# What is the difference between heat transfer coeffiecient and thermal conductivity?

Can you also explain the two in plain words ?

The two are confusingly similar. Heat transfer coefficient is given by: $$h = \frac{q}{\Delta T}$$ where $q$ is heat flux. This corresponds to the ratio of heat flux to the temperature difference between two points. Thermal conductivity is often given by: $$k = -\left|\frac{\mathbf{q}}{\nabla T}\right|$$ i.e. the ratio between the heat flux vector, and the temperature gradient vector (I've assumed the material is isotropic here). The difference is that $h$ is a property of an object or system, whereas $k$ is a property of material, the two can be easily related in 1D: $$h=kl$$ where $l$ is the length of the object.
• how do you find the lenght $l$ in $h=kl$? and can you suggest a book so that I can study this relation? – math Apr 20 '15 at 8:16
the heat transfer coefficient (h) is equal to the thermal conductivity (k) divided by the thickness of the object. $$h=\frac{k}{l}$$ the units for h are $[W/m^2 K]$
the units for k are $[W/mK]$