Visualization and Measurements of Two-Phase Flows in Metallic Ducts Using Neutrons as Microscopic Probes. 4th Report. Effect of Image Gray Scale and Pixel Number on Image Quantification.

Abstract

A study on the effects of image gray scale and pixel number on image quantification was performed analytically and experimentally in order to establish a method of measuring multiphase flows using neutron radiography. It was found from a simplified model that the resolution of an object thickness to be measured had logarithmic characteristics for the object thickness, and there is a possibility that the measured void fraction in high- and low-void-fraction regions might include large error. It was shown from the numerical analysis that the measurement error would be within 5% except for the annular flow region with the void fraction greater than 90%, when void fraction of an air-water two-phase flow in a channel with the local gap smaller than 9mm was measured under the condition of the image gray scale=100. It was revealed from a simplified model that the error due to the number of pixels would be within 5% when the number of pixels projecting the object is ten times greater than that projecting the object boundary.