SharePoint
Aide
IRSN, Institut de radioprotection et de sûreté nucléaire

Search our site :

ok

Contact us :

ok
En Fr

Enhancing Nuclear Safety


Research

Publications

Modeling of the reflooding of a particulate bed: contribution to the estimation of the macroscopic transport properties.

Fabien Duval, doctorate thesis of Institut National Polytechnique of Toulouse, defended in 2002.

Document type > *Mémoire/HDR/Thesis

Keywords >

Research Unit > IRSN/DPAM/SEMIC/LMPC

Authors > DUVAL Fabien

Publication Date > 29/11/2002

Summary

This work deals with the macroscopic modeling of heat and mass transfer in a superheated porous medium subjected to a liquid-vapor flow with phase change. Considering local thermal non-equilibrium between the three phases, a quasi-steady three-temperature macroscopic model is derived using the volume averaging method. An attractive feature of the scaling-up theory lies in the derivation of a closed form of the evaporation rate at the macroscopic level depending on the large scale temperatures and the effective properties. The resulting macroscopic model may be seen as a generalization of existing three-temperature models obtained from a heuristic approach. The main differences are the existence of additional transport terms and a coupling between the macroscopic continua (phases and interface) that seems to be more complex. The major interest of the proposed approach is to provide closure problems that allow to determine the effective transport coefficients, such as the thermal dispersion tensors and the heat exchange coefficients, from a local scale description over a representative cell of the porous medium under consideration.
These problems have been solved for simple unit cells to provide first estimates of the effective properties. For these unit cells and for purely diffusive processes with phase change, comparisons with numerical solutions of the local problem have shown the pratical interest and the potentialities of the macroscopic model. For more complex unit cells, a direct numerical simulation of the two-phase flow at the local scale has been performed to provide the required velocity field and the interface topology.
The direct numerical simulation tool which has been developed is based on a diffuse interface method.
These methods are well suited to the local scale characteristic lengths of the porous medium and the developments carried out show that it is possible to extend them to take into account phase change in the framework of Cahn-Hilliard models. Results obtained on 2D unit cells emphasize a strong impact of the pore-scale phase repartitions and indicate that correlations for the e ective properties involving saturation and Péclet numbers can be relatively complex.

Close

Send to a friend

The information you provide in this page are single use only and will not be saved.
* Required fields

Recipient's email:*  

Sign with your name:* 

Type your email address:*   

Add a message :

Do you want to receive a copy of this email?

Send

Cancel

Close

WP_IMPRIMER_TITLE

WP_IMPRIMER_MESSAGE

Back

Ok