Optical anemometer

Nonintrusive Instrumentation. Essential to quantitatively enlarging fundamental descriptions of flow patterns and flow regimes are localized nonintmsive measurements. Early investigators used time-averaged pressure traverses for holdups, and pilot tubes for velocity measurements. In the 1990s investigators use laser-Doppler and hot film anemometers, conductivity probes, and optical fibers to capture time-averaged turbulent fluctuations (39). 

Optical anemometer An instrument for measuring gas flow rate using a laser, in which small frequency shifts are visualized as interference fringes. 

Figure 6.4. Schematic of optical arrangement in a phase-Doppler anemometer.

An interesting modification of this technique is the fibre-optic dynamic anemometer (FODA)143. A length of fibre-optic cable carries the laser beam to the interior of the dispersion. Back-scattered light, with its Doppler frequency shift, is returned to the detector along with reflected light and, again, the resulting beat frequency pattern is analysed. Since only a very small volume around... 

In this work, measurements of the mean velocity and the turbulent fluctuations in the flows generated by the two impellers were confined to the center line of the radial jet since this is the zone where the flow is most strongly influenced by the impeller style. Turbulent flow parameters were determined using a DISA Electronics Laser Anemometer System. As the name implies, this is an optical device that measures the instantaneous velocity at a point. The technique is linear which allows accurate flow measurements at very high turbulence levels such as found in mixing vessels. Since there is no probe, there are no flow disturbances and the measurement is independent of fluid properties. The anemometer used in this work was sensitive to the direction of the instantaneous velocity. 

Fig. 2. Schematic side view of the wind-wave tank. 1 blower, 2 honeycomb, 3 wave flap, 4 anemometer, 5 rain generator, 6 radar absorber plates, 7 wire, 8 laser, 9 laser optics, 10 X band antennae, 11 beach and overflow baffle, 12 diffusor, 13 slick deployment.

Moreover, the use of extended optical systems combined with additional validation criteria, such as the dual-mode phase-Doppler anemometer (Tropea et al. 1995) may effectively reduce errors resulting from the trajectory ambiguity An overview about extended PDA-systems will be given in section 7.3.4. 

Mignon, H., Grehan, G., Gouesbet, G., Xu, T.-H. and Tropea, C. Measurement of cylindrical particles using phase-Doppler anemometer. Applied Optics,, (1996)... 

Stieglmeier, M. and Tropea, C., Mobile fiber-optic laser doppler anemometer. Appl. Optics, 31, 4096-4105, (1992)... 

If the bubble size is not uniform, the bubble size disttibution can be measured using a variety of measurement tools such as optical probes, multipoint needle probes, or hot-fihn anemometers, and the Sauter mean diameter (i/sm) substituted for the bubble diameter (Azzopardi et al., 2011) (see also Eq. (4.3)). 

Ear-field nanoscopic measuring technique Ear-field optical nanoscopic measuring technique Laser-induced fluorescence photobleaching anemometer Nanoscopy Stimulated emission depletion... 

A Thermo-Systems (TSI) Laser-Doppler Anemometer was used to measure the resulting vortex shedding frequencies. This was accomplished by measuring the velocity fluctuations in the direction of flow at some distance downstream from the cylinders. This type of measurements, being inherently optical in nature, did not disturb the flow field and was not influenced by the presence of the polymer. 

Figure 28.5 Field-deployed TDLAS spectrometer for eddy-correlation trace-gas measurements. The gas sampling head (on the left) incorporates a non-dispersive IR H2O/CO2 sensor and an anemometer. Adapted from Werle and Korman, Appl. Opt., 2001, 40 846, with permission of The Optical Society of America...

Patrose B, Caram HS. Optical fiber probe transit anemometer for particle velocity measurements in fluidized beds. AIChE J 28 604-609, 1982. 

See instruction manual for fibre optic Doppler anemometer, published by SIRE (Scientific Instrument Research Establishment) Ltd., Southhill Chislehurst, Kent, England. W. H. Yanta, Measurement of Aerosol Size Distributions with a Laser Doppler Veloci-meter , National Bureau of Standards Special Publication 412, Aerosol Measurement, proceedings of a seminar on aerosol measurement held at National Bureau of Standards, Gaithersburg, Maryland, May 7, 1974. 

Figure 1. Schematics of the experimental system fibre optic system and hot wire anemometer are described as connected to the Riser Simulator Reactor.

No calibration—no drift. The laser anemometer has a unique intrinsic response to fluid velocity—absolute linearity. The measurement is based on the stability and linearity of optical electromagnetic waves, which for most practical purposes can be considered unaffected by other physical parameters such as temperature and pressure. 

Multicomponent bidirectional measurements. Combinations of laser anemometer systems with component separation based on color, polarization, or frequency shift allow one-, two-, or three-component LDA systems to be put together based on connnon optical modules. Acoustooptical frequency shift allows measurement of reversing flow velocities. 

A number of different optical configurations were proposed during the earlier days of laser-Doppler anemometer systems, they can all be classified as special interferometers in which one of the following interference effects occurs [58] ... 

In the data acquisition system there are 380 measmement channels. Temperature is measured inside the facility in 290 different points, out of which 126 are in the ice condenser, 65 are in the structures or in the insulations and 99 are measuring the temperatures of the atmosphere. Temperatures outside the facility are measured in 10 different locations. Pressures (total pressure, pressure difference between compartments, water level hight) are measured in 7 and humidities are measured in 10 different locations. The local gas velocities in the upper compartment are measured with a fiber-optics laser-doppler anemometer system (LDA), equipped with an industrial robot for maneuvering. 

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