This paper presents an investigation of heat transfer behavior and pressure drop characteristics of subcritical and supercritical water flows inside an inclined rifled tube for near-supercritical and supercritical flows. The operating pressure range was from 15 to 28 MPa, the mass flux range was from 600 to 1000 kg/m(2) s and wall heat flux was from 300 to 500 kW/m(2). The maximum inner diameter of pipe was 19.5 mm and the inclination angle of the tube was 20 with respect to the horizontal plane. The heat transfer to water and pressure drop gradients at various operating pressures for various heat fluxes and mass fluxes were studied. The results show that the effect of mass flux variations on heat transfer at supercritical pressures is more considerable than this effect at subcritical pressures. The same behavior was found for the pressure drop gradient. It was found that as the ratio of the mass flux to the heat flux exceeded 2.46 kg/kWs, heat transfer enhancement occurred near the pseudo critical point for supercritical pressures while maximum heat transfer at subcritical pressures occurred at ratio of the mass flux to the heat flux value of 1.65 kg/kW s for inclined rifled tube. (C) 2015 Elsevier B.V. All rights reserved.