Temporal and Spatial Two-Medium Void Distributions by Radiation Diagnostics

Abstract

<p>Two specific aspects of penetrating radiation diagnostics for application to two-phase flow systems were investigated. In Part I, discrete time interval attenuation measurements of a neutron beam from a research reactor were used to study the effect of the gating (measurement) period on the resulting void probability density distributions. Three idealized two-phase situations were investigated - discrete bubble, slug, and annular flow, for 0.01-10.0 s gating periods. The slug flow condition was readily characterized by a dual maxima PDD for gating intervals below the dominant slug period. In all cases the PDD variance increased with decreasing gating periods and was found to be of use for trend description and regime discrimination. Part II endeavours to reconstruct in two dimensions, the time-averaged void distribution of a dual density system from radiation attenuation measurements. The procedure employed made us of three contemporary algebraic reconstruction methods. Projection data was obtained from a digitized computer model in the first set of tests and later from traverses of a neutron beam across a voided lucite model. With a fixed, large beam size, decoupling of overlapped measurements was needed to permit resolution of fine detail. Extension to the dynamic two-phase flow situation was considered and it was shown that the void variance within a subdivided measurement interval can provide an estimate of the dynamic void bias effect.</p>