Median diameter

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. 

Pj = solids density (kg m" ) d = particle mass median diameter (m)... 

The median diameter is a measure of the general size level, whereas the standard geometric deviation is a measure of the degree of uniformity. A completely uniform material (all particles the same size) would show up as a horizontal line in Fig 3 and have a standard geometric deviation of 1,0. A completely heterogeneous material would be represented by a vertical line which would have a standard geometric deviation of infinity... 

Mass median diameters determined by centrifugal sedimentation. 

Understanding particulate emissions, their formation and control, is another key issue in meeting the new particulate emission Hmits set by the new EURO emission standards. The particulate emissions formed in diesel engines have a mass median diameter of 0.05-1.0 gm. Particle consists of carbon with various HCs adsorbed on it including polyaromatic hydrocarbon (PAH) as well as nitro-PAH compounds. 

In particle size analysis it is important to define three terms. The three important measures of central tendency or averages, the mean, the median, and the mode are depicted in Figure 2.4. The mode, it may be pointed out, is the most common value of the frequency distribution, i.e., it corresponds to the highest point of the frequency curve. The distribution shown in Figure 2.4 (A) is a normal or Gaussian distribution. In this case, the mean, the median and the mode are found to fie in exactly the same position. The distribution shown in Figure 2.4 (B) is bimodal. In this case, the mean diameter is almost exactly halfway between the two distributions as shown. It may be noted that there are no particles which are of this mean size The median diameter lies 1% into the higher of the two distri-... 

The median diameter of limestone pellets in the ball growth region as a function of the granulation time on log-log scales is shown in Fig. 20. The corresponding size distributions are self-similar as illustrated in Fig. 21. 

S3) reported that the size distributions of teconite pellets are self-preserving over a wide pelletizing interval. The scaling factor Dw, weight median diameter, is related to the agglomeration time by the following empirical equation ... 

For several batches of the same catalyst with quite different mass median diameters, Gwyn found the exponent b to be constant, whereas the attrition constant Ka was found to decrease with mean particle size. Equation (1) is, therefore, valid for a particular size distribution only. Other... 

Theoretical calculations of unattached fractions of radon progeny require prediction of an attachment coefficient. Average attachment coefficients for aerosols of various count median diameters, CMD, and geometric standard deviations, ag, are calculated using four different theories. These theories are ... 

Theoretical calculations of unattached fractions of radon or thoron progeny involve four important parameters, namely, 1) the count median diameter of the aerosol, 2) the geometric standard deviation of the particle size distribution, 3) the aerosol concentration, and 4) the age of the air. All of these parameters have a significant effect on the theoretical calculation of the unattached fraction and should be reported with theoretical or experimental values of the unattached fraction. 

Figures 3 and 4 show the variation of the attachment coefficient with count median diameter for the diffusion, kinetic, hybrid and kinetic-diffusion theory for geometric standard deviations of 2 and 3 respectively.

In Figs. 6 and 7 the attachment coefficient is plotted against the geometric standard deviation using the four theories, for count median diameters of 0.2 ym and 0.3 ym respectively. 

Theoretical unattached fractions of RaA using average aerosol concentrations and count median diameters as found in track and trackless Canadian uranium mine are presented in Table III. The reported uranium mine aerosol properties are N 120,000 particles/cm3 and CMD = 0.069 ym for a trackless mine and N =... 

An aerosol size distribution can, therefore, be described in terms of the count median diameter, d, and the geometric standard deviation, a These parameters were obtained from experimental data using a diffusion battery method (Busigin et al., 1980). A diffusion battery is an assembly of a number of cylindrical or rectangular channels. The relative penetration of aerosols through different sizes of diffusion batteries at specified flow rates allows the aerosol size distribution to be calculated. 

The mean values of the activity and aerosol median diameters together with the best estimate of the standard deviation, an, based on the total number of measurements made for each parameter, are listed in Table V. Figures 5-8 show representative size distributions ... 

Table IV. Activity and Aerosol Size Distributions, Count Median Diameter (CMD) and the Geometric Standard Deviation (indicated in brackets)...

The working level concept evaluates the unattached fraction and the activity median diameter in an indirect way, through the dose conversion factor. This paper will show that in the domestic environment this is mostly inaccurate to estimate the dose. 

The fraction of unattached daughters (fp), the equilibrium factor (F) and the activity median diameter (AMD) are plotted in Figure 6 for all the measurements. The AMD is derived from the aerosol measurements. These three parameters are important in the dosimetric models. At the top of Figure 6 the effective dose equivalent is plotted, computed with two models called the J-E (Jacobi-Eisfeld) and J-B (James-Birchall) models in the NEA-report (1983, table 2.9, linear interpolation between AMD=0.1 and 0.2 ym). The figure also shows the effective dose equivalent calculated from the equilibrium equivalent radon concentrations with the NEA dose conversion factor (NEA,1983, table 2.11). 

Figure 6a. Evolution of the activity median diameter (A.M.D.), the equilibrium factor (F), the unattached fraction and the effective dose equivalent (AJ-B, V J-E, + NEA) during the case studies.

Table I. Calculated activity median diameter for attached radon daughters from measured aerosol characteristics (Tu, 1986).

Site Activity median diameter (jam) geometric standard deviation... 

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