Car gas sonic nozzle flow verification system
Published on:2014-12-31 10:46:10 Hits:

Abstract: This paper introduces a new type of automotive gas turbine flowmeter calibration system. The system consists of a computer-controlled CNC nozzle switching valve that can automatically select either 11-caliber sonic nozzle in accordance with a flowmeter calibration gas turbine flowmeter under operating conditions; at the same time the system also has a gas chromatograph Miriam and combine complete sonic nozzle gas mass flow calculations. The article also describes the process flow diagram with sonic nozzle gas turbine flowmeter calibration mass flow equations and formulas passenger traffic volume, and test the system. Using this system, gas turbine flowmeter calibration can be performed directly by the computer temperature, pressure correction, improve test accuracy.

I. Introduction

Arkla Pipeline Group, an automotive research sonic nozzle calibration device that can test gas turbine flowmeter under actual working conditions, accredited meter diameter at 3-16 in. This verification system combined with gas chromatography, gas mass flow calculation is completed.

The verification system approach than in the past has been greatly improved. In most cases, at atmospheric pressure turbine flow meter used for verification of operating state, the original instrument constant drift will occur. The use of sonic nozzle under actual operating pressure and temperature conditions to overcome this lack of verification. In addition, the sonic nozzle system using natural gas instead of air as a medium, but also removed the error introduced by the air.

Car test system can test the entire turbine metering systems, rather than just test a turbine flowmeter. This means that the error is caused by the pulsation can be detected, which is any other verification systems can not do.


The basic definition of sonic nozzle flow is: In the case of the other parameters remain unchanged, when the nozzle downstream pressure is reduced to a certain point, even if the downstream pressure continues to drop, it will not cause the mass flow rate of the nozzle throat is further increased. At this point, the gas velocity at the sonic nozzle throat, known as the "critical flow", "sonic flow" or "choke." Gas mass flow can be accurately determined from the nozzle throat. Early on, the need in the nozzle inlet and outlet pressure is reduced to 50%, in order to obtain the speed of sound, but now the pressure drop can be as small as 5%, while the typical voltage drop does not exceed 10%, which can get the speed of sound.

Third, the equipment onboard calibration device

1, an onboard board room, which was partitioned into the computer room, valve rooms, the air compressor and between the power supply. This will separate the danger zone and non-hazardous areas.

2, a computer control system, including an IBM. 386 computer, which has a 120 MB hard disk 32 printer and a remote terminal (RTU). Remote terminal is the interface between computer and CNC valve, it has to control the output, the state of the input and output switching analog input control solenoid pneumatic valve - Each nozzle has a solenoid valve. Each actuator provides a status input signal by two reed switches, reflecting the position of the actuator, by a microcomputer which nozzle in the working state determination. State of the input signal from the air compressor may indicate the air pressure drops below 751b / in 2 (tables) below, the pressure is the minimum operating pressure of the NC valve. Analog input on behalf of the turbine flowmeter operating temperature and pressure (two inputs), the pressure valve inlet and outlet (three inputs) and the valve inlet temperature (a little input).

3, a Daniel gas chromatograph, which is a key device in the test system. GC once every 6min gas composition analysis in real time, and the results via a RS. 232 communication interface delivered to your computer. Computer applications of molecular weight percentage calculated for the two variable quality formula. Gas chromatograph bar recorders and controllers are installed in the computer room non-hazardous areas. Chromatograph sampling probe is mounted on the pipeline valve NC danger zone.

4,2 verification system to make a power supply unit to maintain the operation. A 2.8kW unit drive small loads, such as chromatography, computer and RTU. A 7kw a motor driven air compressor and an air conditioner.

5, an air compressor to provide 1hp 100lb / in 2 air (Table) pressure to the solenoid valve NC valve to operate the spray

Mouth. The gas source is also used to start a small hand tools.

6, connecting pipelines, by two caliber 4in, a long flexible tube connected to 14ft of instrumentation and test systems were seized. A connection is to test the device import checklist, and another test device is connected to the return line outlet. Each connector has a high pressure quick connectors, pipeline operating pressure of 550lb / in 2 (table).


7, the switching valve NC, NC valve 1 shown in FIG weight 1100lb, it has 11 alternative sonic nozzle channel, which in binary mode control. Since the maximum of two nozzles into the largest channel function and logic control. 10bit binary control valve to the CNC resolution. The result is an incremental order flow for 58.7Ac Hoon Cheng. RIU's electrical control signal controls the pneumatic solenoid valves switch, while controlling a pneumatically operated solenoid valve so that the sonic nozzle into operation. Cylinder in the middle of the valve, with sufficient energy, even if the air supply interruption still allowing rotation of the valve twice.

There are four connection holes CNC Body: two inlet and two outlet. Connectors for temperature transmitters imports and import and export of pressure transmitter. Because the inlet pressure should be very precise, an inlet pressure transmitter should be installed 2, its measuring range are 0-75lb / in 2 (table) and 0-200lb / in 2 (table). When the pressure reaches a first pressure transmitter range of 95%, the computer will load the instrument to convert a pressure change from the first to the second pressure change. Once there is a nozzle opening, the gas from the inlet into the nozzle, and then the casing 4 from the nozzle exits into the outer casing, and then flows out of the valve body.

Fourth, the basic flow equation

Calculate the mass flow verification device using the following formula


Where: mass flow M- condition state, lb;

P- casing pressure, 1b / in 2 (absolute);

A- nozzle throat cross-sectional area, in 2; range Arkla nozzle diameter is 0.0620-0.9941in, therefore, an area ranging from about 0.003-0.776in 2;

C- critical flow coefficient, which is a function of the specific heat value (such as Ping-flow constant). It is a parameter related to the speed of sound of a gas and the gas flow state. In Arkla system, a representative estimate of the critical gas flow coefficient is 0.7 (dimensionless). The value of pressure and temperature. Analysis calculated for C is the percentage of the molecular weight calculated from by chromatography;

Cd- discharge coefficient, or the actual mass flow rate divided by the number obtained in the theoretical mass flow rate. In short, it is the efficiency of the nozzle design, for different nozzles that are different and are determined by calibration. Arkla nozzle discharge coefficient range of 0.96-1.0 (dimensionless);

R- gas constant, whose value is 48.03 divided by the molecular weight of gas; analyzed by gas chromatograph calculated molecular weight is also used for this gas to be measured;

T- temperature within the housing, R (℉ + 460).

Volume flow is the mass flow rate divided by density, density equal to P / ZRT, volume flow calculated using the formula:


Where: V- volume flow;

Compression coefficient (RCJohnson, not AGA) Z- within the housing, is a value close to 1. GC analysis of gas composition and molecular weight can be used for this calculation;

Rv- gas constant, equal to 2.398 divided by the molecular weight of gas. Molecular weight gas chromatograph are also used for this calculation. R and Rv has been adjusted to engineering units.

V. Verification Process

Gas flows through the turbine flow meter, then through the NC valve and send four signals, shown in Figure 2. Measuring gas pressure and temperature of the two signals, the other two pulse signals from the turbine flowmeter pulse sender and the mass flow signal from the NC valve. It should be noted that the pulse signal from the lower part of the turbine flowmeter conversion gear.


2 verification system flow chart diagram

When the meter revolution, computer measured mounted on the turbine flowmeter send data plate information sent. The first stage gear is an intermediate gear wheel, for Rockwell and the American meter turbine flowmeter, their input-output ratio of 122.0555-l. The second stage gear is change gear, ratio between its input and output 1 and 2 to 1.

Meter counter top speed gear fixed, depending on meter diameter output shaft per revolution counter reading is 100 or 1000 Acf. Of 3-6in meter, than the counter with the output shaft 100: 1; therefore, the above change gear output shaft for each revolution representative 1ft 3, for 8in or more flow meters, counters and ratio between the output shaft is 1000: 1. Results flow meter signal, the intermediate gear, the transmission gear and counter gives the actual conditions of the cubic flow (Acf).

Pressure, volume and temperature (PVT) chart mounted on the upper counter and used to verify the counter.

Computer input instrument temperature and pressure, and apply the instrument to measure the Acfh calculated Scfh (Standard A 3 / h); mass flow rate in lb density value is divided by the standard to obtain data from the computer numerical control valve condition. Flows in the system and later by the NC turbine flowmeter gas valve, which is a constant mass flow throughout.

However, in actual cubic feet of volume flow component as the gas, temperature, pressure changes. Therefore, volume flow and volume flow valve at different turbine flowmeter. For a given mass flow rate, when the gas density increases, the actual volume flow (Acfh) decreases. The volume flow valve is higher than its flow at the turbine meter - this is because the valve inlet pressure below the pressure at turbine flowmeter, the fluid flow rate increased slightly. This is the reason why the valve and flow meter at the pressure and temperature measurements are required.

The difference between the turbine flowmeter Scfh indicated Scfh and CNC valve that is given in the error of the turbine flowmeter flow points. The error percentage is relative to the percentage error of the flow drawn. This percentage is based on the actual flow meter error curve for a special meter ruler constant draw. Computer by entering a different gear ratio can be easily changed K constant (the number of pulses / ft 3).

In order to obtain the smallest error, nozzles of different sizes can be applied by a software program, and by changing the gear ratio of the turbine flowmeter to implement test. Use a software program can save time and effort, but in fact instead of changing the gear ratio and can be used repeatedly for meter calibration, until you get a desired result. 10 test results with different flow point can draw detailed diagrams.

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