MODELLING OF HYDROCYCLONES CFD Modelling Group Department of Mechanical Engineering University of British Columbia Process Simulations Limited

OBJECTIVES Feed Reject Accept HYDROCYCLONES lInvestigate the flow, particle, and fiber separation occurring in hydrocyclones lUse suitable turbulence models for high swirl fluid flows lDevelop mathematical models to compute fiber trajectories in complex flows lModel separation and fractionation according to properties in hydro- cyclones

HYDROCYCLONES l3-D turbulent flow is solved in hydrocyclones using k -  turbulence model with curvature correction lLagrangian method for tracking spherical particles three-dimensionally in hydrocyclones to obtain separation curves lSpherical particles are replaced in lagrangian model with rigid fibre, able to swell, and ignoring fibre rotation MODEL CHARACTERISTICS

HYDROCYCLONES NUMERICAL METHODS lDevelop 3D method using cylindrical curvilinear grid - combination of cylindrical co-ordinates and non- orthogonal grids lTake advantage of the cylindrical co-ordinates to calculate the physical geometrical quantities and curvature source terms accurately lCircular co-ordinates are used to account for the curved surface of each control cell in the calculation of geometrical quantities lThe centrifugal force is used to replace the curvature source term in the angular momentum equation

lThe standard k-  model fails to produce reasonable solution lUse modified k-  model proposed by Launder - model adds correction term in dissipation equation HYDROCYCLONES Ri t = Turbulent Richardson number u  = tangential velocity r = radial TURBULENCE MODEL

HYDROCYCLONES lTraced by numerical integration of the particle velocity calculated from the fluid velocity and particle slip velocity lParticle slip velocity is solved from the dynamic force balance in radial, tangential & axial directions u  = tangential velocities U s = settling velocities V p = particle volume A p = projected area Particle Trajectory

HYDROCYCLONES lTurbulence model is proven to be critical lModified k-  model is identified as a good alternative for high swirl flows lModel is accurate for both flow simulation and separation prediction lModel can be used to analyse performance of industrial hydrocyclones - design, separation, optimisation

3 Different Hydrocyclones

COMPARISON (PARTICLES)

FIBER FRACTIONATION (a) Velocity vectors, (b) pressure contours, and (c) swirl velocity contours in a hydrocyclone

FIBER FRACTIONATION Influence of the particle density on fractionation Separation on diameter and length as function of the particle density

FIBER FRACTIONATION The difference between particles carried over at t = 20°C and t = 45°C. The yellow grid represents particles carried over at t = 20°C Influence of the particle diameter on fractionation

FIBER FRACTIONATION The combined influence of coarseness and specific surface on separation Influence of the particle coarseness on separation based on specific surface

FIBER FRACTIONATION Influence of particle length on separation based on diameter Influence of the particle length on fractionation

FIBER FRACTIONATION Influence of entry particle position on separation and fractionation (Fibre A - Early Wood, Fibre B - Late Wood) for an entry feed at the top of hydrocyclone (z = 0) Influence of entry particle position on separation and fractionation (Fibre A - Early Wood, Fibre B - Late Wood) for a 5 mm downward entry feed (z = 5 mm)

BENEFITS lIncrease operating efficiency for hydrocyclones lOptimize the hydrocyclones design lEvaluate the influence on fractionation of fiber wet density, fiber diameter, fiber length, and fiber specific surface lEvaluate the influence of the fluid temperature on fractionation lPredict the fractionation performance of a hydro- cyclone for given fiber properties

COPY OF PRESENTATION lGo to lPress on “FTP” from “Download ” menu lGo to directory “Hydrocyclone” lDownload files