CFD Modelling Of Multiphase Flows - Imperial College London

NTEC1201431Lecture CFD-3CFD modelling of multiphase flowsSimon LoCD-adapcoTrident House, Basil Hill RoadDidcot, OX11 7HJ, UKsimon.lo@cd-adapco.comNTEC2201431Multiphase models and applications VOF– Free surface flows LMP– Droplet flows– Liquid film DEM– Particle flows EMP– Particle flows– Bubbly flows– Population balance– Boiling heat and mass transfers– Interphase mass transfer1

NTEC3201431Volume of Fluid (VOF) model Solve equation for volume fraction (based on conservation of mass) toidentify location of gas and liquid. α i .(α i u ) m! i t Momentum equation for the gas-liquid mixture: (ρmui ) (ρmu j ui τ ij ) p ρm gi M t x j xi Properties of mixture:NGas flowρ m (α i ρ i )i 1Nµ m (α i µi )i 1NTEC4201431Liquid flowSlug flow in interconnected subchannelsCalculation grid 204,512 cellsWater Inlet 0.23 m/s150 mm1.7 mm20 mm18.7 mmAir Inlet 2.0 m/sAir Inlet 0.5 m/s2

NTEC5201431NTEC6201431S. Tension 0.072Slug flow in interconnected subchannelsEffects of surface tensionS. Tension 0.063

NTEC7201431NTEC8201431Free surface flow in drink cartonLagrangian model for particle flows Equation of motion for individual particle:dudxmd d Fud ddtdt F force acting on particleParticleGas flow4

NTEC9201431Spray modelling Modified Han et al atomisation modelCharalambos (2002)!NTEC10201431Droplet collision and coalescence5

NTEC11201431NTEC12201431Spray coatingFluid film boilingSimulation of films and their evaporation on high temperature surfaces Walls above saturation temperature of droplet fluid Required multi-component film6

NTEC13201431DEM (Discrete Element Method) Linear momentum of particle:mid vi F Drag F Contact F Otherdt Angular momentum:Iik!!dω i τ ij M ijdtj 1[]!!!M ij µ roll FContact ωi! M ij rolling torque µ roll rolling friction coefficient.NTEC14201431Pneumatic conveying of particles in pipe7

NTEC15201431NTEC16201431Spreading of particles by conveyor beltsEulerian multiphase model Conservation of mass of phase k:N (α k ρk ) .(α k ρk uk ) (m! jk m! kj ) tj 1 Conservation of momentum of phase k: (α k ρ k uk ) .(α k ρ k uk uk ) tt α k p α k ρ k g .α k (τ k τ k ) M kParticleGas flow8

NTEC17201431Forces on a particle Forces acting on a particles:–––––––L, TBuoyancy, B.Drag, D.Lift, L.Virtual mass, V.Turbulent dispersion, T.Basset force.And others.ucDgB Buoyancy and drag are the dominant ones.udVudB Basset force is complicated and almost alwaysignored. Lift, virtual mass and other forces willbe considered later.gDNTEC18201431Slurry flow in horizontal pipeUniform inletMeasurement plane1mgVLiquid velocityInletParticle volume fractionDL 10mMiddleOutlet9

NTEC19201431Slurry flow horizontal pipeUniform inletMeasurement plane1mgVDL 10md 270 µm, vf 0.2,D 51.5mm V 5.4 m/sd 90 µm, vf 0.19,D 103mm, V 3 m/sd 165 µm, vf 0.189,D 51.5mm, V 4.17 m/sd 480 µm, vf 0.203,D 51.5mm V 3.41 m/sd 165 µm, vf 0.0918D 51.5mm V 3.78 m/sd 165 µm, vf 0.273,D 495mm V 3.46 m/s201431Particle suspension in stirred vesselLiquid Velocities0.50.40.30.20.10-0.1-0.2-0.3-0.4-0.5Uz ExperimentalUz Star-CCM Ur ExperimentalUr Star-CCM 0.81Solids Velocities0.50.40.30.20.10-0.1-0.2-0.3-0.4-0.5Uz ExperimentalUz Star-CCM Ur ExperimentalU/UtipNTECUr Star-CCM UthetaExperimental00.20.4r/R0.60.8110

NTEC21201431Gas dispersion in stirred vesselGas superficial velocity:U 0.0184 m/sNTEC22201431U 0.0448 m/sU 0.0835 m/sU 0.1175 m/sU 0.201 m/sComparison of gas holdup504540G asholdup[% ]353025E xperimentalSSTAR-CCM tar- ‐C C M 2015105000.050.10.150.20.25S uperfic ialveloc ity[m/s ]11

NTEC23201431Adaptive MUSIG ModelAn Eulerian population balance method for poly-disperse multiphase flows.NTEC24201431Adaptive MUSIG ModelMass and number density are redistributed between neighbour groupsso that each group has the same mass but new diameters.12 3 4 567812 3 4 5 6 7 8 d d12

NTEC25201431Droplet breakup through an orificeSauter Mean DiameterBreakup Rate (log scale)Turbulent-induced breakupShear-induced breakupNTEC26201431Boiling heat and mass transfers Conservation of energy for phase k: (α k ρk hk ) .(α k ρk uk hk ) . α k λk Tk µt hk Qk tσh Wall heat flux is modelled by three mechanisms:q!Tʹ′ʹ′ q!cʹ′ʹ′ q! qʹ′ʹ′ q!cʹ′ʹ′q! qʹ′ʹ′q!eʹ′ʹ′13

NTEC27Bartolomei (1982) – 147 bar experiments312014 D 0.012 m L 2mWater steam P 147 bar Tsat 613 K Q 0.42 - 2.21 MW/m2 G 1878 - 2012 kg/m2s ΔTsub 16 - 145 KgLWall heatfluxSub-cooled waterNTEC28201431Void fractionCondensation rateBart 22-26 : Comparison of axial void profiles14

NTEC29201431Multi-component multiphase model General species transport equation for phase k is: (α k ρkYk ) .(α k ρk ukYk ) . α k Dk µt tσY YDσS Yk Sk mass fraction of species or other scalar quantity, diffusion coefficient, Schmidt number, sources.NTEC30201431Oxygen transfer in aeration tankVolume fraction of airOxygen in airWaterAir injectorOxygen in waterOxygen level at water surface and exit15

NTEC31201431Summary VOF– Free surface flows LMP– Droplet flows DEM– Particle flows EMP– Particle flows– Bubbly flows– Population balance– Boiling heat and mass transfers– Interphase mass transfer16

CFD modelling of multiphase flows Simon Lo CD-adapco Trident House, Basil Hill Road Didcot, OX11 7HJ, UK simon.lo@cd-adapco.com NTEC 2014 2 31 Multiphase models and applications . Comparison of gas holdup 0 0.05 0.1 0.15 0.2 0.25 0 5 10 15 20 25 30 35 40 45 50 Experimental Star4CCM