def _Backward2b_T_Ph(P, h):
    """Backward equation for region 2b, T=f(P,h)

    Parameters
    ----------
    P : float
        Pressure, [MPa]
    h : float
        Specific enthalpy, [kJ/kg]

    Returns
    -------
    T : float
        Temperature, [K]

    References
    ----------
    IAPWS, Revised Release on the IAPWS Industrial Formulation 1997 for the
    Thermodynamic Properties of Water and Steam August 2007,
    http://www.iapws.org/relguide/IF97-Rev.html, Eq 23

    Examples
    --------
    >>> _Backward2b_T_Ph(5,4000)
    1015.31583
    >>> _Backward2b_T_Ph(25,3500)
    875.279054
    """
    I = [0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 
        3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 6, 7, 7, 9, 9]
    J = [0, 1, 2, 12, 18, 24, 28, 40, 0, 2, 6, 12, 18, 24, 28, 40, 2, 8, 18,
        40, 1, 2, 12, 24, 2, 12, 18, 24, 28, 40, 18, 24, 40, 28, 2, 28, 1, 40]
    n = [1489.5041079516, 743.07798314034, -97.708318797837, 
        2.4742464705674, -0.63281320016026, 1.1385952129658, -
        0.47811863648625, 0.0085208123431544, 0.93747147377932, 
        3.3593118604916, 3.3809355601454, 0.16844539671904, 
        0.73875745236695, -0.47128737436186, 0.15020273139707, -
        0.002176411421975, -0.021810755324761, -0.10829784403677, -
        0.046333324635812, 7.1280351959551e-05, 0.00011032831789999, 
        0.00018955248387902, 0.0030891541160537, 0.0013555504554949, 
        2.8640237477456e-07, -1.0779857357512e-05, -7.6462712454814e-05, 
        1.4052392818316e-05, -3.1083814331434e-05, -1.0302738212103e-06, 
        2.821728163504e-07, 1.2704902271945e-06, 7.3803353468292e-08, -
        1.1030139238909e-08, -8.1456365207833e-14, -2.5180545682962e-11, -
        1.7565233969407e-18, 8.6934156344163e-15]
    Pr = P / 1
    nu = h / 2000
    T = 0
    for i, j, ni in zip(I, J, n):
        T += ni * (Pr - 2) ** i * (nu - 2.6) ** j
    return T
