Surface median diameter

Using the Hatch-Choate equation for surface median diameter gives... 

Note that this result can also be found by using Eq. 2.11. With a lognormal distribution, the volume or mass median diameter will always be greater than the surface median diameter which will in turn be greater than the number median diameter. 

Thus we see that if the number distribution n (Dp) is lognormal, the surface distribution ns(Dp) is also lognormal with the same geometric standard deviation ag as the parent distribution and with the surface median diameter given by... 

Surface median diameter (SMD) That diameter where 50% of the surface areas are above and 50% below the diameter. 

Measurements of specific surface indicate that 16% of the total specific surface is contributed by particles less than 0.3 pm and 84% by particles less than 1.5 pm. Assuming that the particle size distribution is lognormal, calculate (without the aid of log-probability graph paper) the specific surface median diameter, the CMD, and the GSD. The specific surface is the surface area per gram of particles. 

Figure 4 (A, B) Number-frequency distribution and (C) cumulative number distribution of an aerosol of unit-density spheres. Indicated are the count median diameter (CMD), the surface median diameter (SMD), and the mass median diameter (MMD) of the number-frequency distribution. The 16, 50, and 84% size cut of the cumulative number distribution are shown. For further explanation, see text.

Median Diameter. The median droplet diameter is the diameter that divides the spray into two equal portions by number, length, surface area, or volume. Median diameters may be easily determined from cumulative distribution curves. 

Depending on operation conditions and metal properties, the shapes of the atomized particles may be spheroidal, flaky, acicular, or irregular, but spherical shape is predominant. The spheroidal particles are coarse. For example, roller-atomized Sn particles exhibited a mass median diameter of 220 to 680 pm. The large particle sizes and highly irregular particle shapes suggested that the disintegration process may be arrested either by the premature solidification or by the formation of a thick, viscous oxide layer on the liquid surface. The particle size distributions were found to closely follow a log-normal pattern even for non-uniform particle shapes. 

These equations can be derived from Eq. 2.11. It is important to note that crg will be the same regardless of the definition of diameter used. That is, with a lognormal distribution ag will be the same whether number, surface, or mass median diameters are being measured. 

Example 2.9 Given a lognormally distributed aerosol with a geometric mean diameter of 1.5 pm and a og of 2.3, what are the surface-area median diameter and the mass median diameter of this aerosol ... 

Choice of which average diameter to use in a given situation depends on how the diameter was measured or how it is to be used. For the case where aerosol mass is measured and the fractions collected are associated with specific particle diameters, the resulting average value is the mass median diameter. In studying chemical reaction rates, the volume-surface mean diameter may be more important than just the arithmetic mean or geometric number mean. 

The use of surfactants to modify the surface tension of an aerosol and alter its droplet size distribution has shown that their influence depends strongly on the characteristics of the solution to be aerosoled. The span, defined as 90% undersize —10% undersize/50% undersize, gives a measure of the width of the volume distribution relative to the median diameter of the droplets formed in the aerosoling process. Comparative studies performed with commercial air-jet and US nebulizers have shown that, under similar working conditions, the latter provide less heterodispersed aerosols, with span values ranging from 1.50 to 1.75, which are similar for aqueous drug solutions in the presence and absence of surfactants [156]. 

Fluid Viscosity (cP) Surface tension (dyne/cm) Mass median diameter (nm) 6 L/min 8 L/min ... 

Properties 99% pure, 1% of mica and quartz, specific density 2600 kg/m , BET specific surface area 24.8m-/g, median diameter 2.8 pm [2257]. 

The importance of particle surface and not particle mass was documented for carbon black particles (median diameter... 

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