Heat transfer characteristics of subcooled flow boiling water were experimentally investigated in a vertical evaporator with wire coil inserted.The evaporator was an annular channel consisted of an inner heater rod and an outer quartz pipe.Five kinds of helically wire coils with different coil pitches and different wire diameters were made and used in full length of the heated rod.For each inserted tube and the plain tube

16 testing runs were carried out with different mass velocities and heat fluxes separately.The influences of wire diameter and coil pitch on heat transfer coefficients were investigated and the mechanism was analyzed.The results indicate that the presence of wire coil causes the spiral and separation of fluid

increasing the nucleation site density in nucleate boiling and enhancing the subcooled boiling heat transfer.The heat transfer coefficients increases as the coil pitch decreases and as wire diameter increases

namely as pitch diameter ratio(P/e)reduces.The enhancement effect for the minimum 1.5 of P/e is the best.The maximum heat transfer enhancement of the wire coil inserted tubes over the plain tube is 109%. Four correlations are assessed by the mean absolute error based on the experimental data.The enhancement factor of the coiled wire inserted annuli is given in the form of diagram under different operation conditions.