Bevir, Michael Keith (1969) Induced voltage electromagnetic flowmeters. PhD thesis, University of Warwick.

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Abstract

This thesis analyses the behaviour of electromagnetic
flowmeters in which the flowrate of a suitably conducting liquid
is measured by means of the e.m.f. induced between two electrodes
by the motion in a magnetic field. The distortion of the field
by the induced currents is assumed negligible, thus excluding the
more highly conducting liquid metals, but the method is well-known
to be suitable for certain liquid metals, water-based
liquids and blood. Attention is concentrated entirely on the
flowmetering device itself and not on any associated electronics.
The idea of the contribution of each element of fluid
moving with velocity v in a magnetic field B to the total electrode
e.m.f. is first put on a sound mathematical basis by the
introduction of a weight vector
W = B∧∇G
where
∇G is a vector entirely determined by the flowmeter and
electrode geometry. The contribution is W.v per unit volume.
The ultimate aim of the flowmeter designer is to make the
meter sensitivity (the electrode e.m.f. divided by the flowrate)
entirely independent of the flow pattern, i.e. of v. The
behaviour of a flowmeter is specified entirely by W and the
necessary condition on W to achieve this sensitivity independence
(an ideal meter) is found to be curl W=0.
It is shown that there is no magnetic field that will achieve
this if point electrodes are used. The condition on W weakens
progressively as more assumptions are made about the flow pattern
and weight functions suitable for different types of velocity profile are defined. The effects of different types of electrode
are also discussed.
This basic theory is then applied, first to a class of ideal
uniform field flowmeters with transverse line electrodes. These
meters can, moreover, be used as valves and flowmeters simultaneously.
Their performance has been experimentally checked.
Secondly the theory of long flowmeters (in which all quantities
are assumed invariant in the flow direction) is exhaustively
discussed.
Thirdly the practically important case of circular meters with
non-conducting walls, point electrodes and short magnetic fields is
examined. In view of the difficulty of manufacturing a magnetic
field that may be mathematically desirable, this problem is by-passed
by first choosing a technologically simple method of producding
magnetic fields for these meters using coils specified by certain
parameters and then analysing the relevant weight-function in terms
of these parameters. Design tables for the case of rectilinear
axisymmetric flow are presented (one specimen), and experimental tests
described which check the performance of designs produced
from these tables.
A different method of producing the magnetic field is suggested
which saves power consumption and enables the field to be more
accurately designed, but to which the tables mentioned above still
apply.
Finally some outstanding problems are discussed.

Item Type:	Thesis (PhD)
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering
Library of Congress Subject Headings (LCSH):	Flow meters -- Design and construction, Electromagnetic devices, Electromagnetic fields
Official Date:	April 1969
Dates:	Date Event April 1969 Submitted
Institution:	University of Warwick
Theses Department:	School of Engineering
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Shercliff, J. A. (John Arthur)
Sponsors:	English Electric Company Limited
Extent:	1 v. (various pagings)
Language:	eng

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