Heat Power Engineering: The branch of heat engineering that deals with the conversion of heat into other forms of energy, mainly mechanical and electric. Mechanical energy is generated from heat in heat engines, which power, for example, machine tools, automobiles, and conveyors; the mechanical energy from heat engines also drives certain types of electric generators. The devices in which heat is converted into electric power without the use of an electric generator are known as direct-power generators. Such devices include magnetohydrodynamic generators, thermoelectric generators, and thermionic power generators.