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.