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EXPERIMENTAL STUDY OF EFFECT OF SOLID PARTICLES ON TURBULENCE OF GAS IN TWO - PHASE FLOWS

EXPERIMENTAL STUDY OF EFFECT OF SOLID PARTICLES ON TURBULENCE OF GAS IN TWO - PHASE FLOWS. Medhat Hussainov Laboratory of Multiphase Media Physics Tallinn University of Technology Estonia. Introduction.

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EXPERIMENTAL STUDY OF EFFECT OF SOLID PARTICLES ON TURBULENCE OF GAS IN TWO - PHASE FLOWS

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  1. EXPERIMENTAL STUDY OF EFFECT OF SOLID PARTICLES ON TURBULENCE OF GAS IN TWO - PHASE FLOWS Medhat Hussainov Laboratory of Multiphase MediaPhysicsTallinn University of Technology Estonia

  2. Introduction Dispersion of solid particles in turbulence flows is of importance in many nature and industrial processes. The transport of pollutants in the atmosphere and oceans, pulverized coal particles in furnaces and slurries in pipes are typical examples of these flows. It is well known that particles affect the parameters of turbulence. The influence of the particle on the turbulence intensity is of the most importance.

  3. OUTLOOK • Overview of the criteria of particle influence on turbulence; • The experimental results on two-phase grid-generated turbulence; • New criterion parameter of particle influence on turbulence; • Conclusions

  4. Criteria of the effect of particle on the turbulence intensity Gore and Crowe (1989): Particle size – Decreasing the turbulence intensity Integral length scale

  5. Velocity of the carrier phase Particle size Velocity of the dispersed phase Criteria of the effect of particle on the turbulence intensity G. Hetsroni (1989): - Increasingthe turbulence intensity

  6. S – interparticle distance d - particle diameter - volume fraction of particles - particle relaxation time - Kolmogorov time scale - integral time scale Criteria of the effect of particle on the turbulence intensity S. Elghobashi (1991):

  7. The main objectiveof our investigations is to clarify the dependence of change in the turbulent intensity on the phases velocity slip. The distinctive featureof our experiments was to provide of various velocity slip for the same particles without changing of flow parameters.

  8. Experimental facility

  9. Particle Glass Bronze Particle material density, kg/m3 2500 8900 Particle diameter, 700 109 Particle mass concentration, kg/kg 0.05 – 1.0 0.2 Fluid mean velocity, m/s 9.5 8.5 Grid mesh size, mm 4.8, 10 & 16 4,8 & 10 Grid solidity 0.49 & 0.36 0.49 Slip velocity, m/s 0 – +5 +1.5 – +2.5 Grid Reynolds number ReM 3040 – 10133 2720 – 5667 Experimental conditions

  10. glass particles velocity slip 3-4 m/s bronze particles velocity slip ~1.5 m/s The decay curves behind different grids

  11. æ Turbulence intensity vs the flow mass loading at the location X=450 mm vs the velocity slip at the location X=365 mm Dash lines denote the turbulence intensity for various grids in the single-phase flow.

  12. The change of the turbulence intensity by particles vs StE

  13. The change of the turbulence intensity by particles vsReL for different values of Rep vsRep at the location X=365 mm (*) - Hussainov, M., Kartushinsky, A., Kohnen, G., Sommerfeld, M. 1999.

  14. The change of the turbulence intensity by particles vsRep/ReL flow mass loading æ=0.14 kg dust/kg air (*) - Hussainov, M., Kartushinsky, A., Kohnen, G., Sommerfeld, M. 1999.

  15. The change of the turbulence intensity by particles vsRep/ReL flow mass loading æ=0.14 kg/kg

  16. Conclusions • The turbulence intensity in dependence on the flow mass loading is linear up to concentration 1 kg/kg; • The turbulence attenuation increases with decrease in Stokes number in the case of Stokes number > 1; • The ratio between particle Reynolds number Rep and turbulence Reynolds number ReL is proposed as criterion for considering the combined influence of the parameters of the dispersed phase and the initial single-phase flow on the turbulence intensity of carrier phase; • The value of the ratio Rep/ReL of 0.4 is the limit for our experiments and that value determines the character of the particle influence on the turbulence: at Rep/ReL < 0.4, the turbulence intensity is attenuated; and at Rep/ReL > 0.4, it is enhanced.

  17. The velocity distributions of particles and gas M=10 mm, Solidity=0.49 for large velocity slip for small velocity slip

  18. The velocity distributions of particles and gas M=16 mm, Solidity=0.36 for large velocity slip for small velocity slip

  19. Same physical models of the turbulence modification: Yuan & Michaelides (1992): Yarin & Hetsroni (1994):

  20. Same physical models of the turbulence modification: Kenning & Crowe (1996):

  21. - particle response time - ratio of the drag coefficient to Stokes drag - particle Reynolds number - interparticle spacing - drag coefficient

  22. Feeding/particle-accelerating device reservoir dosaging grids The operation principle was based on the mechanism, which accelerates the particles in thin tubules. The glass beads were brought from the reservoir (1) into the tubes (3) (their number was 50). Particles were accelerated in the tubules by the air flow. At the exit of the tubules, the air was separated by a suction fan through the chamber (5) and particles scattered from the device with zero momentum of the air flow. chamber tubesdiameter of 4 mm and a length of 400 mm

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