def stefan_boltzmann(alpha, e_flame, e_surface, h, Tflame, Tradiative, Tvessel):
    """
    Heat flux from flame to vessel surface from combined radiative
    and convective heat transfer. Returns the heat flux in W/m2
    See also API 521 and Scandpower guidelines.
    """
    sigma = 5.67e-8  # Stefan-Botlzmann constant W/m^2 K^4
    return (
        alpha * e_flame * sigma * Tradiative ** 4
        + h * (Tflame - Tvessel)
        - e_surface * sigma * Tvessel ** 4
    )