Particle concentration, maximum

Desired Magnetic Kecore. In ore concentration, maximum recovery is desHed at all times. Rejection of middling particles, although sometimes desHed, is difficult to accomplish on wet magnetic dmm separators. 

In experiments with bubble-columns containing suspended sand particles with average diameter 0.12 mm, an increase in heat-transfer coefficient was observed with increasing sand concentration, maximum values of 6000 kcal/m2-hr-°C being measured for suspensions containing 50% sand (based on the liquid volume). 

Illustrative Values of Maximum Permissible Cloud Diameter for Various Particle Concentrations (for < , = 1 V/micron pp = 1 gm/cm3 Dp = 10 microns)... 

In the case of Zn and Cd, a subsurface dissolved concentration maximum in the oxic zone suggests supply via remineralization of sinking detrital biogenic particles. As with Pb and Cu, the dissolved concentrations of Zn and Cd decline as the anoxic zone is... 

Infrared spectra suggested that a sulfate ion coordinates to two titanium atoms as a bidentate in particles. The maximum particle size was found at Aerosol OT mole fraction of 0.35 in the mixtures. The particle size increased linearly with increasing the concentration of sulfuric acid at any Wo, but with increasing Wo the effect was the opposite at any sulfuric acid concentration. These effects on the particle size can be explained qualitatively in relation with the extent of number of sulfate ions per micelle droplet. These precursor particles yield amorphous and nanosized TiO particles, reduced by 15% in volume by washing of ammonia water. The Ti02 particles transformed from amorphous to anatase form at 400°C and from anatase form to rutile form about at 800°C. In Triton X-100-n-hexanol-cyclohexane systems, however, spherical and amorphous titanium hydroxide precursor were precipitated by hydrolysis of TiCl4 (30). When the precursor particles were calcinated,... 

Following are the airborne particulate cleanliness classes. Each class is defined by the maximum allowable number of particles equal to or greater than 0.5 and 5.0 pm in size per cubic foot of air. The class is considered met if the measured particle concentration per cubic foot is within the limits specified. 

To avoid the difficulties associated with the spherical diffusion equation, a useful hypothesis is the linear-driving-force concept. This arises when a parabolic concentration profile within the spherical particles is supposed - which is a good approximation in cases where there is a Thiele modulus of a maximum volume of 2-5 (that is, with some intra--particle resistance [50]). In these conditions, the volume-averaged intra-particle concentration is defined as ... 

Figure 6.39 shows the time development of particle concentrations. At long times the kinetics for a symmetric (Da = Db) and asymmetric (Da = 0) cases differ significantly in the latter case reaction proceeds more quickly. Note that the choice of the parameter L — 1 corresponds to the weak electrostatic field the Onsager radius R is small and coincides with the recombination sphere radius r0. The initial dimensionless concentration n(0) = 0.1 is not also too large it is only 10 percent of the maximum concentration which could be achieved under irradiation [12], The magnitudes of these two parameters were chosen to make our computations more time-saving. 

Fig. 7.13. (a) Particle concentration as a function of the temperature 0°C (curve 1), 50°C (curve 2), 100°C (curve 3), 150°C (curve 4), 200°C (curve 5) and 250°C (curve 6). The dashed line indicates that no aggregation takes place at these temperatures (for a given dose rate of p = 1017 cm 3s l). (b) The same for the mean number of particles in aggregates. Dashed curves are obtained by integrating over sphere with the radius 2r(). Note that the aggregation reaches its maximum at 100°C (curve 3). Full curves do not saturate with time-slow... 

These curves show four kinds of structures which are dependent on the current particle concentrations and the oscillation phases of the reaction rate K(t). The moment of time t = 295.0 corresponds to the K(t) maximum whose concentration Na(t) is close to its minimum value. The behaviour of the correlation functions reminds that shown in Fig. 8.5 but the function for the dissimilar particles has now maximum. After a short time interval, at t = 296.0, despite very small change of concentrations and the correlation functions for similar particles, the maximum in the correlation functions for dissimilar particles completely disappeared (K(t) has a minimum). 

The greater changes of the correlation functions are observed near 7Va(f) maximum shown in Fig. 8.6. The pattern for t = 330.7 corresponds to the K(t) maximum the correlation functions of dissimilar particles Y(r, t) has a considerable peak. In its turn, at t = 334.7 we observe K(t) minimum and no peak of Y. When particle concentrations change, so does the correlation function of similar particles. These changes as it is seen in Fig. 8.5 demonstrate the correspondence of the behaviuor of the correlation functions to the current particle concentrations. 

In this experiment the optical and electrical transients were recorded simultaneously for a dispersion containing relatively high particle concentration. The current-time curve reveals that in the initial movement, two species transit the cell at different times. Clearly both cannot be due to the movement of the particles across the cell the simultaneous optical measurement demonstrates that the motion of the charged particles is contributing only to the second maximum. The first peak is due to excess ions in the suspension, presumably the charge control agent which is put in specifically to assure proper charging of the suspended particles. 

In addition, maximum expansion occurred at pH = 12.5 in the PCS experiments compared with approximately 10.5 observed in the sedimentation and viscometry experiments. Since PCS is carried out at much lower particle concentrations, interactions between the charged particles at the higher concentrations are probably involved. Similar comparisons with non-expanding carboxylic latex particles were carried out in an effort to separate interparticle charge effects from true particle expansion in interpreting apparent particle sizes determined by hydrodynamic methods. 

The major limit to the practical use of these results is the maximum particle concentration, N, that can he allowed in order to preserve the single scattering condition. Roughly, Nmax(m-3)/wVp l and the probe volume, Vp, is varying as 1/sin. With Ji 1 , the maximum concentration can he about 10 m 3. With higher fi, the range of a monotonic relation between visibility and particle size is dramatically reduced. It has heen found possible, however, to overcome these difficulties and to measure particle size distributions in fuel sprays. 

The effective probe volume was about 10 mm3, due to the small diameters of the furnace windows, but single scattering conditions were easily achieved indicating a particle concentration of 10°m. Without optical access limitations the maximum allowed concentration could rise up to 10l0 m 3, by using larger. ... 

Determination of the maximum particle concentration is also of interest since it no longer constitutes a purely kinematical problem. Rather, the suspension contained within the unit cell is now a mixed object possessing both solid-like and liquid-like features. In particular, it behaves like a solid insofar as mutual impenetrability demands are concerned, whereas it behaves like a liquid in its ability to change its configuration (i.e., it can flow ). 

Example 17.9 An optical particle counter samples an aerosol at a flow rate of 175 cm3/min into a sensitive volume of 0.01 cm. What is the implied maximum particle concentration (in particles per liter) that can be sampled ... 

If the reactant pressure is 3 atm. at room temperature, the particle concentration is 10 cm. a minimum value of interest might be 10 /cm. Thus the maximum range of the product kA with the above values is 10 > kA > 10 , but the practical range we consider here is... 

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