Measurement of the Local Properties of Multiphase Flows

Flows of mixed fluids in pipes are frequently encountered in several areas of
engineering, such as chemical, petroleum and nuclear. Two key parameters
characterising such flows are the local volume fraction distribution and the axial
velocity distribution of the dispersed phase. In order to achieve a further
understanding of the flow properties, vector velocities are important too. A common
intrusive method that is used for acquiring these parameters is the local conductivity
probe. The reason is that conductivity probes are more accurate than other measuring
techniques, such as ERT (Electrical Resistance Tomography) systems, and are
therefore used for the calibration and validation of ERT systems. Also the
measurements from conductivity probes show a more representative distribution of
volume fraction and velocity of the dispersed phase than other non intrusive methods.
They are also useful for validating data produced by CFD (Computed Fluid
Dynamics) simulations.
In this thesis, research has been done on designing probes, and improving the
related signal processing algorithms, and several experiments have been run in
multiphase loops for measuring the local volume fraction and velocity of the
dispersed phase in vertical and inclined pipes and in swirling flows. All these attempts
have recognised an extra problem that is not negligible when using local conductance
probes. This problem is the interaction between the probe and the bubble. It is known
that local probes alter the true value of the bubble’s vector velocity due to the fact that
bubbles are slowed down by the probe.
A number of experiments were performed and a comparison between ERT and
local conductivity probes was made. Both techniques gave velocity distributions of
the dispersed phase which do not agree, showing that ERT is unable to accurately
measure the gas velocity and volume fraction profiles.
Furthermore the current thesis presents results from dual sensor and four
sensor local conductivity probes in steady vertical and inclined air-water and oil-water
flows and in steady swirling flows, and a proposed new design for fabricating a rotary
index dual sensor probe with a new algorithm for the signal processing scheme is
given. This new type of conductivity probe has a relatively small frontal area that
reduces the bubble-probe interaction hence the probe’s effect on the dispersed phase
is less that of other types of probe.