particle-size segregation patterns in convex rotating drums by d.g.mounty & j.m.n.t gray
Post on 20-Dec-2015
218 views
TRANSCRIPT
Particle-size segregation patterns in convex rotating drums
By D.G.Mounty & J.M.N.T Gray
Motivation for the problem
Industrially important Segregation is important in rotating kilns and mixers used in bulk chemical, mining and pharmaceutical industries
[1] http://www.danntech.co.za
[1]
Axial Banding
In long drums, axial segregation can develop over longer time scales We want to understand the 2D base segregation problem
[2] Newey et al. (2004) Europhys. Lett. 66 (2)
[2]
Band in Band Segregation
Thin two-dimensional rotating drums
Focus on strong segregation Sharp transition between regions of large and small particles Thins drum suppress the axial instability We can perform experiments on the 2D base flow
[3] Hill et al. (1997) Phys. Rev. Lett. 78[4] Gray & Hutter (1997) Contin. Mech. & Thermodyn. 9(6)
Particle-size segregation and remixing
Segregation-Remixing equation
No small particle flux boundary conditions
We will study the non diffusive-remixing limit Dr = 0
[5] Savage & Lun (1988) J. Fluid. Mech. 189[6] Dolgunin & Ukolov (1995) Powder Technol. 83[7] Gray & Thornton (2005) Proc. R. Soc. 461[8] Gray & Chugunov, J. Fluid. Mech (In Press)
[7][8]
Mixture theory framework for segregation in dense flows Small particle concentration 0≤Φ≤1
Concentration shocks
Velocity field must be prescribed Construct exact steady and unsteady solutions Concentration shocks idealize sharp transitions Use shock-capturing numerical methods for general problems
[9]
[9] Gray et al. (2006) Proc. R. Soc. 462
Geometry of the full system
Base flow has two domains Dense avalanche at free surface Solid rotating body underneath
Use segregation theory to compute concentrations in avalanche region
Erosion
Deposition
Segregation in the Avalanche
Large
Small
Mixed
Erosion Deposition
Solve in the parabolic avalanche domain Jump in velocities and behavior at boundary
Segregation in the full system
What you might actually see Thin avalanche, sharp segregation
Simplified model
Find the surface by conservation of area Projection of all free surface positions
The mapping method
Integrate each species between surfaces Place sorted material down slope
Triangle experiment
Triangle simulation
Varying ratio
Varying fill
Symmetry
Symmetry of corresponding low and high fill levels We may restrict analysis to fills over 50%
8.3% 25.0% 41.7%
91.7% 75.0% 58.3%
Fifty percent
Not what the simulation predicts Different time scale Dynamics of avalanche and segregation within are critical
[10] Zuriguel et al. (2006) Phys. Rev. E 73
Various Figures
More sides implies shorter lobes Circle is limiting case
Square simulation
Overview
Fills over 60% and under 40% are well predicted Below 40% is more “industrially important”
Difference time series
At long time there seem to be two groups Fifty percent seems to be a special case
Possible Bifurcation
Very marked jump between 65%/70% More thorough study required