Void fraction measurements of steam-water two-phase flow in vertical rod bundle: Comparison among different techniques

摘要

Void fraction is a fundamental parameter to characterize two-phase flows and is very important for the proper design and safety operation of steam generator in a nuclear power plant. In the present work, void fraction measurements of steam-water two-phase upward flow in a triangular-configured vertical rod bundle were conducted at pressures from 5 to 9 MPa and mass velocities from 100 to 350 kg.m(-2).s(-1). Local, chordal and average void fractions were measured by the optical probe (OP), gamma-ray densitometry (GD), and differential pressure (DP) methods respectively. The effects of pressure and mass velocity on void fractions were investigated in detail. The results showed that a non-uniform distribution of local void fractions could be clearly revealed. The average void fractions obtained by GD and DP were found to approach the volumetric quality under higher pressure and higher mass velocity conditions owing to the homogeneous flow trends. This also occurred under a high volumetric quality condition for the homogeneous vapor flow and low volumetric quality condition for the homogeneous bubble flow. The results obtained from the different techniques were compared for the same experimental conditions. It was found that the void fractions measured by both OP and DP agreed well with that of GD, with relative deviations less than 10% and 15% respectively. Besides, an assessment of four void fraction correlations was carried out to predict the present area-average void fraction data from GD. The results showed that both the Bestion correlation and the Chexal and Lellouche correlation predict the present data well when measured void fraction greater than 0.3.