Thermodynamics of Heat Engines. • A heat engine is any device that can take energy from a warm source and convert a fraction of the heat energy to mechanical energy. Diagrammatically, a heat engine is represented as follows: Heat Source, Thot Qhot Work Output Heat Heat Engine Engine Qcold Heat Sink, Tcold W = Qhot - Qcold
Heat Engines A steam engine is one type of heat engine.
Thermodynamics of Heat Engines. • The thermal efficiency of any system is defined to be the ratio of the work done to the heat input: work done thermal efficiency = heat input • For any heat engine, Q hot − Q cold Q cold 100% Eff th = = 1 − Q hot Q hot • A Carnot engine is an ideal heat engine. For the Carnot Engine, Qcold/Qhot = Tcold/Thot. Therefore, Thot − Tcold Tcold 100% Eff th = = 1 − Thot Thot