suggested that I try asking
in an engineering newsgroup (he also mentioned hearing about "thermal
inertia" being used to describe this phenomenon). I started doing that
today and came across Mr. Kolesnik's account. So I will <repeat> my post
below after a few comments.
In response to a sci.physics respondent (tadchem, Tom Davidson), I would
like to point out in the account I give below that the temperature
measurement was differential with both hands starting at room temperature.
He is generally right in saying "The human nervous system is a notoriously
unreliable and impossible to calibrate sensor", especially with single-ended
measurements (one hand). But the statement also implies an exaggeration to
the exclusion of trusting what we sense as humans and trusting only modern
test data. I see that Mr. Kolesnik experienced some of the same in his
respondents, but in his case he repeatedly experienced the same phenomenon
(I experienced it once), and neither of us fell of the potato truck
yesterday. True, in modern life it is possible to measure the phenomenon
with electronic instrumentation, and wouldn't that be nice to do. But such
a thing requires some effort and costs, which also in modern times is
generally not done without some chance of a payback on the investment. Such
an experiment might be done when someone with authority over efforts and
costs decides that maybe Mr. Kolesnik and I actually experienced something
interesting, interesting enough to imagine a payback of some kind for their
operation. Until then, the rest of us are stuck with our nervous systems to
observe with our hand (differential is better) the heat spike produced when
a steel rod with a red hot end is quenched. Like Mr. Kolesnik, it isn't the
<repeat post 1 on>
As an example, from page 34 of
http://web.mit.edu/2.151/www/Handouts/EnPwrFlow.pdf (other references easy
"Thermal Inductance: No significant physical phenomenon has been observed
which corresponds to energy storage due to heat flow in a "thermal
inductor". Thus only one thermal energy storage element, the thermal
capacitance, is defined."
and of course, we have thermal resistance.
So it appears that thermal resistance and thermal capacitance but no thermal
inductance phenomena have been observed. Does anyone know of any cases
where thermal inductance has been observed?
<repeat post 1 off>
<repeat post 2 on>
Thanks for your response (and Mikko Kiviranta's), as there have been very
few in this (and other newsgroups). I am asking others about their
knowledge of any cases of thermal inductance being observed, because it is
one explanation for an event that I experienced about 20 years ago. I'll
briefly describe the event.
I was holding a 6 foot long piece of rebar (about 1/2" diameter steel rod,
commonly used to reinforce concrete) at arms length while a friend I was
helping was cutting it in half with an oxy-acetylene torch (I think steel
melts at ~1400 C). It was cut in half and both ends were brightly red hot.
After cutting, I moved my hands towards the ends to hold one 3 foot piece in
each hand at the cool end. There was a D-shaped tank (about 12" wide, 3
feet long, 2 feet high, flat of D facing up) filled with water nearby, about
2 inches from the top. So I dipped one of the hot ends in the water
gingerly a few times to cool it at about a 30 degree angle from the floor.
I didn't want to make a lot of steam quickly, as I thought that rapid
cooling might alter the metal somehow and my friend was going to weld the
two pieces to a piece of angle iron afterwards. The steam ball made was
about 4-6 inches in diameter at most as I recall. Within 15 seconds or so,
the 3 foot rod I was cooling became so hot that I couldn't hold it anymore,
so I dropped it into the tank. I was still holding the other rod in my
other hand (still glowing red hot) and it was only slightly warm where I
held it. I cooled it off too and we went about the next step of welding the
two pieces to the angle iron.
I do not have access to a torch or rebar to recreate the event since then,
but I've often thought about what I experienced ever since. I wonder if I
experienced thermal inductance, analogous to an inductive kick in
electronics. I still wonder about it and would appreciate any considered
explanations you may have (or others in this group).
I looked into the case you state regarding the violation of the second law
and found an interesting statement on page 144 of
that leads towards "extended irreversible thermodynamics" (I'm still reading
on this). It notes the same thing you stated, and goes on to say:
"Now we can only draw the conclusion that this effect is usually of no
importance for us, but in no way we can conclude that there is no such thing
like a thermal inductance. An apparent contradiction results between
thermal inductance and the second law of the thermodynamics, which states
the well known fact that entropy is always increasing. By this it is
usually concluded, that a heat flow is directed along the gradient of
temperature. On the other hand, due to the relation (see text) a constant
heat flow can appear at a thermal inductance also if the temperature
difference disappears, which apparently contradicts the statement of the
second law of thermodynamics. The above consideration shows that the
phenomenon of thermal inductance is of importance, if we consider a
high-speed process, for example the heating by short-time laser pulses.
Classical thermodynamics assumes slow changes, so that the system is in a
quasi-stationary status. By inclusion of an additional state variable (i.e.
the flux of energy), it is possible to introduce a definition of entropy,
which is in accordance to the second law of thermodynamic, whereby the
contradiction is eliminated. This theory is call extended irreversible
<repeat post 2 off>