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Can i make a 100% efficient device?

  1. Feb 13, 2015 #1
    hey guys, i have recently thought about an idea to make a 100% efficient device. i have figured out that the friction can be eliminated by putting lots of lubricant. now i need your help to counter the problem of heat and sound. i really need those answers cause its for an inter college in which i am participating. thanks i advance.
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  3. Feb 13, 2015 #2


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    More context please.

    The efficiency of the device will depend on what kind of device it is, and how you are calculating efficiency. Some kinds of device, when evaluated in some contexts, can be 100% efficient. But it is not possible to say whether you have one of those.

    Just as an example: If you were considering some such device as a steam engine, and you were considering the efficiency of converting the energy in the water in the boiler into work done by the engine, then no, it can't be 100% efficient. And this will be the result for the usual kind of engine that uses fuel to do work of some kind.
  4. Feb 13, 2015 #3


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    kaviraay, I realize I may be jumping the gun by over-anticipating where this is going, and for that I apologize.

    In general, discussion involving frictionless methods and devices tend to wander toward perpetual motion machines and over-unity devices. PF does not allow discussion about PPMs or over-unity devices. Your device might not literally be one of these in your view, but discussions about reducing waste energy to zero will likely head you down a slippery slope into banned topics fairly rapidly.

    Carry on.
  5. Feb 13, 2015 #4


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    No you cannot. You can reduce it, but not eliminate it completely.
  6. Feb 13, 2015 #5


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    Can it be any device? eg Something like an electrical resistor/heater?
  7. Feb 13, 2015 #6
    Maybe the OP is trying to say that a whole lotta lube produces something close enough to zero friction for the specific application.

    For heat, the Dewar flask is a good example on combating heat transfer. The Thermos bottle is a cheap Dewar flask that uses those same principles. Sound energy transfer can be reduced by increasing mass, using absorbent materials, etc. Audio enthusiasts usually have good methods for deadening or sound-proofing rooms/cars for cheap.

    EDIT: Isn't the electrical-to-heat energy conversion close to 100%?
  8. Feb 14, 2015 #7
    I'm working on boilers where we burn natural gas and put the released heat into the water (for hot water or central heating) using a heat exchanger. They are > 95% efficient, where efficiency means the percentage of the released heat that ends up in the water. You could get ~100% efficiency if you would submerse the entire heat exchanger in a big water vessel or something like that, but you don't want to shower with 100% efficiently heated water that has increased only 1K in temperature.

    Actually, the 'official' way of calculating efficiency in my field is done by using the lower heating value of the gas. During combustion, a lot of water vapor is created. If you condense the water vapor inside the heat exchanger you can get some extra energy. The efficiency can then be >100%, but this is a matter of definition. It makes more sense to use the higher heating value of the gas, which includes the extra condensation energy of water.
  9. Feb 14, 2015 #8
    What type of efficiency do you have in mind?
    Thermodynamic, mechanical, electrical are just a few of the options.

    For nearly 100% mechanical efficiency, a device called a lever would suffice. And you won't have to worry about heat or sound.
    Drop a ball from a height for nearly 100% efficiency of conversion of potential energy into kinetic energy over a short distance. Again heat and sound should not matter. Friction, if speeds are low, is also low.
  10. Feb 14, 2015 #9
    Assuming that you don't store any energy, every mechanical device turns 100% of its input into heat.
  11. Feb 14, 2015 #10


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    In principle, electrical resistance heating seems to be 100% energy efficient. But that fails when you consider losses generating the electricity and delivering it to the load.

    In real life, almost everything can be 100% efficient if you are liberal about where to draw the boundaries. But if you are rigorous in drawing boundaries, almost nothing is 100% efficient.

    In other words, it is more a matter of definition than of science.
  12. Feb 15, 2015 #11


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    Lubricant is a fluid. Without viscosity it would not remain where it is needed. With viscosity it will be heated by pressure differences and turbulence as it flows. Lubrication cannot therefore be 100% efficient.
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