Abstract
In many scientific communities, the definition of standardized experiments has enabled major progress in process understanding. The investigation of the spray-flame synthesis of nanoparticles at a well-defined standard burner by experiment and simulation makes it possible to produce a comprehensive data set with various established and novel measuring methods. In this work, we introduce the design of the SpraySyn burner as a new standard for a free-jet type burner that offers well-defined and simulation-friendly boundary conditions and geometries as well as accessibility for optical diagnostics. A combustible precursor solution is fed through a centrally located capillary and aerosolized with an oxygen dispersion gas flow. The spray flame is stabilized by a premixed flat methane/oxygen pilot flame fed via a porous bronze matrix surrounded by a stabilizing nitrogen coflow emanating through the same porous matrix, providing easy-to-calculate boundary conditions for simulations. This burner design enables the use of a wide choice of solvents, precursors, and precursor combinations. Best-practice operating instructions and parameters are given, and large-eddy simulations are performed demonstrating the suitability of the SpraySyn burner for computational fluid dynamics simulations. For ensuring reproducible operation across labs, we define a consumer-camera-based flame characterization scheme for the quantitative assessment of the flame geometry such as flame length, diameter, tilt angle, and photometric distribution of visible chemiluminescence along the center axis. These parameters can be used for benchmarking the pilot and spray flame by each user of the SpraySyn burner with the reference flames.
Highlights
The synthesis of nanoparticulate materials in flames is wellestablished.1–4 High-temperature processes enable the generation and stabilization of materials outside the thermodynamic stability limits, and the continuous operation enables scale-up to large production rates as demonstrated for commodities such as silica and titania burners.1 The synthesis of a large variety of materials has been demonstrated on the lab scale, but conventional gas-phase processes require precursors that are either gaseous or can be vaporized and mixed with the burner gases before they react inside the reaction chamber
The spray flame is stabilized by a premixed flat methane/oxygen pilot flame fed via a porous bronze matrix surrounded by a stabilizing nitrogen coflow emanating through the same porous matrix, providing easy-to-calculate boundary conditions for simulations
This paper introduces a standardized spray-flame burner for nanoparticle synthesis, SpraySyn
Summary
The synthesis of nanoparticulate materials in flames is wellestablished. High-temperature processes enable the generation and stabilization of materials outside the thermodynamic stability limits, and the continuous operation enables scale-up to large production rates as demonstrated for commodities such as silica and titania burners. The synthesis of a large variety of materials has been demonstrated on the lab scale, but conventional gas-phase processes require precursors that are either gaseous or can be vaporized and mixed with the burner gases before they react inside the reaction chamber. The approach was based generally on ex situ characterization of the materials and largely empirical variation of starting materials, reaction conditions, and burner geometries This development was often decoupled from the advancement in related topics, in particular, combustion research, the spray formation, the interaction of precursors and fuels, solution stabilization and vaporization, diagnostics capabilities for reacting multiphase flows, and their numerical description. All three simulation cases suffered from similar difficulties: (a) the experimental database and its reproducibility were not sufficient for an exhaustive validation of the results and (b) the burner design necessitates strong simplifications and assumptions at the inlet boundaries These problems were the main motivation for the design of a new, standardized, and easy to operate spray-flame synthesis burner and for the development of workflows to optimize the reproducibility of experiments. Because reproducible operation of a standard flame is crucial, an imaging-based flame characterization approach is introduced that enables each user to ensure the operation of the burner under comparable conditions
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