Copyright (c) 2008 All rights reserved. http://works.bepress.com/paola_lettieri Recent documents in Paola Lettieri en-us Thu, 03 Jan 2008 12:36:39 PST 3600 http://works.bepress.com/paola_lettieri/3 http://works.bepress.com/paola_lettieri/3 Fri, 12 Jan 2007 01:25:33 PST A commercially available Computational Fluid-Dynamics code, CFX-4, has been chosen to carry out computer simulations of gas fluidized beds. In this study, the Eulerian-Eulerian granular kinetic model, which is a standard option of the code, has been used. Fluid-bed simulations of Geldart Group B materials have been performed using the granular kinetic model, spanning three hydrodynamic regimes: bubbling, slugging and turbulent fluidization. Furthermore, an alternative Eulerian-Eulerian model, the so-called "particle-bed model", has been implemented for the first time within a commercial code, and results are presented from simulations of the bubbling and slugging fluidization of a Geldart Group B material, and for the homogeneous fluidization of a Group A material. A numerical procedure has been developed to allow for a tight control of the fluid-bed voidage at maximum packing during the simulations with the particle-bed model. Results show that both the granular kinetic model approach and the particle-bed model are able to describe significant aspects of the investigated fluidization regimes. Paola Lettieri Computational Fluid Dynamics http://works.bepress.com/paola_lettieri/2 http://works.bepress.com/paola_lettieri/2 Fri, 12 Jan 2007 01:25:31 PST The present article describes an algorithm developed for computing the position and the equivalent diameter of bubbles featuring in two-dimensional fluidized beds simulated by means of Computational Fluid Dynamics (CFD) multiphase-flow codes. The program is presented for two-dimensional systems; nevertheless, following the same logic herein outlined, it can be easily extended to the more general case of three-dimensional beds. In this work, by "equivalent diameter" it is meant the diameter of the circle having the same area as the bubble. The procedure is intended as a useful tool in the validation of the results of numerical simulations aimed at investigating the fluid-dynamic behavior of fluidized beds operating in the bubbling regime. The algorithm, presented here without making reference to any specific programming language, can be run in any CFD commercial code, provided that the language and the syntax used are consistent with those required by the particular code adopted. The logic of the program is first illustrated in general terms, and afterwards by making reference to an illustrative example regarding a Geldart Group B powder fluidized by means of air. In this specific case, the equations of motion used to describe the dynamics of the system have been based on the work by Mazzei et al. (2006), the commercial CFD code used has been CFX 4.4 and the programming language applied to implement the algorithm has been Visual Fortran 6.6. Luca Mazzei Computational Fluid Dynamics http://works.bepress.com/paola_lettieri/1 http://works.bepress.com/paola_lettieri/1 Fri, 12 Jan 2007 01:25:26 PST This paper reports on CFD simulations of freely bubbling gas fluidized beds using CFX-4, a commercial code developed by CFX Ltd. (formerly AEA Technology). Two Eulerian-Eulerian modelling approaches, the granular kinetic model and the particle-bed model (Gibilaro, 2001), have been investigated. The particle bed model has been recently implemented in CFX-4 for 2D simulations and a numerical procedure was developed to allow for a tight control of the fluid-bed voidage at maximum packing during the simulations, see Lettieri et al. (2003). The work has now been extended to 3D simulations and qualitative and quantitative results are presented in this paper for both the 2D and 3D simulations of the bubbling fluidization of a Geldart Group B material. Results on bed expansion, bubble size and bubble hold-up are reported. In particular, simulated bubble size is compared with predictions given by the Darton et al. (1977) equation at different bed heights. The paper shows that the bubble size predicted by both the granular kinetic model and the particle-bed model is in good agreement with the Darton's equation. Luca Cammarata Computational Fluid Dynamics