Thermal Efficiency

—1. No heat engine can convert into mechanical energy more than a small fraction of the heat supplied to it, the greater portion being nece arily lost in various ways; in overcoming the molecular resistance of the working sub- “Thermal Efficiency Ratio. stance to changes of form; in overcoming the friction of _the working parts of the mechanism; and by rejection, so that the efficiency becomes the ratio: Heat converted into work Heat absorbed by the working substance which is a fraction always much le than unity, and represents the thermal] efficiency of an engine operating under actual working conditions. 2. The ratio of the heat equivalent of the work done on the piston of a steam engine per unit of time, to the heat supplied to the engine.