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
Qin:heat flow from the hot reservoir to the engine
Qout: heat flow from the engine to the cold reservoir.
Work done by heat engine = Qin – Qout
Efficiency = W/Qin = (Qin – Qout)/Qin
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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