Laser-Doppler velocimetry

The methods described in this book are primarily concerned with the measurement of the microstructure of complex fluids subject to the application of external, orienting fields. In the case of flow, it is also of interest to measure the kinematics of the fluid motion. This chapter describes two experimental techniques that can be used for this purpose laser Doppler velocimetry for the measurement of fluid velocities, and dynamic light scattering (or photon correlation spectroscopy) for the determination of velocity gradients. 

The intensity of the combined beams in the intersection region is simply 

If such a particle traverses the intersection region, light scattered by the particle will have an intensity that is modulated at a temporal frequency, 

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This system produces a steady laminar flow with a flat velocity profile at the burner exit for mean flow velocities up to 5m/s. Velocity fluctuations at the burner outlet are reduced to low levels as v /v< 0.01 on the central axis for free jet injection conditions. The burner is fed with a mixture of methane and air. Experiments-described in what follows are carried out at fixed equivalence ratios. Flow perturbations are produced by the loudspeaker driven by an amplifier, which is fed by a sinusoidal signal s)mthesizer. Velocity perturbations measured by laser doppler velocimetry (LDV) on the burner symmetry axis above the nozzle exit plane are also purely sinusoidal and their spectral... 

There are many nonintrusive experimental tools available that can help scientists to develop a good picture of fluid dynamics and transport in chemical reactors. Laser Doppler velocimetry (LDV), particle image velocimetry (PIV) and sonar Doppler for velocity measurement, planar laser induced fluorescence (PLIF) for mixing studies, and high-speed cameras and tomography are very useful for multiphase studies. These experimental methods combined with computational fluid dynamics (CFDs) provide very good tools to understand what is happening in chemical reactors. 

Davies, R. and Prcece, A.W. (1983). The electrophoretic mobilities of minerals determined by laser Doppler velocimetry and their relationship with the biological effects of dusts towards macrophages. Clin. Phys. Physiol. Meas. 4, 129-140,... 

LCR Locus control region LDH Lactate dehydro nase LDL Low-density lipoprotein LDV Laser Doppler velocimetry Le (Lewis X) leucocyte ligand for selectin... 

See also Planar cavity surface-emitting laser (PCSEL) diodes Vertical cavity surface-emitting laser (VCSEL) diodes compound semiconductor-based, 22 179 Laser Doppler velocimetry (LDV), 11 784 Laser Doppler velocimeters, 11 675 Laser-drilled surgical needles, 24 206 Laser dye energy levels, 14 702-703 Laser fabrication techniques, titanium, 24 857... 

In homogeneous turbulence, the one-point joint velocity PDF can be written as /u(V t), and can be readily measured using hot-wire anemometry or laser Doppler velocimetry (LDV). 

In an earlier phase of this work [9] the intensities of axial and circumferential components of velocity fluctuation were measured in the TC annulus, using Laser Doppler Velocimetry (LDV), for a wide range of cylinder rotation speeds. On average, the intensities of axial velocity fluctuations were found to be within 25% of the intensities of circumferential velocity fluctuations [9]. As in Ronney et al. [5], turbulence intensities were found to be nearly homogeneous along the axial direction and over most of the annulus width, and to be linearly proportional... 

Campbell and Hanratty (1982) used Lau s (1980) measurements with some special optics on a laser Doppler velocimetry system to calculate /3(f) near a fixed interface, in this case, the inside of a clear pipe. They determined w(z,t) from equation (8.52), and solved equations (8.49) and (8.50) numerically for / l(0- Finally, they applied equation (8.51) to determine Kl, which has been the goal all along. The end results (Kl) may then be related to the other, independent parameters that are important to the transfer process, such as diffusivity, viscosity, and turbulence parameters. Campbell and Hanratty performed this operation and found the following correlation ... 

Bickel, W. S., J. F. Davidson, D. R. Huffman, and R. Kilkson, 1976. Application of polarization effects in light scattering a new biophysical tool, Proc. Natl. Acad. Sci. USA, 73, 486-490. Bilbro, J. W., 1980. Atmospheric laser Doppler velocimetry an overview, Opt. Eng., 19, 533-542. Blanchard, D. C., 1967. From Raindrops to Volcanoes Adventure with Sea Surface Meteorology, Doubleday, New York. 

Laser Doppler velocimetry is a powerful technique for the in situ measurement of fluid velocities. The basic optical configuration for the measurement is shown in Figure 6.1. The velocity measurement is made at the intersection of two laser beams that are focused to a point in the flow. The use of laser radiation is essential since the light must be monochromatic and coherent. This is required since the intersection of the two beams must create an interference pattern within the fluid. Such a pattern is shown in Figure 6.2, where two plane waves intersect at an angle 2(J). The two waves will have the following form [55] ... 

Laser Doppler Velocimetry and Dynamic Light Scattering... 

Figure 6.3 Two-component laser Doppler velocimetry beam arrangement.

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