code: def _Backward3_T_Ph(P, h):
      
      hf = _h_3ab(P)
      if h <= hf:
          T = _Backward3a_T_Ph(P, h)
      else:
          T = _Backward3b_T_Ph(P, h)
      return T
docs: Backward equation for region 3, T=f(P,h)
  
      Parameters
      ----------
      P : float
          Pressure, [MPa]
      h : float
          Specific enthalpy, [kJ/kg]
  
      Returns
      -------
      T : float
          Temperature, [K]