Settling of bidispersed small solid particles in a dilute suspension containing gyrotactic micro-organisms

The motivation of this research is to investigate the feasibility of utilizing bioconvection for enhancing mixing in a suspension of small solid particles. This may be important in micro-fluidic applications relevant to biotechnology and medicine, such as analyses of DNA or drugs, screening of patients, and combinatorial synthesis. Traditionally, the mixing of fluids in micro-volumes has been limited to diffusion. Due to the microscopic size of the organisms involved in bioconvection, bioconvective flows are a prospective and novel alternative for micro-fluidic mixing. This paper considers a bidispersed suspension of small solid particles that have different densities and settling velocities in a fluid that contains motile gyrotactic micro-organisms. The particles are assumed to be sufficiently small so that their Brownian diffusion is not negligible. It is found that the number density distribution of solid particles of one type impacts that of particles of the other type as well as that of micro-organisms.