def Lewis(D=None, alpha=None, Cp=None, k=None, rho=None):
    r'''Calculates Lewis number or `Le` for a fluid with the given parameters.

    .. math::
        Le = \frac{k}{\rho C_p D} = \frac{\alpha}{D}

    Inputs can be either of the following sets:

    * Diffusivity and Thermal diffusivity
    * Diffusivity, heat capacity, thermal conductivity, and density

    Parameters
    ----------
    D : float
        Diffusivity of a species, [m^2/s]
    alpha : float, optional
        Thermal diffusivity, [m^2/s]
    Cp : float, optional
        Heat capacity, [J/kg/K]
    k : float, optional
        Thermal conductivity, [W/m/K]
    rho : float, optional
        Density, [kg/m^3]

    Returns
    -------
    Le : float
        Lewis number []

    Notes
    -----
    .. math::
        Le=\frac{\text{Thermal diffusivity}}{\text{Mass diffusivity}} =
        \frac{Sc}{Pr}

    An error is raised if none of the required input sets are provided.

    Examples
    --------
    >>> Lewis(D=22.6E-6, alpha=19.1E-6)
    0.8451327433628318
    >>> Lewis(D=22.6E-6, rho=800., k=.2, Cp=2200)
    0.00502815768302494

    References
    ----------
    .. [1] Green, Don, and Robert Perry. Perry's Chemical Engineers' Handbook,
       Eighth Edition. McGraw-Hill Professional, 2007.
    .. [2] Cengel, Yunus, and John Cimbala. Fluid Mechanics: Fundamentals and
       Applications. Boston: McGraw Hill Higher Education, 2006.
    .. [3] Gesellschaft, V. D. I., ed. VDI Heat Atlas. 2nd edition.
       Berlin; New York:: Springer, 2010.
    '''
    if k and Cp and rho:
        alpha = k/(rho*Cp)
    elif alpha:
        pass
    else:
        raise Exception('Insufficient information provided for Le calculation')
    return alpha/D
def Lewis ( D = None , alpha = None , Cp = None , k = None , rho = None ) : if k and Cp and rho : alpha = k / ( rho * Cp ) elif alpha : pass else : raise Exception ( 'Insufficient information provided for Le calculation' ) return alpha / D
r'''Calculates Lewis number or `Le` for a fluid with the given parameters.

    .. math::
        Le = \frac{k}{\rho C_p D} = \frac{\alpha}{D}

    Inputs can be either of the following sets:

    * Diffusivity and Thermal diffusivity
    * Diffusivity, heat capacity, thermal conductivity, and density

    Parameters
    ----------
    D : float
        Diffusivity of a species, [m^2/s]
    alpha : float, optional
        Thermal diffusivity, [m^2/s]
    Cp : float, optional
        Heat capacity, [J/kg/K]
    k : float, optional
        Thermal conductivity, [W/m/K]
    rho : float, optional
        Density, [kg/m^3]

    Returns
    -------
    Le : float
        Lewis number []

    Notes
    -----
    .. math::
        Le=\frac{\text{Thermal diffusivity}}{\text{Mass diffusivity}} =
        \frac{Sc}{Pr}

    An error is raised if none of the required input sets are provided.

    Examples
    --------
    >>> Lewis(D=22.6E-6, alpha=19.1E-6)
    0.8451327433628318
    >>> Lewis(D=22.6E-6, rho=800., k=.2, Cp=2200)
    0.00502815768302494

    References
    ----------
    .. [1] Green, Don, and Robert Perry. Perry's Chemical Engineers' Handbook,
       Eighth Edition. McGraw-Hill Professional, 2007.
    .. [2] Cengel, Yunus, and John Cimbala. Fluid Mechanics: Fundamentals and
       Applications. Boston: McGraw Hill Higher Education, 2006.
    .. [3] Gesellschaft, V. D. I., ed. VDI Heat Atlas. 2nd edition.
       Berlin; New York:: Springer, 2010.