Shadow Doppler Particle Analyzer ( SDPA )
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Application Examples
Water Spray (Breakup of Liquid Film)
Irregularly shaped pulverized coal particles in a flame can be measured by SDPA together with a two-color pyrometer. Near the central axis of the burner (r/D=0), significant difference of size distribution between “burning” and “ensemble” particles is observed, especially as for the size range larger than 60 micrometers. The is because the larger particles require longer heat-up time to burn, and also because their larger inertial velocity compared with the smaller particles result in less residence time in the high-temperature re-circulation region in flame.
Courtesy of Dr. Prassas and Imperial College (UK)
The droplets in paint sprays are optically inhomogeneous and sometime include metallic components. The SDPA can be applied to such sprays. The velocity histograms, size histograms and size-velocity correlation maps for two nozzles are presented. The left figure below is for the nozzle with good performance (uniform finish of painting), whereas the right one is for the nozzle with bad performance. The size-velocity correlation map for the good nozzle shows small scatter than that of the bad one. The SDPA can evaluate the nozzle performance in advance and without examining if the finish is uniform.
The spray drying has various application fields such as production of coffee powders, medicine, detergent, and so on. For better product quality, optimization of drying tower design and drying process are very important. It is necessary to understand the phenomena taking place in the process, such as wet-wet, wet-dry, and dry-dry particle interactions, as well as particle-turbulent flow interactions. The SDPA measurement is conducted to explain the correlation between numerous setting parameters of the process and the quality of final products.
Courtesy of Mr. Kavounides and Imperial College (UK)
The breakup region of the liquid film in a spray contains measurable fractions of non-spherical droplets. The SDPA can also measure such non-spherical droplets, which is theoretically impossible by phase-Doppler anemometry. The figure below shows some images of non-spherical droplets in the break-up region. A special shape factor is introduced to compare the shape difference between droplets near the breakup region and those far from it. The larger scatter of the shape factor for the droplets near the breakup region result from the larger population of non-spherical droplets, and this tendency is especially distinctive for the larger droplets.
The SDPA is also useful for basic study of fluid-particle interactions. One of such examples is the measurement of free-falling particles. The upper figure shows size/terminal-velocity correlation of free-falling glass beads particles. During the measurement, some agglomerated particles are also observed as in the figure. The size/terminal-velocity correlation depends on the particle shapes (or how they agglomerate). The lower figure shows size/terminal-velocity correlation of copper particles. The left figure is for spherical particles, whereas the right one is for non-spherical particles. Due to the alignment effect for their orientation, the non-spherical particles show smaller aspect ratio than that of the spherical particles (unity in average), resulting in larger drag coefficient and slower terminal velocity.
Courtesy of Dr. Morikita and Keio Univ.(Japan)
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