Fluctuations in Rayleigh breakup induced by particulates

A jet of liquid is intrinsically unstable to radial perturbations and will spontaneously break to form a series of droplets. This well known instability, the Rayleigh-Plateau instability, is controlled and used commercially in continuous inkjet printing. In this application it is important that fluctuations in drop velocity are minimised. However, the addition of particulates to the liquid is observed to strongly increase these fluctuations. The particulates are usually in the form of pigment particles of size O(100 nm) and at a concentration where they may hydrodynamically interact, particularly in the strong shear field within the nozzle (O(10(7) s(-1))). The boundary layer thickness within the nozzle is O(1 μm) and therefore the particulate size is a significant fraction. We therefore expect that the particles are capable of perturbing the boundary layer and hence the jet. Measurement of jet breakup fluctuation leads to a description of particulates interacting within and with the shear field associated with the boundary layer at the nozzle wall.