The thermal efficiency expresses the fraction of heat that becomes useful work. The thermal efficiency is represented by the symbol , and can be calculated using the equation: Where: is the useful work and is the total heat energy input from the hot source. Heat engines often operate at around 30% to 50% efficiency, due to practical limitations

Thermal Efficiency Formula. As a result of this statement, we define the thermal efficiency, η th, of any heat engine as the ratio of the work it does, W, to the heat input at the high temperature, Q H.. The thermal efficiency, η th, represents the fraction of heat, Q H, converted to work.It is a dimensionless performance measure of a heat engine that …