Hostname: page-component-cd9895bd7-lnqnp Total loading time: 0 Render date: 2024-12-19T00:16:07.907Z Has data issue: false hasContentIssue false
  • English
  • Français

A basis for comparing the sensitivities of different electromagnetic flowmeters to velocity distribution

Published online by Cambridge University Press:  20 April 2006

J. Hemp  and
D. G. Wyatt
J. Hemp
Affiliation:
The Nuffield Institute for Medical Research, University of Oxford, Headley Way, Headington, Oxford OX3 9DS Present address: Fluid Engineering Unit, Cranfield Institute of Technology, Cranfield, Bedford MK43 0AL.
D. G. Wyatt
Affiliation:
The Nuffield Institute for Medical Research, University of Oxford, Headley Way, Headington, Oxford OX3 9DS
Get access Rights & Permissions [Opens in a new window]

Abstract

The response of an electromagnetic flowmeter to the flow rate through it should ideally be independent of the velocity distribution of the liquid within it. In general such flowmeters do not exhibit this ideal behaviour and the variation in response with different velocity distributions, for a given flow rate, can be very large. The sensitivity of a flowmeter to velocity distribution is here described in terms of a ‘worst flow’, which is a particular velocity distribution peculiar to a given flowmeter. The ‘worst flow’ is described mathematically in terms of functions which depend upon the design parameters of the flowmeter. The flowmeter response to its ‘worst flow’, for a given kinetic energy of motion, is formulated. This enables a criterion (ε) to be defined which describes the sensitivity of a given flowmeter to velocity profile effects and which permits different flowmeters to be compared in this respect. Methods of evaluating ε are discussed and its value is calculated for a conventional flowmeter, which employs small electrodes and an approximately uniform magnetic field. It is shown that it is possible actually to generate this worst flow in a given flowmeter, by operating the flowmeter in the role of an electromagnetic pump. This could lead to the direct measurement of ε The possibility is discussed of other definitions of ε based on different boundary conditions and constraints and which might lead to a less severe criterion.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 112 , November 1981 , pp. 189 - 201
Copyright
© 1981 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Al-Khazraji, Y. A. 1979 Ph.D. thesis. Dept of Mechanical Engineering, Imperial College of Science and Technology, London.
Al-Khazraji, Y. A., Al-Rabeh, R. H., Baker, R. C. & Hemp, J. 1978 Flow Measurements of Fluids. North Holland.
Bevir, M. K. 1970 J. Fluid Mech. 43, 577.
Bevir, M. K., O'Sullivan, V. T. & Wyatt, D. G. 1981 J. Phys. D, Appl. Phys. 14, 373.
Hemp, J. 1975 J. Phys. D, Appl. Phys. 8, 983.
Shercliff, J. A. 1962 The Theory of Electromagnetic Flow Measurement. Cambridge University Press.
Wyatt, D. G. 1972 In Blood Flow Measurement. London: Sector.
Wyatt, D. G. 1977 In Cardiovascular Flow Dynamics and Measurements. Baltimore: University Park Press.