US Patent 7415824 Steam engine

A steam engine has a pipe shaped fluid container, a heating and cooling devices respectively provided at a heating and cooling portions of the fluid container, and an output device connected to the fluid container, so that the output device is operated by the fluid pressure change in the fluid container, to generate an electric power. In such a steam engine, the fluid pressure in the fluid container is adjusted such that the fluid pressure does not exceed a saturated vapor pressure at the operating temperature. As a result, unnecessary condensation and liquefaction of the steam due to the increased pressure higher than the saturated vapor pressure can be prevented, to improve performance of the steam engine.