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Heat Engines Shrunk By Seven Orders of Magnitude

Posted by kdawson on from the gimme-a-v8-of-those dept.

KentuckyFC writes "The vast majority of motors that power our planes, trains, and automobiles are heat engines. They rely on the rapid expansion of gas as it heats up to generate movement. But attempts to shrink them by any significant amount have mostly ended in failure. Today, the smallest heat engines have a volume of some 10^7 cubic micrometers. Now group of Dutch engineers has built a heat engine that is seven orders of magnitude smaller than this. The engine consists of a piezoelectric bar that expands and contracts in the normal piezoelectric way. However it also heats up and cools at the same time causing a thermal expansion and contraction, which lags the piezoelectric displacement. By carefully choosing the frequency of the driving AC current, the Dutch team found a resonant effect in which the thermal expansion and contraction amplifies the mechanical motion, making it a true heat engine. Operating the thermodynamic cycle in reverse turns the device into a heat pump or refrigerator. The total volume of the device is just 0.5 cubic micrometres."

1 of 168 comments (clear)

  1. Reeedeeeculous by Ancient_Hacker · · Score: 0, Troll

    Sometimes I despair about the level of scientific knowledge imparted to today's youth.

    There is NO WAY to make a heat engine of any efficiency smaller than a few cc's.

    It's the basic SCALING LAW that Galilleo figured out like 600 years ago.

    As you make things smaller, their volume, which is their abilitry to burn fuel, goes down as the CUBE of its linear dimension.

    But its surface area, which is how it loses heat, only goes down as the square.

    So as you shrink things, pretty soon, you can't start a fire. The fire loses heat over its surface area faster than itrs volume can generate it.
    Which is why you don't see flames smaller than a certain, much larger than micrometer, size.

    Even for non-flame sources, the exact same rules apply. So you can't make a heat engine of any usable efficiency below a certain size. Model-airplane engines of 1cc capacity are about the lower practical limit. Anything smaller and you have trouble getting it to light off and even if it does, the heat quickly dissipates.

    So just on general principles, one can guess that this touted device has vanishingly small efficiency.

    And no, no "but we can INSULATE it" or "the RULES are DIFFERENT down there".