8.2. MEASUREMENT TOOLS AND TECHNIQUES
485
Figure 8.4 shows a small backscattering LDV fiber optic probe intended
for immersed use in the laboratory. The beam crossing point for this particular two-component probe is located approximately 100 mm from the front
end of the probe. The operation of the immersed probe is otherwise identical to the operation of the nonintrusive LDV with all the same advantages
(Wessels, et al. 1990).
Figure 8.4: Two-Component Immersible Laser Doppler Probe.
Laser Doppler velocimeters rely on the presence of minute particles in
the flow to scatter the incident laser light. Sometimes the fluid contains
enough naturally occurring particles to get good measurements from the
LDV system. However, best results are obtained when the flow is seeded
with particles of optimal size and in the proper concentration. Commonly
employed LDV seeding particles for water are
• Polystyrene latex (0.5 - 50 pm diameter) in concentrations
of 10 ppm
• Aluminum powder (< 10 pm diameter)
• Titanium dioxide (0.5 - 2 pm diameter)
485
Figure 8.4 shows a small backscattering LDV fiber optic probe intended
for immersed use in the laboratory. The beam crossing point for this particular two-component probe is located approximately 100 mm from the front
end of the probe. The operation of the immersed probe is otherwise identical to the operation of the nonintrusive LDV with all the same advantages
(Wessels, et al. 1990).
Figure 8.4: Two-Component Immersible Laser Doppler Probe.
Laser Doppler velocimeters rely on the presence of minute particles in
the flow to scatter the incident laser light. Sometimes the fluid contains
enough naturally occurring particles to get good measurements from the
LDV system. However, best results are obtained when the flow is seeded
with particles of optimal size and in the proper concentration. Commonly
employed LDV seeding particles for water are
• Polystyrene latex (0.5 - 50 pm diameter) in concentrations
of 10 ppm
• Aluminum powder (< 10 pm diameter)
• Titanium dioxide (0.5 - 2 pm diameter)