Calculation of State Value of Air.

Keyword

Water vapor pressure of saturated air Dry bulb temperature Wet bulb temperature Absolute Temperature Absolute humidity Specific Enthalpy Water vapor pressure Relative humidity Saturation Specific Volume Wexler-Hyland formula,Standard Atmosphere.

Reference

・『空気調和・衛生工学便覧 第13版 1基礎編』(空気調和・衛生工学会).

Remarks

・Water Vapor Pressure of Saturated Air ≒ Saturated Vapor Pressure of Watar.
・T(Absolute Temperature(K))=Temperature(℃)+273.15.
・Wexler-Hyland formula.P≦5MPa,173.15K~372.15K.
ln(Water Vapor Pressure of Saturated Air(kPa)*1000)
:t≧0.01℃
=-0.58002206*10^4/T+0.13914993*10-0.48640239*10^-1*T+0.41764768*10^-4*T^2-0.14452093*10^-7*T^3+0.65459673*10*ln(T).
:t≦0.01℃
=-0.56745359*10^4/T+0.63925247*10-0.96778430*10^-2*T+0.62215701*10^-6*T^2+0.20747825*10^-8*T^3-0.94840240*10^-12*T^4+0.41635019*10*ln(T).
・Molecular Weight of Water/Average Molecular Weight of Dry Air=18.0153(g/mpl)/28.9645(g/mol)≈0.622.
・Absolute Humidity(kg/kg(DA))=0.622*Water Vapor Pressure(kPa)/(Total Pressure(kPa)-Water Vapor Pressure(kPa)).
・Specific Enthalpy of Water(or Ice)(kJ/kg(DA))
:t'≧0℃
≈4.184*t'.
:t≦0℃
≈2.09*t'-334.
・Water Vapor Pressure(kPa)=Total Pressure(kPa)*Absolute Humidity(kg/kg(DA))/(0.622+Absolute humidity(kg/kg(DA))).
・Specific Heat at Constant Pressure of Dry Air(cpa)=1.006(kJ/(kg(DA)・K)).
・Specific Heat at Constant Pressure of Vapor(cpw)=1.805(kJ/(kg(DA)・K)).
・Evaporation Heat of Water at 0°(γ0)=2501(kJ/kg).
・Gas Constant of Dry Air(Ra)=0.28706(kJ/(kg・K)).
・Gas Constant of Vapor(Rw)=0.46152(kJ/(kg・K)).
・Relative Humidity(%)=Water Vapor Pressure(kPa)/Water Vapor Pressure of Saturated Air(kPa).
・Saturation(%)=Absolute Humidity(kg/kg(DA))/Absolute Humidity of Saturated Air(kg/kg(DA)).
・Specific Volume(m^3/kg(DA))=(Ra+x*Rw)*T/P.
・Specific Enthalpy(kJ/kg(DA))=cpa*t+(cpw*t+γ0)*x.

History

・2014/08/08:layout change.
・2009/03/25:Moved from www.am-consulting.co.jp to here.