Fundamento
Variables reducidas
Comparison between substances is expressed through reduced pressure and temperature.
\(P_r=P/P_c,\quad T_r=T/T_c\)
ThermoLab · Chapter 3
Pure substances and equations of state
Compares Van der Waals, Redlich-Kwong and Peng-Robinson with explicit iteration on Z.
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Engineering directory
13 linked modules on a single calculation base
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01
Appendices A-1 to A-28Universal property interpolator
→02Chapters 1 and 2Pressure, temperature and general energy balance
→03Chapter 3Pure substances and equations of state
→04Chapter 4Energy integrals for closed systems
→05Chapter 5Control volumes and the first law
→06Chapters 6 and 7Second law, Carnot and entropy
→07Chapter 8Exergy, destruction and second-law efficiency
→08Chapter 9Gas power cycles
→09Chapter 10Rankine steam power cycles
→10Chapter 11Refrigeration cycles
→11Chapters 12 and 13Gas mixtures and psychrometrics
→12Chapters 14 and 15Combustion and adiabatic flame temperature
→13Chapters 16 and 17Chemical equilibrium and compressible flow
→Engineering framework
Theory, equations and conditions of use
Cubic equations represent non-ideality through attraction and co-volume parameters computed from the critical properties.
Fundamento
Peng-Robinson
It includes the acentric factor through α(T) and usually balances accuracy for vapour and liquid.
\(P=\frac{RT}{v-b}-\frac{a\alpha}{v(v+b)+b(v-b)}\)
Fundamento
Physical root
Newton-Raphson updates Z until the polynomial is satisfied. The largest stable root normally represents vapour.
\(Z_{n+1}=Z_n-\frac{f(Z_n)}{f'(Z_n)}\)
Base documentalÇengel & Boles, 7th edition · SI appendices A-1 to A-28
USCS conversionA-1E to A-27E, via exact factors from the SI base
AlcancePreliminary design, teaching and independent verification
Engineering FAQ
Preguntas frecuentes
Why can there be three roots?+
In the coexistence region, the outer roots correspond to liquid and vapour; the middle one is unstable.
Which equation of state should I use?+
Peng-Robinson is a general choice for hydrocarbons; the final selection depends on the mixture and the range.
Does Z=1 mean a perfect gas?+
Yes, in the ideal limit. A departure from 1 quantifies the non-ideality of the volume.