Theory

With the Prandtl number constant, the thermal conductivity follows from the viscosity and the heat capacity, equation (1). The program evaluates the gas-side and outer-surface heat-transfer correlations of a heat-loss wall (Gnielinski (Gnielinski, 1975) for the pipe flow, Churchill and Chu (Churchill and Chu, 1975) for natural convection, Churchill and Bernstein (Churchill and Bernstein, 1977) for cross flow) with this conductivity, and passes $Pr$ to the JCA / JCAL equivalent-fluid models of an absorbing packing, whose thermal part depends on it (Atalla and Panneton, 2000).

The flow solver itself does not read this value: OpenFOAM's Sutherland transport model computes the gas conductivity from the viscosity and $c_v$ with its own (Eucken-type) relation (OpenFOAM user guide, 2026).

Equations

k = \frac{\mu\,c_p}{Pr}

(1)

where	meaning	unit
$k$	Thermal conductivity of the gas	W/(m K)
$\mu$	Dynamic viscosity (Sutherland)	Pa s
$c_p$	Specific heat capacity at constant pressure	J/(kg K)
$Pr$	Prandtl number (this setting)	-

Default and rule

Default: 0.71
Rule: 0.71 (air).
Source: The program uses the value in the gas-side and outer-surface heat-transfer correlations of heat-loss walls and in the gas properties passed to the JCA / JCAL packing models; the correlations and models are cited under Theory.

Valid range > 0; air 0.7-0.72

Values

Positive. Air and engine exhaust gas lie near 0.7.

Not in the flow solver

The value changes the correlation-based outer heat transfer and the JCA / JCAL packing, not the conductivity inside the compressible solve.

Theory

Equations

Default and rule

Valid range > 0; air 0.7-0.72

Related 4

References 5