Tube inlet gas temperature, T1 = 1045 deg.C

Saturation water temperature, tsat = 186 deg.C

Flue gas temperature, t2 = ?

2 equations to be used here:

Q = U.A.LMTD -------------(1)

Qg = Mg.Cg.(T1 - T2) ------(2)

Mg = mass of flue gas = 2415 kg/hr

Cg = specific heat of gas = 1.92 kJ/kg.K

U = overall heat transfer coefficient = 25.37 W/m2.K

A = heating surface of tube = 26.85 m2

LMTD = log mean temperature difference bet. the 2 medium

Equating both equation 1 & 2, and solve for T2, I get 674 deg.C

Problem is that inside this boiler tube has spiral tube, which will increase the heat transfer and will bring down the temperature of T2.

I just don't know how to go about this spiral tube. How to solve this?