Page 131 - Advanced Mine Ventilation

112 Advanced Mine Ventilation

Figure 8.1 A plot of settling velocity and Brownian motion for respirable dust particles.
To confirm this value from other published data shown in Table 8.1, the average
movement per second by Brownian motion and particle settling velocity were plotted
against log r and shown in Fig. 8.1.
The diameter of particle that has the same velocity as settling velocity as the
displacement by Brownian motion is 0.6 mm (unit density). This is in fair agreement
with the calculated value of 0.52 mm from Eq. (8.17).

8.4 Size Distribution of Respirable Dust Particles

The fine particle universe consists of particles of different sizes. The number of parti-
cles, surface area of particles, or the mass (weight) of the particle associated with
different sizes is called the number distribution, surface distribution, or mass distribu-
tion of the particles, respectively. It can be expressed as a frequency distribution or a
cumulative distribution. In frequency distribution, the percent number or mass (fre-
quency) associated with particle size is plotted on the y-axis against the size on the
x-axis, respectively. In cumulative distribution, all frequencies below the particle x
or above it are plotted against the particles size. Different particle universes follow
different distributions. We will discuss only three distribution laws here.