TSI Incorporated Seeding of Flows TSI LDV/PDPA Workshop & Training Presented by Joseph Shakal Ph.D.

TSI Incorporated Copyright 2008 TSI Incorporated Seeding Most neglected aspect in LDV Proper seeding can significantly increase measurement accuracy and rate Key parameter to optimize SNR Guidelines for selection Related issues TSI Particle Generators

TSI Incorporated Copyright 2008 TSI Incorporated Solid Seed Particles 25um & 40um Glass Beads PSL TiO um Silver Coated HGB 4um Nylon

TSI Incorporated Copyright 2008 TSI Incorporated Requirements Single Particle Parameters –Aerodynamic size –Signal strength (surface properties) –Safety and Compatibility with Test Equipment Composite Parameters –Concentration –Monodispersity –Size of Flow System TSI 3400A Fluidized Bed Particle Generator

TSI Incorporated Copyright 2008 TSI Incorporated Requirements Safety Parameters –Use Olive Oil – Toxicity: see MSDS –Flammability –System Compatibility: will moving parts be damaged by the particles? TSI 9307 Particle Generator

TSI Incorporated Copyright 2008 TSI Incorporated Particle Size Distributions Diameter 20 Volume (Mass) Based VMD = 5  m Number Based NMD =.4  m Diameter Diameter Diameter (Linear) (Log)

TSI Incorporated Copyright 2008 TSI Incorporated Seeding Techniques for Air Flows Generate liquid droplets –Direct use of generated droplets –Start with solution- leaves solid particle of solute when dry –Start with mixture of high & low vapor pressure materials (e.g., oil and alcohol) –Disperse solid particles suspended in a liquid by drying droplets Disperse dry powders Evaporation and condensation of a liquid –(Evaporation condensation generator) –TSI 9308 ‘Fog Generator’

TSI Incorporated Copyright 2008 TSI Incorporated Seed Particle Requirements Water and Air Water (n = 1.33) –Forward-scatter Generally no seeding is required –Backscatter Seeding often necessary Air (n = 1.0) –Seeding usually desirable

TSI Incorporated Copyright 2008 TSI Incorporated Seeding Water for Backscatter Conditions Laser - Argon-ionBeam spacing - 35 mm Power WBeam expansion x F.L mmMaximum velocity - 10 m/s Aperture mmSpherical particles SNR (dB) Settling Velocity (µm/s) ParticleTiO 2 PSLTiO 2 PSL Diameter(n = 2.9)(n = 1.59)(s.g. = 4.26)(s.g. = 1.05)

TSI Incorporated Copyright 2008 TSI Incorporated Particle Motion Relative to Fluid Ref: Feller & Myers (1976 ) Note that these relations could easily be made into a spreadsheet for to help with seeding particle selection.

TSI Incorporated Copyright 2008 TSI Incorporated Particle Response in Air 0.5 µm 1 µm 2 µm f 3db f 3db f 3db Particles in Airn  t 1 (µs)(kHz)t 1 (µs)(kHz)t 1 (µs)(kHz) Silicon Carbide Alumina Polystyrene Peanut Oil Microballoons— For air, settling velocity = 9.8 x Time Constant (t 1 ) in m/s Time Constant and Frequency Response

TSI Incorporated Copyright 2008 TSI Incorporated Particle Response in Water Settling Velocity (µm/s) Particles m 0.5 µm1 µm2 µm5 µm Silicon Carbide Alumina Polystyrene Relative refractive index m = n p /n w

TSI Incorporated Copyright 2008 TSI Incorporated Seed Particles - Air and Water Particles MediumDensityRefractiveDia (g/cc) Index (  m) Silicon Carbide Air/Water Nylon Air/Water PSLAir TiO 2 Air/Water Hollow Glass Beads (HGB)Air ? Silver Coated HGBWater (R) (I) Olive OilAir

TSI Incorporated Copyright 2008 TSI Incorporated Other Comments Anti-static additives can help prevent particles from sticking to glass or acrylic windows. Larostat is commercially available. Hydrophobic (Anti-fogging) coatings are now available for windows. Abrisa Corp can supply this type of window, also with AR coating. ‘Transparent’ conductive film is available to prevent static buildup on windows, & thus prevent particles from sticking. Initial results appear promising. Customer at Brigham-Young Univ. has done testing.

TSI Incorporated Copyright 2008 TSI Incorporated Summary Careful selection of particles can offer much improved signals in backscatter measurements in water In air, TSI atomizers are a proven liquid particle generation technique Solid Particles: –No universal solution –Acceptable particles and dispersion technique normally available for a given application.