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beating thermodynamics to a free lunch

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thezombiekat thezombiekat's picture
beating thermodynamics to a free lunch
beating thermodynamics to a free lunch i cant make this system not work. i don't really expect it to work. its too simple. people with actual physics training would have thought of it but i cant fault the concept and it seems to be offering me a free lunch when the tech improves. there exist devices that can convert waste heat to usable electricity. the efficiency today is rather poor but it will improve. 40% is being predicted from models currently under development. here are some websites. the first is actually trying to sell these things. http://www.customthermoelectric.com/powergen.html?gclid=CNDNs4HMlrwCFUUw... http://physicsworld.com/cws/article/news/2013/dec/09/new-generator-creat... http://unews.utah.edu/news_releases/using-sound-to-turn-heat-into-electr... there exist devices for moving heat energy from one place to another. a basic refrigeration system. i cant find anything on there efficiency in terms of energy moved for energy input, the web is full of ways to save money on refrigeration, if we build a box. coated in thermo electric systems and a refrigeration system with the hot side in the box and the cold side outside, the compressor will also be in the box so any heat it generates will be inside the box. nether of these devices breaks any law of thermodynamics, and would not even if improved to very high levels of efficiency. taken together however if we consider a refrigeration system capable of moving 165J of heat for every 100J of electricity input, and a thermo electric panel capable of capturing 65J of electricity for every 100J leaving the box (the other 35J being lost to the environment) for every 100J electricity input into the combined system we get 107.5J of electricity out. and that's a 7.5% free lunch. of cause we haven't actually created energy. the environment will be cooled as a result.but i think we are still in breach of the second law of thermo dynamics. this would have massive implications for everything from energy supply to maintaining temperature on space ships and habitats and even stealth in space.
Decimator Decimator's picture
Where are you getting those
Where are you getting those efficiency figures for refrigeration?
thezombiekat thezombiekat's picture
i cant find any efficiency
i cant find any efficiency figures for refrigeration. the internet is so chock full of advice on how to improve power efficiency on a refrigeration system resulting in 5% power savings that i cant find anything on how much heat can be moved for a given amount of electricity used in order to get net electricity out i know i need to exceed current technology note that i used a 65% efficient thermo electric system when the bet currently under development is 40%, but anything under 100% isn't going to break the laws of thermodynamics. if the refrigeration system is located inside the box then all losses due to inefficiency will be heat inside the box, some heat will be transferred in from outside so the amount of heat energy inside the box must increase by more than the amount of electricity used. the principle is actually used in reverse cycle air conditioners to heat more efficiency than an electric bar heater (wich is only a shade under 100% efficient). that said i cant find numbers on how much more efficient they are.
Smokeskin Smokeskin's picture
If you want a 65% efficiency
If you want a 65% efficiency from a heat engine, and the cold part is say 5 degrees celsius (278K), then Carnot's theorom tells us that the hot part has to be 527 degrees celsius (800K). That's not exactly operating temperatus for refrigiators. Aside from the technical probems, the amount of energy needed to move heat from a 5 degree celsius reservoir to a 527 degrees celsius reservoir would be EXTREME and the efficiency would be horrible, even under purely theoretical limitations.
Decivre Decivre's picture
One big problem with this
One big problem with this logic is that as the difference in temperature from the inside and outside of the box increases, the joules necessary to maintain and increase the difference goes up as well. Inevitably, this system is going to be lossy, simply by merit of temperature bleed.
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