Electricity from heat

[CraigD]

A Thermocouple used to convert heat energy to electrical energy is somthing we will see expanded in the future.

They’ve been used a lot already – a lot of satellites and space probes use RTGs, which are simply hot piles of radioisotopes wrapped in thermocouples and cooling fins.

 

Used in reverse – to pump heat when connected to an electrical power source – thermocouples (usually called Peltier elements when used this way) can be found all sorts of common places. Hardware geeks like to use them to cool the silly, overclocked CPUs. I have a 12-volt one built into a cooler, which can be used as either a small, vehicle-portable refrigerator, or a warming oven, with the flip of a switch.

 

There are some serious practical and theoretical limits to the efficiency of thermocouples, though. At best, they’re around 10% efficient, in practive about 5%, poor when compared to the 25% of a Sterling cycle engine connected to an electric generator. However, when you’re interested in something with no moving parts, near zero-maintenance, and practically unlimited lifespan (nice in a mini refrigerator, a PC heatsink, or a spacecraft), efficiency isn’t too bad a price to pay.

 

 

The most exciting up-and-coming technology for converting heat differences to energy involve “photonic crystals” and other materials that can convert radiation of various frequencies, including the infrared, into frequencies suitable for photovoltaic cells. Since a narrow-frequency photocell can be 75%+ efficient, and photonic cells can approach 100% efficiency, a device based on these technologies might be able to convert heat into electricity (but not the reverse) with dramatically better efficiency than any existing heat engine.

[televox212]

heres something interesting

A Sound Way To Turn Heat Into Electricity

 

Basically, it uses the difference between hot and cold air in a tube to produce an air current, which then passes through a whistle, producing cohherent, non-chaotic sound energy of an exact frequency, from the chaotic heat energy...then this sound energy can be used to drive a peizo-electric (sp?) device which produces electricy... there is physically no limit to the number of these devices that can be connected into an array.

 

Its still at the early stages of development.

[mdraut]

As The Photovoltic Cells Are There Today Which Can Absorb The Selected Raditions Only And Convert Them Into The Electricity.

So If Infrared Rays Will Be Absorbed They Will Be Of Particular Radiations Only . And Then Again Heat Is Not Only Infrared Raditions But Also The Random Motion Of The Molecules And Atoms .

So It Won't Solve Your Problem

[UncleAl]

Peltier effect. Run in electricity, separate hot from cold. Place between a hot source and and a cold sink, get out electricity. Google "thermoelectric generator". Remember Carnot efficiency vs. source and sink temps.

[skittlesmonkey]

if a change ( chemical or physical) is going to absorb energy, it has to following disorder. in a reversible reaction or cycle you cannot keep getting more disorderly. the energy to reestablish the order equals the entropy ( disorder) but since it is a function dependent on temperate and u absorbed energy ( heat energy) this value is greater and equal to the previous enthalpy and temperate value of the old entropy. in short i cant work unless u find some sort of loophole in the thermodynamic or chemical cycles we know. you need a heat source and a heat sink so u can follow disorder than it will work. nature is a stupid disorderly ***** and that id why this universe is going to die of a heat death.

[skittlesmonkey]

the whole enthalpy entropy thing is based on "statistical improbability" meaning that heat transfer can go either way, if i have 2 gas particles bouncing around in a container it is more likely that their speed will mediate rather than the faster one accelerating and the slower one decelerating. it is still possible, but as the number of particles increases approaches impossibility by chance. if you could build a membrane that lets fast particles pass through it without loosing speed that allowed cold particles to pass trough the other way, you can concentrate heat. you can make your own heat and cold sink making ANY amount of thermal energy in the universe available to us. doesn't matter it 5 K or 5000K we could use it. nanotechnology is the only ways i see how such a membrane could be made if it can ever be made but it would make energy pretty much free. unless mother nature has somehow made sure it doesn't work. god i hate her . :)

[CraigD]

if you could build a membrane that lets fast particles pass through it without loosing speed that allowed cold particles to pass trough the other way, you can concentrate heat. you can make your own heat and cold sink making ANY amount of thermal energy in the universe available to us.

Such a membrane would be an implementation of Maxwell’s famous demon.

 

It’s traditional to refer to a “door” in a “wall” opened and closed by the demon, rather than a nanotech membrane, but the principle is the same – the demon-opened door or the nanotech membrane is somehow “smart” enough to let faster-than-average-moving molecules pass through it in one direction, slower ones in the other.

 

A though experiment by Leo Szilard in 1929, “Szilard’s engine”, described an simple mechanical implementation of a Maxwell’s demon that didn’t require what we intuitively think of as more “smarts” than we credit a simple mechanical device with having, and also neatly explained why such devices don’t violate the 2nd law of thermodynamics: any single-molecule sorting operation requires the use of at least 1 bit of information, which increases entropy by at least as much as the sorting decreases it.

 

So, in principle, you could perform mechanical work with a Szilard-type heat engine, but doing so would “fill up” the machine’s memory. Once full, the engine would stop working until its memory was cleared. Clearing its memory would require at least as much mechanical work as was performed filling it.

 

I discussed this, and linked to a (surprisingly hard to find online) animation of a Szilard engine a few years ago, in this post.

 

The relationship between information and physical work is, IMHO, one of the most beautiful, epiphany-triggering one in science.

[skittlesmonkey]

yea I'm just saying a nanotechnology membrane is the only realistic approach to making this work, besides there has to be some way to sort out the more energetic particles without lowering their speed and without tracking them with bits of information 1 by 1.

[modest]

yea I'm just saying a nanotechnology membrane is the only realistic approach to making this work, besides there has to be some way to sort out the more energetic particles without lowering their speed and without tracking them with bits of information 1 by 1.

 

If it can be done on a small scale with nanotechnology then I'd assume it could be done on a large scale with macrotechnology. Can you think of a way to... let's say... fill a box with ping pong balls bouncing around at different speeds and have a membrane segregating the box allowing the fast ones to move to one side and slower ones move to the other side without lowering their speed or tracking them?

 

~modest

[skittlesmonkey]

what about a 2 story centrifuge with a gas in it. have a flow up close to the center a flow down close to the outside with equal mass flow rates. only the energetic particles make it to the center and are carried up to the hot side and more of the cold particles are going to be on the outside and forced down. the energy the hot particles needed to travel closer to the center in returned when they fly to the outside on the other side. with equal mass flow rates and playing into the natural convection current the whole thing is " free" disregarding friction of course. the top will be hotter and the bottom colder. right or is there something I'm not seeing here? ( dont think doing this with ping pong balls is an accurate representation as they loose energy to friction on a "molecular" level unlike gas particles)

[modest]

the top will be hotter and the bottom colder

You really don't need a centrifuge to accomplish that. Warm air rises and cold air descends because we are in a gravity well.

 

what about a 2 story centrifuge with a gas in it. have a flow up close to the center a flow down close to the outside with equal mass flow rates. only the energetic particles make it to the center and are carried up to the hot side and more of the cold particles are going to be on the outside and forced down. the energy the hot particles needed to travel closer to the center in returned when they fly to the outside on the other side. with equal mass flow rates and playing into the natural convection current the whole thing is " free" disregarding friction of course. the top will be hotter and the bottom colder. right or is there something I'm not seeing here? ( dont think doing this with ping pong balls is an accurate representation as they loose energy to friction on a "molecular" level unlike gas particles)

 

Assume both the top and bottom start at the same temp. With the centrifuge running the warmest air on the bottom will make it to the center and be free to move upward. The warmest air on the top will make it to the center and be free to move downward. The coldest air on the top and bottom will also mix freely. In this situation, I don't see what the centrifuge accomplishes.

 

~modest

[President Haruru]

Howdy guys,

 

I know heat is pretty chaotic, but, is there any chance we could order some charged material (make it easier too order too) and have it vibrate in a useful direction?

Or are these vibrations far too small for anything to usefully pick up?

 

Ta :Exclamati

[modest]

Howdy guys,

 

I know heat is pretty chaotic, but, is there any chance we could order some charged material (make it easier too order too) and have it vibrate in a useful direction?

Or are these vibrations far too small for anything to usefully pick up?

 

Ta :naughty:

 

Hello President Haruru.

 

I'm not sure I quite follow. You could certainly put a north-south magnet between two other magnets and make it oscillate between them (kind of like a pendulum except that two repulsive forces take the place of gravity). But, friction would slow the oscillation. If you tried to do useful work form the oscillation then it would slow it as well. The oscillation eventually stops just like a pendulum.

 

~modest

[jazztracss]

It sure would be great if heat could be made into electricicty. Another place for such a device is on an air conditioning compressor, they each create a fair amount of heat which is often just let out into the atmosphere further adding to the problem of global warming. Let me know if you find anything.

[modest]

Welcome to Hypography Jazztracss :(

 

It sure would be great if heat could be made into electricicty.

 

As long as you have somewhere cold (or 'colder') to put that heat then you sure can convert it to electricity. You can use a heat engine.

 

Another place for such a device is on an air conditioning compressor

 

I think this might have an unintended side effect. An air conditioner compressor compresses a gas on the outside of a building then decompresses it on the inside of the building. It essentially moves the heat from inside the house to the outside by using mechanical work (mechanical work by way of electricity).

 

If you tried to use the heat from the outside radiator to work a heat engine and make electricity then you would lower the efficiency of the air conditioner because the harder it is for heat to escape the radiator the less efficient the system is. Adding a heat engine to the outdoor radiator would then require more electricity to keep the building at a constant indoor temperature.

 

The second law of thermodynamics says that it is more efficient to convert electricity into heat than to convert heat into electricity so the end result would be that overall electricity will be lost. The amount you gain from the heat engine would be less than the amount you lose from the added drain on the compressor.

 

It's an interesting idea though.

 

~modest

[Qfwfq]

It sure would be great if heat could be made into electricicty.

It can be done, but only to an extent limited by temperature difference. If it were not for this limitation, refrigeration could always be accomplished with production of useful energy and not at the cost of it.

 

Another place for such a device is on an air conditioning compressor, they each create a fair amount of heat which is often just let out into the atmosphere further adding to the problem of global warming.

It makes more sense to just improve the dissipation and also to use the lowest available temperature around, for the purpose. The lower the temperature at which the fluid needs to be compressed, the less power needs to be consumed.

 

In order for heat to be absorbed at a reasonable rate through a given surface, there is inevitably some temperature difference between what is absorbing it and what it is being absorbed from. Reducing this difference can save power requirement. If the difference is such that could be exploited to generate power, it only means that the same amount could be saved by reducing the difference.