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Stirling Engine Regenerator

  1. Nov 12, 2012 #1
    Stirling engines use regenerators(heat pumps) to recover heat and increase their efficiency.The basic problem here is "The regenerator constitutes a (dead) volume which thwarts the benefit of its presence.There is never absolute truth" I believe I have a working concept of the heat pipe.My idea is to replace the regenerator with curved heat pipes.This would efficiently transfer the heat but illiminate the dead space between the hot and cold side.I have posted an illustration to make it easier to visulize.Will it work or have I missed something? Thanks for any comments.

    The thermodynamics of the Stirling beta engine are similar to those of the alpha engine but the physical configuration is quite different.

    The beta engine has only one cylinder which is heated at one end and cooled at the other. A single power piston is arranged coaxially with a displacer piston and both pistons move within this cylinder. The displacer piston does not extract any power from the expanding gas but only serves to shuttle the working gas back and forth between the hot and cold ends. As in the alpha engine, the cyclic motions of the pistons are 90 degrees apart with the motion of the displacer piston leading the power piston by a quarter revolution of the crankshaft.

    The mechanism for linking the motions of the two pistons is quite complex. The connecting rod for the displacer is made up from two parts. The upper link is rigidly attached to the displacer and passes through the centre of the power piston and must maintain an airtight seal with the piston so that the working gas does not escape. The second part of the displacer linkage is a normal connecting rod connecting the upper link to the crankshaft. Since the displacer mechanism occupies the space normally occupied by the power piston connecting rod, the linkage for the power piston must also be split into two parts, one on either side of the displacer linkage to maintain balanced forces on the power piston.




    As the gas heats up in the hot end of the cylinder it expands and is forced through the regenerator into the cold end of the cylinder.
    As the displacer moves up, the gas moves into the cold end it and pushes the piston downwards
    As the displacer reaches the top of its stroke, all the gas is transferred to the cold end where is cooled and contracts. At the same time the piston follows the displacer upwards.
    As the displacer begins to move down the piston continues to move up and the cold gas is transferred to the hot end of the cylinder and the cycle starts again.

    The engine may also incorporate a regenerator to improve efficiency. For clarity this has been shown as being separate from the cylinder. In practice it is more likely to be incorporated into the cylinder wall. In some designs, the displacer piston itself acts as the regenerator.
     
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  3. Nov 13, 2012 #2

    Simon Bridge

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    Welcome to PF;
    Have not seen any picture.

    Most of your post looks like copy-and-paste: please provide a citation.

    How would the heat-pipes recover heat that would otherwise be irreversably lost?
     
  4. Nov 13, 2012 #3

    sophiecentaur

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    This doesn't look promising as a heat pipe only works 'downhill'. You want any thermal energy to be flowing through the heat engine, surely and not through a shunt path(?).
     
  5. Nov 14, 2012 #4
    I've forgotten the drawback of the regenerator's volume... Does it limit a compression ratio?

    I believe to understand you want to reduce the regenerator's dead volume by separating its exchanger function from its accumulator function, with heat pipes in between. Is that it? Why not; it all depends on figures, technical feasibility, drawbacks - short, engineering. But the nice aspect I see in the Stirling is exactly that its heat exchanger needs not be gas tight, hence is light and easy.

    Other methods could improve this regenerator (which isn't a heat pump): as only a clean gas flow in it, its matter can be divided as finely as you want, accelerating the heat exchange, and the faster engine is lighter. To limit the pressure drop, spread and gather the gas in arteries, arterioles, capillaries, veinules and veins.

    -----------------

    What I don't grasp is why so many people spend time on the Stirling engine, which is heavy and inefficient. If building a heat exchanger, then put it at a gas turbine and get >40% efficiency at 1/100 the mass.

    If the temperature difference is small, then make a liquid-vapour cycle with carbon dioxide, pass it through turbines. Smaller, better.
     
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