Investigation on heat transfer characteristics of subcritical and supercritical water in an inclined rifled tube

To explore the heat transfer characteristics of rifled tube water wall in the supercritical (ultra-supercritical) boiler, an experiment was carried out in a ϕ35 mm×7.75 mm upwards inclined rifled tube at different inclination angles from 5° to 90°. The experimental parameters are as follows: pressures from 15 to 28 MPa, mass flow rate from 600 to 1000 kg∙m-2∙s-1, heat flux from 300 to 500 kW∙m-2. The wall temperature characteristics were compared between the rifled tube and the ϕ25 mm×3 mm smooth tube. The effects of inclination angles, mass flow rate and pressures on the heat transfer characteristics of subcritical, near-critical and supercritical water in the rifled tube were discussed. The heat transfer correlations of supercritical water in the rifled tube at different inclination angles were developed. The results revealed that the rifled tube used in the experiment had the property of delaying heat transfer deterioration and enhancing heat transfer. The heat transfer characteristics of the rifled tube at different inclination angles were different. The mass flow rate had little influence on the heat transfer coefficients in the two-phase region at subcritical pressure. And with the increase of mass flow rate, the heat transfer coefficients increased at near-critical and supercritical pressure. The heat transfer coefficients at 15 MPa were higher than those at other pressures.Under supercritical pressure, as the pressure increases, the heat transfer coefficient of the large specific heat zone decreases. © 2021, Editorial Board of CIESC Journal. All right reserved.