The theory and application of conductance probes for the measurement of liquid film thickness in two-phase flow

The thickness of a rapidly moving, wavy film of water can be continuously measured and recorded using a probe, which consists of two surface-mounted parallel conductors across which a high frequency AC signal is applied. A theory is given which allows prediction of the electrical conductance of the probe as a function of the film thickness and shows how the useful range of particular probe designs can be assessed. The theory, which can be applied to probes in either flat or curved surfaces, also includes the effect of a step change in the film thickness, so that the resolution of the probe may be predicted.