Turbulent Diffusion Coefficient in Mine Airways

1. N. P. Widodo K. Sasaki, Y. Sugai R.S. Sayoga Risono Turbulent Diffusion Coefficient in Mine Airways Kyushu University – ITB – Aneka Tambang, Pongkor Presentation at 12thUS/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. laminar y u x Tracer distribution (downstream) turbulent Initial tracer (upstream) Accumulation AdvectionDiffusion 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 1869.4 Pa, 49.9 m3/s 630 Pa, 53.3 m3/s 663.8 Pa, 55.5 m3/s Main Fan 3 Intake (Portal L.600 m) 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. z a R y x 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 Experiment’s discussion with Taylor Eq. straight R/a=120 R/a=80 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 > Run 1 & 3 E : Run 2 > Run 1 & 3

13. Tracer Gas Measurements for Straight Airways

14. Turbulent Diffusion Coefficient Mine (complex curved): Ecurved airways>ETaylor(1954) Lab (Single direction curved) : Ecurved airways<ETaylor(1954) Mine Estraight airwaysETaylor(1954) Laboratory

15. Curved Mine- Airways Taylor (1954) Airways with small R/a ratio tend to have small E due to the secondary flow at curve Taylor (1954) 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. agung@mining.itb.ac.id Thank YOU for your attention