Comparison of flow patterns and droplet deformations of modified sharp-edged and conical orifices during high-pressure homogenisation using µPIV

Abstract

Micro-particle image velocimetry was used as an optical, non-intrusive measurement method to measure the flow pattern and visualise droplet deformation in high-pressure homogenisation disruption units of two different inlet designs (sharp-edged and conical). The flow patterns were compared either at same Reynolds numbers $${\text{(}}Re=980)$$ or pressure differences ( $$\Delta p=52~{\text{bar}}$$ ) each, to describe the influence of inlet geometry on the droplet disruption efficiency. Therefore, the shear and elongation rates were calculated from the velocity profiles and discussed regarding the visualised deformation of the emulsion droplets. For this, the viscosity ratio between the droplet and continuous phase was varied. Afterwards, the droplet size distributions (DSD) of emulsions with corresponding viscosity ratio passing the sharp-edged and the conical orifice were characterised. The inlet geometry influenced the flow pattern, shear and elongation rate profile, droplet deformation and finally droplet size distributions during the high-pressure homogenisation. On the one hand, sharp-edged inlet design resulted in higher axial velocity profiles and smaller droplets with slightly bimodal character. On the other hand, conical inlet design resulted in perfectly monomodal DSD but comparatively bigger droplets.