\[\eta=\frac{W}{Q_H}\]
Variables
eta[η]thermal efficiency (dimensionless)
Wnet work output (J)
Qh[Q_H]heat supplied by the hot reservoir (J)
Description
What is this formula?
Heat engine efficiency measures how effectively a thermal engine converts supplied heat into useful mechanical work. It is defined as the ratio of useful work output to the heat energy received from the hot reservoir.
When to use it
Use this formula when evaluating the performance of engines, turbines, power plants, or any thermodynamic cycle that converts heat into work.
Example
Given:
W = 450 J
QH = 1200 J
Formula:
η = W/QH
Substitution:
η = 450/1200
Result:
η = 0.375 = 37.5%
Applications
Steam power plants, gas turbines, internal combustion engines, Rankine cycles, Brayton cycles, and energy efficiency studies.