# The relationship between the gas constant for dry

The relationship between the gas constant for dry air RdRd and that HS-173 for water vapor dc=210dc=210 can be denoted by the ratio Rd/Rv = 287.08/461.52 ≈ 0.622. Consequently, the gas constant for the humid air can be defined as:equation(5)R=Rd+wRv=(1+w/0.622)RdR=Rd+wRv=(1+w/0.622)Rd
The constant-volume specific heat capacity of wet air cv can be given byequation(6)cv=cp-R=(1+1.9w)cpd-(1+w/0.622)Rdcv=cp-R=(1+1.9w)cpd-(1+w/0.622)Rd
The specific heat ratio of moist air γ is then calculated byequation(7)γ=cp/cv=(1+1.9w)cpd/((1+1.9w)cpd-(1+w/0.622)Rd)γ=cp/cv=(1+1.9w)cpd/((1+1.9w)cpd-(1+w/0.622)Rd)
The humid air current in SUPP is usually regarded as an ideal gas mixture that obeys the ideal gas law. The state equation of the ideal gas is:equation(8)ρ=pRTwhere ρρ is the density of the humid air in the collector. According to the concept of the density, the expression of humid air density can be rewritten as:equation(9)ρ=(1+w)ρd=(1+w)pdRdT=1+wp-pvRdT=(1+w)1-w0.622+wpRdT