Naked Science Forum

General Science => General Science => Topic started by: Geezer on 21/09/2011 22:57:23

Title: Can something be hotter than the heater?
Post by: Geezer on 21/09/2011 22:57:23

When heating something, is it possible to make the thing that is being heated hotter than the thing that's heating it without doing anything other than transferring heat? (No compression, chemical changes, etc.)

Title: Can something be hotter than the heater?
Post by: RD on 22/09/2011 01:04:17

Not all the molecules are moving at the same speed ...

http://www.saskschools.ca/curr_content/chem30_05/1_energy/energy1_4.htm

So some of the heater molecules could be moving slower than some of the heated molecules.

Title: Can something be hotter than the heater?
Post by: Bored chemist on 22/09/2011 06:53:06

It's a matter of definition but you can get things very hot with laser heating.

Title: Can something be hotter than the heater?
Post by: Geezer on 22/09/2011 07:02:03

Quote from: Bored chemist on 22/09/2011 06:53:06

It's a matter of definition but you can get things very hot with laser heating.

Yes, that would work. A magnifying glass might work too.

I should probably qualify the question a bit. I was thinking of a situation where the heat is transferred primarily by conduction in some sort of heat exchanger.

Title: Can something be hotter than the heater?
Post by: peppercorn on 22/09/2011 11:42:23

Quote from: Geezer on 22/09/2011 07:02:03

I should probably qualify the question a bit. I was thinking of a situation where the heat is transferred primarily by conduction in some sort of heat exchanger.

This seems an odd question from someone of your, er, experience to be asking, Geezer.
...I'm guessing there must be something that makes you think that, what appears to be an unworkable situation, isn't necessarily so - could you share your thinking?


I actually had a similar thought some years ago when trying to think up a design for a solar-powered engine.
Ultimately though, any device I could conceive would still require a gas (air for simplicity) to be able to expand as it heated and then there is no way to avoid extra work being added if it's to be compressed (to allow higher T) again.

Title: Can something be hotter than the heater?
Post by: lightarrow on 22/09/2011 13:20:59

Quote from: Geezer on 22/09/2011 07:02:03

Quote from: Bored chemist on 22/09/2011 06:53:06

It's a matter of definition but you can get things very hot with laser heating.

Yes, that would work. A magnifying glass might work too.

I should probably qualify the question a bit. I was thinking of a situation where the heat is transferred primarily by conduction in some sort of heat exchanger.

But if you use laser, lenses, ecc, you are not using heat.
By definition, heat is the exchange of energy caused by a temperature difference only.
So, the heater *must* be hotter than the heated. Otherwise it's not heat...

Title: Can something be hotter than the heater?
Post by: Geezer on 22/09/2011 16:41:58

Quote from: peppercorn on 22/09/2011 11:42:23

This seems an odd question from someone of your, er, experience to be asking, Geezer.
...I'm guessing there must be something that makes you think that, what appears to be an unworkable situation, isn't necessarily so - could you share your thinking?

I'm a amateur, particularly in matters Thermodynamic. I was playing around with a thermodynamic calculator and it allows the situation I'm referring to. At first I thought it was ridiculous, but I think it's legitimate.

Title: Can something be hotter than the heater?
Post by: CZARCAR on 22/09/2011 18:31:25

a cold brick is placed atop a hot brick in a perfectly insulated enclosure. Eventually, the 2 bricks the same temp & then?
a hot brick is placed atop a hot brick with same scenario, & then what?
Q= does conductive heat act like convective in that it rises vs gravity?

Title: Can something be hotter than the heater?
Post by: CliffordK on 22/09/2011 20:04:58

Heat is just a form of energy.

"Hotter than the Heater"?

What about a heat pump?  Start with a rarefied gas.  Heat it up.  Compress the gas, and your end product is hotter than the initial gas.

Focused light was mentioned above.  Cubic Zirconium is made with an interesting process, I believe with essentially focusing a beam of microwaves at the middle of the crucible which is made out of powdered cubic zirconium.  Anyway, since it must be quite hot, the middle of the powdered precursor is heated without heating the edges to a temperature hot enough to melt the container.

Title: Can something be hotter than the heater?
Post by: Geezer on 22/09/2011 20:14:33

Quote from: CliffordK on 22/09/2011 20:04:58

Heat is just a form of energy.

"Hotter than the Heater"?

What about a heat pump?  Start with a rarefied gas.  Heat it up.  Compress the gas, and your end product is hotter than the initial gas.

Nope. No gas compression during the heat transfer.