In sub-critical pressure region

the heat transfer characteristics of water flowing in a vertical upward internally ribbed tube with diameter of φ28.6 mm×5.8 mm were experimentally investigated. The tests were performed under various conditions with pressures from 9 to 22 MPa

mass velocities from 450 to 2000 kg·m-2·s-1

and inner wall heat fluxes from 200 to 700 kW·m-2. The results show that the internally ribs of tube can effectively restrain the heat transfer from deterioration by keeping nucleate boiling. The heat transfer deterioration of dry out occurs at high steam quality in the internally ribbed tube. The increase of mass velocity can defer the sharp rise of wall temperature. The range of the sharp rise of wall temperature decreases as the mass velocity increases. With the increase of inner wall heat flux

the sharp rise of wall temperature occurs ahead at smaller steam quality

and the peak wall temperature after heat transfer deterioration increases. The steam quality corresponding to the sharp rise of wall temperature decreases at higher pressure. The heat transfer coefficient distribution curve of internally ribbed tube is in a shape of π. The top region of heat transfer coefficient is in steam-water flow boiling region. Based on the experiments

correlations of heat transfer coefficients are presented for vertical upward internally ribbed tubes.