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Thermal Inductance

Thermal Inductance - Physics Forum

Thermal Inductance - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


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  #1  
Old 08-16-2005, 10:22 PM
s.morra
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Default Thermal Inductance



As an example, from page 34 of
[Only registered users see links. ] (other references easy
to find)

"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?


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  #2  
Old 08-17-2005, 12:07 AM
N:dlzc D:aol T:com \(dlzc\)
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Default Thermal Inductance

Dear s.morra:

"s.morra" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

Convective heat flow? Fluid momentum might provide phase change,
or some other "enabler". I seem to recall they have been able to
do "acoustic refrigeration", which shows a similar effect to what
you seek.

David A. Smith


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  #3  
Old 08-17-2005, 09:19 PM
tadchem
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Default Thermal Inductance


"s.morra" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...
thermal

Flow of electrons through a conductor induces a *magnetic field.* Motion of
a conductor through a magnetic field induces an *electric current.*

What do you believe the flow of *heat* should induce? Should some motion of
(whatever this induced phenomenon is) in turn induce a *flow of heat?*

"Analogies are like ropes - they ties things together well, but you won't
get very far if you try to push them." - Thaddeus Stout


Tom Davidson
Richmond, VA


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  #4  
Old 08-23-2005, 06:48 AM
s.morra
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Default Thermal Inductance

Thanks for your response (and Tadchem'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 looked into the acoustic refrigeration topic,
but I don't think it applies here (very interesting topic though).

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).

"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:[Only registered users see links. ]> wrote in
message news:1dvMe.57061$E95.21249@fed1read01...


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  #5  
Old 08-23-2005, 08:02 AM
tadchem
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Default Thermal Inductance


The human nervous system is a notoriously unreliable and impossible to
calibrate sensor.

Try the following:

Set up three bowls of water in a row before yourself. Fill one on one end
with very warm water (but not so warm that it would scald you) - about
50-55 C should do it. Fill the one on the other end with ice water at 0
C. Fill the one in the middle with water at room temperature - about 20-25
C.

Place one hand in each of the end bowls and hold it there for 30-60 seconds.
Then simultaneously move both hands into the middle bowl.

The hand that came from the hot water will tell you that the water in the
middle bowl is cold. The hand that came from the cold water will tell you
that the water in the middle bowl is hot.

Your anecdotal report suggests the experiment should be repeated with more
objective instrumentation.


Tom Davidson
Richmond, VA


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  #6  
Old 08-23-2005, 01:18 PM
N:dlzc D:aol T:com \(dlzc\)
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Default Thermal Inductance

Dear s.morra:

"s.morra" <[Only registered users see links. ]> wrote in message
news:[Only registered users see links. ]...

It hardens it. But welding will remove that "cold work stress",
and replace it with other stresses.


No.

Note that anything in excess of about 140 deg F is "too hot to
handle". Steam is hotter than this. Water, even heated water,
is an excellent conductor of heat... much better in fact that the
steel of the rebar. Quenching more of the rebar than just the
cut end, caused your impression of "thermal inductance".

We had a similar discussion on sci.engr.mech, where a blacksmith
indicated a similar "phenomenon". When sparks are flying, and
people are "wielding the axe", you can lose all track of time.
He didn't call it inductance, however.

David A. Smith


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