ASHRAE Journal - June 2024 - 45
FEATURE
Comparison of Ideal Cycles
FIGURE 1 - CARNOT CYCLE
PV Chart
1000
100
10
1
0.05
0.1
Volume (m3/kg)
0.15
0.2
400
300
200
100
Ts Chart
1000
100
10
1
5.5 5.7 5.9
6.1 6.3
6.5 6.7 6.9
Entropy (kJ/kgK)
7.1
200
300
400
500
Enthalpy (kJ/kg)
600
700
Ph Chart
PV Chart
FIGURE 2 - STIRLING CYCLE
Ts Chart
1000
100
10
1
0.05
0.1
Volume (m3/kg)
0.15
0.2
400
300
200
100
1000
100
10
1
5.5 5.7 5.9 6.1
6.3 6.5
Entropy (kJ/kgK)
6.7 6.9
7.1
200
300
400
500
Enthalpy (kJ/kg)
600
700
Ph Chart
PV Chart
FIGURE 3 - BRAYTON CYCLE
Ts Chart
1000
100
10
1
0.05
0.1
Volume (m3/kg)
0.15
0.2
400
300
200
100
1000
100
10
1
5.5 5.7 5.9 6.1
6.3 6.5
Entropy (kJ/kgK)
The Carnot cycle comprises the reduction of volume at constant
temperature (heat is removed), the reduction of volume with no heat
removal, the increase of volume at constant temperature (heat is added)
and the increase of volume with no heat addition. Work input is required to
reduce the volume, and work is extracted when the volume is increased.
The Stirling cycle comprises the reduction of volume at constant
temperature (heat is removed), the increase of temperature at constant
volume (heat is added), the increase of volume at constant temperature
(heat is added) and the reduction of temperature at constant volume (heat
is removed).
The Brayton cycle comprises the reduction of temperature at constant
pressure, the reduction of volume with no heat removal, the increase of
6.7 6.9
7.1
200
300
400
500
Enthalpy (kJ/kg)
temperature at constant pressure and the increase of volume with no heat
addition.
The Carnot and Stirling cycles have the same ideal conversion ratio, known
as the Carnot effi ciency and expressed as 1 - T2/T1 where T2 is the sink
(lower) temperature and T1 is the source (higher) temperature for a power
generation heat engine. Carnot was aware of the Stirling cycle, which Sir
William Thomson described as " the beautiful engine invented by Mr. Stirling
of Galston, " but he had no details, saying only, " it is said that successful tests
have been made very recently in England on the development of motive power
by the action of heat on the atmospheric air. We have no idea what these tests
consisted of, if indeed they are real. " This is not surprising as Stirling's patent
is dated 1820, and he was working in rural Ayrshire, southwest Scotland.
J U N E 2 0 2 4 ashrae.org ASHRAE JOURNAL
45
600
700
Ph Chart
Pressure (bar)
Pressure (bar)
Pressure (bar)
Temperature (°C)
Temperature (°C)
Temperature (°C)
Pressure (bar)
Pressure (bar)
Pressure (bar)
http://www.ashrae.org
ASHRAE Journal - June 2024
Table of Contents for the Digital Edition of ASHRAE Journal - June 2024
Contents
ASHRAE Journal - June 2024 - Intro
ASHRAE Journal - June 2024 - CT1
ASHRAE Journal - June 2024 - CT2
ASHRAE Journal - June 2024 - Cover1
ASHRAE Journal - June 2024 - Cover2
ASHRAE Journal - June 2024 - 1
ASHRAE Journal - June 2024 - Contents
ASHRAE Journal - June 2024 - 3
ASHRAE Journal - June 2024 - 4
ASHRAE Journal - June 2024 - 5
ASHRAE Journal - June 2024 - 6
ASHRAE Journal - June 2024 - 7
ASHRAE Journal - June 2024 - 8
ASHRAE Journal - June 2024 - 9
ASHRAE Journal - June 2024 - 10
ASHRAE Journal - June 2024 - 11
ASHRAE Journal - June 2024 - 12
ASHRAE Journal - June 2024 - 13
ASHRAE Journal - June 2024 - 14
ASHRAE Journal - June 2024 - 15
ASHRAE Journal - June 2024 - 16
ASHRAE Journal - June 2024 - 17
ASHRAE Journal - June 2024 - 18
ASHRAE Journal - June 2024 - 19
ASHRAE Journal - June 2024 - 20
ASHRAE Journal - June 2024 - 21
ASHRAE Journal - June 2024 - 22
ASHRAE Journal - June 2024 - 23
ASHRAE Journal - June 2024 - 24
ASHRAE Journal - June 2024 - 25
ASHRAE Journal - June 2024 - 26
ASHRAE Journal - June 2024 - 27
ASHRAE Journal - June 2024 - 28
ASHRAE Journal - June 2024 - 29
ASHRAE Journal - June 2024 - 30
ASHRAE Journal - June 2024 - 31
ASHRAE Journal - June 2024 - 32
ASHRAE Journal - June 2024 - 33
ASHRAE Journal - June 2024 - 34
ASHRAE Journal - June 2024 - 35
ASHRAE Journal - June 2024 - 36
ASHRAE Journal - June 2024 - 37
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ASHRAE Journal - June 2024 - 40
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ASHRAE Journal - June 2024 - 43
ASHRAE Journal - June 2024 - 44
ASHRAE Journal - June 2024 - 45
ASHRAE Journal - June 2024 - 46
ASHRAE Journal - June 2024 - 47
ASHRAE Journal - June 2024 - 48
ASHRAE Journal - June 2024 - 49
ASHRAE Journal - June 2024 - 50
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ASHRAE Journal - June 2024 - 72
ASHRAE Journal - June 2024 - Cover3
ASHRAE Journal - June 2024 - Cover4
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