Visualization and measurements of two-phase flows in metallic ducts using neutrons as microscopic probes. 5. Void distribution measurement method for two-phase flow in a round tube

A method was proposed for measuring the radial void distribution of a two-phase flow in a round tube using neutrons as probes. This method involves (1) assuming an appropriate function which could approximate the radial void distribution, (2) deriving a function to approximate the void distribution projected on a plane perpendicular to the incident neutron beam and along the transverse direction (x-direction) by integrating the function of the radial void distribution, and (3) determining parameters in the function of the radial void distribution by the least squares method. It was shown analytically and experimentally that the effect of scattered neutrons and unparallelness of the incident neutron beam, which might affect the applicability of this method, could be corrected and ignored, respectively, by taking an appropriate distance between the converter and the test section. This method was applied to the measurement of a temporally averaged radial void distribution of an air-water flow in a round tube of 3.90 mm inner diameter. It was revealed that complex void distribution with a saddle-shaped profile could be measured by assuming an appropriate function. (author)