ABSTRACT
Given the fluctuating character of two-phase flows, a complete and rational presentation of the describing parameters requires the use of phase density functions and averaging operators. Void fraction is a term that has several meanings. For this reason, its use should be avoided and replaced by the specific name of the quantity dealt with, i.e., local void fraction, line void fraction, area void fraction, or volumetric void fraction. Signal analysis is accomplished through an adjustable threshold, which enables the signal to be transformed into a binary signal. Consequently, the local void fraction is a function of this threshold, which is adjusted and then held fixed during a traverse in order to obtain agreement between the profile average and a γ-ray measurement of the line void fraction. The interest given to finely dispersed bubbly or droplet flow has brought about the development of single fiber optical probes.
