Turbulent Diffusion Coefficient in Mine Airways

1
Turbulent Diffusion Coefficient in Mine Airways

• N. P. Widodo
• K. Sasaki, Y. Sugai
• R.S. Sayoga
• Risono

Kyushu University ITB Aneka Tambang, Pongkor
Presentation at 12th US/N.A. Mine Ventilation
Symposium, Reno
2
Presentation Outline

• Tracer gas method
• Diffusion coefficient
• Tracer gas measurements at Pongkor mine
• Tracer gas experiments
• Results
• Concluding remarks

3
Tracer Gas Method
Air leakages (where how much air) ?
(a) Measurement of SF6 volume based on its weight
Concentration time curve calculated at
downstream node
Gas release at upstream
(b) Injection of SF6 into airflow by breaking
the balloon
Blue line is total concentration
C
t
(c) Tracer gas concentration monitoring
Gas monitor at downstream
Airflow routes and quantity estimation by
matching measured concentration-time curves with
simulation
4
Diffusion Coefficient
Taylor (1954)
D is one of important parameters in simulation
D Diffusion coefficient for one
dimension E Effective diffusion coefficient
for airflow with velocity profile
Sasaki and Dindiwe (2002)
5
Pongkor Mine Ventilation
Mining method Cut-and-fill Production 852 ton
ore/day Diesel Equipments 7.7 185 kW
6
Estimation of Turbulent Diffusion Coefficient
with L/d Parameter
Taylor (1954)
Q Other parameters which affect E (?)
7
Experimental Apparatus
8
Curved Airways
Coordinate system
R/a 120
R 0.9 m
1.8 m
R/a 80
3.3 m
Circular - setting
Ellipse - setting
9
Laboratory Results
Re 5100
Re 3000
Laminar (Re 670)
Turbulent (Re 5100)
10
Laboratory Experiments discussion with Taylor
Eq.
R/a80
On the curved airways, secondary vortex flow give
an effect of reducing gas dispersion in axial
direction, so the diffusion coefficient becomes
smaller compare with that in the straight
airways.
11
Tracer Gas Measurements for Curved Airways
12
Curvature Effect on E for Mine Measurements
R/a Run 2 gt Run 1 3 E Run 2 gt Run 1 3
13
Tracer Gas Measurements for Straight Airways
14
Turbulent Diffusion Coefficient
Mine (complex curved) Ecurved airways
gt ETaylor (1954)
Lab (Single direction curved) Ecurved airways
lt ETaylor (1954)
Mine
Estraight airways ? ETaylor (1954)
Laboratory
15
Curved Mine- Airways
Airways with small R/a ratio tend to have small E
due to the secondary flow at curve
E has positive correlation with number of
curvature
16
Curved Mine- Airways
Turbulent diffusion coefficient in curved mine
airways plotted with L/d, R/a, and Nc
17
Conclusion

• Effective turbulent diffusion coefficients, E, in
  the mine ventilation airways have been evaluated
  as E 4 - 200 m2/s.
• Effective diffusion coefficient in mine straight
  airways can be estimated by Taylor equation
  (1954).
• For complex and long mine ventilation airways
  with branches and junctions, much higher of E
  value were evaluated. It can be expressed with
  empirical equation E 0.08 (L/d), where L/d is
  ratio of distance over equivalent diameter of
  airway.
• Curvature effect were observed in the lab and it
  was also indicated in mine.

18
Conclusion

• For single direction curved airways at laboratory
  experiments, secondary vortex flow give an effect
  of reducing gas dispersion in axial direction, so
  the E curved becomes smaller than E straight.
• On the other hand, 56 of the Pongkor mine
  measurements results show that E curved is larger
  than E straight, it may be due to complex
  velocity profiles and larger roughness on curved
  mine-airways which make stronger mixing effects
  on gas more than secondary vortex flow at curved
  airways.
• Other parameters which may affect diffusion
  coefficient is the number of curves. Airways with
  larger curves number tend to have larger E.

19
Thank YOU for your attention

• agung_at_mining.itb.ac.id