J. Malet

Experimental investigation of water droplet binary collisions and description of outcomes with a symmetric Weber number

The outcomes of binary collisions of water droplets are investigated experimentally for the range of parameters of a spray system used during a severe nuclear reactor accident. Droplets diameters range from 220 to 450 μm with a diameter ratio between 0.5 and 1 and impact velocities between 3 and 10 m s−1. Values of the Weber number based on the small droplet size are between 20 and 280. For droplets with a Weber number up to 120, results in a map of impact parameters versus Weber number show the various regimes, namely, stretching separation, coalescence and reflexive separation. For a higher Weber number, between 120 and 280, the only observed outcomes are the two separation regimes. It is shown that results obtained for unequal droplet sizes match on a single map in terms of the impact parameter and of a new “symmetric” Weber number based on the sum of kinetic energies in the frame of the center of mass and on the sum of surface energies of the two droplets. Ashgriz and Poo [“Coalescence and separation ...

Eulerian Simulation of Interacting PWR Sprays Including Droplet Collisions

Abstract A numerical simulation of the interaction between two real pressurized water reactor containment sprays is performed with a new model implemented into the Eulerian computational fluid dynamics (CFD) code NEPTUNE_CFD. The water droplet polydispersion in size has been treated with a sectional approach. The influence of collisions between droplets is taken into account with a statistical approach based on the various outcomes of binary collision. Experiments were performed in a new facility, and data obtained are compared with this two-fluid simulation. The results show good agreement.

Dispersed Two-Phase Flow Modelling for Nuclear Safety in the NEPTUNE_CFD Code

The objective of this paper is to give an overview of the capabilities of Eulerian bifluid approach to meet the needs of studies for nuclear safety regarding hydrogen risk, boiling crisis, and pipes and valves maintenance. The Eulerian bifluid approach has been implemented in a CFD code named NEPTUNE_CFD. NEPTUNE_CFD is a three-dimensional multifluid code developed especially for nuclear reactor applications by EDF, CEA, AREVA, and IRSN. The first set of models is dedicated to wall vapor condensation and spray modelling. Moreover, boiling crisis remains a major limiting phenomenon for the analysis of operation and safety of both nuclear reactors and conventional thermal power systems. The paper aims at presenting the generalization of the previous DNB model and its validation against 1500 validation cases. The modelling and the numerical simulation of cavitation phenomena are of relevant interest in many industrial applications, especially regarding pipes and valves maintenance where cavitating flows are responsible for harmful acoustics effects. In the last section, models are validated against experimental data of pressure profiles and void fraction visualisations obtained downstream of an orifice with the EPOCA facility (EDF R&D). Finally, a multifield approach is presented as an efficient tool to run all models together.

Containment Thermal-Hydraulic Simulations With an LP-CFD Approach: Qualification Matrix of the TONUS Code

The French Atomic Energy Commission (CEA) and the Institute for Radiological Protection and Nuclear Safety (IRSN) are developing a hydrogen risk analysis code (safety code) which incorporates both lumped parameter (LP) and computational fluid dynamics (CFD) formulations. In this paper we present briefly the main physical models for containment thermal-hydraulics. Validation and typical numerical results will be presented for hydrogen distribution and combustion applications in small and realistic large geometries.Copyright