Proposal of Design Criteria for Gas Entrainment from Vortex Dimples Based on a Computational Fluid Dynamics Method

Abstract

Design criteria for gas entrainments (GE) from the liquid surface in a fast breeder reactor system were proposed in this paper for the two types of GE phenomena from a vortex dimple based on a computational fluid dynamics (CFD) method. The first gas entrainment phenomenon is a gas core extension directly to the outlet piping level, which induces large amount of GE to the flow system. The second is continuous bubble detachments from the tip of the vortex dimple. Based on CFD calculations for elemental experiments of the surface vortex, local CFD non-dimensional numbers were defined as the design criteria to prevent GE. In conclusion, it was found that the CFD non-dimensional numbers are useful for the design parameters of GE prevention.

Experimental Investigation on Free Surface Vortices Driven by Tangential Inlets

“…The values of circulation, computed for each case according to the method proposed by Sakai et al in [12], employed in previous section to derive the potential profiles of tangential velocity, have been also used here to show the circulation number N D Q   as a function of Reynolds number, Re, and of the height of the measuring plane z* (normalized by the level of water in the tank, H = 50 mm). As reported in Fig.…”

“…8). The input circulation   in Eq (3) has been computed for each test case according to a method specified in [25] and used by Sakai et al [12]. Following this method, the isoline of the second invariant of the velocity deformation tensor is determined.…”

“…A different approach consists in performing numerical simulations in order to reproduce the formation and evolution of free surface vortices. Several studies (Sakai et al [12], Ito et al [13], Cristofano et al [14]) were performed in the last years, adopting this approach, but the deformation of gas-liquid interface, combined with the swirling motion in the vortex core, makes the numerical simulation of free surface vortex extremely difficult to be performed accurately.…”

CFD-based Evaluation of Interfacial Flows

“…In this case, CFD can be the efficient tool to evaluate the vortical flows in such a complicated FR system. Therefore, the authors propose a GE evaluation methodology in combination with CFD results (CFD-based prediction methodology) (Sakai et al, 2008). In the CFD-based prediction methodology, first, a transient numerical simulation of vortical flows is performed on a relatively coarse mesh to reduce the computational cost.…”

“…In this Chapter, the authors propose two methodologies to evaluate the GE phenomena in fast reactors (FRs) as an example of interfacial flows. One is a CFD-based prediction methodology (Sakai et al, 2008) and the other is a high-precision numerical simulation of interfacial flows. In the CFD-based prediction methodology, a transient numerical simulation is performed on a relatively coarse computational mesh arrangement to evaluate flow patterns in FRs as the first step.…”