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Title: The Implementation Of Toroidal Throat Venturi Nozzles To Maximize Precision In Gas Flow Transfer Standard Applications
Author: P. Delajoud, m. Girard, m. Bair
Source: 2004 Measurement Science Conference
Year Published: 2004
Abstract: The use of toroidal throat critical flow Venturi nozzles for the measurement of the mass flow of gasses is well known and described in ISO and ANSI/ASME standards. A new flow module uses nozzles as the basis of a high precision transfer standard system to cover the range of flow from 0.02 to 40 gs-1 (1 to 2 000 Nlmin-1) and beyond. In the new module, a gas conditioning system defining an isothermal, unidirectional flow stream is combined with a toroidal throat Venturi nozzle. The calculations used to derive flow include secondary corrections not usually considered and are applied at Reynolds numbers well below the limit defined by the ISO standard. The back pressure ratios necessary to assure critical flow in these conditions have been determined experimentally over the full flow range as a function of Reynolds number and at absolute upstream pressures from 20 to 500 kPa for a variety of nozzle sizes. Experiments to evaluate the influence of operating conditions on the measurement precision of the modules have been conducted. The results confirm the suitably of the new design as an intercomparison artifact and as a tool for the dissemination of reference mass flow values.

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