Flerfasforskning vid Kemisk reaktionsteknik Chalmers. Bengt Andersson Love Håkansson Ronnie Andersson

Transcription

1 Flerfasforskning vid Kemisk reaktionsteknik Chalmers Bengt Andersson Love Håkansson Ronnie Andersson

2 Mass transfer in turbulent boundary layers y + ()3effTDDDDKy+=+=+ >99% is transported by turbulence at y + =1 and Sc-number =2000

3 Planar Laser Induced Fluorescence PLIF Up to frames/second

4 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

5 FLIF measurement Membrane Surface 18 y + =1 Cmean Re= Cavg _m

6 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

7 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.

8 Simulation techniques Turbulence modeling RANS LES Multiphase modeling Mixture model VOF model

9 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.

10 Results from the phenomenological studies Bubble breakup dynamics Water-Air Bubble breakup, record rate 4000 Hz _ = [N/m], _ = 16 [m 2 /s 3 ], _ = 6 [ms]

11 Results from the phenomenological studies Drop breakup dynamics Drop breakup, record rate 1000 Hz _ = [N/m], _ = 8.5 [m 2 /s 3 ], _ = 8 [ms]

12 Results from the phenomenological studies Drop breakup dynamics Drop breakup, record rate 1000 Hz _ = [N/m], _ = 3.7 [m 2 /s 3 ], _ = 10 [ms]

13 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

14 Energy transfer to bubbles and drops Available energy in turbulent eddies in inertial sub-range () ccueλπρλεπλλρ== Bubbles Turbulent normal stress Drops Turbulent normal stress Shear stress

15 Results from model development ()maxmin0 BddλλλΩ= ()0,dωλ& ()0,Pdλ ()() , 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 =

16 Results from model development Cumulative breakup rate for fluid particles a.) a.) close to equilibrium size b.) b.) far from equilibrium size

17 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

18 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

19 Spray formation

20 Spray nozzle 0.3mm water-dodecane 50 [l/h] 1 vol-% 50 [l/h] 2.5 vol-% 50 [l/h] 5 vol-%

21 Spray nozzle 0.3mm water-dodecane 100 [l/h] 1 vol-% 100 [l/h] 2.5 vol-% 100 [l/h] 5 vol-%

22 Spray formation can be identified Stable emulsion Drop formation Intense spray jet formation spray formation 100 X* , Re Weak jet