code: def _Vapor_Pressure(cls, T):
          
          Tita = 1-T/cls.Tc
          suma = 0
          for n, x in zip(cls._Pv["ao"], cls._Pv["exp"]):
              suma += n*Tita**x
          Pr = exp(cls.Tc/T*suma)
          Pv = Pr*cls.Pc
          return Pv
docs: Auxiliary equation for the vapour pressure
  
          Parameters
          ----------
          T : float
              Temperature, [K]
  
          Returns
          -------
          Pv : float
              Vapour pressure, [Pa]
  
          References
          ----------
          IAPWS, Revised Supplementary Release on Saturation Properties of
          Ordinary Water Substance September 1992,
          http://www.iapws.org/relguide/Supp-sat.html, Eq.1