Applications - Particle Tracing

Tracer Particles - for optical flow measurement procedures

Optical procedures for the measurement of flow velocities don't measure the velocity of the flowing medium, but the velocity of optically detectable tracer particles, which must therefore be present in the flow. Some examples of procedures include:

  • Particle Tracking Velocimetry (PTV)
  • Phase Doppler Anemometry (PDA)
  • Laser Doppler Anemometary (LDA)
  • Particle Image Velocimetry (PIV)

We can offer a range of generators suitable for producing accurate and repeatable tracer particles including:

The behaviour of the tracer particles in the flow, as well as the light-scattering characteristics of these particles, are very important, so choosing a suitable particle and generator is therefore essential for the successful solution of a measuring task. This is often given low priority, even thought the cost of generation of tracer particles is considerably lower than a complete LDV system.

The required characteristics for tracer particles in gases are typically:

  • good flow following behaviour, which depends on the particle diameter, form and density
  • good light scattering behaviour, which depends on the particle; diameter, form and refractive index but also on the laser power, the wavelength of the laser as well as the optical setup e.g. forward or backward scattering.
  • particle size distribution and concentration stability
  • chemical nature of the particles e.g. with flame measurements they must be inert
  • safety - they must be physiologically harmless

A nice example of the impact of tracer particle size (all other parameters unchanged) on a visualisation is shown by the two pictures below:

4 micron DEHS 2 micron DEHS

The RHS used DEHS particles of 2µm and the LHS 4 ┬Ám. The turbulence is created by the leading edge of the delta wing and the smaller the particle, the smaller the turbulence core.

Please contact us for more detailed information.