A two-dimensional void fraction distribution fast prediction model and application to a rod bundle

Abstract

Accurate prediction of void fraction distribution is essential for system optimization, design, and safety analysis which involves gas-liquid two-phase flow. This paper introduces a novel conceptual two-dimensional Void Fraction Distribution Fast Prediction model (VDFP) designed to rapidly predict the void fraction distribution of fully developed two-phase pipe flow. By achieving this, the N-S equations were simplified into a readily solvable Laplacian form. The simplification was based on two assumptions: 1) For the steady simulation of fully developed pipe flow, the convective and axial diffusion terms in the time-averaged N-S equations are negligible; 2) The pressure field can be predefined as linearly decreasing along the axial direction while ignoring the radial pressure difference. After determining the axial velocity distribution, the void fraction distribution can be calculated through the balance of interfacial forces (lift force, wall lubrication force, and turbulent dispersion force) in the radial direction, which has a solid physical foundation and is applicable across a wide range of operating conditions. The feasibility of the VDFP model was validated by comparing the predicted results with experimental data of air-water two-phase flow in a rod bundle channel with a rod diameter of 25 mm and a rod pitch of 34 mm. Additionally, considering the constraints imposed by the rod bundle subchannel, the impact of bubble geometric restrictions on void fraction prediction was also evaluated. The validation results indicate that the VDFP model predicts the wall peak and core peak void fraction distribution results with satisfactory accuracy, and its solving time is <3 s, showing considerable potential for further reduction.