Multiphase flow rate measurement using a novel conductance Venturi meter : experimental and theoretical study in different flow regimes

摘要

Multiphase flows, where two or even three fluids flow simultaneously in a pipe are becoming increasingly important in industry. Although much research has been done to measure the phase flow rates of two-phase flows using a Venturi meter, accurate flow rate measurements of two phase flows in vertical and horizontal pipes at different flow regimes using a Venturi meter remain elusive. In water continuous multiphase flow, the electrical conductance technique has proven attractive for many industrial applications. In gas-water two phase flows, the electrical conductance technique can be used to measure the gas volume fraction. The electrical conductance is typically measured by passing a known electrical current through the flow and then measure the voltage drop between two electrodes in the pipe. Once the current and the voltage drop are obtained, the conductance (or resistance) of the mixture, which depends on the gas volume fraction in the water, can then be calculated. The principal aim of the research described in this thesis was to develop a novel conductance multiphase flow meter which is capable of measuring the gas and the water flow rates in vertical annular flows and horizontal stratified gas water two phase flows. This thesis investigates the homogenous and separated (vertical annular and horizontal stratified) gas-water two phase flows through Venturi meters. In bubbly(approximately homogenous) two phase flow, the universal Venturi meter (nonconductance Venturi) was used in conjunction with the Flow Density Meter, FDM (which is capable of measuring the gas volume fraction at the inlet of the Venturi) to measure the mixture flow rate using the homogenous flow model. Since the separated flow in a Venturi meter is highly complex and the application of the homogenous flow model could not be expected to lead to highly accurate results, a novel conductance multiphase flow meter, which consists of the Conductance Inlet Void Fraction Meter, CIVFM (that is capable of measuring the gas volume fraction at the inlet of the Venturi) and the Conductance Multiphase Venturi Meter, CMVM (that is capable of measuring the gas volume fraction at the throat of the Venturi) was designed and manufactured allowing the new separated flow model to be used to determine the gas and the water flow rates. A new model for separated flows has been investigated. This model was used to calculate the phase flow rates of water and gas flows in a horizontal stratified flow. This model was also modified to be used in a vertical annular flow. The new separated flow model is based on the measurement of the gas volume fraction at the inlet and the throat of the Venturi meter rather than relying on prior knowledge of the mass flow quality x. Online measurement of x is difficult and not practical in nearly all multiphase flow applications. The advantage of the new model described in this thesis over the previous models available in the literature is that the new model does not require prior knowledge of the mass flow quality which makes the measurement technique described in this thesis more practical.