Void fraction uncertainty via measurement with wire-mesh sensors is less than 11% relative to secondary measurement methods (e.g. radiative, high speed camera…) regardless of flow regimes.
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An overview of the algorithms available for the measurement of bubble size, bubble volume, interfacial area, and velocity are presented.
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Wire-mesh sensors are found to be applicable to most flow regimes for the measurement of void fraction, but secondary measurement applicability (velocity, bubble size, and interfacial area) are affected by the intrusiveness of the sensor, sensor physical dimensions, and flow parameters.
Abstract
Void fraction has always been an important parameter in the study of multiphase flows and its measurement has proven difficult over the years. This paper is a state of the art review of the application of conductivity based wire-mesh sensors (WMS) for the measurement of void fraction, bubble size, and gas fraction velocity in multiphase flows and their associated uncertainties. At this point in time there is no golden standard for void fraction measurement, so a large bulk of this work is on the uncertainty of the WMSs relative to other void fraction measurement methods, namely radiative methods. It is shown using the available data that the WMS have a void fraction measurement uncertainty of ±10.5% over a variety of flow regimes relative to other measurement methods. However, the accuracy of the instrument is largely based on its applicability to a particular flow. For example, the WMS is an excellent choice when entrapment in the sensor due to surface tension is minimized resulting in best results at higher flow rates compared to radiative methods. An assessment into the uncertainty of velocity and bubble size measurements is also performed: analyzing the current algorithms available and studies on these measurements in comparison with high speed cameras and ultrafast X-ray tomography. The current functioning form of the wire-mesh sensors were developed by Prasser in 1998 as a tomographic technique for the measurement of void fraction using a conductivity approach, as performed by earlier researchers. Later developments with the senors resulted in various techniques that allow for the measurement of velocity and interfacial area concentration.