Electromagnetic flowmeter

Shirato, Gotoh, Osasa, and Usami [J. Chem. Eng. Japan, 1, 164— 167 (January 1968)] present a method for determining the mass flow rate of suspended sohds in a liqiiid stream wherein the liquid velocity is measured By an electromagnetic flowmeter and the flow of sohds is calculated from the pressure drops across each of two vertical sections of pipe of different diameter through which the suspension flows in series. 

In a recent study of the transport of coarse solids in a horizontal pipeline of 38 mrrt diameter, pressure drop, as a function not only of mixture velocity (determined by an electromagnetic flowmeter) but also of in-line concentration of solids and liquid velocity. The solids concentration was determined using a y-ray absorption technique, which depends on the difference in the attenuation of y-rays by solid and liquid. The liquid velocity was determined by a sail injection method,1"1 in which a pulse of salt solution was injected into the flowing mixture, and the time taken for the pulse to travel between two electrode pairs a fixed distance apart was measured, It was then possible, using equation 5.17, to calculate the relative velocity of the liquid to the solids. This relative velocity was found to increase with particle size and to be of the same order as the terminal falling velocity of the particles in the liquid. 

Heineman, J. B., J. F. Marchaterre, and S. Metha, 1963, Electromagnetic Flowmeters for Void Fraction Measurement in Two-Phase Metal Flow, Rev. Sci. Instrum. 34(4) 319. (3)... 

Knoll, K. E., 1991, Investigation of an Electromagnetic Flowmeter for Gas-Liquid Two-Phase Flow Measurement, ANS Trans. TANS AO 64 720. (3)... 

Electromagnetic compatibility (EMC), ferrites and, 11 11 Electromagnetic field, 23 133 Electromagnetic flowmeters, 11 654, 669-676 pipe cutoffs in, 11 611 Electromagnetic force compensation (EMFC) technology, 26 234-236 advantages and disadvantages of,... 

Although electromagnetic flowmeters are expensive they are especially suitable for metering liquids containing suspended solids. Furthermore, unlike head flowmeters, they are unaffected by variations in fluid viscosity, density or temperature. Since they are also unaffected by turbulence or variations in velocity profile, they can be installed close to valves, bends, fittings, etc. 

Rotameters, velocity flowmeters, and electromagnetic flowmeters have the advantage that they can be used with a linear scale in which the volumetric flow rate Q is directly proportional to the scale reading s. 

Other important classes of velocity meters include electromagnetic flowmeters and ultrasonic flowmeters. Both are described in Sec. 8. 

Other sensors which are described in Volume 1 (Sections 6.3.7-6.3.9) are the variable area meter, the notch or weir, the hot wire anemometer, the electromagnetic flowmeter and the positive displacement meter. Some of these flowmeters are relatively less suitable for producing signals which can be transmitted to the control room for display (e.g. weir, rotameter) and others are used in more specialist or limited applications (e.g. magnetic flowmeter, hot wire anemometer). The major characteristics of different types of flow sensor are summarised in Table 6.1. Brief descriptions follow of the principles underlying the more important types of flowmeter not described in Volume 1. In many instances such flow sensors are taking the place of those more traditional meters which rely upon pressure drop measurement. This is for reasons of versatility, energy conservation and convenience. 

Measure either change in wire resistance or heating current to determine flow Electromagnetic Flowmeter... 

Jacobson et al. (1966, 1967) studied gastric secretion in relation to mucosal blood flow by an antipyrine clearance technique in conscious dogs with vagally denervated gastric fundic (Heidenhain) pouches. A vagally denervated fundic pouch is so constructed that the entire arterial blood supply is delivered by the splenic artery. A non-cannulating transducer (electromagnetic flowmeter) and a hydraulic occluder were implanted on the vessel. 

Electromagnetic flowmeters can be applied only to solid/liquid slurries that contain electrical conducting liquids. A common problem of EM flowmeters is their temperature dependence for magnet stability. Thermal flowmeters, which measure the heating power that is required to maintain a constant temperature difference between two points along the stream, have not been successful in multiphase streams because varying composition changes the thermal conductivity of the flow rate. 

FIGURE 6-1 Schematic representation of conventional electromagnetic flowmeter. (Source Hoske, 1998)... 

Electromagnetic flowmeters are mainly applied to single-phase conducting fluids, for example liquid metals, water-based industrial liquids, and blood. However, they are also being used to measure solid/liquid flows such as water-based slurries and sludge as long as conductivity of the liquid medium exceeds 50 microsiemens per centimeter (pS/cm). Output signals from an EM flowmeter are basically proportional to the volumetric flow rate, which is applicable to solid/liquid flows only if the solids particles are uniformly distributed in the liquid. Moreover, to obtain the mass flow rate of a solid/liquid flow, the EM flowmeter requires other means to measure solids concentration. 

O Sullivan, V. T. and Wyatt, D. G., Computation of electromagnetic flowmeter characteristics from magnetic field data Part III. rectilinear weight function, J. Phys. D Appl. Phys. 16, pp. 1461-1476, 1983. 

Bulk Velocity. Electromagnetic Flowmeters. An electromagnetic flowmeter is based on the principle of electromagnetic induction as expressed by Faraday s law. An electric current is induced in a conductor when it moves across a magnetic field. The flowmeter consists of a pair of electrodes placed diametrically opposite one another on the same section of pipe (Figure 23). A conductive slurry flowing through the... 

For slurry systems, electromagnetic flowmeters are often installed in a vertical pipe to reduce the risk of solids deposition on one of the electrodes and to avoid inaccuracies caused by asymmetric velocity profiles encountered in horizontal pipes. However, if horizontal mounting is unavoidable, then the meter should never be installed with the electrodes at the ends of a vertical diameter, because the electrode at the top of the pipe would be affected by the occasional air bubble passing (24). 

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