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E. von Lavante, M. Ishibashi, G. Wendt
INVESTIGATION OF FLOWFIELDS IN SMALL SONIC VENTURI-NOZZLES

Detailed investigation of flow fields assocciated with several sonic Venturi nozzles with small Reynolds numbers used for flow metering was carried out. The range of Reynolds numbers considered in this work extended from 4 × 103 to 4.4 × 104. In the experimental part, global parameters such as discharge coefficient Cd and local flow variables such as recovery temperature Tr were investigated independently at two different scientific institutions. Both discovered flow phenomena that were not explainable using simple linear theories. Therefore, in the numerical part of the present investigation, the corresponding flow fields were simulated using compressible viscous flow solver ACHIEVE. The qualitative agreement of the numerical and experimental results was satisfactory; the comparison enabled the authors to explain most of the physical phenomena observed.

G. Wendt, E. von Lavante
INFLUENCE OF SURFACE ROUGHNESS ON THE FLOWRATE BEHAVIOUR OF SMALL CRITICAL VENTURI NOZZLES

The paper describes the results of experiments carried out with a set of 50 critical Venturi nozzles with diameters between 0.15 mm and 10 mm with special emphasis on small nozzles with diameters of less than 1 mm. All nozzles were shaped in accordance with the current ISO Standard 9300, only the quality of surface finish having average roughness heights between 0.1 mm and 1 mm differed from the requirements of this standard.
The present investigations contain the determination of common relations used to characterize critical flow through Venturi nozzles and their dependence on surface quality. The paper also offers photographs of different inner nozzle surfaces and the results of mechanical throat scans of larger nozzles as well as the results of computational simulations of flow characteristics through a nozzle with comparable imitated surface perturbation.
All results of the investigations come to the same conclusion: No systematic or significant difference between the flowrate behaviour of small critical Venturi nozzles could be found when the surface roughness was changed between 0.1 mm and 1 mm (this range of surface roughness corresponds to the usual manufacturing surface qualities, from common lathe finish to well polished surface). Therefore, critical nozzles can be used without changes in their flowrate behaviour even in cases where the requirements of the valid standards can not be strictly met.

E. von Lavante, A. Zachcial, D. Zeitz, B. Nath, H. Dietrich
EFFECTS OF VARIOUS GEOMETRIC PARAMETERS ON FLOW BEHAVIOR IN SONIC NOZZLES

Numerical analysis of flow fields associated with sonic Venturi nozzles with various modifications of its basic geometry was carried out. The baseline nozzle, used for gas flow metering, was simulated at Reynolds number 1.5 × 105. The modifications included a backward facing step in the nozzle wall just after the throat, suction through the wall and three different diffuser opening angles. The flow was simulated using compressible viscous flow solver ACHIEVE developed by the authors. ln some cases, a noticable improvement in the flowrate and, consequently, increase in the discharge coefficient Cd was achieved.

P. Schley, E. von Lavante, D. Zeitz, M. Jaeschke, H. Dietrich, B. Nath
SIMULATION OF CRITICAL NOZZLE FLOW CONSIDERING REAL GAS EFFECTS

Critical nozzle flow is predicted for high pressure natural gas by way of numerical simulation. The CFD-program used was developed for simulating two- dimensional and axially symmetric, viscous flow. The thermodynamic properties significantly affecting nozzle flow of high pressure natural gas were computed using the AGA8-DC92 equation of state. To verify the present theoretical results, mass flow measurements of natural gas were made using the Pigsar high-pressure test rig. A comparison between theoretical and experimental results is presented for one test case.

J. P. Vallet, C. Windenberger, F. Vulovic, R. Bouard
IMPROVEMENT OF THERMODYNAMIC CALCULATIONS USED FOR THE FLOW RATE OF SONIC NOZZLES

Nozzles operating under sonic conditions are already used widely as reference flowmeters in many countries to measure gas flow rate under pressure. These Nozzles are calibrated, in each of the countries concerned, on approved primary test rigs. The techniques used in these countries today are the fruit of R&D carried out on nozzles for more than twenty years. The outcome has been standard ISO 9300, published in 1990, on the technique for measuring gas flowrates using a sonic nozzle.
In the past years, it was decided to revise the ISO 9300 in order to improve the values of the thermodynamic coefficients used to calculate the mass flow rate through the sonic nozzles.
The paper describes the results of the comparison on the thermodynamic calculations used by the participants to establish the critical mass flow rate through a sonic nozzle. It was initially conducted in line with the activities of EUROMET, a grouping of European flow metering laboratories which were subsequently joined by NOVA, CEESI, and NIST.
The comparison was more specifically made between the methods used by those laboratories to calculate the critical flow function C*. The calculation methods considered were the ISO 9300 standardized equations for dry air and natural gaz, the different versions of the AGA8 method, as well as several other methods developed by the laboratories, some of them based on the free energy equations.
The 1992 version of the AGA8 calculation method appreciably improves the calculation uncertainty of the critical flow coefficient C* for natural gas. The most recent thermodynamic values obtained for dry air using the NEL / Panasati method is more reliable than the method developed on the basis of the Johnson data (basis in ISO 9300 for air).
From this study, the most accurate calculation methods are selected in order to re calculate the results obtained from sonic nozzle international intercomparisons and thus to improve significantly the accuracy of the experimental discharge coefficient equation obtained from all calibration results.
All these results will be used for the revision of ISO 9300.

K. A Park, Y. M. Choi, H. M. Choi, T. S. Cha, B. H. Yoon
CHARACTERISTICS OF SMALL SONIC NOZZLES

Small sonic nozzles (throat diameter 0.28 4.48 mm) were tested in the gas flow standard system. This standard system is composed of two bell provers and 5 column piston provers, compressor, filters, and dehumidifier. The discharge coefficients of small sonic nozzles are obtained and correlated as a function of throat Reynolds numbers with 0.33 % uncertainty at a confidence level 95 %. The tested high Reynolds number was the lower limit of ISO 9300 specifications. The data are useful as data base for revision of ISO 9300.

H. Dietrich, B. Nath, E. v. Lavante, M. Jaeschke, P. Schley , H.-J. Hotze
FLOW METER CALIBRATION WITH SONIC NOZZLES IN HIGH- PRESSURE NATURAL GAS

A new CEN-Standard for gas flow meters requires meters, which working at operating pressures of more than 4 bar to be calibrated accordingly. However in this pressure range, and especially for small flow rates, only a few suitable test rigs exist world-wide. Based on the good experience with sonic nozzles for air at atmospheric conditions, their use for the calibration of gas flow meters in high pressure natural gas is anticipated.
The present paper presents a novel concept for the design and usage of sonic nozzles in high pressure natural gas test rigs. It is based on theory, simulation and measurement results. This concept includes accurate procedures to take into account the gas composition as well as boundary layer and thermal effects of the nozzle flow.

S. Silva, K. Kawakita, M. T. Pereira, M. Cattani, M. C. Salvadori
MANUFACTURE OF DIAMOND SONIC MICRONOZZLES

A process to manufacture diamond sonic micronozzle has been described. Tungsten wires was used as a mold to make diamond microtubes. A pretreatment of the wire surface with diamond powder provided a continuous diamond film deposited by Chemical Vapor Deposition. An acid etching of the tungsten was performed to remove the mold, obtaining a cylindrical diamond micronozzle.

Paulo J. S. Jabardo, Kazuto Kawakita
NUMERICAL STUDY OF CRITICAL FLOW IN SMALL ORIFICES

This paper presents a numerical investigation of critical flow in small cylindrical orifices. Microorifices with diameters ranging from 16 to 423mm with length to diameter ratios (L/D) ranging from 0,6 to 16 were simulated using a numerical solver. Flow simulations were carried out under several back to upstream pressure ratios (Pb / P0) under pressurized (increasing upstream pressure P0) and vacuum (decreasing back pressure Pb) modes of operation. Numerical results were validated by comparing calculated flow rates with experimental data. This comparison showed a good agreement between simulation and experimental data. Results also showed that, when operating with small diameter orifices under vacuum conditions, both the Reynolds number and the volumetric flow rate remain constant at critical flow regime. However, when operating under pressure, the volumetric flow rate refered to the upstream stagnation conditions does not stabilise even at critical flow conditions, and the Reynolds number increases by decreasing the back to upstream pressure ratio.

Luciana Casciny, Nilson Massami Taira
DIVIDED FLOW TECHNIQUE FOR THE CALIBRATION OF GASFLOWMETERS

This article describes the Flow Laboratory necessities for a new facility, and how to extend the calibration flow rate using a meter with no moving parts, easy to operate and with low uncertainty. The proposal alternative is using two meters in parallel as the working standard: one sonic nozzle and one rotary piston (CVM) its the measurement uncertainty and some results.

Page 407 of 977 Results 4061 - 4070 of 9762