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    What is the name of a hypothetical reversible engine that is 100% efficient? Will we ever have such a working engine, and if not, why not?

    Question #94310. Asked by rxbigdawg. (Apr 04 08 8:26 AM)


    triviapaul

    		A perpetuum mobile.

    "In thermodynamics, a reversible process, or reversible cycle if the process is cyclic, is a process that can be "reversed" by means of infinitesimal changes in some property of the system without loss or dissipation of energy."

    http://en.wikipedia.org/wiki/Thermodynamic_reversibility

    "Carnot realised that in reality it is not possible to build a thermodynamically reversible engine, so real heat engines are less efficient than indicated by Equation."

    http://en.wikipedia.org/wiki/Carnot_heat_engine

    "The term perpetual motion, taken literally, refers to movement that goes on forever. However, perpetual motion usually refers to a device or system that delivers more energy than was put into it. Such a device or system would be in violation of the law of conservation of energy, which states that energy can never be created or destroyed, and is therefore deemed impossible by the laws of physics."

    http://en.wikipedia.org/wiki/Perpetual_motion

    Apr 04 08, 8:42 AM
    gentlegiant17

    		The Carnot engine: http://en.wikipedia.org/wiki/Carnot_heat_engine

    A realization of the Carnot engine: http://www.shermanlab.com/xmwang/myGUI/CarnotG.html

    Apr 04 08, 8:48 AM
    Baloo55th

    		The things people forget about perpetual motion machines are: 1. Friction - even if you use PTFE and slipperier substances - which nibbles away at your efficiency; 2. You cannot get any useful work out of them - if you try, you lower the energy level just as you do in a battery, and batteries are far easier to use (and are used to power most perpetual motion machines that are 'demonstrated'.
    Source: New Scientist over many years. One columnist, the author of the Ariadne page, actually took a PM machine around to several scientific conferences and meetings and no-one seemed able to explain it. He could, of course, but I don't know how he'd fiddled it.

    Apr 04 08, 1:24 PM
    MonkeyOnALeash

    		The answer is this: Conservation of Energy. Nothing more. It CAN NOT be done. It defies Newtonian Laws.

    Apr 04 08, 1:56 PM

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