Air Standard Cycles Effect of Variation in Specific Heat

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Air Standard CyclesEffect of Variation in
Specific Heat

• A more realistic solution

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Isentropic Compression Process
For an infinitesimal compression process
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Now, since
For a small compression ratio
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Explicit method
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Global Isentropic Compression Process
The overall isentropic process between states 1
2
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Isentropic expansion process
For an infinitesimal expansion process
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Explicit Method
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Global Isentropic Expansion Process
The overall isentropic process between states 3
4
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Cp of Air Gases
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Correlation for gamma

• For example
• ? 1.4 7.18 x 10-5T
• T is in Kelvin
• Also

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Correlations for cp of air

• cp 0.9211 0.0002306 T kJ/kg-K
• T is in Kelvin
• Other properties can be obtained.
• A third order equation was proposed by Partha
  Pratim Saha, 89085
• cp 26.430213692 8.443567110-3T
• 2.156769249610-6T2
• 1.946195410 -10T3 kJ /kmole K
• T is in Kelvin
• Molecular weight of air is 29

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One more correlation for air

• Given by Krieger and Borman (ASME Paper)
• Internal energy for air is given by
• u 0.6919943T 0.3917296x10-4T2
  0.5292534x10-7T3 0.2286286x10-10T4
  0.277589x10-14T5 kJ/kg
• cv du/dT and
• cp R cv
• T is in Kelvin

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Lucas Correlations for air and other gases

• The cp of any gas is given as follows
• cp aij (T/1000)i-1
• where i 1 to 7 and j represents the particular
  species, isooctane, oxygen or nitrogen. The units
  are kJ kmole-1 K-1
• Values of aij are given elsewhere

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Tabulated form of air property data
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Effect of moisture on properties of air
kg moisture/kg air ?