Presentation on theme: "EXPERIMENTAL STUDY OF EFFECT OF SOLID PARTICLES ON TURBULENCE OF GAS IN TWO - PHASE FLOWS Medhat Hussainov Laboratory of Multiphase Media Physics Tallinn."— Presentation transcript:
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 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.
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
Criteria of the effect of particle on the turbulence intensity Gore and Crowe (1989): – Decreasing the turbulence intensity Integral length scale Particle size
Criteria of the effect of particle on the turbulence intensity G. Hetsroni (1989): - Increasing the turbulence intensity Particle size Velocity of the dispersed phase Velocity of the carrier phase
Criteria of the effect of particle on the turbulence intensity S. Elghobashi (1991): - volume fraction of particles - Kolmogorov time scale S – interparticle distance d - particle diameter - particle relaxation time - integral time scale
The main objective of our investigations is to clarify the dependence of change in the turbulent intensity on the phases velocity slip. The distinctive feature of our experiments was to provide of various velocity slip for the same particles without changing of flow parameters.
Experimental conditions 2720 – 5667 3040 – 10133 Grid Reynolds number Re M +1.5 – +2.50 – +5Slip velocity, m/s 0.490.49 & 0.36Grid solidity 4,8 & 104.8, 10 & 16Grid mesh size, mm 8.59.5Fluid mean velocity, m/s 0.20.05 – 1.0Particle mass concentration, kg/kg 109700Particle diameter, 89002500Particle material density, kg/m 3 BronzeGlass Particle
The decay curves behind different grids bronze particles velocity slip ~1.5 m/s glass particles velocity slip 3-4 m/s
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. æ
The change of the turbulence intensity by particles vs St E
The change of the turbulence intensity by particles vs Re p at the location X=365 mm vs Re L for different values of Re p (*) - Hussainov, M., Kartushinsky, A., Kohnen, G., Sommerfeld, M. 1999.
The change of the turbulence intensity by particles vs Re p /Re L flow mass loading æ=0.14 kg dust/kg air
The change of the turbulence intensity by particles vs Re p /Re L flow mass loading æ=0.14 kg/kg
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 Re p and turbulence Reynolds number Re L 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 Re p /Re L of 0.4 is the limit for our experiments and that value determines the character of the particle influence on the turbulence: at Re p /Re L 0.4, it is enhanced.
The velocity distributions of particles and gas M=10 mm, Solidity=0.49 for large velocity slipfor small velocity slip
The velocity distributions of particles and gas M=16 mm, Solidity=0.36 for large velocity slipfor small velocity slip
ParameterGrid М, mm4.81016 700109700109700 25008900250089002500 æ, kg/kg0,140,20,140,20,14 1,35E-043,29E-051,19E-043,07E-051,15E-04 U-U p m/s4,41,53,71,003,5 Re p 205,3310,90172,677,27163,33 3,760,323,760,323,76 St K 245017817301251130 St E 14912,974,86,3650,8 14,7224,1515,4124,7415,59 0,0730,0120,0360,00540,029
Same physical models of the turbulence modification: Yuan & Michaelides (1992): Yarin & Hetsroni (1994):
Kenning & Crowe (1996): Same physical models of the turbulence modification:
- particle response time - particle Reynolds number - interparticle spacing - drag coefficient - ratio of the drag coefficient to Stokes drag
Feeding/particle-accelerating device reservoir tubes diameter of 4 mm and a length of 400 mm chamber 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.