Ultrasonic pulse-Doppler flow meter application for hydraulic power plants

At hydraulic power stations, Pitot tubes have commonly been used to measure flow rates in steel penstocks for performance testing of hydraulic turbines. Due to the difficulties of Pitot tube installation, transit-time ultrasonic flow meters are becoming a popular replacement, but their accuracy is sensitive to velocity profiles that depend on Reynolds numbers and pipe surface roughness. Ultrasonic pulse Doppler flow meters have recently gained favor as suitable tools to measure flow rates in steel penstocks because they can measure instantaneous velocity profiles directly. Field tests were conducted at an actual hydraulic power plant using an ultrasonic pulse Doppler flow meter, and it was found capable of measuring velocity profiles in a large steel penstock with a diameter of over one meter and Reynolds number of more than five million. Furthermore, two ultrasonic transducers were placed on the pipe surface to validate the multi-line measurement of asymmetric flow. Each transducer recorded the velocity profile simultaneously from the pipe centerline to its far wall during plant operation. Velocity profiles were obtained from three-minute measurements to improve the accuracy of flow rate measurements.     

Performance of the LDA Volumetric Flow Rate Standard Under Severely Disturbed Flow Conditions

Flow meters in thermal power plants are operated at high temperatures and pressures and often encounter disturbed flow profiles. This leads to an increased measurement uncertainty, limiting the safe operating range of flow rates and thus, the plant's power output. To respond to this shortcoming, the laser optical flow rate standard (LFS) was developed. The LFS is designed to allow the on-site calibration of industrial flow meters in power plants at high temperatures and pressures. It makes use of the laser Doppler anemometry (LDA), as a fundamental and non-invasive method, to measure the velocity field simultaneously with two LDA systems. The volumetric flow rate is then determined by means of integration. Here, we present flow rate measurements for a fully developed pipe flow and for six pipe diameters downstream of a disturbance generator. The mean deviation in flow rate between the two LDA systems was 0.05%, with a mean deviation from the gravimetric reference flow rate of 0.12%. The highest deviations from the reference were 0.21% and 0.31%, for the first and second system respectively.     

Diagnostic flow metering using ultrasound tomography

For an accurate flow metering without considering the influences of flow control devices such as valves and elbows in closed conduits, velocity distribution in the cross-sectional area must be integrated. However, most flow meters, including multi-path ultrasonic, electromagnetic or Coriolis mass flow meters, require assumptions on the fully-developed turbulent flows to calculate flow rates from physical quantities of their own concern. Therefore, a long straight pipe has been a necessary element for accurate flow metering because the straight pipe can reduce flow disturbances caused by flow control devices. To reduce costs due to the installation of long straight pipes, another flow metering technique is required. For example, flow rates can be estimated by integrating velocity distributions in the crosssection of conduits. In the present study, ultrasound tomography was used to find the velocity distribution in the cross-section of a closed conduit where flow was disturbed by a Coriolis mass flow meter or a butterfly valve. A commercial multi-path ultrasonic flow meter was installed in the pipeline to measure the line-averaged velocity distribution in the pipe flow. The ultrasonic flow meter was rotated 180° at intervals of 10° to construct line-averaged velocity distributions in Radon space. Flow images were reconstructed by using a backprojection algorithm (inverse Radon transform). Flow diagnostic parameters were defined by calculating statistical moments, i.e., average, standard deviation, skewness, and kurtosis, based on the normalized velocity distribution. The flow diagnostic parameters were applied to flow images to find whether the parameters could discern flow disturbances in the reconstructed velocity distribution.     

Systematic investigation of pipe flows and installation effects using laser Doppler anemometry—Part II. The effect of disturbed flow profiles on turbine gas meters—a describing empirical model

For systematic investigations of installation effects and for finding efficient ways to minimise these effects, a research project was initiated at the PTB. It covers the design of an automated test facility using a laser Doppler anemometer, the measurement of velocity profiles downstream of several pipe configurations and flow conditioners, as well as the measurement of the change in the gas meter behaviour, namely the shift of the error curve due to the disturbed velocity profiles.

Part I of this paper (presented in this issue) describes the test facility for the investigation of installation effects and shows the relation between pipe configuration and disturbed flow profile for a wide variety of pipe configurations and flow conditioners.

The second part compares the error shift of turbine meters with the characteristic of disturbed flow profiles. For this, three flow field parameters are used to quantify the disturbances of the velocity profiles such as the swirl intensity, flatness and asymmetry of the profile. Considering this, an empirical model is presented to explain the error shift of a turbine meter as a function of these three flow field parameters. The model will be verified for three types of turbine meters and the results will be discussed.     

Pitometry as a validation tool for water flow measurement in large diameter pipelines

Accurate measurement of water flow rates in large diameter pipelines is a challenge for water companies that need to produce, transport and distribute increasing quantities of water. To a large extent, this challenge results from the impossibility of recalibration of the flow meters within the periodicity established in the metrological regulations since the removal of a large size flow meter from its site of operation in the field and its transport to a calibration laboratory is in most cases technically and economically impracticable. Because of this scenario, this paper presents the pitometry technique as an interesting alternative to solve problems related to the validation of water flow measurements performed by flow measurement systems installed in large diameter conduits. The technique is based on the determination of the water flow rate by mapping the velocity profile of the water flow inside the pipe by means of Cole type Pitot tubes. The water flow rate is determined in a cross section of the pipe located near and in series to the flowmeter to be evaluated. Based on the results obtained in a great number of water flow measurements already performed by applying the pitometry technique in large diameter pipelines in the field, it is possible to conclude that this methodology is perfectly applicable in the validation of the performance of flow meters installed in these conduits solving satisfactorily the issues related to its operation.     

Flow imaging for multi-component flow measurement

For pseudo-homogeneous flows, measurements of density and mean velocity can give the component mass flow rate of a two-component mixture. However, for accurate measurement of non-homogeneous flow rate, the density and velocity distribution across the cross-section of the pipe must be known. The most practical way of obtaining this information is by using the flow imaging technique.

A recently developed capacitance system gives 60 frames per second images of oil/water flow in a 78 mm pipe. The target spatial resolution is one part in 20 by distance (one in 400 by area). The electrical properties of each imaged boundary are functionally related to the imaged value, so the component ratio of a two-component mixture within a boundary can be measured, although individual particles cannot be imaged. Design data shows how the basic system can be part of a complete system for component mass flow measurement.     

Note: Ultrasonic liquid flow meter for small pipes

An ultrasonic flow meter for small pipes is presented. For metal pipe diameter smaller than 10 mm, clamp-on ultrasonic contrapropagation flow meters may encounter difficulties if cross talk or the short acoustic path contributes to large uncertainty in transit time measurement. Axial inline flow meters can avoid these problems, but they may introduce other problems if the transducer port is not properly positioned. Three types of pipe connecting tees are compared using the computational fluid dynamics (CFD) method. CFD shows the 45° tee has more uniform velocity distribution over the measuring section. A prototype flow meter using the 45° tee was designed and tested. The zero flow experiment shows the flow meter has a maximum of 0.002 m∕s shift over 24 h. The flow meter is calibrated by only 1 meter factor. After calibration, inaccuracy lower than 0.1% of reading was achieved in the laboratory, for a measuring range from 15 to 150 g∕s (0.29 to 2.99 m∕s; Re = 2688 to 26,876).     

An investigation into the effects of installation on the performance of insertion flowmeters

An electromagnetic and a turbine insertion flowmeter were tested in three different flow conditions inside a 0.590-m bore pipe inserted in the National Engineering Laboratory (NEL) large water flow measurement facility. The results were compared with velocity measurements obtained from a laser Doppler velocimeter (LDV). The advantage of using such a reference measurement is that LDV is non-intrusive and does not affect the velocity profile itself.Of the meters tested, one was supplied with a whole meter calibration factor and the other was supplied with a calibration factor for the D/2 position.For both meters, application of the respective manufacturer's blockage correction improved the velocity measurements, reducing the differences between the LDV and corrected insertion meter measurements and the difference between the integrated insertion meter measurements and the gravimetric measurements.Swirling and skew flow profiles were generated by the installation of the NEL designed swirl generator and flow disturber, respectively. Neither of these disturbed profiles affected the performance of either of the meters in terms of accuracy of measurement compared with the LDV readings. The profiles themselves, however, changed the velocities at the D/8 and 7D/8 points, making single point estimates of the mean velocity inappropriate. A complete 13-point traverse, integrated using the method of cubics as described in BS 1042 [1] (Section 2.3: Measurement of fluid flow in closed conduits, 1992), gave acceptable estimates of mean velocity in both swirling and skew flow for both probes.     

Flow rate measurements in turbulent pipe flows with minimal loss of pressure using a defect-law

In the paper, a simple and very accurate measurement technique is presented to determine the volumetric or mass flow rate. It is based on the fully-developed turbulent pipe flow, a new analytical universal velocity-profile over the entire pipe section and a single-point measurement. In combination with an optimized straightener this technique has to show minimal pressure loss, very moderate costs and high measuring accuracy compared to LDA-measurements. It is possible to apply the measuring prinicple to nonisothermal gas flows, too.     

The fractal flow conditioner for orifice plate flow meters

The sensitivity of orifice plate flow meters to the quality of the approaching flow continues to be a cause for concern in flow metering. The distortions caused by pipe fittings such as valves, bends, compressors and other devices located upstream of the orifice plate can lead to non-standard velocity profiles and give errors in measurement. The design of orifice plate meters that are independent of the initial flow conditions of the upstream is a major goal in flow metering. Either using a long straight pipe, or a flow conditioner upstream of an orifice plate, usually achieves this goal.The effect of a fractal flow conditioner for both standard and non-standard flow conditions was obtained in experimental work and also using simulations. The measurement of mass flow rate under different conditions and different Reynolds numbers was used to establish a change in discharge coefficient relative to a standard one. The experimental results using the fractal flow conditioner show that the combination of an orifice plate and a fractal flow conditioner is broadly insensitive to upstream disturbances.The simulation results also show that the device can be used as a part of a flow metering package that will considerably reduce installation lengths. Previous work with orifice plates has shown that a combination of flow conditioner and orifice plate was promising. The results of using a combination of the fractal flow conditioner and orifice plate for non-standard flow conditions including swirling flow and asymmetric flow show that this package can preserve the accuracy of metering up to the level required in the Standards.     

Accurate mass flow and density of bubbly liquids using speed of sound augmented Coriolis technology

Speed of sound augmented Coriolis technology utilizes a process fluid sound speed measurement to improve the accuracy of Coriolis meters operating on bubbly liquids. This paper presents a theoretical development and experimental validation of speed of sound augmented Coriolis meters. The approach utilizes a process fluid sound speed measurement, based on a beam-forming interpretation of a pair of acoustic pressure transducers installed on either side of a Coriolis meter, to quantify, and mitigate, errors in the mass flow, density, and volumetric flow reported by two modern, dual bent-tube Coriolis meters operating on bubbly mixtures of air and water with gas void fractions ranging from 0% to 5%. By improving accuracy of Coriolis meters operating on bubbly liquids, speed of sound augmented Coriolis meters offer the potential to improve the utility of Coriolis meters on many existing applications and expand the application space of Coriolis meters to address additional multiphase measurement challenges.The sources of measurement errors in Coriolis meters operating on bubbly liquids have been well-characterized in the literature. In general, conventional Coriolis meters interpret the mass flow and density of the process fluid using calibrations developed for single-phase process fluids which are essentially incompressible and homogeneous. While these calibrations typically provide sufficient accuracy for single-phase flow applications, their use on bubbly liquids often results in significant errors in both the reported mass flow, density and volumetric flow. Utilizing a process fluid sound speed measurement and an empirically-informed aeroelastic model of bubbly flows in Coriolis meters, the methodology developed herein compensates the output of conventional Coriolis meters for the effects of entrained gas to provide accurate mass flow, density, volumetric flow, and gas void fraction of bubbly liquids.Data presented are limited to air and water mixtures. However, by influencing the effective bubble size through mixture flow velocity, the bubbly liquids tested exhibit decoupling characteristics which spanned theoretical limits from nearly fully-coupled to nearly fully-decoupled flows. Thus, from a non-dimensional parameter perspective, the data presented is representative of a broad range of bubbly liquids likely to be encountered in practice.     

A neural network to correct mass flow errors caused by two-phase flow in a digital coriolis mass flowmeter

Coriolis mass flow meters provide accurate measurement of single-phase flows, typically to 0.2%. However gas–liquid two-phase flow regimes may cause severe operating difficulties as well as measurement errors in these flow meters. As part of the Sensor Validation (SEVA) research at Oxford University a new fully digital coriolis transmitter has been developed which can operate with highly aerated fluids. This paper describes how a neural network has been used to correct the mass flow measurement for two-phase flow effects, based entirely on internally observed parameters, keeping errors to within 2%. The correction strategy has been successfully implemented on-line in the coriolis transmitter. As required by the SEVA philosophy, the quality of the corrected measurement is indicated by the on-line uncertainty provided with each measurement value.     

Generation,validation and application of dynamic load profiles in flow measurement using cavitating Herschel–Venturi nozzles

Today, utility meters for water are tested for measurement behavior at stable operating conditions at specified flow rates as part of the approval process. The measurement error that occurs during start and stop or when changing between flow rates may not be taken into account. In addition, there are new technologies whose measuring behavior under real-world conditions is only known to a limited extend. To take these facts into account, a new method has been developed and tested to determine the measurement behavior of water meters under dynamic load profiles as they occur in the real application. For this purpose, a test rig for flow rate measurement was extended by a cavitation nozzle apparatus and the generation of dynamic load profiles was validated. For the cavitation nozzles used, possible factors influencing the flow rate, such as temperature and purity of the water as well as the upstream pressure were investigated. Using different types of domestic water meters, the applicability of the dynamic test procedure was demonstrated and the measurement behavior of the meters was characterised.     

为实现节能降耗亟待推广应用流量测量新技术

为加强能源计量、实现节能降耗，在大管径、大流量的使用场合有必要淘汰高能耗的能源计量仪表，并推广应用流量测量新技术。该文将从理论和实验两方面分析和论证这一问题。并提出新的流量计选型原则。     

Approach for Acoustic Transit Time flow measurement in sections of varying shape: Theoretical fundamentals and implementation in practice

This paper focuses on the generalization of the Acoustic Transit Time (ATT) flow measurement method currently embodied in ultrasonic flow meters. First, the existing theoretical fundamentals that cover flow measurement in regular conduits are presented and relevant design features of typical ultrasonic flow meters are described. A detailed derivation of a measurement method for the generalized theoretical fundamentals of multipath ATT flow is then presented. This generalization consists of extending the existing theoretical background in the case of an irregular section, which is defined as a section that has a non-standard shape and/or a varying shape and size, e.g. one that has transition from a rectangular to a circular section. On the basis of the derived generalized theory, the approach for flow measurement in such irregular sections is developed. This approach is then tested numerically using an example of a converging measurement section that represents the water intake of the Kaplan unit. During the test of the new approach, the flow rate and flow profile at the inlet were varied to investigate the effect of such variations on the accuracy of flow rate determination. Results for a significant flow profile and flow rate variations show that the overall error dispersion of the flow rate evaluation is of the order of 0.5%.     

A method based on a novel flow pattern model for the flow adaptability study of ultrasonic flowmeter

Ultrasonic flowmeters are widely used in industry for accurate measurement. Flow adaptabilities of meters in non-ideal flow fields are usually concerned about by researchers. This paper presents a theoretical analysis method to study the measurement performance of ultrasonic flowmeter. For the specific water flow in single elbow pipe, a novel three-dimensional flow pattern model is invented by the trust region Newton algorithm based on computational fluid dynamics simulation results. In order to verify the correctness of the model, a typical ultrasonic flowmeter with single diametric acoustic path is mainly analyzed. By comparing flow adaptabilities of the meter downstream of the single elbow with both the novel theoretic model analysis approach and simulation method, good agreement is achieved. It is indicated that both the three-dimensional model and its invention method are valid for this study, which is not only helpful to get knowledge of characteristics of disturbed flows, but also provides a practical method to study the flow adaptability of ultrasonic flowmeter in non-ideal flow fields.     

Measurement of vertical oil-in-water two-phase flow using dual-modality ERT–EMF system

Oil-in-water two-phase flows are often encountered in the upstream petroleum industry. The measurement of phase flow rates is of particular importance for managing oil production and water disposal and/or water reinjection. The complexity of oil-in-water flow structures creates a challenge to flow measurement. This paper proposes a new method of two-phase flow metering, which is based on the use of dual-modality system and multidimensional data fusion. The Electrical Resistance Tomography system (ERT) is used in combination with a commercial off-the-shelf Electromagnetic Flow meter (EMF) to measure the volumetric flow rate of each constituent phase. The water flow rate is determined from the EMF with an input of the mean oil-fraction measured by the ERT. The dispersed oil-phase flow rate is determined from the mean oil-fraction and the mean oil velocity measured by the ERT cross-correlation velocity profiling. Experiments were carried out on a vertical upward oil-in-water pipe flow, 50 mm inner-diameter test section, at different total liquid flow rates covering the range of 8–16 m³/hr. The oil and water flow rate measurements obtained from the ERT and the EMF are compared to their respective references. The accuracy of these measurements is discussed and the capability of the measurement system is assessed.     

Mass flow measurement of pneumatically conveyed solids using radiometric sensors

This paper describes the design and experimental evaluation of a novel radiometric instrumentation system that has been recently developed for the measurement of velocity, concentration and mass flow rate of solids in a pneumatic pipeline. The system employs a novel multi-beam, micro-sensing field interrogating the entire pipe cross-section to accommodate the irregularity of the solids velocity profile and inhomogeneity of the solids distribution within the pipeline. Experimental results obtained on a pneumatic conveyer circulating ilmenite powder demonstrate that the system is capable of detecting various velocity profiles and solids distributions across the pipe section and providing an absolute mass flow rate of solids within a good agreement to the reference reading from load cells.