Flerfasforskning vid Kemisk reaktionsteknik Chalmers Bengt Andersson Love Håkansson Ronnie Andersson
Mass transfer in turbulent boundary layers y + ()3effTDDDDKy+=+=+ >99% is transported by turbulence at y + =1 and Sc-number =2000
Planar Laser Induced Fluorescence PLIF Up to 64000 frames/second
Mass transfer in turbulent boundary layers PLIF measurement of dissolution and flux of fluorescent dye PIV measurement of the flow Develop a CFD model (Rans or LES) describing the flow close to the wall for different geometries Develop a general model for laminar and turbulent diffusion in boundary layers. ()3effTDDDDKy+=+=+ For flow parallel with surface
FLIF measurement Membrane Surface 18 y + =1 Cmean 16 14 Re=20000 12 10 8 Cavg 6 4 2 0-2 0 100 200 300 400 500 600 _m
Future work Identification of large turbulent eddies Develop tools for identifying eddies in time sequences (Wavelets?) Size and frequence Develop wall functions for mass transfer in liquids for solid surfaces, bubbles and drops Develop an understanding of the behaviour of turbulent eddies close to solid, porous and plexible walls
Ronnie Anderssons thesis Experimental equipment Studies performed in a novel reactor developed by AlfaLaval High turbulence levels can be achieved at low and moderate flow rates. Production and dissipation of turbulent kinetic energy occurs throughout the entire reactor and turbulence is much more homogeneous than in a STR. Flow-directing insert. Geometry of the Alfa Laval reactor, from patent application. Mixing elements in the flow insert.
Simulation techniques Turbulence modeling RANS LES Multiphase modeling Mixture model VOF model
Results from CFD simulations Comparison between simulations and experimental measurements. a.) Sauter mean diameter b.) cumulative volume fraction. System: water-octanol 1 vol% holdup, three different hydrodynamic conditions.
Results from the phenomenological studies Bubble breakup dynamics Water-Air Bubble breakup, record rate 4000 Hz _ = 0.072 [N/m], _ = 16 [m 2 /s 3 ], _ = 6 [ms]
Results from the phenomenological studies Drop breakup dynamics Drop breakup, record rate 1000 Hz _ = 0.053 [N/m], _ = 8.5 [m 2 /s 3 ], _ = 8 [ms]
Results from the phenomenological studies Drop breakup dynamics Drop breakup, record rate 1000 Hz _ = 0.0085 [N/m], _ = 3.7 [m 2 /s 3 ], _ = 10 [ms]
Results from model development New model describing the interaction frequency between turbulent structures and fluid particles New model for the breakup probability based on: two physical criteria, stress and energy, must be fulfilled for breakup to occur energy distribution of turbulent eddies of given size
Energy transfer to bubbles and drops Available energy in turbulent eddies in inertial sub-range ()2113233626ccueλπρλεπλλρ== Bubbles Turbulent normal stress Drops Turbulent normal stress Shear stress
Results from model development ()maxmin0 BddλλλΩ= ()0,dωλ& ()0,Pdλ ()()03133001431, 6ddcdndπαεωλλ =& ()()min0,pddχλϕχχ = mininterfacial energydisruptive stressmax,χχχ = ()()interfacial energy0interfacial energy0,availabl disruptive stress24cduλσρχ ()23.62cueλπλλρ= ()()expϕχχ= Comparison of predicted and measured breakup rates, dodecane drops, _ = 8.5 m 2 /s 3. ()222353limited00,4ceddρπλελ= ()()()0limited0,min,, availableedeedλλλ =
Results from model development Cumulative breakup rate for fluid particles a.) a.) close to equilibrium size b.) b.) far from equilibrium size
Results from the phenomenological studies Large scale deformations observed prior to breakup a.) bubble deformation b.) drop deformation. Statistics of bubble and drop breakup completely different for the same hydrodynamic conditions a.) b.) a.) bubbles b.) drops
Results from the phenomenological studies Summary of major observations. Characteristic feature Bubbles Drops Deformation degree Large scale Large scale Internal flow mechanism Yes No Daughter size PDF Unequal-sized Equal-sized Fragmentation Binary Multiple Not accounted for correctly in the models available in the literature
Spray formation
Spray nozzle 0.3mm water-dodecane 50 [l/h] 1 vol-% 50 [l/h] 2.5 vol-% 50 [l/h] 5 vol-%
Spray nozzle 0.3mm water-dodecane 100 [l/h] 1 vol-% 100 [l/h] 2.5 vol-% 100 [l/h] 5 vol-%
Spray formation can be identified Stable emulsion 10000 1000 Drop formation Intense spray jet formation spray formation 100 X* 10 1 0,1 10 100 1000 10000 Re Weak jet