Turbulence, Heat and Mass Transfer (THMT 09) Poiseuille flow of liquid methane in nanoscopic graphite channels by molecular dynamics simulation Sapienza Università di Roma, September 14, 2009 M. T. HORSCH, J. VRABEC, M. BERNREUTHER, H. R. HASSE SFB 716
Molecular modeling Geometry: Bond lengths and angles Electrostatics: Position and magnitude of point polarities Dispersion and repulsion: Lennard-Jones potential parameters THERMODYNAMIK UND ENERGIETECHNIK
Ethylene oxide: Simulation challenge Industrial Fluid Properties Simulation Collective
Ethylene oxide: Deviation from experimental data sat. liquid density sat. vapor density 2nd virial coefficient vapor pressure enthalpy of vaporization normal boiling temperature critical density critical temperature sat. liquid isob. heat capacity sat. vapor isob. heat capacity sat. liq. isoth. compressib. sat. vap. isoth. compressib. surface tension sat. liquid shear viscosity sat. vapor shear viscosity sat. liq. thermal conductivity sat. vap. thermal conductivity uncertainty of reference molecular model -40-20 0 20 40 60 deviation from experiment reference / /%
Flow induced by an additional force z z Poiseuille flow periodic boundary condition acceleration a z of fluid molecules in z direction wall velocity v z = 0 in z direction -z Pressure drop: dp Fz = = dz V ρa z
Graphite model and implementation RDF 100 rescaled Tersoff 75 speedup 50 1.35 1.40 1.45 1.50 radius in units of Å Optimized potential parameters for graphite: Cutoff Attraction 25 0 no load balancing static load balancing 0 50 100 150 number of processes Repulsion R = 2.0 Å (1.8 Å) S = 2.35 Å (2.1 Å) μ = 2.275 Å -1 (2.2119 Å -1 ) λ = 3.587 Å -1 (3.4879 Å -1 )
Boundary layers and adsorption fluid density in units of σ -3 1.2 0.9 0.6 0.3 0.0 W = 0.075 d = 1 W = 0.160 d = 1 W = 0.353 d = 0.947 W = 0.497 d = 0.957 Wang et al. Kalra et al. 2 3 4 5 6 y coordinate in units of nm Lennard-Jones energy parameter: ε FW = W ε Lennard-Jones size parameter: σ FW = d σ T = 0.95 ε/k ρ = 1.005 ρ
Poiseuille flow of methane in a graphite channel
Fluid velocity profile 60 dσ center wall 60 50 50 density in units of mol/l 40 30 20 40 30 20 velocity in units of m/s 10 10 THERMODYNAMIK UND ENERGIETECHNIK 0 0 2 4 6 8 y coordinate in units of nm 0
Fluid velocity profile 60 50 wall dσ center wall 60 50 density in units of mol/l 40 30 20 40 30 20 velocity in units of m/s 10 10 0-4 -2 0 2 4 6 8 y coordinate in units of nm THERMODYNAMIK UND ENERGIETECHNIK 0
Fluid velocity profile 60 wall dσ wall velocity in units of m/s 50 40 30 20 r slip = 3.7 nm v slip = 40 m/s 10 0-4 -2 0 2 4 6 8 y coordinate in units of nm THERMODYNAMIK UND ENERGIETECHNIK
Properties of nanoscopic Poiseuille flow
Conclusion Molecular simulation is of increasing relevance for chemical engineering can be applied to nanoscopic flow, heat and mass transfer can analyze systems up to the μm scale as a HPC application Fluid flow in nanoscopic channels can be simulated by imposing an additional uniform acceleration on fluid molecules Highly accurate effective potentials for many fluids and solids are available, facilitating the simulation of real surface effects