# Heat engines

Heat engines are machines which accept energy from a hot heat source, convert a fraction of it to work, and reject the remainder to a cold heat sink. The maximum possible fraction converted to work is $\frac{T_\mathrm{hot}-T_\mathrm{cold}}{T_\mathrm{hot}} = \frac{\Delta T}{T_\mathrm{hot}}$. (T_hot - T_cold) / T_hot.