CFD Modeling of Wall Steam Condensation: Two-Phase Flow Approach versus Homogeneous Flow Approach
The present work is focused on the condensation heat transfer that plays a dominant role in many accident scenarios postulated to occur in the containment of nuclear reactors. The study compares a general multiphase approach implemented in NEPTUNE_CFD with a homogeneous model, of widespread use for engineering studies, implemented in Code_Saturne. The model implemented in NEPTUNE_CFD assumes that liquid droplets form along the wall within nucleation sites. Vapor condensation on droplets makes them grow. Once the droplet diameter reaches a critical value, gravitational forces compensate surface tension force and then droplets slide over the wall and form a liquid film. This approach allows taking into account simultaneously the mechanical drift between the droplet and the gas, the heat and mass transfer on droplets in the core of the flow and the condensation/evaporation phenomena on the walls. As concern the homogeneous approach, the motion of the liquid film due to the gravitational forces is neglected, as well as the volume occupied by the liquid. Both condensation models and compressible procedures are validated and compared to experimental data provided by the TOSQAN ISP47 experiment (IRSN Saclay). Computational results compare favorably with experimental data, particularly for the Helium and steam volume fractions.
The TONUS CFD code for hydrogen risk analysis: Physical models, numerical schemes and validation matrix
The French Atomic Energy Commission (CEA) and the Radiation protection and Nuclear Safety Institute (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 the governing equations, numerical strategy and schemes used for the CFD approach. Typical numerical studies will be presented for hydrogen distribution and combustion applications in realistic large geometries.
Minimum thickness of a flowing down liquid film on a vertical surface
Abstract The minimum total energy (MTE) criteria for determining the minimum wetting rate and the minimum thickness of an isothermal, thin liquid film flowing down a vertical adiabatic surface are examined. An analytical expression of the profile of a stable liquid rivulet and of the two-dimensional velocity distribution in the rivulet developed using the Ritz method are incorporated into the MTE criterion to improve its predictions of the minimum wetting rate (MWR) and the corresponding minimum liquid film thickness (MLFT). The present predictions of the MWR and MLFT are in good agreement, to within ±10–20%, with experimental data for water and glycerol–water mixtures and with the values calculated from the MWR measurements, respectively. The accuracy of the present predictions is demonstrated for three conditions, namely: (a) incipient breakup of liquid film, (b) formation of a stable dry patch, and (c) rewetting of a dry surface. For the latter the advancing contact angle is substituted for the equilibrium contact angle in the developed analytical expressions for the MLFT and corresponding MWR.