Atmospheric Air is a mixture of dry air and water vapour. It can be treated as ideal gas and the gas laws can be applied to it.
General gas law
pV = mRT
r = m/V = p/RT
paVa = RaT
pwVw=RwT
Daltons law
p = pa + pw (Pa, N/m2)
where
p = total pressure of air (Pa, N/m2)
pa = partial pressure dry air (Pa, N/m2)
pw = partial pressure water vapour (Pa, N/m2)
--------------------------------------------------------------------------------
Density of dry air ra = 0,0035 pa/T (kg/m3)
where
ra = density dry air (kg/m3)
T = absolute dry bulb temperature (K)
--------------------------------------------------------------------------------
Density of water vapour rw = 0,0022 pw/T (kg/m3)
where
pw = partial pressure water vapour (Pa, N/m2)
rw = density water vapour (kg/m3)
--------------------------------------------------------------------------------
Density of air-water vapour mixture r = 0,0035 pt/T ? 0,00133 pws? /100T (kg/m3)
where
r = density air-vapour mixture (kg/m3)
pt = total pressure of the mixture (Pa, N/m2)
pws = saturation pressure of water vapour (Pa, N/m2)
? = relative humidity %
--------------------------------------------------------------------------------
Humidity is the term applied to the quantity of water vapour present in the air.
--------------------------------------------------------------------------------
Absolute Humidity is the actual mass of water vapour present, expressed in grams water vapour per kilogram mixture.
--------------------------------------------------------------------------------
Specific Humidity is the actual mass of water vapour present, expressed in grams water vapour per kilogram dry air.
X = 0,622 ? r ws/(r -r ws)100 kg/kg
where
X = specific humidity of air vapour mixture g/kg
--------------------------------------------------------------------------------
Specific Humidity of Saturated Air Xs = 0,622 ? r ws/(r -r ws) kg/kg
--------------------------------------------------------------------------------
Relative Humidity is
ratio of actual partial pressure of water vapour to vapour pressure at saturation at actual dry bulb temperature.
or
ratio of actual vapour density to vapour density at saturation at actual dry bulb temperature.
or
ratio at actual mass of water vapour in a given air volume to mass of water vapour required to saturate this volume.
Relative Humidity is usually expressed in %.
? = pw/pws x100 = r w/r ws x100 = X/ Xs x 100 %
--------------------------------------------------------------------------------
Saturated Air holds the maximum mass of water vapour at the given temperature. Lower air temperature will cause condensation of water vapour.
--------------------------------------------------------------------------------
Dry Bulb Temperature is the air temperature indicated by a thermometer not affected by the moisture of the air.
--------------------------------------------------------------------------------
Wet Bulb Temperature is the temperature of adiabatic saturation. It is the temperature indicated by a moistened thermometer bulb exposed to a current of air.
--------------------------------------------------------------------------------
Dew Point Temperature is the temperature to which air with a given moisture content must be cooled to produce saturation of the air and the commencement of the vapour in the air.
--------------------------------------------------------------------------------
Specific Enthalpy of dry air
H = 1,01t kJ/kg
where
H = enthalpy kJ/kg
1,01 = specific heat capacity of dry air kJ/kg oC
t = temperature oC
--------------------------------------------------------------------------------
Specific Enthalpy of air-water vapour mixture is composed to the sensible heat of the air and the latent heat of vapourisation of the water vapour present in the air and the sensible heat of the vapour.
H = 1,01t + X(2463 + 1,88t) kJ/kg
2463 = latent heat of vapouration of water at 0 oC kJ/kg
1,88 = specific heat capacity of water vapour at constant pressure kJ/kg oC
--------------------------------------------------------------------------------
Thermal expansion of air Dry air expands uniformly 1/886 (0,112%) of its volume per oC under constant pressure.
--------------------------------------------------------------------------------
Specific Heat Capacity of dry air
Cp = 1.01 kJ/kgK
= 1,23 kJ/m3K at standard pressure
*shrugs* I dunno