Keywords: powder discharge, fire extinguisher, discrete element method, computational fluid dynamics, fluid-particle interactions.

This paper presents the simulations of a powder extinguisher discharge, by coupling the discrete element method (DEM) and with the computational fluid dynamics (CFD) method. The final aim of the work is to optimize, through numerical simulations, the properties of the powder ensuring a full and rapid discharge of the extinguisher. To our knowledge, very few papers deal with extinguisher discharge. We can cite some experimental works, such as Yang et al. [1], Liu et al. [2], and numerical work on spray water extinguishment [3]. The flow rate study for a powder discharge, use a Lagrangian approach to investigate particle behavior. Here, the first step of the study is presented and discussed, dealing with the hydrodynamics of the discharge, neglecting the cohesive and electrostatic forces between powder particles. One can notice that, the use of DEM simulation coupled with CFD in chemical engineering is a recent growth area, in particular to investigate fluidized bed behavior [4].

Within recent decades, special finite element software has been developed for DEM simulation. Mayor improvements have been obtained recently in the reduction of the time for conducting the numerical simulations. Furthermore with the actual version of our computer program (MULTICOR) there are no limitations with regard to the shape of the structure. Details of this model are given in the literature [5,6] and will be briefly summarized.

The simulations were performed in two dimensions, and the reconstruction model in three dimensions is presented. Numerical results are compared with a simplified theoretical model assuming an ordinate rectangular placement of the particles during discharge. The initial outlet flow rate for the particles is comparable in both numerical and theoretical results, but the simulations highlight a rapid decrease of the outlet flow rate due to inter-particle and wall-particle collisions and friction. Moreover, the simulations have demonstrated the small influence of the tube diameter on the outlet particle flow rate, as predicted by the theoretical model.

As a possible extension to this study, a thermal and, or pressure problems can be coupled to this algorithm, to provide the temperature and, or pressure evolution, which is important for the simulation of the discharge of the fire extinguisher process. The consideration of adhesion between particles (namely electrostatic or liquid bridge forces) will also be a further study.

1

J.C. Yang, W.M. Pitts, B.D. Breuel, W.L. Grosshandler, W.G. Cleveland, "Rapid discharge of a fire suppressing agent", Int. Comm. Heat Mass Transfert, 23, 835-844, 1996. doi:10.1016/0735-1933(96)00066-8

2

Z. Liu, A.Z. Kim, D. Carpenter, "A study of portable water mist fire extinguishers used for extinguishment of multiple fire types", Fire safety Journal, 42, 25-42, 2007. doi:10.1016/j.firesaf.2006.06.008

3

V. Novozhilov, B. Moghtaderi, J.H. Kent, D.F. Fletcher, "Solid Fire extinguishment by a water spray", Fire safety Journal, 32, 119-135, 1999. doi:10.1016/S0379-7112(98)00036-8

4

E. Helland, R. Occelli, L. Tadrist, "Computational study of fluctuating motions and cluster structures in gas-particle flows", International Journal of Multiphase Flow, 28, 199-223, 2002. doi:10.1016/S0301-9322(01)00041-6

5

J. Fortin, P. Coorevits, "Selecting contact particles in dynamics granular mechanics systems", Journal of Computational and Applied Mathematics, 168, 207-213, 2004. doi:10.1016/j.cam.2003.05.025

6

C. Marie, K. Benhabib, P. Coorevits, "Etude numérique d'un réacteur à lit fluidisé par modélisation éléments discrets", XIIème Congrès de la Société Française de Génie des Procédés (SFGP), Marseille, 14-16 Octobre, 2009.

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