Modelling and Measurement of the Gas Flow Rate in Vertical Annular Gas-Water Flow Using a ‘Conductance Multiphase Venturi meter’

Separated flow in a Venturi meter is highly complex and the application of a homogenous
flow model could not reasonably be expected to lead to highly accurate results. If this is the
case, a gas volume fraction measurement technique at the throat must also be introduced
instead of just relying on the gas volume fraction measurement at the inlet of the Venturi.
This paper presents an advanced Conductance Multiphase Venturi Meter (CMVM) which is
capable of measuring the gas volume fractions at the inlet and the throat of the Venturi. A
new model was investigated to measure the gas flow rate. This model is based on the
measurement of the gas volume fractions at the inlet and the throat of the Venturi meter using
a conductance technique rather than relying on the prior knowledge of the mass flow quality x.
We measure conductance using two ring electrodes flush with the inner surface of the Venturi
throat and two ring electrodes flush with the inner surface of the Venturi inlet. The basic
operation of the electrical conductance technique in a multiphase flow is that the conductance
of the mixture depends on the gas volume fraction in the water. An electronic circuit was
built and calibrated to give a dc voltage output which is proportional to the conductance of
the mixture which can then be related to the water film thickness in annular flow (and hence
to the gas volume fraction). It was inferred from the experimental results that the error of the
measured gas flow rates was within ± 1.9%.