On Sep 15, 2011, at 2:01 PM, Jed Rothwell wrote:

Horace Heffner wrote:

A 0.7°C temperature rise is significant with any thermocouple. That can't be noise. There is no question there must be a heat source in the cell.

Yes - it is the 80 kg of cell metal which has stored heat.

Stored heat can only be released monotonically declining. The rate cannot increase, as far as I know. It is passive. The temperature can only rise if you increase the insulation or slow down the flow rate with this system. Or generate heat, of course.

What Catania calls "thermal inertia" can only release heat at a declining rate.

This is not true. There can be a slow transmission rate in the flow of heat pulses through matter.

Of course there can be a slow transmission rate or flow of heat! I didn't say you can't have slow transmission; I said it cannot speed up on its own without some external or internal change. As far as I know that is thermodynamically impossible. Can you explain how this would work, or cite an example of this happening elsewhere? The flow of heat can only slow down, as the temperature difference between the two bodies decreases, per Newton's law.

It can never increase the temperature above where it reached when there was power going into the cell.

Again not true.

Sez who?

Sez me.  Who else?  8^)   The magic words are open sez a me.

Lemme put it this way: that is my understanding of thermodynamics, and I have never seen data from a calorimeter that contradicts it. Calorimeters would not work if this was possible. You could not tell the difference between power and a situation in which metal suddenly decides to increase conduction for no apparent reason, with no change in the lattice.

- Jed

Metal does not change its characteristics.

Jed, it appears you need to read up on "thermal diffusivity".


Your misconceptions demonstrate why high precision thermal FEA analysis is required to understand dynamic thermal systems. Using FEA you can see thermal pulses migrate through systems, and get an intuitive feel for the dynamics.

Here is a site that might be of use to you:

http://ccl.northwestern.edu/papers/ABMVisualizationGuidelines/palette/ examples/Heat%20Difussion/


However it only shows dynamic thermal flows through a single plate made all of the same material. There is no facility for insulating plate edges etc. Note that you can move the edge temperature sliders while the simulation is running.

If you visualize chunks of metal as capacitors and the heat conduction paths between them is resistors, then you can see that if you apply a variable signal to an RC network that it can propagate the signal in the form of pulses. It is possible I suppose to build the thermal equivalent of an RC transmission line for carrying thermal pulses. I don't know what application such a thing would have though.

Best regards,

Horace Heffner

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