SPP 1980
Priority Program Description
Spray flame synthesis is a promising approach for the production of functional nanoparticles, which are, for example, expected to lead to major advances in the development of batteries or catalysts. Compared to existing large-scale gas phase processes, spray flame synthesis offers a higher variety of material systems and a good scalability. However, industrial-scale implementation is currently failing due to an insufficient understanding of the process. The DFG priority program SPP1980 (Link to homepage: www.uni-due.de/spp1980/) aims to overcome these challenges in an interdisciplinary approach and lay the foundations for industrial distribution. In recent years, closely related sub-processes of spray flame synthesis have been successfully investigated in the various disciplines and a wealth of experimental, simulative, and theoretical instruments have been developed. In the priority program, these methodologies are brought together to analyze the individual sub-processes and to classify them into an overall model. This intends to create a comprehensive understanding of the process.
Project: Influence of atomization on particle synthesis in spray flames
Spray flame synthesis of nanoparticles is significantly influenced by the atomization of the precursor solutions. The characteristic droplet and gas phase in the vicinity of the nozzle is an essential input condition for the formation of local synthesis conditions in the flame along the trajectories of particles during their formation. Thus, any change of the atomization will directly affect the particle properties. In this context, the nozzle design represents an essential degree of freedom, which can be used to gain a better understanding of the coupling of spray flame and particle formation mechanisms. On this basis, a targeted manipulation of particle properties will be enabled in the long term. The high importance of the nozzle geometry for spray flame synthesis was demonstrated by this project in the first phase of the priority program. However, further research is needed to clarify whether and under which conditions a direct correlation between spray characteristics and particle properties exists. Furthermore, it is unknown how the responsible individual mechanisms of particle formation are influenced by the nozzle-dependent local synthesis conditions along the trajectory. This research project aims to provide a fundamental understanding of the influence of local synthesis conditions on spray flame mechanisms by means of a targeted variation of spray characteristics and high-resolution experimental and numerical methods. To address these questions, an interdisciplinary research group (WSA, RWTH Aachen; PVT, Paderborn University; ITV, RWTH Aachen) has been established to provide expertise from different sub-areas of spray flame synthesis and to combine state-of-the-art complementary investigation methods such as high-fidelity numerical simulations as well as high-resolution in-situ measurement techniques.
Simulation of spray flame synthesis
In order to simulate the entire process chain of spray flame synthesis, a simulation framework is required, which accounts for the wide range of length and time scales. Similar to the simulation framework, which was developed for compression ignition engines (Link to: www.itv.rwth-aachen.de/forschung/aktuelle-forschung/sustainable-energy-carriers/simulation-dieselmotorischer-verbrennung/), three one-way coupled simulation are used, starting with the nozzle internal flow.
Nozzle internal flow simulation
In coaxial atomizers, spray formation is governed by the complex nozzle internal flow of the dispersion gas. To resolve the relevant flow features, state-of-the-art predictive Large-Eddy-Simulation (LES) are used. Besides supporting the design process of nozzle geometries, the outflow conditions are used as boundary conditions for the subsequent interface resolving Direct Numerical Simulation (DNS).
Interface resolving DNS
Interface resolving DNS of the liquid jet disintegration provide a deep insight in the physical processes and are needed for a detailed study as experimental measurement techniques are limited in the dense spray region. Furthermore, DNS provides information simultaneously about both phases, which allows studying of the complex and application relevant interaction of the nozzle dependent gas flow and the disintegrating liquid jet. From a numerical point of view, interface resolving DNS are very challenging due to discontinuities in some flow variables (density, viscosity, pressure, etc.). To obtain reliable simulation results, high-fidelity simulation methods are required and a continuous improvement is needed. During this project the interface capturing method was significantly improved.
Reactive Euler-Lagrange LES
Downstream the spray breakup, the flame is computed using a LES that employs a Lagrangian spray model and a turbulent combustion model. Liquid and gas phase information from the interface resolving DNS are used as initial and boundary conditions, respectively. Particle formation is modeled with two different approaches with a varying degree of detail. The first approach uses a statistical description of the particle formation and is integrated into the LES. In contrast, the second approach uses exported trajectories from the LES to simulate the structure evolution of particle ensembles in a subsequent step. The particle structure simulations are performed by our project partners from PVT, Paderborn University.
