Fundamento
Humidity ratio
The constant 0.62198 is the ratio of the molar masses of water and dry air.
\(\omega=0.62198\frac{P_v}{P-P_v}\)
ThermoLab · Chapters 12 and 13
Gas mixtures and psychrometrics
Computes humidity, dew point, enthalpy and the loads of an air-conditioning process.
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Engineering directory
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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
Moist air is modelled as a mixture of dry air and vapour. At a known total pressure, the relative humidity fixes the partial pressure of the vapour.
Fundamento
Moist air enthalpy
The usual basis is one kilogram of dry air.
\(h=1.006T+\omega(2501+1.86T)\)
Fundamento
Dew point
It is the temperature at which the saturation pressure equals the current partial pressure.
\(P_{sat}(T_{dp})=P_v\)
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
Are relative humidity and ω the same thing?+
No. Relative humidity depends on saturation at that temperature; ω is a mass ratio.
When does water condense?+
When the process crosses the saturation curve or cools below the dew point.
Does the chart change with altitude?+
Yes; the local barometric pressure must be used.