Benjamin A. Südholt, Arne Witte, Greg J. Smallwood, Sebastian A. Kaiser, Lutz Mädler, Niklas Jüngst
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引用次数: 0
Abstract
When producing metal-oxide nanoparticles via flame spray pyrolysis, precursor-laden droplets are ignited and undergo thermally induced disintegration, called ‘puffing’ and ‘micro-explosion’. In a manner that is not fully understood, these processes are associated with the formation of dispersed phases inside the droplets. This work aims at visualizing the interior of precursor-laden burning single droplets via diffuse back illumination and microscopic high-speed imaging. Solutions containing iron(III) nitrate nonahydrate (INN) and tin(II) 2-ethylhexanoate (Sn-EH) were dispersed into single droplets of sub-100 μm diameter that were ignited by passing through a heated coil. At low precursor concentration, 50% of the INN-laden droplets indicate a gas bubble of about 5 μm diameter in the center of the droplet. The bubble persists for several hundred microseconds at a similar size. In almost all of these cases, the bubble expands at some point and the droplet ends up in a micro-explosion. In some of these instances, the droplet’s surface shows spatial brightness modulations, i.e., surface undulations, indicating the formation of a viscous shell. With increasing INN concentration, the fraction of droplets showing surface undulations, gas bubbles, and micro-explosions drastically decreases. This may be associated with a more rigid viscous shell and reduced mobility of bubbles. Bright incandescent streaks originating from the disrupting INN-laden droplets, may indicate sub-micrometer droplets or particles from within the droplets or formed in the gas phase. In contrast, Sn-EH-laden droplets show very fast disruptions, typically less than 10 μs from first visible deformation to ejection of secondary droplets. Bubbles and surface undulations were not observed.
期刊介绍:
Experiments in Fluids examines the advancement, extension, and improvement of new techniques of flow measurement. The journal also publishes contributions that employ existing experimental techniques to gain an understanding of the underlying flow physics in the areas of turbulence, aerodynamics, hydrodynamics, convective heat transfer, combustion, turbomachinery, multi-phase flows, and chemical, biological and geological flows. In addition, readers will find papers that report on investigations combining experimental and analytical/numerical approaches.