Project Details
Projekt
Numerical prediction of hetero-aggregate composition from electrospray processes and their product-oriented optimisation
Applicant
Professor Dr.-Ing. Martin Sommerfeld
Subject Area
Mechanical Process Engineering
Term
since 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 542432634
The interaction of bipolar charged electrosprays is an innovative idea for producing defined hetero-aggregates. A comprehensive numerical simulation tool would allow a product-oriented optimisation with respect to the operational parameters. The purpose of the project is the development of a fully coupled numerical method based on the point-mass Euler/Lagrange approach. This implies that fluid flow, electric field and droplet phase will be interactively simulated. The fluid flow shall be computed by a large eddy simulation (LES) method affected by both the electrostatic field as well as the droplet phase. The electrostatic field is computed based on field strength, electric potential and current density including also the space charge density of the droplets. Droplet tracking (i.e., consisting of suspensions or solutions) will consider evaporation, relevant fluid forces, electric field force and Coulomb interaction forces as well as sub-grid-scale dispersion. The first application case will be a simple electrospray where the basic models shall be implemented and validated. This includes the droplet injection procedure with all relevant properties (i.e., size, velocity, temperature, charge and solids content) and the development of an efficient stochastic model for the electrostatic interaction between droplets. The model developments for the computation of bipolar interacting electrosprays will focus on describing the collision process of charged droplet through a stochastic model. For that purpose, also charged droplet collision experiments need to be conducted for quantifying the collision outcome (i.e., coalescence or separation). Droplet collisions between the two oppositely charged droplets (components A and B) essentially determine the composition of the hetero-aggregates at the end of the process. The mixing of particles from the two fractions inside the coalesced droplet will be analysed through droplet-resolved direct numerical simulations based on VOF (volume of fluid method). The particles inside the droplet are considered as Lagrangian point masses. A deterministic particle collision model will be used and agglomeration shall be modelled on the basis of the DLVO theory using the agglomeration history model. Finally, the entire process will be simulated in accordance with the experimental setup (project Weber/Will), including gas injection, two interacting electrosprays and the outlet pipe functioning as ground electrode and heater for complete evaporation of solvent and sintering of solids. For this process the Euler/Lagrange simulations will yield the composition of the produced hetero-aggregates, both for injected suspension and solution droplets. This composition is of course affected by the operational conditions. Hence, the obtained mean values and standard deviations for the composition will be correlated with the operational conditions to obtain material and process functions. These allow for a target-oriented optimisation.
DFG Programme
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