# Thermal Conductivity

Written by Jerry Ratzlaff on . Posted in Thermodynamics

Thermal conductivity, abbreviated as k, is the ability to transfer heat within a material without any motion of the material.  Depending on the material, the transfer rate will vary.  The lower the conductivity, the slower the transfer.  The higher the conductivity, the faster the transfer.

Typical thermal conductivity values for non-metallic solids can be found here.

## Thermal conductivity formulas

 $$\large{ k = \frac{Q \; l}{A \; \Delta T} }$$ $$\large{ k = \frac{Q \; l}{A \; \left( T_h \;- \; T_l \right) } }$$ $$\large{ k = \alpha \; \rho \; Q }$$

### Where:

 Units English SI $$\large{ k }$$ = thermal conductivity $$\large{\frac{Btu-ft}{hr-ft^2-F}}$$ $$\large{\frac{W}{m-K}}$$ $$\large{ A }$$ = area of object $$\large{ in^2 }$$ $$\large{ mm^2 }$$ $$\large{ \rho }$$  (Greek symbol rho) = density $$\large{\frac{lbm}{ft^3}}$$ $$\large{\frac{kg}{m^3}}$$ $$\large{ l }$$ = length or thickness of material $$\large{ in }$$ $$\large{ mm }$$ $$\large{ Q }$$ = specific heat capacity $$\large{\frac{Btu}{lbm-F}}$$ $$\large{\frac{kJ}{kg-K}}$$ $$\large{ \Delta T }$$ = temperature differential $$\large{ F }$$ $$\large{ K }$$ $$\large{ T_h }$$ = high temperature $$\large{ F }$$ $$\large{ K }$$ $$\large{ T_l }$$ = low temperature $$\large{ F }$$ $$\large{ K }$$ $$\large{ \alpha }$$  (Greek symbol alpha) = thermal diffusivity $$\large{\frac{ft^2}{sec}}$$ $$\large{\frac{m^2}{s}}$$

## Related Thermal Conductivity formulas

 $$\large{ k = \frac{ h \; l_c }{ Nu } }$$ (Nusselt number) $$\large{ k = \frac { v \; \rho \; C \; l_c }{ Pe } }$$ (Peclet number)

### Where:

$$\large{ k }$$ = thermal conductivity

$$\large{ l_c }$$ = characteristic length

$$\large{ \rho }$$  (Greek symbol rho) = density

$$\large{ C }$$ = heat capacity

$$\large{ h }$$ = heat transfer coefficient

$$\large{ Nu }$$ = Nusselt number

$$\large{ Pe }$$ = Peclet number

$$\large{ v }$$ = velocity