Particle Velocity Measurement

The cross-correlation technique is used in the ANL capacitive instrument to measure particle velocity. The outputs from the velocity-sensing electrodes were amplitude-modulated capacitor currents. If one assumes that the output capacitance signals vary sinusoidally (Aasincoat), and the applied voltage to the 

FIGURE 6-23 Typical cross-correlation function obtained by ANL capacitive flowmeter for two slurry velocities (0.26 and 0.4 m/s) and two electrode spacings (1.52 and 15.2 cm). Coal concentration was 60 wt.%. 

FIGURE 6-24 Particle-velocity data obtained by flow diversion (Sv) in the ANL capacitive flowmeter over a range of coal concentrations. 

In conclusion, the capacitive mass flowmeter can be a reliable instrument for measuring the flow of dilute suspended solids. For the flow of high concentrations of suspended solids, the velocity measurement becomes inaccurate. The inaccuracy may be caused by the velocity profile effect, but further study is required to confirm the observation. 

FIGURE 6-26 PNA profile of 56% solid coal/oil slurry flow at 0.95m/s in a 2-inch pipe, at source-to-detector distance of 3.40 m. 

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In principle, there is no upper bound in measurements of particle velocity (or stress) using laser velocity interferometry. In practice, very high-pressure shock fronts can cause copious jetting of microparticles from the free surface (Asay et al., 1976), obscuring the surface from the laser beam. To alleviate this, optically transparent materials can be bonded to the specimen, and particle velocity measurements are then made at the specimen/window interface. This has the added advantage of simulating in situ particle velocity... 

Shock-compression science originated during and after World War II when experimental facilities for creating planar shock waves were developed, along with prompt instrumentation techniques enabling shock velocity and particle velocity measurements to be made. The main thrust of shock-compression science is to understand the physics and to measure the material properties which govern the outcome of shock-compression events. Experiments involving planar shock waves are the most useful in shock-compression science. 

Figure 7.2. Response of elastic-plastic solid to planar impact at X = 0 u = longitudinal particle velocity. Measurements are made as a function of time at fixed Lagrangian position X.

The different pressure measurement techniques alluded to in Kamlet s complaint may be grouped into particle velocity measurements, transmitted shock velocity measurements, pres-... 

Figure 3.31 Single fiber optic probe used for particle velocity measurement. (From Sekoguci et al., 1985. Copyright 1985 by American Society of Mechanical Engineers, New York. Reprinted with permission.)...

Solids Circulation Rate. The solids circulation rate was obtained from the particle velocity measurements at the downcomer side by following visually the tracer particles at the wall with a stop watch. The data reported here by Yang and Keaims (1983) are for polyethylene beads (907 kg/m in density and 2800 pm in average particle size) and hollow epoxy spheres (210 kg/cm3 in density and 2800 pm in average particle size). The experiments were carried out in a semicircular transparent Plexiglas apparatus, 28.6 cm in diameter and 610 cm in height. 

For more detailed description of particle-velocity measurements, see "Detonation, Particle Velocity in and Its Determination Andreev Belyaev (Ref 44, pp 247-49) describe a method of experimental determination of pressure of detonation, using the arrangement shown in Fig B, Here 1 is charge of an explosive enclosed in a metallic container, and 2 is a metallic (usually aluminum) plate, 1-2mm thick, firmly inserted as a cover at the end of cartridge opposite detonator, 3. On initiation of charge, a shock wave will spread to plate 2 and, when the wave reaches the outer surface of the plate, it will start to move with initial velocity VH (here H is nachaT-naya, which means initial). After determining this velocity experimentally, the... 

In a more recent study, Davis (Ref 13) again points out the nagging uncertainty in the interpretation of particle velocity measurements in detonations. Measured PHX 9404 particle velocities, according to Davis, agree with C-J theory, but measurements in Comp B or TATB/ Kel F 95/5 do not... 

W.A. Fraar, Pressure and Particle Velocity Measurements in DASACON , KN-69-478 tR), Kaman Nuclear, Colorado Springs (1969)... 

Qian, G., and Li, J. Particle-Velocity Measurement in CFB with an Integrated Probe, in "Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 320-325. Somerset, Pennsylvania (1993). 

Another method of particle velocity measurement is the double tip optical fiber, which consists of two groups of optical fibers with a certain distance between each other, as shown in Fig. 6. When a solid particle passes the probe tip, two signals with a certain time interval in between would be detected. This time lag can be computed by means of the cross-correlation function (Qin and Liu, 1982) ... 

Direct measurements of spout voidage have been made by Soviet workers, using the piezoelectric technique mentioned in Section IV,B. Simultaneously with particle-velocity measurements, they recorded the frequency with which the solid particles collided with the piezo-crystal from the number of peaks observed on the oscilloscope per unit time. The local voidage at the probe tip was calculated from these data using the equation... 

Class 3-Methods Based on Direct Mechanical Effects. These include the use of acoustical probes [57-71], acoustic impedance measurements [72—75], acoustic fluxmeter [76], the measurement of radiation forces [17,21,77—112], the distortion of liquid surface [ 113-115], surface cleaning, dispersive effects, emulsification [ 116-118], erosion [ 19,22,119-125], mass transfer measurements (electrochemical probe) [26,129], absorption methods [93,132], particle velocity measurements [132], and optical methods [133-141],... 

Particle velocity measurement in multiphase systems can be approximately categorized as invasive (probes, impaction devices) and noninvasive (rings, coils, optical beams). Yan (1996) has further detailed particle velocity measurement according to (1) Doppler methods laser and microwave (2) Cross-correlations methods capacitance, electrodynamic, acoustic or... 

Klinzing, G. E., A. Zaltash, and C. A. Myler, Particle Velocity Measurements Through Electrostatic Field Fluctuations Using External Probes, Particle Sci. Tech., 5, 1, 1987, pp. 95-104. 

Yan, Y., Spatial Filtering Method of Particle Velocity Measurement in a Pneumatic Suspension Using a Single Capacitance Sensor, Second Internl. Particle Tech. Forum, 5th World Congress of Chemical Engineering, Vol. VI, AIChE, San Diego, CA., July 14-18, 1996, pp. 581-586. 

FIGURE 4-24 Different types of fiber optic probes for particle velocity measurement. 

In order to obtain the instantaneous particle velocity directly from the signals of the reflected light of the probe for particle velocity measurement, Qin and Liu (1982) proposed a method to acquire the instantaneous particle velocity distribution with a logic discrimination method. 

The accuracy of the radioactive tracer velocity measurement was within 1.5%. Detector separation was measured to 0.02%, and the count rate peak locations were within 0.5% of the reading. The averaging of 15 particle velocity measurements reduced the typical velocity dispersion of 5.8% to 1.5%. 

Birchenough, A. and Mason, J. S., Local particle velocity measurement with a laser anemometer in an upward flowing gas-solids suspension, Powder Technol. 14, pp. 139-152, 1976. 

The findings described above are the basis for the application of LDA for particle velocity measurements in two-phase flows. A pre-requisite for successful applications of LDA for velocity measurements in two-phase flows is an unhindered optical access, putting a constraint on the permissible volume concentration and/or penetration depth. Nevertheless, numerous studies have... 

As indicated by Eq. 4, the particle velocity measured from the micro-PIV technique is a combination of the electrophoresis velocity of the tracer particles which is related to the particle zeta potential, p, and the electroosmotic flow field which is associated with the zeta potential of the channel surface, If micro-PIV experiments are carried out in an electrolyte in open-end and closed-end microchannels, according to Eq. 4, we can write the expressions for the micro-PlV-measured velocity of the tracer particles in open-end and closed-end rectangular microchannels as below ... 

The data set included particle velocity measurements of Yang et al. [125] and Rhodes et al. [126]. We assumed that the slip velocity at the center was equal to the particle terminal velocity. 

Klinzing GE, Zaltash A, Myler C. Particle velocity measurements through electrostatic field fluctuations using external probes. Particulate Science and Technology 5(1) 95-104, 1987. 

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

Methods based on direct mechanical effects, including measurements using acoustic probes, optical methods and acoustic impedance, radiation forces, liquid surface distortion or particle velocity measurements. 

The accuracy of the particle velocity measurements is normally approximated to 5 % of the maximum velocity for a well-aligned system. 

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