2nd Law of Thermodynamics

2nd Law of Thermodynamics: Entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium - i.e. entropy increases & all processes tend towards chaos

Temperature gradient: Heat flows from a region of hot temperature to a region of cold temperature

All heat engines give up their energy to a cold reservoir

Q_in:heat flow from the hot reservoir to the engine

Q_out: heat flow from the engine to the cold reservoir.

Work done by heat engine = Q_in – Q_out

Efficiency = W/Q_in = (Q_in– Q_out)/Q_in

Limitations to Thermal Efficiency: - in an engine:

TH cannot be too high > components could melt
TC will be in the range of atmospheric temperatures
Analysis of the engine cycle can help to improve efficiency
Design of ports so that gas can get enter & exit with min. resistance
Lubrication reduces friction in bearings

Therefore an engine will never work at its theoretical efficiency

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