US Patent 7424802 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, an inner radius “r1” of the cooling portion is made to almost equal to a depth “δ1” of thermal penetration, which is calculated by the following formula (1);