Numerical investigation of subcooled flow boiling in an annulus under the influence of eccentricity

Abstract

The subcooled flow boiling phenomenon usually occurs in a number of industrial applications, such as Pressurized Heavy Water Reactors (PHWR) and heat exchangers in nuclear power plants. The pressure tube deformation, presence of spacer pads, etc., may result in the eccentricity (e) of the rod bundle which causes coolant flow maldistribution and hence influence the heat transfer characteristics. In the present study, the entire rod bundle is modeled as a single inner rod and Eulerian Eulerian Multiphase Flow (EEMF) and Wall Heat Flux Partition (WHFP) model framework is used to simulate the effect of eccentricity (e). This model is validated against the available experimental data in the literature and found to be in reasonably good agreement. This framework is also compared and contrasted against the subchannel analysis predictions to highlight the importance of detailed CFD simulations. Furthermore, in the present study, the thermal hydraulics of narrow and wide gap regions are numerically investigated in an eccentric annulus. Due to eccentricity, early phase change, higher wall temperature and vapour volume fraction were noticed in the narrow gap region, compared to the concentric case (e=0.0), which is undesirable in the PHWR type reactors.