Microstreaming effects on particle concentration in an ultrasonic standing wave

Authors

  • J. F. Spengler,

    1. Cardiff University, School of Biosciences, PO Box 915, Cardiff CF10 3TL, U.K.
    Current affiliation:
    1. Gelsenwasser AG, Abt PIA, Willy-Brandt-Allee 26, D-45891 Gelsenkirchen, Germany
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  • W. T. Coakley,

    Corresponding author
    1. Cardiff University, School of Biosciences, PO Box 915, Cardiff CF10 3TL, U.K.
    • Cardiff University, School of Biosciences, PO Box 915, Cardiff CF10 3TL, U.K.
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  • K. T. Christensen

    1. University of Illinois, Laboratory for Turbulence and Complex Flow, Dept. Theoretical and Applied Mechanics, 216 Talbot Laboratory, 104 South Wright Street, Urbana, IL 61801
    Current affiliation:
    1. University of New Mexico, Dept. Mechanical Engineering, ALbuquerque, NM 87131
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Abstract

It is shown that the magnitude of Rayleigh microstreaming convective drag on microparticles in water in a 3.2-MHz ultrasonic standing wave can be comparable to the lateral direct radiation force in the nodal plane (DRF1) and can significantly influence the microparticle aggregation. The transducer of a single half-wavelength chamber was excited to give a single particle aggregate. The estimated sound pressure amplitude was 0.5 MPa. Particle image velocimetry (PIV) measurements gave the average microstreaming velocity in the nodal plane as 450 μm·s−1, which is comparable to the 340-μm·s−1 value calculated from Rayleigh's theory. Movement of 25-μm latex particles was primarily determined by DRF1, while that of smaller 1.0 μm, particles was determined by Rayleigh microstreaming. A 15-μm latex particle velocity map, simulated from microstreaming data, the measured velocity map of 25-μm particles, and the cube-dependent relationship between DRF1's on particles of different sizes, was in reasonable agreement with a measured velocity map. Further evidence for the importance of microstreaming came from the result that velocities for 1- and 25-μm particles were of similar magnitude, but were opposite in direction.

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