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7.7 The Tds Relations 7.7 The Tds Relations
The T-ds equations...
dVT
p
T
dTCds v
dpT
V
T
dTCds p
Note that the specific heats are generally a function of temperature.Note that the specific heats are generally a function of temperature.
The T-dS equations
T
s
p
v
.Constpv k .Constpv n
.ConstV
.ConstP
kn
Isentropic processes - ideal gases
7.9 The Entropy Change of Ideal Gases 7.9 The Entropy Change of Ideal Gases
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FIGURE 7-36The isentropic relations of ideal gases are valid for the isentropic processes of ideal gases only.
7.10 Reversible Steady-Flow Work 7.10 Reversible Steady-Flow Work
FIGURE 7-43Schematic and T-s diagram for Example 6–12.
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7.11 Minimizing the Compressor Work 7.11 Minimizing the Compressor Work
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.FIGURE 7-45P-v diagrams of isentropic, polytropic, and isothermal compression processes between the same pressure limits.
Multistage Compression with IntercoolingMultistage Compression with Intercooling
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FIGURE 7-46P-v and T-s diagrams for a two-stage steady-flow compression process.
7.12 Isentropic Efficiencies of Steady-Flow Devices
7.12 Isentropic Efficiencies of Steady-Flow Devices
• Common open system components– Nozzles– Compressors– Turbines– Pumps
• The concept of isentropic efficiency comes from the combination of the 1st and 2nd Laws.
Isentropic efficiency
Isentropic process, s = constant,Maximum enthalpy change.,
p1
p2
1
2
h
ss1 = s2
Al accessible states lieto the right of this line.
h-s diagram
Isentropic efficiency
shh
hh
,21
21
h
s
pp22
pp11
h2,s
h2
h1
Isentropic expansion, entropy production is zero.
Actual expansion, h2 < h2,s
Turbines and compressors
pp11
IrreversibleIrreversible
h
s
h
s
pp2 2 > p> p11 pp2 2 > p> p11
p1
IrreversibleIrreversible
CompressorTurbine
Reversible,Reversible,adiabaticadiabatic
Reversible,Reversible, adiabaticadiabatic
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FIGURE 7-49The h-s diagram for the actual and isentropic processes of an adiabatic turbine.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 7-51The h-s diagram of the actual and isentropic processes of an adiabatic compressor.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 7-53Schematic and T-s diagram for Example 6–15.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
FIGURE 7-54The h-s diagram of the actual and isentropic processes of an adiabatic nozzle.
