{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Chapter 5. The Second Law-student

# Chapter 5. The Second Law-student - The Second Law of...

This preview shows pages 1–7. Sign up to view the full content.

The Second Law of Thermodynamics

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Differences between heat and work First law: the transformation of energy, heat and work. All the efforts to make perpetual motion machine have failed The second law deals with the reaction direction and efficiency All efforts to devise a process for the continuous conversion of heat completely into work or into mechanical or electrical energy have failed. Conversion efficiencies do not exceed about 40%. All efforts to convert heat to work from a single heat reservoir have failed The flow of heat between two bodies always takes place from the hotter to the cooler body, and never in the reverse direction. The second law No apparatus can operate in such a way that its only effect is to convert heat absorbed by a system completely into work done by the system. No process is possible which consists solely into the transfer of heat from one temperature level to a higher one.
Heat engine: devices or machines that produce work from heat in a cyclic process. Essential to all heat-engine cycles are absorption of heat into the system at a high temperature, rejection of heat to the surroundings at a lower temperature, and production of work. Q H Q c Engine returns back to original position so ΔU=0

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
A heat engine operating in a completely reversible manner is called a Carnot engine (N.L.S. Carnot, 1824) More commonly, Carnot engine has the following cycles: T H T C b c a d P V |Q H | |Q C | a b c a a to b: Adiabatic compression b c b to c: Isothermal expansion, adsorb Q H from hot reservoir d c to d: adiabatic expansion d d to a: Isothermal compression, discard Q c to cold reservoir Q H Q C
T H T C b c a d P V |Q H | |Q C | For the isothermal steps b → c and d → a For adiabatic processes a → b and c → d 5 . 0 600 300 1 = - = η Actual heat engines are irreversible and η rarely exceed 0.35. For ideal gases If T C =300k and T H = 600 K,

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Carnot’s Theorem For two given heat reservoirs no engine can have a thermal efficiency higher than that of a Carnot engine The thermal efficiency of a Carnot engine depends only on the temperature levels and not upon the working substances of the engine.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 27

Chapter 5. The Second Law-student - The Second Law of...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online