Mean-Free-Path

Mean free path of air molecules. Migrated from Aerosol.jl@c8c640bb src/single_particle_dynamics.jl:22 (`MeanFreePath` @component). Calculates the mean free path from dynamic viscosity, pressure, molecular weight, and temperature (Seinfeld & Pandis 2006, Chapter 9, Eq. 9.6).

Mean free path of gas molecules in air for aerosol mass transfer. Uses the kinetic-theory relation λ = 2μ/(ρ_air c̄_air) where μ is the dynamic viscosity, ρ_air = PM_air/(RT) is the ideal-gas air density, and c̄_air = √(8RT/(πM_air)) is the mean molecular speed of air (S&P 2006, Chapter 12, Section 12.1.3). The resulting λ is the mean free path used to compute the Knudsen number Kn = λ/R_p (see knudsen.esm) and hence the appropriate mass-transfer regime (continuum, transition, or free-molecular). At standard conditions (T=298.15 K, P=101325 Pa) λ ≈ 65 nm. Migrated from Aerosol.jl src/mass_transfer.jl `MeanFreePathMassTransfer`.