Ultrasonic Gas Flowmeter Research Articles

Electric spark discharge as an ultrasonic generator in flow measurement situations

In this paper, a gap discharge approach to create acoustic signals for ultrasonic low pressure gas flow measurements is investigated. The objective is to develop an ultrasonic gas flow meter system that is capable of operation in extreme industrial environments. These environments might have extremely high temperatures (1200 °C), moisture, steam, dust, low gas pressure and large transmission distances. Most other types of ultrasonic transducers found show sensitivity to such conditions: their operation suffers, or they may even stop functioning if exposed to such environments. The development of new transducer technology is therefore crucial to allow ultrasonic flow measurements in extreme industrial environments. In this paper, the gap discharge emitter is evaluated as a candidate to be used in these applications. Its capabilities as a sound source are investigated, and its impact on flow meter performance is estimated. It can be concluded that, despite the uncertainties it introduces to a flow meter system, it stands out as a strong candidate to be used as an acoustic emitter in a gas flow meter system for extreme environments.

Ultrasonic-based gas flowmeter for harsh environmental conditions

The applicability of an ultrasonic transit-time gas flowmeter can be extended regarding its gas temperature range (up to 450°C). We used computational fluid dynamics and ray-tracing techniques to investigate thermally-related effects that influence the sound propagation inside the flowmeter. This allowed us to optimize the geometry and the method of how to operate the flowmeter. Our results prove that such a flowmeter can be used to measure pulsating gas flows over wide temperature and velocity ranges such as found in the exhaust gas train of an automotive combustion engine.

Self-Monitoring Ultrasonic Gas Flow Meter Based on Vortex and Correlation Method

Ultrasound is advantageous for gas flow velocity measurements, owing to its high sensitivity to all kinds of turbulences in the streaming fluid. The cross-correlation method and vortex measurement behind a bluff body have been proven to be good. The most important and difficult problem is ultrasound signal processing. A complex modulated signal has be demodulated by undersampling. The real and imaginary parts of the complex signal can be determined by Hilbert transformation. The demodulated phase or amplitude signal can be applied to cross-correlation functions for the detection of flow velocity. The vortex frequency can be detected by a simple analog signal processing device. The combination of vortex and cross-correlation measurements results in a self-monitoring system. The pattern of a group of vortices is used to determine the transition time of the fluid between two sensor pairs. Measurement results show that the relative error of gas flow velocity with the bluff body is evidently smaller than that without the bluff body.

A Capacitance Ultrasonic Transducer With Micromachined Backplate for Fast Flow Measurements in Hot Pulsating Gases

A novel high-temperature resistant capacitance ultrasonic transducer is presented. It is designed for an ultrasonic transit-time gas flowmeter and meets two main requirements not fulfilled by common piezoelectric transducers: First, a special construction based on an oxidized and patterned silicon backplate combined with a metallic membrane enables transducer operation at elevated gas temperatures of up to 600 degC. Second, the geometry and material parameters were chosen to obtain a broadband device that allows high signal slew rates and pulse repetition rates. As proven by measurements in an automotive combustion engine test bed environment, this new transducer suits for internal combustion engine exhaust flow measurements in between the catalytic converter and the end of the exhaust pipe. Preliminary results for the exhaust mass flow (up to 160 kg/h) of a typical automotive engine measured with these novel transducers are given and compared with the mass flow calculated from fuel consumption and air/fuel ratio (lambda)

Adaptive Pulse Repetition Frequency Technique for an Ultrasonic Transit-Time Gas Flowmeter for Hot Pulsating Gases

A technique of using an adaptive pulse repetition frequency (PRF) to operate an ultrasonic contrapropagation transit-time gas flowmeter (UFM) is introduced. This adaptive PRF technique allows transient measurements of hot (up to 450 degC) and pulsating (up to 1.5 kHz) gas flows. Such conditions occur in the exhaust gas of a combustion engine. Here, a UFM with the widely used fixed PRF technique is not applicable, because the large gas temperature variations would prevent a reliable detection of ultrasonic pulse arrival times. Coherently reflected waves are generated within the gas because of the unavoidable acoustic impedance mismatch between the gas and the transducers, and, depending on the gas temperatures, these echoes overlap with the main signal. The adaptive PRF technique overcomes this problem and allows correct pulse detection over the whole temperature range required. The UFM utilizes special high-temperature-resistant capacitance ultrasonic transducers (CUTs) to meet the requirements in terms of operating temperature range and dynamic response. Results, which are obtained with a preliminary laboratory prototype, are presented for the exhaust gas mass flow rate in a otimes 50-mm pipe measured at gas temperatures of up to 450 degC and at PRFs of up to 5.5 kHz, which is an increase in frequency response of one order of magnitude in comparison to existing measurement systems

Self-monitoring ultrasonic gas flow meter

Ultrasound is predestined for gas flow velocity measurements on account of its high sensitivity to all kinds of natural and artificial turbulences in the fluid. Vortex measurements behind a bluff body as well as cross-correlation methods have been proved good. Cross-correlation measurements of natural structures determine the most frequent velocity components in the fluid. Therefore, the measured flow velocity deviates from the real mean flow velocity because of a skewed probability density distribution of the velocity components. Vortex measurements base on the principle that the frequency of the vortices generated in the wake of a bluff body is proportional to the mean flow velocity. The measurement of the periodic vortices with cross-correlation functions leads to the direct determination of the real mean flow velocity. The combination of both measuring methods results in a self-monitoring system.

Study on Direct Measurement of Diesel Exhaust Gas Flow Rate(Transient Characteristics of Ultrasonic Exhaust Gas Flowmeter)

The partial flow dilution system is one of the typical measurement systems for particulate matter emission from diesel engines. In this system, exhaust gas at a transient flow rate should be transferred to a dilution tunnel at a constant split ratio of exhaust gas. The current partial flow dilution system is used under steady-state engine operating conditions in lieu of direct flow rate measurement of exhaust gas. Therefore development of an exhaust gas flowmeter is indispensable in the partial flow dilution system for transient engine operating conditions. An ultrasonic exhaust gas flowmeter had been developed. As for the developed ultrasonic exhaust gas flowmeter, the transient characteristics measuring exactly and instantaneously temperature, pressure and velocity that are the components of the exhaust gas mass flow rate, has not been perfectly verified. We have inspected the transient characteristics of the developed ultrasonic exhaust gas flowmeter by using a laser Doppler velocimeter and numerical calculation. Consequently, an ultrasonic exhaust gas flowmeter has been confirmed to be capable of measuring the exhaust gas flow rate with sufficient transient characteristics.

초음파 가스 유량계 개발 연구

Ultrasonic flowmeters have more advantages than the conventional method using pressure-difference. In these reasons, many advanced nations are already selling the commercial model. In RIST, we have been developed ultrasonic gas flow meter for the localization since a project was been contracted with POSCO in 1997. This paper describes a new ultrasonic gas flowmeter. This ultrasonic gas flowmeter is developed for<br/> accurate measurement of gases in a harsh environmental conditions. It is especially suited for measuring LOG, COG, BFG gases produced in iron & steel making process. In this study, we had developed the commercial model about the first tested model and applied a completed system to the POSCO gas line. Its performance has been proven by extensive field tests for several months in POSCO, iron & steel making company.<br/>

Ultrasonic measurement of gas flow using electrostatic transducers

Ultrasonic gas flowmeters typically use narrowband piezoelectric transducer arrangements for interrogating the flow of gas in a pipe. In this work, the suitability of broadband electrostatic transducers operating at frequencies of up to 1 MHz for ultrasonic measurement of gas flow has been investigated. The transit time method of ultrasonic gas flow measurement was adopted and experiments were carried out using a laboratory test rig capable of producing a range of gas flowrates up to 17.5 m/s. The test rig also allowed easy interchange of different prototype flowmetering sections. Times of flight of ultrasonic waves interrogating the gas flow were measured using separate send/receive electrostatic transducer arrangements. Two flowmeter configurations were considered. The first interrogated the flow at 45° in contra-propagating upstream and downstream directions. The second consisted of an upstream interrogation at 45° to the gas flow and an interrogation made normal to the flow direction. k factors correlating the fluid velocity along the ultrasonic path with the mean fluid velocity in the pipe were calculated using experimental ultrasonic data and anemometer measurements. All transducer configurations were numerically modelled using the computational fluid dynamics software package FLOTRAN © (ANSYS Inc.). Theoretical gas flow velocities for both transducer arrangements were subsequently compared with experimental values and found to be in excellent agreement. A flow-dependent frequency shift of the received ultrasonic signals was also observed simultaneously with the transit time measurement.

High-frequency transducers and correlation method to enhance ultrasonic gas flow metering

Research activities carried out in past years have shown that in gas networks some constraints exist on the frequency at which ultrasonic transducers can be operated. The study of the transmission and attenuation of the signal and noise mechanisms gives us a defined suitable frequency range (K.R. Wild, A European collaboration to evaluate the application of multi-path ultrasonic gas flow meters, paper presented at 4th International Symposium on Fluid Flow Measurement, Denver, CO, 1999). A working frequency of 500 kHz proves to be the most suitable to avoid noise effects. This frequency is above the noise level detected in gas pipelines. Moreover, the signal loss due to attenuation of ultrasound in gas is still negligible. In parallel, the use of this frequency allows the application of efficient numerical techniques such as the cross-correlation method for signal processing. An initial process based on this method has been developed for gas flowmeters. It provides low uncertainty for the parameters involved in the flow measurement process. A single-path flowmeter equipped with this system has been tested on the Gaz de France test facilities. Its accuracy is better than 1.5% from 250 to 1000 m 3/h without initial adjustment. An auto-calibration process also forms part of the system, using a systematic comparison between ultrasonic measurement of sound velocity and a theoretical approach. The signal-to-noise ratio remains large enough to perform the measurements correctly, even with a control valve installed close to the flowmeter.

Effect of wall roughness changes on ultrasonic gas flowmeters

A theoretical flow model has been developed to describe accurately a fully developed velocity profile of a gas flow in pipe lines with wall roughness as parameter. The model applies the Colebrook and White skin friction correlation which has been adjusted based on experimental data from Princeton SuperPipe facilities. This has resulted in a flow profile model in line with the latest views. The model has shown a significant flow profile variation for wall roughness changes. An ultrasonic ray propagation model of a single path meter has been developed to study the influence of the mentioned flow profile variations on ultrasonic meters. The model has been applied for various cases with different Reynolds number and wall roughness. The results of the study confirm field data that ultrasonic meters are affected by wall roughness changes. To quantify the effect for multipath ultrasonic meters the flow meter algorithm and path position is required.

The manufacturing of ultrasonic gas flow meters

From their introduction, ultrasonic flow meters have received a rapid acceptance as being one of the favored measurement methods for high accuracy custody transfer applications in high-pressure gas transmission systems. There are many benefits when using ultrasonic technology; increased rangeability and capacity over conventional measurement technology with unparalleled accuracy are near the top of the list. But in many cases, even more important are the cost savings obtained due to the decrease in maintenance costs and savings in compressor fuel cost by the reduction of the pressure drop through the station. Key elements in the success of the ultrasonic technology are the manufacturing methods and procedures that result in tight tolerances in the geometry of the meter. Whereas the accuracy of the meter is mainly dependent on the quality of the geometry and accuracy of the time measurement, the stated performance of the meter can be guaranteed based on a dry calibration only; a practice identical to the widely accepted orifice measurement. The purpose of this paper is to focus on the influence of the manufacturing tolerances on the uncertainty of the measurement, the dry calibration procedure and the final comparison with the results obtained after wet calibrations.

Computational modeling of dilute gas-particle flows in an ultrasonic gas flowmeter

A computational procedure is presented to predict particle-laden turbulent gas flows in an ultrasonic flowmeter using curvilinear coordinates. The Eulerian-Lagrangian hybrid model is used for the two-phase flow predictions. The turbulent gas phase is formulated using the Eulerian governing equations whereas the particle phase is formulated using the Lagrangian governing equations. The effect of the gas turbulence on discrete particle dispersion is accounted for using a particle-eddy interaction model. An efficient numerical algorithm is described to locate particles with an optimized search path in three-dimensional Eulerian control volumes. Numerical results are compared with experimental measurements for both the gas and particle phases. In addition, the sensitivity of particle deposition onto the meter-duct wall is investigated by using different particle diameters and densities.

Effects of pulsating flow on an ultrasonic gas flowmeter

A series of tests was carried out to assess the effects of pulsating flow on a small-dimension ultrasonic gas flowmeter. Three different parameters were investigated: pulsation amplitude, pulsation frequency and mean flow velocity. The measurements were carried out in air using a 100 D straight pipe upstream of the ultrasonic gas flowmeter. The performance of the flowmeter was tested at mean flow rates from 1.2 to 9.6 m s −1, using four different pulsation frequencies (2, 5, 10 and 20 Hz) with pulsation amplitudes from 0 to ∼70% r.m.s. Our measurements reveal three major phenomena affecting the ultrasonic flowmeter performance. (1) Sampling phenomena, i.e. aliasing: it is shown that a mismatch between the setting of the sampling parameters in the flowmeter and the frequency of the pulsations can result in large positive and negative errors due to aliasing. (2) Errors due to changes of the flow profile caused by an imaginary high Reynolds number due to the pulsating flow: it is shown that these errors are proportional to the pulsation amplitude and inversely proportional to the pulsation frequency. Further, the error caused by a change in the flow profile generally appears in the laminar and transition areas. (3) Non-linearities when averaging very high or low flow velocities, respectively: very large pulsation amplitudes result in instantaneous flow velocities, sometimes exceeding both the maximum and the minimum limits of the calibrated range of the meter. For the ultrasonic meter tested, this results in large negative errors due to non-linearities on the extremes of the error curve of the meter.

The effect of ultrasonic frequency on the accuracy of gas flowmeters

In time-of-flight ultrasonic gas flowmeters, the reflection of ultrasonic energy causes significant measurement uncertainties if a fast response to changing gas flow rates is required. The reflections can be attenuated by using a sufficiently high ultrasonic frequency. The direct signal is, however, also attenuated and this also makes accurate measurement difficult. The selection of the best frequency range to be used for various pipe diameters is given and it is shown that, for a large pipe diameter, the choice is very restricted.

Chirp excitation of ultrasonic probes and algorithm for filtering transit times in high-rangeability gas flow metering

The signal processing used in an ultrasonic high-rangeability gas flow meter using times of flight is presented. The flow meter under discussion uses a combination of continuous wave and chirp signals to measure at low flow velocities, below 20 m/s, and chirp signals alone to measure high flow velocities, above 20 m/s. Because of the need for a pulse compression technique in the signal waveform design the technique of pulse compression and the choice of signal waveforms are discussed. The advantages and disadvantages of amplitude weighting vis-a-vis frequency domain manipulations of the waveforms are also discussed. To eliminate spurious times of flight, a special filtering technique is used, based on assessing the gradient of ascendingly ordered time series of time-of-flight measurements. A summary of user experience with high-rangeability gas flow meters in use on different offshore platforms and in refineries is given. Long-term tests that examined the accuracy of the high-rangeability flow meter are also described.

Effects of flow disturbance on an ultrasonic gas flowmeter

A series of tests are carried out to assess the effects of flow disturbance on a small dimension ultrasonic gas flowmeter. Flow disturbances generated by cone couplings, and single and double elbows are investigated. Measurements with a 100 D straight pipe upstream with a smooth connection to the meter body are used as a reference. Our measurements show that the symmetrical disturbance produced by a cone coupling at a 12 D distance from the transducer path does not impair the performance of the flowmeter. An asymmetrical disturbance, such as a single or a double elbow at the same distance, seems generally to give an underestimation of the flow velocity, resulting in reading errors of −1% or worse. Measurements with straight pipes of 10 D, 20 D, 40 D and 80 D between the disturbance and the flowmeter have also been made showing that 10 D can cause an overestimation of flow velocity. Increasing the length of the straight pipe generally decreases the error. More than 80 D straight pipe between the disturbance and the flowmeter is required to give a result within ±1% of reference conditions. The angle between the elbow plane and the transducer plane is changed from 0 to 315° in 45° steps. The meter error is plotted as a function of inlet angle, showing a clear relationship between these values.

Ultrasonic gas flow meter with corrections for large dynamic metering range

Extreme accuracy is required in sing-around type gas flow meters in the sing-around period measurement. Thus the detection of the ultrasound is critical. Accurate detection of an ultrasound pulse transmitted through gas is not straightforward. Normally a zero crossing technique is applied, where a level trigger determines when to enable the zero crossing triggering. In a flowing gas, the ultrasound amplitude is modulated due to turbulence, humidity and changes in dynamic gas pressure. This introduces uncertainty as to the cycle in which the ultrasound pulse is detected. This in turn results in large errors in sing-around type gas flow meters. This paper discusses a new correction algorithm which will eliminate such trigger errors. To accomplish the verification of the new correction algorithm, a microprocessor-based sing-around gas flow meter, using 500 kHz ultrasound has been designed. The correction algorithm significantly increases the repeatability of this meter. Repeatability better than 0.5% over a dynamic meter range of 1 to 35 has been measured. Limitations of the sing-around method imposed by the new correction algorithm have been derived theoretically.

High-rangeability ultrasonic gas flowmeter for monitoring flare gas

A transit-time ultrasonic gas flowmeter for high-rangeability requirements, such as those encountered in flare-gas flow-metering, is presented. The concept of ray rescue angle for the orientation of the ultrasonic transducers in single-beam transit-time ultrasonic flowmeters is introduced to overcome the problem of ultrasonic beam drift in high-velocity flows. To overcome problems associated with noise at high velocities, a chirp signal is used. To preserve the accuracy of the meter at low velocities near zero flow, a combination of chirp and continuous-wave signals is used to interrogate the flow. Overall system performance is presented, based on results from extensive wind-tunnel tests.

A pulsed phase measurement ultrasonic flowmeter for medical gases.

Pneumotachometers are used to measure instantaneous flowrate in the respiratory gas streams. The presently available devices suffer from lack of linearity, slow response times, and gas density sensitivity. A new design of an ultrasonic gas flowmeter is presented in this paper: We investigate the acoustic characteristics of ring and piston shaped transducers, and describe a sampling method to avoid the error due to reflection. A microcomputer is used to overcome the 360 degrees detection ambiguity problem associated with phase detection technique. This design has been tested in clinical settings and has been shown to give linear response, independent of gas density, and to have a wide dynamic range.