity

Pressure and temperature driven fully-developed rarefied gas flow in a channel with uniform injection/suction through its permeable walls

The pressure and temperature driven fully-developed rarefied gas flow between two parallel permeable plates, with uniform gas injection and suction from the bottom and top plates respectively, is investigated, based on the linearized Shakhov (S) model and the linearized Boltzmann equation (BE). Both flow configurations are characterized by the gas rarefaction parameter and the injection/suction velocity magnitude. Computational results for the so-called kinetic coefficients, as well as for the macroscopic quantities are provided in a wide range of the two parameters. The Onsager-Casimir reciprocity relation between the mechanocaloric and thermal creep coefficients has been proven to hold for arbitrary values of the injection velocity and has been used to validate the accuracy of the obtained results. It is shown that, the kinetic coefficients and macroscopic quantities are significantly affected as the injection velocity is increased. In addition, the kinetic results properly recover the corresponding analytical solutions in the free molecular and slip regimes. The examined prototype rarefied injection/suction flows may be useful to the investigation of more complex and realistic flow configurations in channels of various cross-sections with permeable walls where the injection velocity is not constant in the whole flow domain