Converting Thermal Conductivity to Thermal Conduction/Resistance

Hi all

I want to convert thermal conductivity to thermal conductance. The problem is with the units.

for thermal conductivity the units are [W/(m.K)] and for thermal conductance the units are [W/K]

For E.g for copper thermal conductivity is 400[W/m.K]
how can I convert it to thermal conductance?Can it be simply by multiplying it my the length of the copper wire I am using?

Any help with be really appreciated.

Thanks and Regards
Hamza

tiny-tim
Homework Helper
Hi Hamza!
for thermal conductivity the units are [W/(m.K)] and for thermal conductance the units are [W/K]

For E.g for copper thermal conductivity is 400[W/m.K]
how can I convert it to thermal conductance?Can it be simply by multiplying it my the length of the copper wire I am using?

Yup!

You can always rely on the units …

just multiply by the length (in metres) …

"/m" means exactly what it says

hmm.. I think you need to multiply by the cross-sectional area and then divide by the length. The conductance should decrease with increased length and increase with larger area.

Consider if you add a second wire of equal size. You would expect the conductance to increase by a factor of 2 (and resistance drop by a factor of 2).

tiny-tim
Homework Helper
oops!

hmm.. I think you need to multiply by the cross-sectional area and then divide by the length. The conductance should decrease with increased length and increase with larger area.

Consider if you add a second wire of equal size. You would expect the conductance to increase by a factor of 2 (and resistance drop by a factor of 2).

oops! davidrit is right!

(I thought the thermal conductivity was of the wire, but I see now it's of the material … see http://en.wikipedia.org/wiki/Thermal_conductivity)

Thanks all...
very much appreciated.
I have a further query now which I have posted separately.