Modelling particle random walk in a confined environment for inclusion in fluidised bed applications

In many particulate systems, e.g., a particulate flow or a fluidised bed, particles are subjected to consecutive particle-particle collisions. From a stochastic point of view, these particle-particle collisions give rise to a random particle motion that in most processes is superposed onto a forced particle motion caused by well-described external forces that initialise and/or maintain the overall motion of the particulate system (pressure and concentration gradients, gravity, electromagnetic and mechanical forces). Modelling each individual particle-particle collision requires lots of computational time and power. For process control purposes however, models describing many-particle systems such as fluidised beds need to be able to describe the random particle motion in a relatively short amount of time. Therefore, a new stochastic and discrete method was developed that is able to simulate random walk in a confined and relatively dense environment without considering the underlying physics of the phenomena (e.g., particle-particle collisions in a particulate flow) that cause the random walk. The method was successfully tested for relatively dense particulate systems and will be incorporated in a process control model that is currently being developed for fluidised bed coating processes in which particle-particle collisions occur frequently and for which the description of the motion of individual particles is required. (C) 2011 Elsevier B.V. All rights reserved.