Ultrasound Velocity Profiling (UVP) is a technique originally developed for studying blood flow in humans. This method was extended in the mid 1980’s to include measurements also in general fluids and has since become an important tool within research and fluid engineering.
UVP is sometimes also called Pulsed Ultrasound Velocimentry (PUV) and it is a technique to measure an instantaneous velocity profile in a liquid flow by echography. With Ultrasound Velocity Profiling (UVP), pulses of ultrasound are transmitted through the pipe where the liquid flows. When the ultrasound hits the fluid, or particles in the fluid, it is echoed back and the returning pulse is measured using a sensor. In this process, when the pulse is reflected by a scattering particle suspended in the fluid, the signal frequency is altered. In other words, there is a slight difference in frequency/time between the pulse sent out and the pulse coming back.
It is however important to note that the classical Doppler effect causing this is only an artefect in UVP systems. This small difference or shifts in positions between transmitted pulses can then be analyzed and related to the local fluid velocity.
The measurement is unidimensional (1D) providing a velocity profile projected along the probing axis. Since the majority of the small scattering particles are assumed to travel at a velocity equal to that of the continuous phase the true velocity distribution along the probing axis is obtained.
Ultrasound Velocity Profiling (UVP) can be combined with simultanous Pressure Difference (PD) measurements over a fixed length of a pipe. This novel method for in-line rheometry, commonly known as UVP+PD, has been developed and optimised by our research team while they were working at RISE - Research Institutes of Sweden AB and Cape Peninsula University of Technology (CPUT). The method is a multi-point version of the traditional single point tube viscometer concept. It allows real-time measurements of radial velocity profiles, volume flow rate as well as acoustic and complex rheological properties directly in-line while under true dynamic process conditions. It has advantages over commercially available process viscometers and and off-line rheometers instruments in being non-invasive, applicable to opaque and concentrated suspensions, having small sensors dimensions and suitable for Industry 4.0.
A number of industrial applications require accurate volumetric flow measurement. Ultrasonic based flow metering has its main advantages where non-invasive and non-intrusive installations are required. Our unique hybridflow meter method combines the transit time and Doppler techniques for accurate industrial flow measurement.
The transit time method
Two transducers are normally installed on opposite sides of the pipe (Z-mode), where one is more downstream than the other as shown in the Figure (right). In this setup one transducer (transmitter) sends pulses to the second transducer which then captures the sound waves after a time delay. The second transducer which was the receiver during the first interval becomes the receiver. The upstream ultrasound signal is delayed and the downstream signal is speeded up by the moving fluid. The line averaged flow velocity for two transducers that are a distance 𝐿 apart along the acoustic axis, can be calculated.
Doppler flow measurement
For this type of flow meters the setup arrangements with a single ultrasound sensor is normally used as shown in the Figure (right). By assuming that the velocity profile is symmetrical about the pipe axis the volumetric flow rate is calculated by integrating half the profile i.e. across the pipe radius. The accuracy can be increased further by integrating profiles from more sensors.
INCIPIENTUS ULTRASOUND FLOW TECHNOLGIES AB
Frans Perssons Väg 6, SE-412 76 Gothenburg, Sweden
Copyright @ All Rights Reserved
Prodly associated with RI.SE-Research Institutes of Sweden