def Diff_20(Massl, Massh, A , B, mu_solv, nul, nuh):
    """
    Calculates the diffusion coefficient at 20 degrees celcium.
    Parameters
    ----------
    Massl : float
        The molar mass of low-boilling component, [g/mol]
    Massh : float
        The molar mass of high-boilling component, [g/mol]
    A : float
        The correction coefficient depending on the properties solute, [dimensionless]
    B : float
        The correction coefficient depending on the properties solvent, [dimensionless]
    mu_solv : float
        The viscocity of solvent liquid, [Pa/s]
    nul : float
        The molar volume of solute, [sm**3/s]
    nuh : float
        The molar volume of solvent, [sm**3/s]
    Returns
    -------
    Diff_20 : float
        The diffusion coefficient at 20 degrees celcium, [m**2/s]
    References
    ----------
    Романков, страница 289, формула 6.22
    """
    return 1e-6 * ((1/Massl) + (1/Massh))**0.5 / (A * B * mu_solv**0.5 * ((nul)**0.66 + (nuh)*0.66)**2)