@staticmethod
def T3_ph(p, h):
    """function T3_ph = T3_ph(p, h)

        Revised Supplementary Release on Backward Equations for the functions T(p,h), v(p,h) and T(p,s), v(p,s) for Region 3 of the IAPWS Industrial formulation 1997 for the Thermodynamic Properties of Water and Steam 2004

        Section 3.3 Backward Equations T(p,h) and v(p,h) for Subregions 3a and 3b

        Boundary equation, Eq 1 Page 5
        """
    h3ab = (2014.64004206875 + 3.74696550136983 * p - 0.0219921901054187 * 
        p ** 2 + 8.7513168600995e-05 * p ** 3)
    if h < h3ab:
        Ii = [-12, -12, -12, -12, -12, -12, -12, -12, -10, -10, -10, -8, -8,
            -8, -8, -5, -3, -2, -2, -2, -1, -1, 0, 0, 1, 3, 3, 4, 4, 10, 12]
        Ji = [0, 1, 2, 6, 14, 16, 20, 22, 1, 5, 12, 0, 2, 4, 10, 2, 0, 1, 3,
            4, 0, 2, 0, 1, 1, 0, 1, 0, 3, 4, 5]
        ni = [-1.33645667811215e-07, 4.55912656802978e-06, -
            1.46294640700979e-05, 0.0063934131297008, 372.783927268847, -
            7186.54377460447, 573494.7521034, -2675693.29111439, -
            3.34066283302614e-05, -0.0245479214069597, 47.8087847764996, 
            7.64664131818904e-06, 0.00128350627676972, 0.0171219081377331, 
            -8.51007304583213, -0.0136513461629781, -3.84460997596657e-06, 
            0.00337423807911655, -0.551624873066791, 0.72920227710747, -
            0.00992522757376041, -0.119308831407288, 0.793929190615421, 
            0.454270731799386, 0.20999859125991, -0.00642109823904738, -
            0.023515586860454, 0.00252233108341612, -0.00764885133368119, 
            0.0136176427574291, -0.0133027883575669]
        ps = p / 100
        hs = h / 2300
        Ts = 0
        for i in range(0, 31):
            Ts = Ts + ni[i] * (ps + 0.24) ** Ii[i] * (hs - 0.615) ** Ji[i]
        T3_ph = Ts * 760
    else:
        Ii = [-12, -12, -10, -10, -10, -10, -10, -8, -8, -8, -8, -8, -6, -6,
            -6, -4, -4, -3, -2, -2, -1, -1, -1, -1, -1, -1, 0, 0, 1, 3, 5, 6, 8
            ]
        Ji = [0, 1, 0, 1, 5, 10, 12, 0, 1, 2, 4, 10, 0, 1, 2, 0, 1, 5, 0, 4,
            2, 4, 6, 10, 14, 16, 0, 2, 1, 1, 1, 1, 1]
        ni = [3.2325457364492e-05, -0.000127575556587181, -
            0.000475851877356068, 0.00156183014181602, 0.105724860113781, -
            85.8514221132534, 724.140095480911, 0.00296475810273257, -
            0.00592721983365988, -0.0126305422818666, -0.115716196364853, 
            84.9000969739595, -0.0108602260086615, 0.0154304475328851, 
            0.0750455441524466, 0.0252520973612982, -0.0602507901232996, -
            3.07622221350501, -0.0574011959864879, 5.03471360939849, -
            0.925081888584834, 3.91733882917546, -77.314600713019, 
            9493.08762098587, -1410437.19679409, 8491662.30819026, 
            0.861095729446704, 0.32334644281172, 0.873281936020439, -
            0.436653048526683, 0.286596714529479, -0.131778331276228, 
            0.00676682064330275]
        hs = h / 2800
        ps = p / 100
        Ts = 0
        for i in range(0, 33):
            Ts = Ts + ni[i] * (ps + 0.298) ** Ii[i] * (hs - 0.72) ** Ji[i]
        T3_ph = Ts * 860
    return T3_ph
