Abstract
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.
Highlights
Numerical simulations have been performed for all 5 piston-cylinder assemblies (PCAs) based on the dimensional datasets provided by the National Metrology Institutes (NMIs) (PTB, Research Institutes of Sweden (RISE), Istituto Nazionale di Ricerca Metrologica (INRiM) and Czech Metrology Institute (CMI))
The effective area of three FPG8601, one FRS4 and one FRS5 in the whole operational pressure range of each device varying between 1 Pa and 15 kPa has been computed
Geometrical data for the PCAs have been provided by PTB, RISE, INRiM and CMI
Summary
In many industrial sectors, such as cleanroom technologies, petrochemicals, pharmaceuticals, storage of nuclear and toxic. The Bhatnagar–Gross–Krook (BGK) kinetic equation, where the collision term of the BE is replaced with a simplified model expression, has been applied in various pressure driven flow configurations and produced excellent results, especially when isothermal flows are examined This approach is valid in the whole range of the Knudsen number which allows the flow to be simulated in a unified manner without the need of combining meso- and macroscale (viscous) approaches. A detailed computational investigation of the gas flow in PCAs is performed via the BGK kinetic model approach and the effective area of the PCAs is computed in the whole range of the operational pressure for both the gauge and absolute modes. The uncertainties due to measurements as well as to the various flow conditions and parameters are considered and their effect on the computed effective area for each device is provided
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