Convection and Thermal Resistance

[sonofptolomey]

I have a question...

Suppose you have a thin and long rectangular piece of aluminum.

You heat one end (pt A). The thermal resistance (steady state) from one end (pt A) to the other (pt B) would be

θ=ΔT/W
Where W= Watts of heat energy.
ΔT = temperature of ptA - temperature of ptB

Now suppose you expose ptB to significant convection, cooling it down and letting the system reach steady state.

Would the thermal resistance be different? Or is it constant?

I'm just confused conceptually.

I can easily argue both ways. I'm on the fence.

 

[sonofptolomey]

Really? No replies?

 

[gsal]

thermal resistance is a material property...so, depending on the material and the operating conditions you are interested in, you may consider its value a constant (if it does not vary much) or may have keep track of it if it varies significantly with temperature.

for your aluminum rod, with a temperature differential between one end and the other one...you probably have different thermal resistance values along the entire length...sure, you can always estimate a total, lumped value for it by taking dT/W.

 

[sonofptolomey]

Thanks, that's what I expected. So in the case of extreme convection, the aluminum rod temperature will steady (if convection continues unchanged) such that the ΔT/W will be constant.

Thanks!