def b(mul_20, rhol_20):
    """
    Calculates the temperature coefficient.
    Parameters
    ----------
    mul_20 : float
        The viscocity of low-boilling component of liquid at 20 degrees celcium, [Pa/s]
    rhol_20 : float
        The destinity of low-boilling component of liquid at 20 degrees celcium, [kg/m**3]
    Returns
    -------
    b : float
        The temperature coefficient, [dimensionless]
    References
    ----------
    Романков, страница 289, формула 6.24
    """
    return mul_20**0.5/rhol_20**0.66