AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A Hybrid Continuum-Molecular Dynamics Flux Matching Calculation Method for Collision Rate Coefficients
TOMOYA TAMADATE, Christopher Hogan Jr., Hidenori Higashi, Yoshio Otani, Takafumi Seto, Kanazawa University
Abstract Number: 882 Working Group: Aerosol Physics
Abstract Particle-ion or ion-ion collision in the gas phase, i.e. charging processes, are important in a variety of aerosol technologies and measurement systems. A central challenge in aerosol science is hence the accurate calculation of charging rates, defined as the collision rates between particles and ions, and recombination rates, which are ion-ion collision rates. Such collision rate coefficients are challenging to calculate in aerosols because neither continuum or free molecular approaches are strictly applicable. Fuchs’s limiting sphere model (Fuchs, 1963) is normally adapted to calculate collision rate coefficients for charging. However, Fuchs’ theory has a number of shortcomings; the theory assumes that when the colliding species are sufficiently far from one another (outside the limiting sphere), continuum equations of motion are valid and then inside the limiting sphere, motion is free molecular. Filippov (1993) noted that Fuchs’s model could be made much more general by choosing a sufficiently large critical distance beyond which continuum equations apply, and then noting that collisions with gas molecules inside limiting sphere should be accounted for. Limitations in computational speed at the time prevented complete implementation of Filippov’s approach. However, vastly increased computational power now enables application of this method, hence we have developed a hybrid continuum-molecular dynamics approach for collision rate calculations, where continuum equations describe motion for species farther apart than a prescribed sphere radius, and molecular dynamics calculations with LAMMPS are used to monitor motion inside the sphere radius. We show that the method is general, and enables all atom based models to be employed in charging rate calculations, along with a wide variety of transition regime rate calculations.