Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Particle tracers

If the light-scattering objects originally present in the airflow are unsuitable for LDA measurements due to insufficient concentration or incorrect estimated flow-tracking capability, the air must be seeded with oil smoke, tobacco smoke, or titanium dioxide tracer particles or droplets. A simple smoke candle is generally suitable for seeding, even if the enclosure is large and the air path is not closed as in several cases of industrial ventilation. [Pg.1171]

PIV has become the most popular technique to measure velocity and turbulent properties (Figure 15.1). The movement of seed particles in a millimeter-thick laser sheet is measured by correlating two photos taken a few milliseconds apart. With two cameras, it is also possible to obtain a 3D vector of the velocity in that plane. The method gives, in general, very good resolution of the flow, but it requires optical access. Also, measurement close to walls can be problematic due to light reflections that disturb the measurements. One extension of PIV is the micro-PIV that uses fluorescent tracer particles, which allows all direct light, for example, reflections at the walls, to be filtered out [1]. [Pg.332]

LDV is the traditional method using tracer particles to measure velocity and one-point statistics of turbulent properties [2]. It is still a very useful technique and has the advantage that it can measure closer to walls compared to PIV. An inherent problem with LDV is that it does not measure at a specific point but rather at places... [Pg.332]

Radioactive particle tracking (RPT) can be used to map the velocity field by tracking the position of a single radioactive tracer particle in a reactor. The particle which may consist of a polypropylene shell contains a radionuclide that emits y-rays. [Pg.337]

Figure 15.10 Lagrangian trace of the tracer particle during one stay in a riser (From [14]). Figure 15.10 Lagrangian trace of the tracer particle during one stay in a riser (From [14]).
Figure 2.46 Section of a micro channel with electrodes embedded in the channel walls (left). When an electric field is applied along the channel, different flow patterns may be created depending on the potential of the individual electrodes. The right side shows the time evolution of an ensemble of tracer particles initially positioned in the center of the channel for a flow field alternating between the single- and the four-vortex pattern shown on the left [144]. Figure 2.46 Section of a micro channel with electrodes embedded in the channel walls (left). When an electric field is applied along the channel, different flow patterns may be created depending on the potential of the individual electrodes. The right side shows the time evolution of an ensemble of tracer particles initially positioned in the center of the channel for a flow field alternating between the single- and the four-vortex pattern shown on the left [144].
K. Luby-Phelps, P. E. Castle, D. L. Taylor, and F. Lanni, Hindered diffusion of inert tracer particles in the cytoplasm of mouse 3T3 cells, Proc. Natl. Acad. Sci. USA 84, 4910 (1987). [Pg.145]

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. [Pg.251]

The bed was first operated at the preselected conditions at a steady state then about 455 kg of the coarse crushed-acrylic particles, similar to that used as the bed material but of sizes larger than 6-mesh, were injected into the bed as fast as possible to serve as the tracer particles. Solids samples were then continuously collected from five different sampling locations at 30-second intervals for the first 18 minutes and at 60-second intervals thereafter. The samples were then sieved and analyzed for coarse tracer particle concentration. Typical tracer particle concentration profiles vs. time at each sampling location are presented in Figs. 38-42 for set point 3. [Pg.296]

Typically it took about 160 to 200 seconds to inject a pulse of about 455 kg coarse tracer particles into the bed pneumatically from the coaxial solid feed tube. It can be clearly seen from Figs. 38 to 42 that the tracer particle concentration increases from essentially zero to a final equilibrium value, depending on the location of the sampling port. The steady state was usually reached within about 5 minutes. There is considerable scatter in the data in some cases. This is to be expected because the tracer concentration to be detected is small, on the order of 4%, and absolute uniformity of mixing inside a heterogeneous fluidized bed is difficult to obtain. [Pg.296]

Case I. Instantaneous Injection of Tracer Particles. If itis assumed that the tracer particles are injected instantaneously, Wt = Wt° = a constant, Eq. (42) can be integrated with the boundary condition that X, = 0 at t = t0 to give... [Pg.305]

Case II. Uniform Injection of Tracer Particles. Since the large amount of tracer particles usually required more than 75 seconds to inject, the other limiting case would be to assume that the injection rate was uniform over the injection period, or... [Pg.305]

The solids mixing study by injection of tracer particles indicated that the axial mixing of solids in the bubble street is apparently very fast. Radial mixing flux depends primarily on the bubble size, bubble velocity, and bubble frequency, which in turn depend on the size of the jet nozzle employed and the operating jet velocity. [Pg.307]

Regular and high-speed movies were taken of the tracer particle movement around the jets at different velocities and different solid loadings. The tracer particles used are red plastic pellets of similar size and density to the bed material. The movies were then analyzed frame by frame using a motion analyzer to record the particle trajectories and the particle velocities. [Pg.308]

Typical particle trajectories observed in the movies are shown in Fig. 47 for a jet velocity of 62.5 m/s and a solid loading of 1.52. The time elapsed between dots shown in Fig. 47 was typically 5 movie frames, while the movie speed was 24 frames/s. The colored tracer particles were followed in the vicinity of the jet until they disappeared into the jet, as... [Pg.308]

Wt = cumulative weight of tracer particles inj ected after time t W = radial solids mixing flux... [Pg.322]

Xj0 = tracer particle weight fraction in the bed after complete mixing... [Pg.322]

Xj, X j = tracer particle weight fractions in annulus and in bubble street, respectively... [Pg.322]

The movement of individual particles in a liquid-solid fluidised bed has been measured by Handley et a/.(40) Carlos(41,42), and Latif(43). In all cases, the method involved fluidising transparent particles in a liquid of the same refractive index so that the whole system became transparent. The movement of coloured tracer particles, whose other physical properties were identical to those of the bed particles, could then be followed photographically. [Pg.313]

Carlos and Latif both fluidised glass particles in dimethyl phthalate. Data on the movement of the tracer particle, in the form of spatial co-ordinates as a function of time, were used as direct input to a computer programmed to calculate vertical, radial, tangential and radial velocities of the particle as a function of location. When plotted as a histogram, the total velocity distribution was found to be of the same form as that predicted by the kinetic theory for the molecules in a gas. A typical result is shown in Figure 6.11(41 Effective diffusion or mixing coefficients for the particles were then calculated from the product of the mean velocity and mean free path of the particles, using the simple kinetic theory. [Pg.313]

Solids mixing was also studied by Carlos(42) in the same apparatus, starting with a bed composed of transparent particles and a layer of tracer particles at the base of the bed. The concentration of particles in a control zone was then determined at various intervals of time... [Pg.313]

Internal circulation measurements are very difficult to obtain for gas bubbles (D8). Some results have been obtained for large liquid skirted drops using tracer particles (W2), and provide a qualitative picture of the internal motion as shown in Fig. 8.5. It is not clear whether there is a reverse vortex motion in the interior of a large fluid particle (as indicated by the dotted lines). Such a secondary vortex would appear to be necessary to satisfy velocity and stress continuity, but experimental evidence is inconclusive. [Pg.210]

In Fig. 3.38 let WF be the mass hold-up of particles in the reactor, Ga the mass rate of outflow in the steady state (i.e. the holding time or residence time r= If>/G0), and c the number of tracer particles per unit mass of all particles. Consider a shot of tracer particles input at t = 0, giving an initial value Co "mo/1Vr >n the bed. Applying a material balance ... [Pg.188]

Number of tracer particles per unit mass of all particles... [Pg.192]


See other pages where Particle tracers is mentioned: [Pg.316]    [Pg.328]    [Pg.333]    [Pg.508]    [Pg.204]    [Pg.210]    [Pg.236]    [Pg.236]    [Pg.493]    [Pg.220]    [Pg.221]    [Pg.296]    [Pg.309]    [Pg.321]    [Pg.322]    [Pg.55]    [Pg.355]    [Pg.326]    [Pg.144]    [Pg.145]    [Pg.337]    [Pg.381]    [Pg.265]    [Pg.193]    [Pg.160]   
See also in sourсe #XX -- [ Pg.305 ]




SEARCH



Radioactive Tracer Particle

Tracer particles, concentration

© 2024 chempedia.info