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International comparisons of small gas flow measurements were carried out between the National Institute of Standards and Technology (NIST) in the United States of America and the National Research Laboratory of Metrology (NRLM) in Japan. An NRLM transfer standard package composed of sonic venturis, two pressure transducers, and two temperature sen...
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Due to its simplicity and accuracy, sonic nozzle is widely used in gas flow measurement, gas flow meter calibration standard, and flow control. The nozzle obtains mass flow rate by measuring temperature and pressure in the inlet during choked flow condition and calculate the flow rate using the one-dimensional isentropic flow equation multiplied by...
Sonic nozzles are widely used as flow measurement and transfer standard. The thermal effect of sonic nozzle is significant at low Reynolds number. It includes two correction factors, CT for the thermal boundary layer and Cα for constrained thermal deformation of throat area. Firstly, using the similarity solution, the formula for correction factor...
Citations
... Additional efforts have been spent to compare the apparatuses from different national metrology labs, where at least one of them was the PVTt apparatus (Wright et al 1998b). ...
... Indeed, the PVTt method is the recognized worldwide standard. Workshops have been conducted wherein the US NIST PVTt apparatus has been compared to that of other nations (Wright et al 1998b). ...
The measurement of gas flow rates is of great importance in a wide range of modern technologies. This paper introduces a simple, yet accurate technique for in-house calibration of gas FMs (mass and volumetric) even under harsh environmental conditions such as encountered during field measurement campaigns. The method requires only readily available, low cost components: a vessel of known volume, an air pump, a pressure sensor and a metal plate orifice or a needle valve to act as a CO. The unique property of choked flow in the CO is used here for flow calibration. In the method presented here a vessel is evacuated to below the critical pressure (<0.53 of upstream pressure) and then allowed to refill with ambient air (or some other process gas) under so-called choked flow conditions through the CO. The method presented here leverages that the flow rate upstream of the CO is not only constant but readily determined from (a) the known V VESS , (b) the measured time rate of change of the absolute pressure in the vessel and (c) the ideal gas law. This calculated flow rate can be used for calibration of FMs. The accuracy of the method depends only on the accuracy of the pressure measurement, the timer and the value of the V VESS . The flow rate computed in this way is found to be in excellent agreement (typically 1% difference) with the flow rate measured by a soap film FM (Gilibrator). As expected from theory this method is found to work for all kinds of CFRs (here: various types of metal plate orifices and needle valves were tested), gas types (here: air, Argon, and CO 2 ) and upstream pressures (here: between 650 hPa and 1400 hPa). The accuracy of this technique (∼1%) is as good as that of standard volume displacement methods (e.g. soap film FMs) (typically 1% difference), the standard of laboratory-based flow calibrators, but less expensive and more suitable for harsh environments.
... Piston provers are commonly used as primary standards in the field of gas flow rate measurements (see e.g. [1][2][3][4][5]). In general, piston provers determine the gas flow rate by measuring the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
... It is evident that the integrated sensor is exposed to a lower temperature in the filling part of the measuring stroke than in the exhaust part of the measuring stroke. So, the indication of the prover's integrated temperature sensor Ti/o, which is in general also affected by the dynamic properties of the sensor, is in this case expected to be lower than the actual gas temperature in the measuring cylinder, causing an erroneous estimation of the density of gas in the measurement model(1). This also explains the positive sign of the measurement deviations of the piston prover in the up phase. ...
This paper deals with the quantification of ambient temperature effects on the measured mass flow rate of a gas using a clearance-sealed piston prover. The variations of temperature were simulated by placing the piston prover in a climate chamber. The tests were made for flow rates of air between 13 mg/min and 15 g/min for three different flow cells. The temperature in the chamber and the piston prover, and the deviations of the piston prover’s readings from the flow source, were recorded. The results confirm that the temperature inhomogeneity in the piston prover can be related to the observed mass flow errors, which increase with the magnitude and the rate of temperature change and decrease with the gas flow rate. Placing the measurement cylinder under a protective cover reduces the sensitivity to variable ambient conditions, but introduces a systematic mass flow error, even in the case of a stable temperature.
... M a n u s c r i p t INTRODUCTION Piston provers are commonly used volumetric primary standards for gas flow metering. The general principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature [1][2][3][4][5][6][7]. ...
The leakage flow rate represents an important input quantity in the measurement model for the gas flow rate in a clearance-sealed piston prover, especially when measuring small flow rates. This study deals with the experimental identification of leakage flow effects. The following influences were examined: the flow rate supplied to the piston prover, the inclination of the flow cell, the type of gas and the temperature of the gas. The leakage flow rate was measured during the typical operation of the piston prover using the dynamic summation method. The tests were carried out in a climate chamber to ensure stable and homogenous temperature conditions. It is demonstrated that the leakage flow rate is significantly affected by the piston prover's inclination and the viscosity of the gas, which depends mainly on the type and the temperature of the gas. Based on the experimental findings that confirm the leakage flow rate is inversely proportional to the gas viscosity, a correction model was proposed. The uncertainty analysis shows that reproducibility is the most important component in the combined uncertainty of the leakage flow rate.
... The piston-prover concept is widely used for primary standards in the field of gas flow measurements [1][2][3][4][5][6][7][8][9][10]. The general principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
... The measurement model (2)(3)(4)(5) can be derived from the general model (1) Accounting for the heat exchange effects, which arise due to the temperature difference between the gas flow and the cylinder wall, the density correction factor is modified to [16]: ...
This paper deals with an uncertainty analysis of gas flow measurements using a compact,
high-speed, clearance-sealed realization of a piston prover. A detailed methodology for
the uncertainty analysis, covering the components due to the gas density, dimensional and
time measurements, the leakage flow, the density correction factor and the repeatability,
is presented. The paper also deals with the selection of the isothermal and adiabatic
measurement models, the treatment of the leakage flow and discusses the need for averaging
multiple consecutive readings of the piston prover. The analysis is prepared for the flow range
(50 000:1) covered by the three interchangeable flow cells. The results show that using the
adiabatic measurement model and averaging the multiple readings, the estimated expanded
measurement uncertainty of the gas mass flow rate is less than 0.15% in the flow range above
0.012 g min−1, whereas it increases for lower mass flow rates due to the leakage flow related
effects. At the upper end of the measuring range, using the adiabatic instead of the isothermal
measurement model, as well as averaging multiple readings, proves important.
... The piston-prover concept is commonly used for primary standards in the field of gas flow measurements [1][2][3][4][5][6][7][8][9][10]. Its principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
... The measurement model, as defined by Eqs. (1) and (2), requires that the pressure and temperature measurements are representative for an estimation of the spatially averaged densities in the volumes m V and d V at the times 1 t and 2 t . This requirement can become especially critical for temperature measurements under dynamic conditions, raising questions about the appropriate locations and the dynamic characteristics of the temperature sensors. ...
This paper deals with heat exchange effects in a compact, high-speed, clearance-sealed version of a piston prover for gas flow measurements that has the temperature measurements limited to the time-averaged temperature of the gas flow. A lumped-element mathematical model is used to study the physical background of the heat exchange effects. Experimental testing is performed to validate the theoretical results, estimate the required temperature homogeneity in the piston prover and propose a modified measurement model that considers the heat exchange effects. These effects are almost linearly related to the temperature difference between the gas flow into the piston prover and the cylinder wall, with the sensitivity coefficient being dependent on the measured flow rate. The piston-prover configuration with the gas temperature sensor in the mixed inlet /outlet flow is found to be advantageous in comparison to a measurement of the inlet temperature.
... The piston-prover concept is widely used for primary standards in the field of gas flow measurements [1][2][3][4][5][6][7][8][9][10]. The general principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
... which is originally employed in the piston prover. The measurement model (2)(3)(4)(5) can be derived from the general model (1) using the following assumptions: spatially homogenous gas density in V m and V d at each time instant, 1 ,1 d ρ =ρ and 2 ,2 ,2 m d ρ =ρ =ρ , a thermal equilibrium between the inlet gas flow and the wall of the cylinder and negligible gas compressibility effects in the density correction factor, 1 2 a Z Z Z = = . ...
... The measurement time interval for a specific mass flow rate can be calculated using the measurement model(2). ...
... The piston-prover concept is widely used for primary standards in the field of gas flow measurements [1][2][3][4][5][6][7]. The general principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
This paper deals with the dynamic temperature effects in a high-speed, clearance-sealed realization of a piston prover. A dynamic mathematical model was built to study the temperature variations and to estimate their influence on the flow measurements. The mathematical model is formulated on the basis of lumped-element models of the piston and the gas cavity. The energy balance for the gas cavity includes the convective heat exchange with the surroundings. One of the potential effects results from the temperature differences between the inlet gas flow and the cylinder wall. In addition, the piston prover's operation generates dynamic temperature variations, which are mainly related to the pressure change due to the flow redirection and to the pressure oscillations due to the piston's resonance effects.
... The piston-prover concept is widely used for primary standards in the field of gas flow measurements1234567. The general principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
The dynamic pressure effects and their corrections in a high-speed, clearance-sealed realization of a piston prover for gas flow measurements are discussed. The experimental results show the deterministic, rather than stochastic, nature of the dynamic pressure conditions and, consequently, the repeatable nature of their influence on the flow measurements. The experimental validation proves the advantage of the polytropic/adiabatic pressure correction model, which was proposed by the authors, as compared with the isothermal pressure correction model. The paper ends with an estimation of the measurement uncertainty related to the pressure corrections using either the adiabatic or isothermal model.
... The piston prover represents a common gas flow primary standard12345. Its principle of operation is based on determining the time interval that a piston needs to pass a known volume of gas at a defined pressure and temperature. ...
A piston prover determines the gas flow rate by measuring the time interval that a movable piston inside a cylinder needs to pass a known volume of gas at a defined pressure and temperature. This paper deals with the dynamic effects related to the operation of a high-speed, clearance-sealed realization of the piston prover concept. Its dynamic characteristics are analysed by means of pressure-response measurements and lumped-element mathematical modelling. The experimental results show that the pressure oscillations during the timing cycle increase significantly above a certain flow rate and have multiple frequency components. They could be related to the resonance effects of the piston oscillator, which is excited by the flow instabilities of the gas flowing in the cylinder below the piston. The simulations show that the sensitivity to the dynamic pressure effects depends on the properties of the thermodynamic gas processes being adiabatic, polytropic or isothermal. A new, modified flow equation of the piston prover, which considers the polytropic index as an input variable, is proposed.
... Comparisons conducted with this transfer standard between five national laboratories between 1996 and 1998 showed agreement generally better than ±0.2 % (Nakao et al., 1999). The CFV's used in the transfer standard have shown calibration stability of <0.02 % (Wright et al., 1998). Rotary gas meters, positive displacement meters, or Roots type meters were used as transfer standards in EUROMET Projects No. 419 and No. 425. ...
National metrology institutes around the world have embarked on an effort to compare their primary gas flow standards under the supervision of the Comité International des Poids et Mesures and its Working Group on Fluid Flow. As the pilot laboratory for the key comparison of low-pressure gas flows below 1500 L/min (CCM.FF-K6), NIST is designing the transfer standard package with the assistance and advice of the other participants. A number of topics are studied as part of the transfer standard design process. An analysis of the flow ranges and types of primary standards used by the possible key comparison participants based on their Calibration and Measurement Capabilities is given. The goals of the key comparison and the desirable characteristics of the transfer standard are considered in a general way. Next, a survey of the gas flow comparison literature suggests that laminar flow elements a nd critical flow venturis are the most practical candidates as transfer standards. These two flowmeter types are compared analytically and experimentally regarding their sensitivity to the external influences of temperature and gas composition. Finally, the calibration stability for these two flowmeter types is considered.
