Friction Coefficient and Mobility Radius of Fractal-Like Aggregates in the Transition Regime

The influence of geometric properties and particle size on dynamic properties of fractal-like aggregates was studied in the mass and momentum-transfer transition regimes. Two different methodologies were investigated. The Collision Rate Method (CRM) that determines the slip correction factor through the ratio of two molecule-aggregate collision rates, and the Adjusted Sphere Method (ASM) that assumes the existence of a virtual, flow-independent adjusted sphere with the same slip correction factor as the aggregate over the entire transition regime. The fractal-like aggregates were generated via a cluster-cluster aggregation algorithm. The CRM was used to calculate the adjusted-sphere radius of different aggregates: it was found to be approximately constant for monomer Knudsen numbers greater than 0:5, suggesting that it is independent of flow conditions. Two numerical expressions are proposed: one for the aggregate orientationally averaged projected area, which is proportional to its squared free molecular mobility radius, and one for the adjusted-sphere radius. Both expressions depend on geometric, non-ensemble averaged quantities: the radius of gyration and the number of monomers. The slip correction factor and the mobility radius of DLCA and RLCA aggregates were calculated using the ASM; for a given number of monomers, fractal dimension and prefactor, and Knudsen number their values were approximately constant. A fractal-like scaling law based on the mobility radius was found to hold. The corresponding mobility fractal dimension and prefactor were determined for different aggregates. Finally, the hydrodynamic radius, proportional to the friction coefficient, and the dynamic shape factor of DLCA and RLCA aggregates were also calculated.

MELAS Anastasios D.;  ISELLA Lorenzo;  KONSTANDOPOULOS A.;  DROSSINOS Ioannis; 

2014-12-17

TAYLOR & FRANCIS INC

JRC91997

0278-6826,   

http://www.tandfonline.com/doi/abs/10.1080/02786826.2014.985781#.VJA2EmM098E,    https://publications.jrc.ec.europa.eu/repository/handle/JRC91997,   

10.1080/02786826.2014.985781,