10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Finite-Element Method (FEM) Study on the Deposition of Non-spherical Graphite Particles in High Temperature Gas-cooled Reactor (HGTR)
ZHU FANG, Yiyang Zhang, Mingzhe Wei, Xinxin Wu, Tsinghua University
Abstract Number: 755 Working Group: Aerosol Modeling
Abstract In this study we discuss the deposition of non-spherical particles in cross-bundle flows. The background is the transport of graphite dust particles in the primary circuit of high-temperature gas-cooled reactors (HTGR). These highly non-spherical particles, coupling with fission products, partly deposit when flowing through the tube bundles of steam generator. In severe accident e.g. water ingress or loss-of-coolant, the deposited particles may re-suspend and contribute to the radiation source term. Therefore it is important to obtain a good estimation of deposition rate and distribution of graphite particles in HTGRs. The understanding of non-spherical particles deposition is limited by the lack of tool. Discrete element method (DEM) is more suitable for spherical and quasi-spherical particles. Molecular dynamics (MD) simulation is too expensive for micro-sized particles. Here we present a modified finite element method (FEM) study on the impact of micro-sized non-spherical particles. Our main effort is to include the effect of adhesion and damping. The adhesion force is derived from JKR model, correlated with contact area and then manually applied at the contact zone. The damping is incorporated through Rayleigh damping. First we validate the simulation results by comparing to Wall’s experiments. Then the method is extended to disk-like graphite particles. The critical capture velocities for different sized particles and different impacting angle are obtained. The results show the mass equivalent diameter is the dominant factor. The stable restitution coefficient increases with the decrease of particle size, while the critical velocity decreases rapidly. When the mass equivalent diameter remains constant, the restitution coefficient decreases with the lager sphericity. Then the particle impact model is incorporated to the LES modelling of particle-laden flow in tube bundles. The result shows that the deposition rate of small particles (<2 μm) is mainly controlled by the collision rate rather than sticky efficiency due to larger critical velocity. The turbulence and thermophoresis are the essential mechanisms. In contrast, the deposition rate of larger particles mainly depends on sticky efficiency. Thus the deposition rate first increases first and then decreases with the increase of the mass equivalent diameter. All those results can help to obtain a more credible estimation for deposition rate of the graphite particles in HGTRs.