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Thermodynamics Answered

Is it possible to take a low heat spread over a large area and convert it into a high heat in a small area? For example a normal fireplace can't melt cast iron, but 2 or three create enough energy. Could you concentrate that? (thats just an example, I have a much more brilliant plan) Thanks

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guyfrom7up (author)2008-02-11

It's easy: Lets say you have a long fire. If you insulate it like a pryramid and have a hole at the top all of the heat has to go at that tiny hole. Take a magnifying glass, focus the sun's rays and presto, another example.

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tech-king (author)guyfrom7up2008-02-12

that pyramid may have draft problems though.

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CameronSS (author)2008-02-10

Nope. Entropy and energy dispersal. Energy will always flow from higher concentration to lower concentration.

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CameronSS (author)CameronSS2008-02-10

Ha! Beat Kiteman to a chemistry question! Eric, I DON'T want to hear about some magic doctorate work you did at MIT just to prove me wrong.

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Kiteman (author)CameronSS2008-02-11

>Raspberry<

Possibly something to do with you being awake hours after me?

Anyhoo, what you need to do is look into heat exchangers - such as the system used in Stockholm to pump the (widely dispersed) bodyheat of rail passengers into an office block.

Link to builder's website article.

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killerjackalope (author)Kiteman2008-02-11

how does my post up there sound, reasonable? the ones about pletiers and whatnot...

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Kiteman (author)killerjackalope2008-02-12

It does - we still don't know what Linux actually wants to do, though. I don't think peltier stuff will get hot enough to melt more than ice.

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killerjackalope (author)Kiteman2008-02-12

The idea is to use the peltier with something like say a heatsink on the 'cold' side to gather heat energy as an exchanger, make the hot side very hot... At the very least there may be some way of using these as a nice way to keep your coffee warm...

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user

I either proved you wrong or made an ass of myself, eric will have to decide... or kiteman

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killerjackalope (author)2008-02-10

i wondered if this was possible to do, so far I've had some crazy ideas involving heatsinks but I havn't even got a plausible enough idea for testing, There's probably a way to do this, involving a peltier unit or some such, what we need is basically a heat valve... The peltier idea would be using the unit to take heat in like active uptake in digestion - yeah wierd parallel but same principle, some energy is needed to fight the concentration gradient, if you have a plan involving fire you could make a concentrated spot of heat using some sort of 'energy focus-amajig' whether it's work in the slightest is a very big question...

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user

using a peltier unit like those of mini fridges too 'move' the heat

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user

I got that, I meant what would you do with it?

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user

"A Peltier cooler/heater or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other. Peltier cooling is also called thermo-electric cooling (TEC)." I wikipedia'd it and that seems capable of moving against a heat gradient... Also think about what a fridge does all day, it heats it's elements by taking heat out of a colder place... I just reworded this so it makes sense, there are ways to get high temp from low temp so you could 'concentrate' your three fireplaces in to something hotter...

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user

Sorry, I meant whet application were you going to use it for (to heat what?)

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user

oh right I thought you had an idea when you asked the question, I suppose it could be used as reverse air conditioning, from what i have figured the units are reversible polarity so you could make a big active air conditioner that heats and cools for less than a condensing type, not sure how efficient it would be but it's and idea. Also if the cold side was at say 100C and a small sealed chamber of these units was created it may become a useful 'super-oven' It might be possible to get massive temperatures for the like of smelting and casting... I don't know the limitations of these units but they might be quite useful.

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user

I thought you wanted to concentrate energy to make higher temperatures, peltiers appear to do that, they are cold on one side and hot on the other because energy is being moved... those mini fridges can be heated to around 70C in a cold room, and the energy input isn't anywhere near enough to make the heat itself... they must have some way of doing it...

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Goodhart (author)2008-02-11

Thinking of this from the physics end of things; "heat" is in the range of the IR when it is not within an opaque solid. It is the radiation emitted by excited molecules giving off energy. It is a form of energy that is sometimes difficult to "direct" or conduct efficiently.

[http://adsabs.harvard.edu/abs/1977soen.conf...64A Solar heat concentrators] are being developed. And there are several different styles of heat exchangers around, as well as a few patents for such.
There are other approaches as well....

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tech-king (author)2008-02-11

here are the three very abridged laws of heat transfer: 1) you cannot win 2) you cannot break even 3) although you can quit, you look bad.

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Gordon Freeman (author)2008-02-10

Sound plausible but I think you have the same problem of horses pulling a wagon, how dose this relate you may ask. You could have 100 horses but they all run at the same speed.

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user

True, but you could put them on a giant treadmill with a outrageous gear ratio

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Austringer (author)2008-02-10

You can push heat from a cold place to a warmer place but it takes work. For your example, it'd be a lot easier to make one big fire.

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