Thermodynamic processes 1.4-1

Chapter 1.4: Thermodynamic processes

Goal: generate work from heat Example: isothermal expansion

Ideal gas laws: TNkE B23

TNkpV B

Thermodynamic processes 1.4-2

We know WQE but WQ , are not unique Guy Lussac thought experiment (1807)

Reversible and irreversible expansion

p

V

Thermodynamic processes 1.4-3

Def. 1.12: A reversible cyclic process periodically takes a work-substance through a cycle of equilibrium states under exchange of heat and work only. Practically: Stirling engine, heat pumps, refrigerator

Tho

Tcol

Thermodynamic processes 1.4-4

Def. 1.13: The efficiency of a reversible cyclic process as an engine is hotQ

W

All reversible cyclic processes have the same efficiency as a function of Thot and Tcold

Tho

Tcol

Thermodynamic processes 1.4-5

Carnot cycle

p

V

T

S

Thermodynamic processes 1.4-6

The efficiency of all reversible cyclic processes is cold

hot

hot

1TT

QW

Thermodynamic processes 1.4-7

Stirling cycle

p

V

Thermodynamic processes 1.4-8

Non reversible engines: real machines

Coal powered plants:

Theoretical: KT 2100hot KT 300cold 85.01hot

hot

hot

TT

QW

Thermodynamic processes 1.4-9

Examples: heating and cooling

KJ

TTQS

hotcold

37.011

KT 300hot

KT 270cold

JQ 1000