Convert heat into work operating between hot and cold reservoirs.
Efficiency η=W_net/Q_H=1-Q_L/Q_H, always below Carnot. Practical engines: steam, gas turbines, internal combustion, Stirling. Waste heat is rejected to a cold sink. Improve by raising T_H, lowering T_L and reducing irreversibility.
A power plant taking 1000 MW heat and producing 400 MW has η=40%.
A heat engine converts heat into work, and its efficiency is limited by the temperatures between which it operates.
Convert heat into work operating between hot and cold reservoirs.
A heat engine converts heat into work, and its efficiency is limited by the temperatures between which it operates.
The net work output divided by the heat input, which is the fraction of heat energy turned into useful work.
Some heat must be rejected to a cold reservoir to satisfy the second law, so the efficiency is always less than one.
Typical applications include estimating the efficiency of a steam power plant from its boiler and condenser temperatures, comparing the performance of two engines running between the same temperatures and predicting the work from a fuel-fired heat source and a cooling tower.
Study "Second law of thermodynamics" first (topic 21 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
Real efficiency 30–60%. Thermal reservoirs. Cogeneration uses the rejected heat.
A power plant taking 1000 MW heat and producing 400 MW has η=40%.
The next topic is "Refrigerators and heat pumps", which builds directly on this one.
It is classed as Beginner in Thermodynamics & Fluids (topic 22 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.