Rising of 3D catalyst particles in a natural convection dominated flow by a parallel DNS method

We investigate the problem of particulate flows with heat transfer by parallel direct numerical simulation (DNS). Among other heat transfer problems, we examine in detail the case of a 3D spherical catalyst rising in an enclosure due to natural convection though it is heavier than the suspending fluid. Natural convection is created by heat transferred from the warmer particle to the fluid. Heat is assumed to be produced at a constant rate in the particle bulk. As expected, there exists a critical production rate that leads to the rising of the catalyst. Compared to the 2D circular cylinder counterpart, momentum and heat transfers are slower in 3D and the spherical catalyst rises for a lower production rate. At the numerical level, we employ a Distributed Lagrange Multiplier/Fictitious Domain formulation together with an operator-splitting algorithm to solve the coupled problem. Two families of Lagrange multiplier are introduced to relax the velocity and temperature constraints respectively. As suggested in Wachs (2009), particle collisions are handled by an efficient Discrete Element Method granular solver. As it is, the model is restricted to the case of homogeneous temperature over the particles. From a computational viewpoint, this work might be regarded as an extension of the method proposed in our previous contributions (Dan & Wachs, 2010; Yu, Shao, et al., 2006) to distributed computing with our new parallel code PeliGRIFF.(1) This opens up new possibilities to study a broad range of applications in 3D and to get more insight in the comprehension of particulate flows with heat transfer. In particular, we examine how a bed of spherical catalysts can be self-fluidized as a result of the heat produced in the particles bulk, mimicking an exothermic catalyst reaction in a chemical engineering reactor. (C) 2011 Elsevier Ltd. All rights reserved.