Method of Comparison for Calibration of Critical Nozzles

The paper describes primary calibration of high-precision nozzles (HPNs), which have ideal geometries, at critical condition, theoretical calculation of the discharge coefficient to be verified by the primary calibration, concept of fluid dynamical standard using HPN, precise measurement of boundary layer transition in HPNs in terms of flowrate, superfine structure in the critical flowrate, discrepancy which can occur between primary calibrations and field applications of critical nozzles, and 3D flow velocity field measurements based on recovery temperature, which visualizes many interesting phenomena in axi-symmetric transonic flow as shock interactions, acceleration by edge, reflection of shocks, Fano flow and so on.

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Research on collaborative control of double-plunger gas prover based on EtherCAT

Thermal Science ◽

10.2298/tsci191022002x ◽

2020 ◽

Vol 24 (5 Part A) ◽

pp. 2667-2687

Author(s):

Zhipeng Xu ◽

Feipeng Xu ◽

Dailiang Xie

Keyword(s):

Flow Rate ◽

High Speed ◽

Gas Flow ◽

Control Unit ◽

External Diameter ◽

Piston Cylinder ◽

Collaborative Control ◽

Critical Nozzles ◽

Parallel Mode ◽

Working Principle

Piston prover has been widely used as a gas flow standard for its advantages of high accuracy in standard volume, flow stability and repeatability. It has also been employed as the primary gas flow standard in many countries to calibrate meters. However, it is difficult to ensure the uniformity of the inside dimension of the piston, thus the application of conventional piston provers are limited by the maximum calibration flow generated by the piston cylinder volume. In this paper, an improved piston gas prover that mainly consists of two uniform plungers was proposed. Their external diameter constitutes the flow standard. The plungers are driven by servo motor, and the high speed fieldbus EtherCAT has been introduced as the control unit. Hence the two pistons could work collaboratively and operate in three modes: single-piston mode, double-pistons parallel mode, and double-pistons reciprocating mode. Besides generating steady-flow rate, the double-plunger prover can even produce an unsteady-flow rate which could be used to research the dynamic characteristics of flow meters. The structure and working principle of the three modes were carefully introduced. Then experiments for calibrating critical nozzles were carried out, and the results show that the repeatability of the discharge coefficient could be better than 0.06%, and the pressure fluctuation during the process was less than 50 Pa.

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Calibration of Critical Nozzles Against Another One Connected in Series and Its Application

Transactions of the Society of Instrument and Control Engineers ◽

10.9746/sicetr1965.34.698 ◽

1998 ◽

Vol 34 (7) ◽

pp. 698-706

Author(s):

Masahiro ISHIBASHI ◽

Masaki TAKAMOTO ◽

Yu-ichi NAKAO ◽

Toshio YOKOMIZO

Keyword(s):

Critical Nozzles ◽

In Series

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Review of Critical Flowmeters for Gas Flow Measurements

Journal of Basic Engineering ◽

10.1115/1.3658664 ◽

1962 ◽

Vol 84 (4) ◽

pp. 447-457 ◽

Cited By ~ 23

Author(s):

B. T. Arnberg

Keyword(s):

Mass Flow ◽

Flow Measurement ◽

Gas Flow ◽

Flow Measurements ◽

Flow Rates ◽

Real Gas ◽

Discharge Coefficients ◽

Critical Nozzles ◽

Mass Flow Rates ◽

Flow Functions

Critical flowmeters for accurately measuring the mass flow rates of nonreacting real gases were reviewed. Discussions were presented on theoretical flow functions, on parameters for correlating discharge coefficients, and on the importance of real gas properties. The performance characteristics of critical nozzles and orifices of several designs were reviewed. Approaches were discussed to problems which must be researched before the fullest potential of this type of flow measurement can be realized.

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Tests on a turbine-type gas flowmeter with a computerized system containing standard critical nozzles

Measurement Techniques ◽

10.1007/bf02159467 ◽

1989 ◽

Vol 32 (11) ◽

pp. 1092-1094

Author(s):

M. Kh. Khamatov ◽

O. K. Semenova ◽

T. A. Smolina

Keyword(s):

Critical Nozzles ◽

Computerized System

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Relaxation Effects in Small Critical Nozzles

Journal of Fluids Engineering ◽

10.1115/1.2137346 ◽

2005 ◽

Vol 128 (1) ◽

pp. 170-176

Author(s):

Aaron N. Johnson ◽

Charles L. Merkle ◽

Michael R. Moldover ◽

John D. Wright

Keyword(s):

Experimental Data ◽

Degrees Of Freedom ◽

Critical Flow ◽

Worst Case ◽

Relaxation Effects ◽

Critical Nozzles ◽

Rotational Degrees Of Freedom ◽

Computational Fluid Dynamics Cfd ◽

Flow Through ◽

Throat Diameter

We computed the flow of four gases (He, N2, CO2, and SF6) through a critical flow venturi (CFV) by augmenting traditional computational fluid dynamics (CFD) with a rate equation that accounts for τrelax, a species-dependent relaxation time that characterizes the equilibration of the vibrational degrees of freedom with the translational and rotational degrees of freedom. Conventional CFD (τrelax=0) underpredicts the flow through small CFVs (throat diameter d=0.593mm) by up to 2.3% for CO2 and by up to 1.2% for SF6. When we used values of τrelax from the acoustics literature, the augmented CFD underpredicted the flow for SF6 by only 0.3%, in the worst case. The augmented predictions for CO2 were within the scatter of previously published experimental data (±0.1%). As expected, both conventional and augmented CFD agree with experiments for He and N2. Thus, augmented CFD enables one to calibrate a small CFV with one gas (e.g., N2) and to use these results as a flow standard with other gases (e.g., CO2) for which reliable values of τrelax and the relaxing heat capacity are available.

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Mathematical analysis of the effect of the constant temperature assumption in the leak test of PTB Testing Instructions, Volume 25

ACTA IMEKO ◽

10.21014/acta_imeko.v7i1.491 ◽

2018 ◽

Vol 7 (1) ◽

pp. 68

Author(s):

Oscar Yazit Salah García ◽

Carlos Eduardo García Sánchez

Keyword(s):

Constant Temperature ◽

Flow Rate ◽

Test Time ◽

Leak Test ◽

Maximum Value ◽

Critical Nozzles ◽

S Model ◽

The Mathematical Model ◽

Allowable Temperature ◽

Test Result

<p class="Abstract">"PTB Testing Instructions, Volume 25: Gas meters – Test rigs with critical nozzles" (PTB 25) includes a detailed description of a test to evaluate the tightness of the rig (leak test). The mathematical modeling of this test assumes that temperature remains constant, and it is established a maximum allowable change of 0.1 K during the test. PTB 25 defines a maximum value of the leak flow rate as criteria for approval of the test.</p><p class="Abstract">In this work, the effect of the assumption of constant temperature over the leak test result was analyzed. Different processes in which the real leak flow rate was zero and there was a change in the temperature of the system equal to the maximum permissible (according to PTB 25) were simulated, and the leak flow rate calculated by PTB 25’s model was determined. The assumption of constant temperature does not simplifies drastically the mathematical model. It is concluded that PTB 25’s maximum allowable temperature change is too high for most practical situations, leading to errors that exceeds the maximum allowable leakage rate. The factors “test time” and “enclosed volume” have a high effect over the magnitude of the error given by PTB 25’s leak flow rate model.</p>

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