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CHE 3010 - Thermodynamics Tennessee Tech University
Venkat Padmanabhan, PhD Department of Chemical Engineering
Tennessee Tech University
CHE 3010 - Thermodynamics of Chemical Processes
Lecture 7 - Cyclic Processes 9/13/2017
1
Tennessee Tech UniversityCHE 3010 - Thermodynamics
WAB = PΔV = P1(V2-V1)
WBC = 0 (constant volume)
W = WAB + WBC = P1(V2-V1)
W = area under the line AB
2
Processes in Series
A series of thermodynamic processes
V
P
V1 V2
P1
P2
AB
CA → B — constant P heating/expansion
B → C — constant V heating
What is the work done by the gas as it goes from A to C?
Tennessee Tech UniversityCHE 3010 - Thermodynamics
WAB = 0 (constant volume)
WBC = PΔV = P2(V2-V1)
W = WAB + WBC = P2(V2-V1)
W = area under the line BC
3
Processes in Series
A series of thermodynamic processes
V
P
V1 V2
P1
P2
A
B C A → B — constant V heating
B → C — constant P heating/expansion
What is the work done by the gas as it goes from A to C?
Tennessee Tech UniversityCHE 3010 - Thermodynamics 4
Processes in Series
Heat and work are path properties
Work done by the gas in process I is smaller than the work done by the gas in process II.
V
P
V1 V2
P1
P2
AB
CI
W
V
P
V1 V2
P1
P2
A
B CII
W
Tennessee Tech UniversityCHE 3010 - Thermodynamics
W = area of the triangle ABC
5
Thermodynamic Cycle
A series of thermodynamic processes that returns the system to its initial state
A → B — constant V heating
B → C — constant P heating/expansion
C → A — cooling
V
P
V1 V2
P1
P2
A
B C
Q
Q W
Q W
V
P
V1 V2
P1
P2
A
B C
D
W
Tennessee Tech UniversityCHE 3010 - Thermodynamics 6
Thermodynamic Cycle
V
P
V1 V2
P1
P2
A
B C
D
V
P
V1 V2
P1
P2
A
B C
D
Net heat IN Net work OUT Net heat OUT Net work IN
Tennessee Tech UniversityCHE 3010 - Thermodynamics 7
Example
P7.1 — 10 moles of an ideal gas undergoes a cyclic process as shown below. The gas, initially at room temperature (25oC) and a pressure of 2 atm, is heated to 75oC and cooled back to room temperature at the end of the cycle. If the pressure of the gas just before the cooling process is 1 atm, what is the work done by the gas? R = 8.314 J/molK.
V
P
V1 V2
A
B
C
D
isothermal
Tennessee Tech UniversityCHE 3010 - Thermodynamics 8
Example
Tennessee Tech UniversityCHE 3010 - Thermodynamics 9
Example