Numerical simulation of sedimentation in the presence of 2D compressible convection and reconstruction of the particle-radius distribution function

Abstract

Numerical simulation of the sedimentation of a polydisperse suspension in a convectively unstable medium is presented. For the simulation of 2D compressible convection, the full system of hydrodynamic equations is solved by the explicit MacCormack scheme. Velocities and positions of suspension particles are calculated simultaneously with the solution of the equations. Initially, the particles are randomly distributed in the computational region. The total weight of sedimented matter is recorded during the numerical experiment. The results are compared with the sedimentation of the same suspension without convection. To reconstruct the particle-radius distribution function from the sedimentation curve, a new method is used. This method is based on the solution of the sedimentation integral equation by the Tikhonov regularization method and was recently developed by the author. To illustrate this technique, sedimentation of cement powder in air is simulated. The suspension contains 50 000 particles. The particle radii are assumed to be log-normally distributed. Heat-driven convection is completely determined by the top and bottom boundary temperatures of the computational region and lateral boundary conditions. It is shown that convective motions of a medium with sedimented particles lead to the following effect: the fine disperse fraction of the suspension remains suspended much longer than without convection. Some particles will not sediment at all. The maximum radius of the particles of this fraction depends on the convection parameters (e.g. on convection cell size and convection velocities). These parameters, in their turn, depend only on the temperature difference of the top and bottom boundaries. The results of these calculations can be applied in geology and meteorology for studying dust sedimentation in air as well as in technology. Heat-driven convection can be used for separation of suspensions with the cut-off particle radius depending on temperature difference only.