= Stirling engine
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A Stirling engine repeatedly heats and cools a confined <gas>, whose expansion and compression drive a moving mechanical load. This makes it a particularly accessible example of a <heat engine>: both the repeating motion and the two regions exchanging <heat> can be observed.
In the published <Demonstration experiments with a Stirling engine by Christopher G Deacon and others>, an electrical heater warms one end of a cylinder and flowing <water> cools the other at $12\,{}^\circ\mathrm C$. A moving displacer shuttles <gas> through <copper> wool that temporarily stores and returns <internal energy>. A <laser> spot traces a closed <pressure>-<volume (thermodynamics)> path on a screen: mechanical motion controls one coordinate, <pressure> the other. Calibrating both scales converts the enclosed <area> to <work> per <thermodynamic cycle>; multiplying by rotation <frequency> gives gas-cycle <power>. At $97\,\mathrm W$ heater input, the paper reports $4.4\,\mathrm W$ gas-cycle <power>, while a separate <Prony brake> measures $3.4\,\mathrm W$ shaft output. The cold-side <temperature> is controlled and two higher heater settings are compared. The gas has a nonuniform <temperature>, and heater <energy> also escapes to the room: neither output/input ratio measures $W/Q_h$ for an ideal two-<thermal reservoir> engine. These observations demonstrate <work> production and losses, not a direct measurement of the bound in <Carnot's theorem>. The inspected apparatus, readouts and results are on pp. 180–182, Figures 1–3 and Table 1.
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