How to use this calculator
Enter the hot and cold reservoir temperatures in any scale (they are converted to kelvin). Add a heat input to get the maximum work and heat rejected.
Formulas
Carnot efficiencyη = 1 − TCTH
Refrigerator and heat pumpCOPR = TCTH − TC COPHP = THTH − TC
Worked example
Engine between 500 °C and 25 °C with 100 kJ of heat (the default)
- TH = 773.15 K, TC = 298.15 K.
- η = 1 − 298.15/773.15 = 61.4%.
- Wmax = 0.614 × 100 = 61.4 kJ; at least 38.6 kJ must be rejected.
Frequently asked questions
Why can no engine beat Carnot?
The second law of thermodynamics: a more efficient engine could be paired with a reversed Carnot engine to move heat from cold to hot with no work, which never happens.
Why must I use kelvin?
The formula comes from an absolute temperature scale. Using °C would give nonsense, even negative efficiencies.