A density variant drift flux model for density wave oscillations

Abstract

The present model emphasises on the development of an analytical model to describe density wave oscillation in a heated channel. The study includes linear stability analysis of density wave instability in vertical flow channels for high system pressure conditions. Unlike the previous models where the coolant density in single phase region was assumed to be constant (equal to saturated liquid density at given system pressure), the present work considers the density variation in the subcooled region. Drift flux model has been used to characterise the two-phase flow. The stability characteristics of the system have been depicted by stability boundaries plotted in parameter planes namely phase-change number (Npch) and subcooling number (Nsub). The experimental data sets from Saha et al. (1974) [11] have been re-evaluated and are shown with corresponding operating conditions. Compared to the existing models where the equations run into several pages (Karve, 1998 [8]; Dokhane, 2004 [9]), it is seen that in the presence of linear–linear approximations for single phase enthalpy and two-phase quality that lead to simpler equations, the results obtained show good agreement with experimental data sets. In addition to higher subcooling numbers, the present model also best predicts the stability boundary for lower subcooling numbers.