Velocimeters, laser Doppler

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

Sullivan, J. R, Windnall, S. E., and Ezekiel, S., Study of vortex rings using a laser Doppler velocimeter, AIAA Journal, 11, 1384-1389, 1973. 

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... 

Figure 6.1 Optical configuration for a laser Doppler velocimeter.

Schematic diagram showing the integration of a polarization modulated birefringence apparatus within a laser Doppler velocimeter. This shows the side view. L light source (a diode laser was used) PSG rotating half-wave plate design LS lens FC flow cell (flow is into the plane of the figure) CP circular polarizer D detector 2D-T two dimensional translation stage 3D-T three dimensional translation stage LDVP laser Doppler velocimeter probe.

The current status of prediction and modelling in the area of fuel spray combustion requires, among other parameters, the measurement of droplet or solid particle size distribution and the relative velocity between the fuel and the surrounding gas. Many optical techniques, based on laser light scattering, have been investigated to this purpose (Refs.1,2,2,]+,, 6 and j), but the only system able to simultaneously determine the size and the velocity is the dual-beam laser Doppler velocimeter shown in Figure 1. 

In measurement and visualization of gas-solid flow in fast fluidization, various techniques have been developed and used, such as pressure gradient, pressure fluctuation, capacitance probe, optical fiber probe, momentum probe, laser Doppler velocimeter, night-television, and video camera. The resulting data on local gas and solid velocity, solids concentration and its... 

The fiber-optic laser doppler velocimeter (LDV) is also used to measure particle velocity in gas-solid two-phase flow (Yang et al, 1991 Bai, 1991). Figure 8 shows a schematic diagram of the working principle. The... 

Velocity measurements were taken by using a laser doppler velocimeter with a green laser beam [25, 36]. Fig. 9 shows the velocity profiles measured with this... 

The flow pattern of the vortex in the secondary combustion chamber was measured with a Laser Doppler Velocimeter (LDV). The profile measurements were performed at various feed rates and air settings as well as different hardware configurations. The LDV measured the axial and tangential velocity vectors of the flow in the hot flame simultaneously. 

Left Laser Doppler Velocimeter (LDV) for profile velocity measuring system in the secondary combustion chamber. 

The flow pattern in the secondaiy combustion chamber was measured with a Laser Doppler Velocimeter (LDV). The burner was equipped with a heat resistant glass cover to give the laser diagnostic access to the combustion process. To make the flow patterns visible, magnesia powder particles were added to the primary and secondary... 

Instrument used (measured response) Dia-Stron erythema meter , Minolta Chromameter , Cortex Dermaspectrometer (all measure a redness index of erythema) laser Doppler Velocimeter (blood flow) Servo-Med evaporimeter (transepidermal or skin surface water loss)... 

Laser Doppler velocimetry has been combined with acoustic excitation to allow the derivation of the relaxation time for particles, from which the aerodynamic diameter can be calculated [132-136], The particle relaxation time is derived from the velocity amplitude of the aerosol particle and that of the medium while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure the velocity amplitude of the particle, and a microphone is used to measure the velocity amplitude of the medium. The aerodynamic diameter of the particle can be derived from the relaxation time and the known particle density. The method can be applied to real-time in situ measurement of the size distribution of an aerosol containing both solid and liquid droplets in the diameter range of 0.1 -10 pm. 

Intrusive measurement techniques such as a Pitot static tube and hot-wire anemometer [24-26], and nonintrusive techniques such as laser Doppler velocimeter and particle image velocimetry (PIV) have been used to study the flow field. Goh, Kusadomi, and Gollahalli [13-15] mapped the velocity field in the flame using a Pitot static tube with a pressure transducer (Barocel). Details of the techniques and selection guidelines are presented in books on experimental aspects of fluid mechanics. Interested readers are referred to Holman [27], Goldstein [28], and Miller [29], to name a few. 

It was intended, in this work, to give a possible explanation for the drag reduction phenomenon using a statistical analysis of the turbulent fluctuating velocity. For this purpose, a laser-Doppler velocimeter was used to measure the longitudinal local velocity in a round tube flow. The results support the previous experimental evidence in drag... 

Nakajima K. Laser Doppler velocimeter. Kikai-no-Kenkyu 47 65-71, 1995. 

Finding the path of the particle lends much information to the flow behavior of gas-solid systems. Very few measurement techniques can deal with the individual particle trajectory and its velocity. Some very important technological questions about particle flow may be made with such measurements. Laser Doppler velocimeters (LDV) are available to provide such experimental data. Numerical simulation offers another path for such analysis. The different aspect about finding the path of the particle is that the basic equation defining such behavior is nonlinear, requiring a numerical solution of the equations. This procedure should not be considered as too much of an obstacle, and one should be able to apply knowledge of numerical analysis and experience to such a problem. The basic equation or definition relates the particle position to its velocity and time as... 

The particle velocity is a very difficult parameter to determine experimentally. Pulse-injection techniques have been suggested for its measurement, as well as isolation of a section of the flow system by selenoid valves. The laser Doppler velocimeter system can be employed on dilute systems to measure the solids velocity. Table 4-3 gives a hsting of expressions for the determination of Up. 

Carlson, C. R. Turbulent Gas-Solids Flow Measurements Utilizing a Laser Doppler Velocimeter, Ph.D. Thesis, Rutgers University, New Brunswick, NJ, 1973. 

Lasers are power tools in gas-solids flows they can be used in dilute-phase systems to measure the particle velocities. These laser Doppler velocimeters (LDVs) require... 

For a standard PBT the error is on the order of 5% if the perpendicular distance is used. For the large-bladed impeller with a shallower angle, the errors are up to 70% This D also makes sense when measuring the primary flow with a laser Doppler velocimeter for determination of the flow number (see Chapter 6). It is very important in a mixing installation when one has to be concerned with clearances from the tips of the blades. 

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