def Prl(self):
        r'''Prandtl number of the liquid phase of the chemical at its
        current temperature and pressure, [dimensionless].

        .. math::
            Pr = \frac{C_p \mu}{k}

        Utilizes the temperature and pressure dependent object oriented
        interfaces :obj:`thermo.viscosity.ViscosityLiquid`,
        :obj:`thermo.thermal_conductivity.ThermalConductivityLiquid`,
        and :obj:`thermo.heat_capacity.HeatCapacityLiquid` to calculate the
        actual properties.

        Examples
        --------
        >>> Chemical('nitrogen', T=70).Prl
        2.7828214501488886
        '''
        Cpl, mul, kl = self.Cpl, self.mul, self.kl
        if all([Cpl, mul, kl]):
            return Prandtl(Cp=Cpl, mu=mul, k=kl)
        return None
r'''Prandtl number of the liquid phase of the chemical at its
        current temperature and pressure, [dimensionless].

        .. math::
            Pr = \frac{C_p \mu}{k}

        Utilizes the temperature and pressure dependent object oriented
        interfaces :obj:`thermo.viscosity.ViscosityLiquid`,
        :obj:`thermo.thermal_conductivity.ThermalConductivityLiquid`,
        and :obj:`thermo.heat_capacity.HeatCapacityLiquid` to calculate the
        actual properties.

        Examples
        --------
        >>> Chemical('nitrogen', T=70).Prl
        2.7828214501488886