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  • 12th International Symposium on Particle Image Velcoimetry

    Particle Image Velocimetry and Seeding Particles

    I recently attended the 12th International Symposium on Particle Image Velocimetry in Busan, Korea on behalf of Cospheric, a company that specializes in precision microspheres. With the hope of learning more about seeding particles involved in PIV research and what advancements in microsphere technology would benefit the work being done in flow visualization. Through conversations with many attendees I was able to gather information on some of the important factors involved in tracer particle and their ideal capabilities. An interesting addition to seeding particles brought up by several individuals was temperature sensitive spheres which could potentially provide temperature field information.

    Below is an example of neutrally buoyant microspheres which are used as flow tracers in PIV applications.

    Fluorescent Red Polyethylene Microspheres

    The venue, Haeundae Grand Hotel, was spectacular with multiple large halls available for the over 200 presentations. The surrounding city was a maze of markets and skyscrapers nestled between the mountains and coast. Wonderful weather graced us, even rivaling that of Santa Barbara. Which was not something I had considered possible. I had the pleasure and displeasure of trying many unique foods. With bibimbap from a shop near the beach and shrimp dumplings from a small business steeped in the steam used to cook their dumplings being definite highlights. While the eel which I am still unsure whether was cooked or not falling on the other side of the spectrum. I am still processing the wealth of information from ISPIV 2017 and will express my conclusions as it manages to leak from my head.

  • PIV Seeding – Microparticle Recommendations

    Flow Visualization can best be accomplished with colored or fluorescent tracing particles of the same density as the fluid being studied.Particle image velocimetry (PIV) is the term used for imaging the fluid flow using colored tracer particles.  Through high speed particle imaging the velocity of the particles can be obtained and mapped.

    Photo Courtesy of Wiki-CommonsFor PIV experiments in water there are a wide variety of 1g/ml microspheres available as seeding particles, Cospheric offers polyethylene seeding particles in a variety of colors (fluorescent and non-fluorescent) and sizes from 10-20um, on up to 1mm.

    Particle size selection is important to ensure that observations can be accurately made.  For imaging systems without any magnification or unaided human observation it is recommended to use micro-spheres that are larger than 200um.   Human eyes can resolve features down to about 75um, at 200um+ the particles will be large enough to be discernible.

    Correctly seeding the system is also important.  For most applications loadings of 0.1-0.3% are sufficient.  This is the equivalent of about 1 gram of particles per gallon of fluid in systems of 10-50 gallons (40-200 liters) .  Exact loading levels will depend on the individual experiment requirements.

    For aqueous systems, polyethylene micro-particles will require a surfactant to wet properly.  For general flow studies pre-wetting the PE microspheres with Simple Green concentrated cleaner works well.  For biological systems a bio-compatable surfactant such as Tween 20 or Tween 80 is recommended.

    Seeding particle color selection is important to ensure that sufficient contrast is achieved during testing.  Very bright fluorescent micro-particles are available in densities of 1g/cc  these offer not only bright testing under daylight conditions, but also the option of illumination with lasers or uv lights for increased system contrast.

    The recommended PIV seeding particles are available from Cospheric.

    For green lasers (530nm)  we recommend UVPMS-BR
    For dark backgrounds: UVPMS-BY, UVPMS-BG, BLPMS, ORGPMS, BSPMS, or WPMS
    For light backgrounds: GRYPMS, VIOPMS, UVPMS-BR, UVPMS-BO