Page:Journal of the American Society of Mechanical Engineers, Volume 33.pdf/668

Rh

For $$r'$$ may be substituted the approximate value $$r' = 1091.6 - 0.56 t'$$ and for $$S'$$ the value $$S' = 0.6215 + 0.000034 t'$$ (approximately). Hence

and if Swann’s value of $$0.24112 + 0.000009 t$$ is accepted for the value of $$C_{pa}$$ as in the charts,

This equation has been carefully tested by comparing with values of the psychrometric coefficient as determined by means of the