화학공학소재연구정보센터
Chemical Engineering Research & Design, Vol.91, No.4, 640-648, 2013
Modelling of a CO2-gas jet into liquid-sodium following a heat exchanger leakage scenario in Sodium Fast Reactors
Sodium-cooled Fast Reactors (SFRs) represent one of the most promising technologies in the context of generation IV nuclear power reactors. In order to avoid a reaction between sodium and water when Rankine cycles are employed, the concept of Brayton cycles using supercritical CO2 (SCCBCs) is being investigated as alternative energy conversion cycle. However, an accidental scenario must be evaluated, since a leakage inside the CO2-sodium heat exchanger would cause a reactive underexpanded CO2-into-sodium jet, which in turn could lead to mechanical and thermal problems. A two-fluid approach has been investigated for the modelling of the two-phase jet: according to flow maps, mist flow has been assumed at the leak exit, where high gas volume fraction and high interfacial slip velocity exist, and bubbly flow has been assumed for lower gas volume fraction and slip velocity. An interfacial friction model has been developed. Droplet and bubble diameters have been estimated following literature experimental results and using critical Weber number. For the drag coefficients, consistent correlations have been developed. A two-phase mixture turbulence model has been added. The interfacial friction approach has been implemented into the two-fluid model of the CFD software Ansys Fluent 14.0. 3D numerical simulations of gas-into-water jets have been performed for vertical upward jets and optical probe technique has been employed for the experimental measurement of void fraction inside an underexpanded N-2-into-water jet: numerical results agree with experimental results in terms of axial and radial void fraction profile. The two-fluid approach presented here will be the base for the implementation of a chemical reaction model, in order to account for the exothermic chemical reaction between the CO2 and the sodium. (C) 2013 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.