Onset of Convection in Bidisperse Colloidal Suspension

The convection of colloidal suspension in a horizontal layer is investigated in the frame of the bidisperse model. It is assumed that the colloidal suspension consists of a three components: carrier liquid, and two types (small and large) of the nanoparticles with average concentrations (C) over bar (s) and (C) over bar (1), respectively. The influence of the Soret (thermodiffusion) effect on the convection thresholds is investigated. The gravitational sedimentation of the nanoparticles in colloidal suspension is also taken into account in contrast to the traditional consideration of ternary mixtures. The influence of the bidisperse model characteristics (the ratio of radii of the large and small nanoparticles and the proportion of large nanoparticles) on the convective thresholds is discussed. The instability boundaries are found analytically in the long-wave approximation, and numerically for the finite wavelengths. The regions of the monotonic and oscillatory instabilities are determined in the parameter space. The dependences of the critical wave number, the Rayleigh number, and the marginal oscillation frequency on the net separation ratio are obtained.

Automated summary

This study investigates the convection of colloidal suspension in a horizontal layer using a bidisperse model, considering the influence of the Soret effect and gravitational sedimentation of nanoparticles. The characteristics of the bidisperse model and the instability boundaries are analyzed.