All IO in the KineticGas package is in SI units, on a molar basis.

To support working in reduced units, pykingas uses the Units struct, found in pykingas/units.py. Models may implement the method get_reducing_units, which returns an instance of this struct, which holds conversion factors for quickly computing non-dimensional quantities from the SI-quantities returned by pykingas models.

The Units struct has the attributes

• T : Temperature (K)
• E : Energy (J)
• L : Length (m)
• m : Mass (kg)
• V : Volume (m$^3$)
• t : Time (s)
• F : Force (N)
• speed : Speed (m / s)
• rho : Density (mol / m$^3$)
• D : Diffusion coefficient (m$^2$ / s)
• p : Pressure (Pa)
• visc : Viscosity (Pa s)
• kvisc : Kinematic viscosity (m$^2$ / s)
• tcond : Thermal conductivity (W / K m)
• tdiff : Thermal diffusivity (m$^2$ / s)

Different models may use different scaling parameters to deduce the reducing factors. The MieKinGas model uses the Mie potential parameters, such that e.g. the dimensionless viscosity may be computed as

from pykingas.MieKinGas import MieKinGas
mie = MieKinGas('LJF') # RET-Mie for Lennard-Jones fluid
unt = mie.get_reducing_units()
T, p = 300, 1e5 # Temperature and pressure
visc = mie.viscosity_tp(T, p, [1], N=2) # Viscosity in SI-units (Pa s)

visc_red = visc / unt.visc # Viscosity in Lennard-Jones units

mie2 = MieKinGas('CO2,H2') # RET-Mie for CO2 / H2 mixture
unt1 = mie2.get_reducing_units(0) # Use potential parameters of first component for reducing units
unt2 = mie2.get_reducing_units(1) # Use potential parameters of second component

An overview of what reducing units different models use is found below

• HardSphere : No reducing units (has no energy unit)
• MieKinGas : Mie potential parameters
• ModTangToennies : Potential root (sigma) and well depth (epsilon)