Air properties are evaluated at the ambient temperature using curve fits to tabulated air data in U.S. customary units. Each property is expressed as a fourth-order polynomial in temperature \(T\) (°R):

\begin{equation}\label{eq:insulated-tank-poly} p(T) = c_4 T^4 + c_3 T^3 + c_2 T^2 + c_1 T + c_0\end{equation}

The following properties are computed (with scaling applied after polynomial evaluation):

Property	Unit	Scaling
Specific heat, \(c_p\)	BTU/(lb·°F)	× 1
Density, \(\rho\)	lb/ft³	× 10⁻²
Kinematic viscosity, \(\nu\)	ft²/s	× 10⁻⁴ / 3600
Thermal conductivity, \(k\)	BTU/(hr·ft·°F)	× 1

Thermal diffusivity is derived from these fitted properties:

\begin{equation}\label{eq:insulated-tank-thermal-diffusivity} \alpha = \frac{k}{\rho \, c_p}\end{equation}

Symbols

\(\alpha\)	Thermal diffusivity of air \([\unit{ \foot\squared\per\hour}]\)
\(k\)	Thermal conductivity of air \([\unit{ \btu\per\hour\foot\degreeFahrenheit}]\)
\(\rho\)	Density of air \([\unit{ \pound\per\foot\cubed}]\)
\(c_p\)	Specific heat of air \([\unit{ \btu\per\pound\degreeFahrenheit}]\)