# A question in heat transfer

1. Dec 2, 2014

### leftsaidfred

Hi, I'm new to this forum.

A colleague and me have a discussion in heat transfer between to bodies (thermal contact conductance)

Let's say yo have a body A and B (witch are identical), A is heated to a hundred degree Celsius, B is 0 degree Celsius. You then put the bodies A and B together. You record that the it took 10 seconds before the bodies A and B are at the same temperature (50 degrees Celsius).

You now to the same experiment again, but this time body A is heated to 1000 degrees Celsius, will it then take 100 seconds before body A and B are at the same temperature?

2. Dec 2, 2014

### Staff: Mentor

Welcome to PF!

The answer is approximately the same 10 sec. If you graph the temperature change it will look like a hyperbola, with the initial slope being a direct proportion of the temperature difference. So 10x larger DT means 10x faster heat transfer.

I say "approximately" though because mathematically they never actually reach equilibrium and you have to arbitrarily decide how close is close enough.

3. Dec 2, 2014

### leftsaidfred

Thank you russ watters for the answer :) so the "flow" of energy is like to vessels with pressure interconnected with a pipe and a valve, when the valve opens, the flow is equal to the square of the differential pressure? f=Sqr(P2-P1) ?

4. Dec 2, 2014

### Staff: Mentor

Sorry, that's a no on both counts: velocity in fluids is a square ROOT function of pressure (doubling DP yields a 1.4x increase in flow -- your equation was right but you said it wrong) but heat transfer is a direct/exact proportion (doubling DT doubles heat flow).

(Mod note: moved to mech - e)

Last edited: Dec 2, 2014
5. Dec 3, 2014

### leftsaidfred

Tank you Russ Watters :) You saved me and my coworker a lot of discussion