Abstract
The droplet deformation in dispersing units of high-pressure homogenizers (HPH) is examined experimentally and numerically. Due to the small size of common homogenizer nozzles, the visual analysis of the transient droplet generation is usually not possible. Therefore, a scaled setup was used. The droplet deformation was determined quantitatively by using a shadow imaging technique. It is shown that the influence of transient stresses on the droplets caused by laminar extensional flow upstream the orifice is highly relevant for the droplet breakup behind the nozzle. Classical approaches based on an equilibrium assumption on the other side are not adequate to explain the observed droplet distributions. Based on the experimental results, a relationship from the literature with numerical simulations adopting different models are used to determine the transient droplet deformation during transition through orifices. It is shown that numerical and experimental results are in fairly good agreement at limited settings. It can be concluded that a scaled apparatus is well suited to estimate the transient droplet formation up to the outlet of the orifice.
Highlights
The integral correlation approaches are important for the industrial design of high-pressure homogenizers (HPH), as this empirical approach leads to the desired droplet distribution, even without knowing the mechanisms responsible for the break-up in all its details
The investigations show that the elongation of the primary droplets at constant Reynolds number in the laminar inlet area increases with decreasing viscosity ratio starting from a very low elongation at the viscositydroplets ratio investigated
The investigations show that the elongation ofhighest the primary at constant elongation of drops with constant viscosity ratio to the continuous phase increases with number in the laminar inlet area increases with decreasing viscosity ratio starting increasing Reynolds number
Summary
The break-up of tiny droplets due to the action of a flow field and instabilities has been widely studied, as this process is very important in many industrial sectors. Among the many investigations carried out, a distinction can be made between studies dealing with the integral process of emulsification, where, for example, correlations between the energy input and the resulting drop size are obtained, or studies focusing on the individual processes of single drop break-up under different conditions. The integral correlation approaches are important for the industrial design of HPH, as this empirical approach leads to the desired droplet distribution, even without knowing the mechanisms responsible for the break-up in all its details. Due to the complexity of the drop break-up mechanism, technical designs are usually carried out empirically using integral correlation approaches [2]
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