def epsi_vapor(Fr):
    """
    Calculates the vapor content of bubble layer
    Parameters
    ----------
    Fr : float
        The Frudo criterion, [dimensionless]
    Returns
    -------
    epsi_vapor : float
        The vapor content of bubble layer, [dimensionless]
    References
    ----------
    Дытнерский, страница 207, формула 5.47
    """
    return Fr**0.5 / (1 + Fr**0.5)