Page 201 - Advanced Mine Ventilation

Diesel Exhaust Control 181

11.4.7.2 Coefficients of Transverse Turbulent Dispersion

In turbulent systems, particularly in the face areas of mines, there is a strong tendency
for isotropy (i.e., E x ¼ E r ). Consequently, a fairly good estimate of E r is obtained from
Eq. (11.41).
A generalized estimate of E r can be obtained by analogy with the calculation of E x
as given below:
p ffiffiffi
E r ¼ 3:57 au Sc 0:4 Sc t l (11.44)

For values of Sc and Sc t as given earlier, Eq. (11.44) reduces to

p ffiffiffi
E r ¼ 2:35 au l (11.45)
The value of E r for rough pipes is obtained by substituting l r for l in Eq. (11.45)
where l r is the friction factor for rough pipes.
The relation of l r with Atkinson coefficient K was discussed earlier in Chapter 2.

11.4.8 Main Conclusion of Mathematical Modeling

Main conclusions and practical applications of mathematical models developed in the
chapter and computer models of Chapter 5 are as follows:

1. To calculate air for a single engine in the stationary mode, Eq. (11.8) provides satisfactory
results. For large values of E r , these quantities are approximately 50%e100% of that pro-
vided by the static dilution formula which is currently used for certification.
2. For a single engine moving in a roadway for a long travel time, the results from the effective
ventilation formula developed by Holtz and Dalzell [10] are in good agreement with Eq.
(11.5) developed here as a limiting case for Eq. (11.13). At present, effective ventilation is
not used for the certification of diesel engines.
3. When multiple diesel engines work in a roadway, it is difficult to generalize the air require-
ments. Eqs. (11.29) and (11.36) were used to determine the amount of air needed with mul-
tiple engines. The present certification requirements are that with a second and a third unit in
the same roadway, the air quantities should be 200% and 300%, respectively, of that required
2
with one unit. Under negligible leakage conditions (Eq. 11.36), the model predicts air re-
quirements of only 130% and 160% of that needed with one unit for two and three units,
respectively. For high leakage conditions, no generalized conclusion is possible. In such
cases, the actual leakage coefficient should be determined and air requirements calculated us-
ing Eq. (11.29).
4. Field studies conducted for multiple engines in a network of airways indicate good agreement
with computed values of diesel exhaust emissions. Concentrations were computed by aver-
aging emissions in the various modes of operation; e.g., idling, accelerating, cruising, and
decelerating by suitable weight factors.

2
Leakage coefficient less than 0.00005/m.