Thermal Resistivity

Overview

Engineering reference data for Thermal Resistivity in heat transfer.

Key Formulas

Fourier's Law

$q = -k \nabla T$

Heat flux proportional to temperature gradient.

Convective Heat Transfer

$Q = hA(T_s - T_\infty)$

Heat transfer between surface and fluid.

Stefan-Boltzmann Law

$q = \varepsilon \sigma T^4$

Radiative heat flux from a surface.

Thermal Resistance

$R_{th} = \frac{L}{kA}$

Resistance to heat conduction.

Variables

Symbol	Description	Unit
$q$	Heat flux	W/m²
$k$	Thermal conductivity	W/(m·K)
$h$	Convection coefficient	W/(m²·K)
$T$	Temperature	K
$\varepsilon$	Emissivity	—
$\sigma$	Stefan-Boltzmann constant	5.67×10⁻⁸ W/(m²·K⁴)

Thermal Resistivity and Thermal Conductivity Relationship

Thermal resistivity is a fundamental material property that quantifies how effectively a material impedes heat flow. It is defined as the reciprocal of thermal conductivity:

$r = \frac{1}{k}$

where:

• $r$ = thermal resistivity (m·°C/W or hr·ft²·°F/(Btu·in))
• $k$ = thermal conductivity (W/(m·°C) or Btu·in/(hr·ft²·°F))

This inverse relationship means that materials with high thermal conductivity (good heat conductors like metals) have low thermal resistivity, while materials with low thermal conductivity (good insulators like wood or foam) have high thermal resistivity.

Physical Interpretation

• Thermal conductivity ($k$) measures a material's ability to conduct heat
• Thermal resistivity ($r$) measures a material's ability to resist heat transfer
• A higher thermal resistivity value indicates better insulating properties
• This property is essential for calculating heat transfer through composite structures and selecting appropriate insulation materials

Unit Equivalences

The units for thermal resistivity and conductivity are reciprocals of each other:

• SI: $\text{m·°C/W} = 1 / (\text{W/(m·°C)})$
• Imperial: $\text{hr·ft²·°F/(Btu·in)} = 1 / (\text{Btu·in/(hr·ft²·°F)})$

References

• Original Source