Mean size

One of the most important uses of specific surface determination is for the estimation of the particles size of finely divided solids the inverse relationship between these two properties has already been dealt with at some length. The adsorption method is particularly relevant to powders having particle sizes below about 1 pm, where methods based on the optical microscope are inapplicable. If, as is usually the case, the powder has a raiige of particle sizes, the specific surface will lead to a mean particle size directly, whereas in any microscopic method, whether optical or electron-optical, a large number of particles, constituting a representative sample, would have to be examined and the mean size then calculated. 

Atomization. Droplet heatup and evaporation calculations can be done for any droplet size, but are most often carried out to reflect the behavior of a mean-sized droplet. The finer the droplet, the less time required for the various steps in the destmction of the waste. 

Droplet trajectories for limiting cases can be calculated by combining the equations of motion with the droplet evaporation rate equation to assess the likelihood that drops exit or hit the wall before evaporating. It is best to consider upper bound droplet sizes in addition to the mean size in these calculations. If desired, an instantaneous value for the evaporation rate constant may also be used based on an instantaneous Reynolds number calculated not from the terminal velocity but at a resultant velocity. In this case, equation 37 is substituted for equation 32 ... 

L As subscript, referring to discharge Mean size of increment in size- cm in... 

In design, to predict the mean size and size distribution of product granules... 

In general, analytical solutions are only available for specific initial or inlet size distributions. However, for batch granulation where the only growth mechanism is coalescence, at long times the size distribution may become self-preserving. The size distribution is selfpreserving if the normahzed size distributions

[Pg.1906]

A well-designed atomizer will generate a cloud of droplets with a mean size of about 30 to 40 [Lm and a top size of about 100 lm for light oils such as No. 2 fuel oil. Mean and top sizes are somewhat larger than this for heavier fuel oils. 

To gather information which will enable selection of appropriate control equipment. If a source test determines that the emission is 3000 mg of particulate per cubic meter and that it has a weight mean size of 5 p.m, a control device must be chosen which will collect enough particulate to meet some required standard, such as 200 mg per cubic meter. (4) To determine the efficiency of control equipment installed to reduce emissions. If a manufacturer supplies a device guaranteed to be 95% efficient for removal of particulate with a weight mean size of 5 /rm, the effluent stream must be sampled at the inlet and outlet of the device to determine if the guarantee has been met. 

The effect of varying the mean pore size and number of pores on the predicted strength distributions of grade H-451 graphite are shown in Fig. 25. In this instance, both the mean size (SJ and number (N) of pores per unit volume was varied in the "SIFTING" code. This was necessary because the density was held constant, i.e., the pore fraction remains unchanged, and therefore a decrease of the mean pore size must be accompanied by an increase in the number of pores per unit... 

Comparing this result with Eq. (14.48) and Fig. 14.5, we see that the mean size of the particle in the sense of linear momentum, and therefore also in the sense of free-falling velocity, is always greater than the mean mass size... 

FIGURE 14.6 Log-normal probability size distributions, illustrating geometrical transposition between number, mass, and linear momentum curves and the mean size particle d,, which can be used in estimating the free-falling velocity of the particle group. 

Property mean sizes are derived by calculation from the actual distribution using a defined weighting for each size interval. 

Note In general, property mean size is not equal to mean property size, (i) property mean size is the more commonly used definition. 

The speeifie surfaee is the surfaee area of a powder per unit mass (or volume). It ean be ealeulated from the Sauter Mean size... 

The eoeffieient of variation is a statistieal measure of the spread of the distribution about the mean. In effeet, it is a seeond term to quantify a distribution in terms of its shape sinee many distributions may have a eommon mean size (in some respeet) but differ eonsiderably in the spread about that mean. 

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