Gusztáv Mayer

Lattice Boltzmann methods for two-phase flow modeling

Abstract In this paper the most important properties of the lattice Boltzmann methods are reviewed with focus on two-phase flow modeling. The lattice methods are compared with the conventional computational fluid dynamics methods, their advantages and disadvantages are highlighted. Necessary improvements for practical applications are summarized.

Estimation of the liquid-vapor spinodal from interfacial properties obtained from molecular dynamics and lattice Boltzmann simulations

Interfacial pressure and density profiles are calculated from molecular dynamics and lattice Boltzmann simulations of a liquid film in equilibrium with its vapor. The set of local values of tangential pressure and density along an interface exhibits a van der Waals-type loop; starting from the stable vapor bulk phase one passes through metastable and unstable states to the stable liquid bulk phase. The minimum and maximum values of the profile of tangential pressure are related to the liquid and vapor spinodal states, respectively. The spinodal pressures turn out to be linearly related to the extreme values of the tangential pressure in the interface. The comparison with equations of state shows good agreement with the simulation results of the spinodals. In addition the properties of the metastable region are obtained. Based on this investigation a method is proposed for the estimation of the liquid spinodal from experimentally obtained interfacial properties. Estimations for water and helium are presented.

LATTICE BOLTZMANN SIMULATION OF VAPOR–LIQUID EQUILIBRIUM ON 3D FINITE LATTICE

Numerical calculations for three-dimensional vapor–liquid equilibria have been accomplished by lattice Boltzmann simulations. The aim of this investigation is to test the capability of the lattice Boltzmann method in comparison with solutions obtained by the underlying equation of state. As a result we have found a finite-size effect (just like the ones obtained in one and two dimensions) at small lattice sizes for all phase equilibrium properties and related constants such as the critical exponent β. Here, systems with up to 1003 lattice sites are investigated. Reasonable convergence has been obtained from about 323 lattice sites.

ON THE SYSTEM SIZE OF LATTICE BOLTZMANN SIMULATIONS

In lattice Boltzmann simulations particle groups — represented by scalar velocity distributions — are moved on a finite lattice. The size of these particle groups is not well-defined although it is crucial to assume that they should be big enough for using a continuous distribution. Here we propose to use the liquid–vapor interface as an internal yardstick to scale the system. Comparison with existing experimental data and with molecular dynamics simulation of Lennard–Jones-argon shows that the number of atoms located on one lattice site is in the order of few atoms. This contradicts the initial assumption concerning the number of particles in the group, therefore seems to raise some doubts about the applicability of the lattice Boltzmann method in certain problems whenever interfaces play important role and ergodicity does not hold.

First experience with a six-loop nodalization of a VVER-440 using a new coupled neutronic-thermohydraulics system KIKO3D-RETINA V1.1D

Abstract In this paper, we introduce a new, coupled neutronic-thermohydraulics system. The three-dimensional neutron kinetic code KIKO3D and the two-phase flow code RETINA V1.1D have been coupled for modeling complex transients of nuclear power plants. Using a six-loop nodalization of a VVER-440, several test calculations have been carried out. Results obtained for a trip of one main circulation pump are compared with real measurements and reference calculations provided by other neutronic-thermohydraulics systems. The ability of our coupled system is demonstrated.

Transient Analysis of Crossduct Break Scenarios Using the CATHARE2 Code for the 75MW ALLEGRO Demonstrator

The helium cooled Gas Fast Reactor (GFR) is one of the six reactor concepts selected in the frame of the Generation IV International Forum. Since no gas cooled fast reactor has ever been built, a medium power demonstrator reactor — named ALLEGRO — is necessary on the road towards the 2400MWth GFR power reactor. The French CEA completed a wide range of studies on the early stage of development of ALLEGRO, and later the ALLEGRO reactor have been developed in several European Union projects in parallel with the GFR2400. The 75 MW thermal power ALLEGRO is recently being developed in the frame of European ALLIANCE project. As a result of the collaboration between CEA and MTA EK new improvements were done in the CATHARE modeling of ALLEGRO. In particular, the capability of simulation of breaks located in the crossduct (concentrically arranged pipes with the hotduct located inside the colduct) has been developed. A first scenario of hotduct break has been simulated, that does not lead to the depressurization of the system because of the crossduct technology. Nevertheless this transient leads to a high bypass of the core. Then a scenario of full rupture of the hotduct and the colduct has been tested, leading to beyond design state with depressurized situation combined with a large bypass of the core. However this study shows that the peak cladding temperature can be kept below the cladding melting point using nitrogen injection. In this paper the CATHARE model implemented for the crossduct rupture scenario and the results of the simulation are presented and discussed.Copyright