Numerical study of particle separation from heterogeneous suspensions in inertial microfluidics

Sorting particles in heterogeneous suspensions has applications from disease diagnosis to water filtration. A number of separation methods exist, however, there is a need for label-free methods that passively separate particles with high throughput and without dilution. Inertial microfluidics is an emerging technology that passively manipulates particles by exploiting inertial forces which are relevant at Reynolds number of the order of 10-100. Due to these forces, particles migrate to equilibrium positions within a channel cross-section based on their properties, and can therefore be separated. Inertial microfluidic devices are used in real-world applications using dilute suspensions. However, there is significant scope to identify new applications with dense suspensions (up to 45%). In particular, particle size and softness heterogeneity effects are not well understood. We use an in-house lattice-Boltzmann-immersed-boundary-finite-element code to uncover underlying physical mechanisms. We investigate concentration effects on the separation of dense heterogeneous suspensions (5-45%). We also investigate size and softness heterogeneity effects. We compare heterogeneous and homogeneous suspension behaviour. We show that particles of different size and softness migrate to different locations, and these locations are concentration dependent. Our results provide evidence that inertial microfluidic devices can be used for separation in dense heterogeneous suspensions.