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Reversibility

Reversibility. Quasi-static processes meant that each step was slo enough to maintain equilibrium. If the process is reversed the work and heat also just reverse sign. Heat lost to friction is not reversible. Reversible Process.

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Reversibility

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  1. Reversibility

  2. Quasi-static processes meant that each step was slo enough to maintain equilibrium. If the process is reversed the work and heat also just reverse sign. Heat lost to friction is not reversible. Reversible Process Reversible process is infinitely slow; system stays at equilibrium. Irreversible process has heat loss to friction; system has net loss of useful energy.

  3. P P V V Plotting Reversibility • The PV diagram can plot a quasi-static, reversible process. • Irreversible processes cannot be plotted.

  4. Reversible Cycle • A series of reversible processes can be plotted on a PV diagram. • A reversible cycle is a set of reversible processes that return to the initial state. P V

  5. Carnot Engine • An ideal Carnot engine consists of four processes. 1) expand gas isothermally. 2) expand gas adiabatically. 3) compress gas isothermally. 4) compress gas adiabatically.

  6. Expansion • During the isothermal expansion there is work done with heat in. • There is no heat flow during the adiabatic expansion, but work is done. P V

  7. Compression • During the isothermal compression work is returned with heat out. • There is no heat flow during the adiabatic compression, but work is returned. P V

  8. Carnot Efficiency • The heat and temperatures are related in a Carnot engine. • |QL| / |QH| = TL / TH • This is the ideal engine efficiency.

  9. A nuclear plant produces 540 MW of power while the fuel releases 1590 MW. Steam enters the turbine at 556 K and is discharged at 313 K. What is the ideal and actual efficiency? The ideal efficiency assumes a Carnot engine. The actual efficiency is found from the power usage. Underwater

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