Investigations regarding the measurement of relevant flow conditions for droplet deformation and disruption in high pressure homogenization with orifices and scalability of mechanisms

• Applicants: Professorin Dr.-Ing. Heike Karbstein; Professor Dr. Christian Joachim Kähler; Professor Dr. Peter Walzel
• Subject Area: Mechanical Process Engineering
• Term: from 2015 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 265685259

High pressure homogenization is a well established industrial process for the production of emulsions containing droplets within a submicron range. This technology has been applied for many decades. However, mechanisms leading to droplet breakup are still not completely understood. As a consequence, the optimization of process and disruption units is still realized on a trial and error basis. Reasons for this are the complex flow field inside a disruption unit due to high velocity gradients and fluctuations as well as the presence of multiple phases. Additionally, access to small geometries is limited by process conditions such as high pressures. These cirsumstances set high demands on inline measurement techniques. The aim of this research project is to characterize flow conditions and physical mechanisms of droplet breakup during high pressure homogenization under realistic conditions. Applying the optical measurement technique µPIV allows the realization of this objective with high pre-cision. Initially, the proposed project will focus only on single-phase, Newtonian, non-cavitating fluids. After flow characterization, droplet breakup will be investigated using single droplets (dispersed phase fraction << 1 %) without surface-active additives. However, spatial and temporal resolution limit the characterization of the complete process on a realistic microscale. Therefore, specific questions are investigated in scaled up devices (M = 5 und 50). This procedure allows verifying the scalability of droplet breakup. The investigations on a realistic microscale (M = 1, orifice diameter d = 0.2 mm, resp.) as well as a scaled up system of M = 5 (d = 1 mm) will be conducted by the KIT in Karlsruhe. Years of experience in emulsification technology will be used to systematically study flow conditions and droplet breakup. Parameters that will be varied are the Reynolds number, geometry of the orifice, size, and starting position of the droplets. Material parameters such as viscosity of each phase and surface tension will be changed likewise. By utilizing their knowhow in flow measurement techniques, the UniBw in Munich will focus on investigating selected aspects within a large scale system (M = 50, orifice diameter d = 10 mm, resp.). Here, the main emphasis lies on a detailed acquisition of droplet disruption mechanisms at selected parameters as well as describing the droplets' shape and dynamics. This research project will build the foundation to predict resulting droplet size distributions from boundary conditions like material, process and geometrical parameters. Therefore, a function describing the disruption of droplets will be developed. In the long term, this will help to improve high pressure homogenization processes in a targeted way regarding selectivity, product yield as well as energy input.

• DFG Programme: Research Grants