Ultrasonic flow measurement

Foster, G. A., Karplus, H. B., and Mulcahey, T. P., Multipath Ultrasonic Flow Measurements in Water, A Final Report, Argonne National Laboratory Report, 1985 ANL-85-14. 

Apart from echocardiography, another promising clinical application of synthetic microbubbles is the ultrasonic monitoring of local blood flow in the abdomen (analogous to the earlier use of gas microbubbles to monitor myocardial perfusion (ref. 443)). Such refined ultrasonic blood flow measurements, utilizing injected... 

The principal classes of flow-measuring instruments used in the process industries are variable-head, variable-area, positive-displacement, and turbine instruments mass flowmeters vortex-shedding and ultrasonic flowmeters magnetic flowmeters and more recently, Coriolis mass flowmeters. Head meters are covered in detail in Sec. 5. 

Devices such as ultrasonic flow equipment use the Doppler frequency shift of ultrasonic signals reflected from discontinuities in the fluid stream to obtain flow measurements. These discontinuities can be suspended solids, bubbles, or interfaces generated by turbulent eddies in the flow stream. The sensor is mounted on the outside of the pipe, and an ultrasonic beam from a piezoelectric crystal is transmitted through the pipe wall into the fluid at an angle to the flow stream. Signals reflected off flow disturbances are detected by a second piezoelectric crystal located in the same sensor. Transmitted and reflected signals are compared in an electrical circuit, and the corresponding frequency shift is proportional to the flow velocity. 

Cross-correlation flowmeters in combination with concentration detectors are available for the measurement of the mass flow of solids in pneumatic conveying systems or for volumetric flow measurements. The cross-correlation flowmeter uses a microwave (or gamma ray, ultrasonic, or photometric detectors) as the densitometer and a measurement of the time it takes for particles to travel a known distance to determine velocity. 

There are many other flow measurement devices including Onlicc/Venturi meters, turbine meters, and more sophisticated instruments using ultrasonic, magnetic, and Coriolis effect techniques. Orifice/Venturi type meters have a restriction causing a pressure drop related to the flow rate of liquid. Such meters are popular because of their low cost however, their accuracy can be compromised by upstream elbows and valves. Turbine meters are designed so that rotation speed varies linearly with the... 

In addition to the originally described method, it is possible to measure blood flow by means of an ultrasonic flow probe, attached distally to the position of the cotton threads on the vein. 

In principle, the ultrasonic techniques described for solid-liquid flow measurement can be applied to measure air flow rate and particle velocity. Direct measurement of air flow rate by measuring upstream and downstream transit times has been demonstrated. But, the Doppler and cross-correlation techniques have never been applied to solid/gas flow because the attenuation of ultrasound in the air is high. Recent developments have shown that high-frequency (0.5-MHz) air-coupled transducers can be built and 0.5-MI Iz ultrasound can be transmitted through air for a distance of at least 1 in. Thus, the cross-correlation technique should be applicable to monitoring of solid/gas flow. Here, we present a new cross-correlation technique that does not require transmission of ultrasonic waves through the solid/gas flow. The new technique detects chiefly the noise that interacts with the acoustic field established within the pipe wall. Because noise may be related to particle concentration, as we discussed earlier, the noise-modulated sound field in the pipe wall may contain flow information that is related to the variation in particle concentration. Therefore, crosscorrelation of the noise modulation may yield a velocity-dependent correlation function. 

Sheen, S. H., Raptis, A. C., Bobis, J. P., Lee, S., and Simpson, T., Evaluation of Active Ultrasonic Cross-Correlation Technique in Coal/Liquid Pipe Flow Measurements, Argonne National Laboratory Report, 1985 ANL/FE-85-12. 

Ultrasonic Flowmeters. Ultrasonic methods have been used to measure flow velocity and concentration in slurry pipelines (22) and emulsion pipelines (65). There are three methods of ultrasonic flow meter applications transmission of ultrasonic wave, beam deflection, and frequency shift method (22). The frequency shift method (the ultrasonic Doppler flowmeter) consists of a transducer and an electronic control box. The transducer is either clamped on the outside of the pipe or inserted into the pipe so that it is flush with the inside of the pipe wall. The transducer comprises the sensors to transmit and receive the Doppler signal. These sensors are either in a single transducer or in two separate transducers. The control box processes transmitted and received signals (Figure 25). 

Time-of-flight ultrasonic flow meter multipath type. (Adapted from Miller, R. W., Flow Measurement Engineering Handbook, New York McGraw-Hill, Inc., 1989.)... 

Anemometry is a general term to represent the measurement of wind speed— anemos is the Greek word for wind. The earliest anemometer for meteorology is credited to Alberti in 1450. Hooke reinvented the device, which relied on cups or disks mounted on a pole that would rotate by the force of wind. Modern instruments to measure wind speed rely on laser Doppler shift, ultrasonic waves, propellers, and hot wire anemometers. The hot wire anemometer is commonly used for fluid flow measurements and in particular for research applications that require a detailed analysis of velocity in localized areas or for conditions... 

B. Schrope, V. Newhouse, V. Uhlendorf, Simulated capillary blood flow measurement using a nonlinear ultrasonic contrast agent, Ultrason. Imaging 14 (2) (1992) 134-158. 

In the injection molding of PLC, the nematic melt is subjected to both shear and elongational stresses during the filling of the mold. Therefore the flow pattern of the melt is more complicated than in extrusion. Because of this, all the ultrasonic modulus measurements have been made only on samples cut from the middle sections of plaques or bars ([7-9], C.L. Choy, Y.W. Wong and K.W.E. Lau, unpublished results). Since this section is at some distance from the gate of the injection mold, the melt has a straight flow front across almost the entire width of the mold. Consequently, this section of the solidified material has orthorhombic symmetry and is characterized by the nine stiffness... 

Flow and pressure sensors A very important parameter that is often measured in most industrial process streams is flow rate. The range of flow sensors that are available for measuring liquid and gas flow rate in industrial process streams is summarized in Table 2. Of these, the accuracy, resolution, and cost of ultrasonic flow sensors are attractive and comparable to other flow sensors. Furthermore, it is now possible to use this flow sensor to monitor process... 

Some flow calorimeters (continuous calorimeters) make use of air as a heat transfer medium in other cases, gases or liquids react with each other or are products of the reaction. In the latter case, a possible approach to the measurement of amounts of substances consists in allowing the newly formed phase (usually a gas) to leave the system via a flow meter. Here the flow rate provides a measure of the quantity of substance transformed per unit time. Usually a pressure difference is the measurand as in capillary flow meters or is caused by the back pressure of the measuring instrument however, the possibility of pressure rises (caused by a buildup ) in the vessel must be taken into account. Other techniques for measuring amounts of gas make use of displacement gas meters, turbine meters, or ultrasonic meters. In these cases, the volume flow is the measured quantity. For measuring the mass flow, Coriolis or thermal mass flow meters can be used. In any case, it is very difficult to reduce the uncertainty of flow measurements below approximately 1%. This can only be achieved in exceptional cases when great effort is made to calibrate the meter with fluids of similar and known thermophysical properties (e.g., heat capacity, thermal conductivity, viscosity, density, etc.). 

Rotameter Ultrasonic type Turbine flow meter Electromagnetic flow meter Good for upstream flow measurements Used in conjunction with variable inductance sensor Good for very high flow rates Can be used for both upstream and downstream flow measurements Not suited for fluids containing abrasive particles Relationship between flow rate and angular velocity is linear Least intrusive as it is noncontact type Can be used with fluids that are corrosive, contaminated, etc. The fluid has to be electrically conductive... 

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