﻿ 000154_Calculation of State Value of Air

# 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.