A hybrid multiphase flow model for the prediction of both low and high void fraction nucleate boiling regimes

• Published in: Applied thermal engineering Vol. 178; p. 115625
• Main Authors: Amidu, Muritala Alade, Addad, Yacine, Riahi, M.K.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2020; Elsevier BV
• Subjects: Bubbles; Coarseness; Computational fluid dynamics; Cooling systems; Dispersed flow; Fluid dynamics; Fluid flow; Heat transfer; Hybrid model; Multiphase flow; Nuclear power plants; Nuclear reactors; Nucleate boiling; Numerical prediction; Radial velocity; Slug flow; Slugs; Studies; Temperature profiles; Turbulence; Velocity; Velocity distribution; Void fraction; Wall function, hydrodynamic roughness, subcooled flow boiling; Dispersed flow; Hybrid model; Slug flow; Wall function, hydrodynamic roughness, subcooled flow boiling
• ISSN: 1359-4311; 1873-5606
• DOI: 10.1016/j.applthermaleng.2020.115625

•A hybrid VOF-Eulerian multifluid model is presented.•A turbulent rough wall function is proposed to enhance the prediction of the velocity profile.•The hybrid model reasonably predict the features of low void fraction flow boiling.•The hybrid model could captures large scale interface in high void fraction flow boiling.•Need to extend the wall boiling model to accommodate heat transfer beneath vapor slugs. The improvement of a hybrid (a combination of Volume-of-Fluid (VOF) and Eulerian model) multiphase flow solver for the numerical prediction of high- and low-void fraction flow boiling regimes is presented in this article. These flow regimes could simultaneously occur in core-catcher and in-vessel retention-external reactor cooling systems during a severe accident in nuclear power plant. To enhance the prediction of the low void fraction boiling regime, a turbulent rough wall function model is implemented in the hybrid model to reproduce the impact of coarseness induced by the existence of growing bubbles along the heating wall on the liquid velocity profile. With this wall function, a more accurate prediction of the radial velocity profile is achieved within the uncertainty of the velocity measurements. Moreover, an improved prediction of the radial void fraction is achieved using the model proposed by Lopez de Bertodano for turbulence dispersion force without compromising the prediction of the radial gas velocity profile and radial liquid temperature profile. Although the hybrid model shows potential in capturing the interface and dynamic behavior of large-scale bubbles (vapor slug) for high void fraction regime, the predicted wall superheat is higher than the measured values. This highlighted the need for the extension of the present wall boiling model to cover flow boiling involving sliding vapor slugs on the heated wall.