Abstract
Being able to predict the void fraction is essential for a numerical prediction of the thermohydraulic behaviour in steam generators. Indeed, it determines two-phase mixture density and affects two-phase mixture velocity which enable to evaluate the pressure drop of heat exchanger, the mass transfer and heat transfer coefficients. In this study, the flow is modelled by coupling Ansys Fluent with an in-house code library where a CFD porous media approach is implemented. In this code, the two-phase flow has been modelled so far using the Eulerian model. However, this two-phase model requires interaction laws between phases which are not known and/or reliable for a flow within a tube bundle. The aim of this paper is to use the mixture model, for which it is easier to implement suitable correlations for tube bundles. By expressing the relative velocity, as a function of slip, the void fraction model of Feenstra et al. developed for upward cross-flow through horizontal tube bundles is introduced. With this method, physical phenomena that occur in tube bundles are taken into consideration in the mixture model. The developed approach is validated based on the experimental results obtained by Dowlati et al.
Highlights
Steam generators are heat exchangers used in particular in nuclear propulsion
The developed method consisted of rewriting the relative velocity as a function of slip in order to introduce a slip model adapted to the modelled geometry
The two-phase cross-flow through a horizontal tube bundle was modelled and the slip model of Feenstra et al was used
Summary
Steam generators are heat exchangers used in particular in nuclear propulsion. Water, heated by the reactor core, flows through a tube bundle, which is a closed circuit called the primary circuit. The heat of the primary fluid is diffused by conduction through metallic tube walls to the water which flows outside of the tubes. Water in the secondary circuit, called the secondary fluid, enters in a liquid state and becomes a two-phase mixture of steam and water as heat transfer occurs along the heat exchanger. Modelling and simulating these heat exchangers by taking into account the tube bundle in detail, where there may be thousands of tubes, would require unacceptable computational cost and time. To decrease the computing time, the tube bundle can be modelled using the porous media theory
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