Abstract
Series of experiments have been performed at different pressures from 12 to 19 MPa, mass velocities from 400 to 1000 kg・m^<-2>・s^<-1>, inner wall heat fluxes from 300 to 500 kW・m^<-2> and bulk fluid enthalpy from 800 to 3100 kJ・kg^<-1>, to study flow boiling heat transfer characteristics of water in seven vertically-upward spirally-ribbed tubes with different rib structures. Based on the experimental results, effects of pressure, mass velocity and heat flux on flow boiling heat transfer coefficient (HTC) were discussed. It was found that, saturated flow boiling HTC was nearly invariable with an increase in mass velocity, but it increased distinctly with the increase in heat flux. As the pressure increased, the flow boiling HTC increased. Some existing correlations for predicting flow boiling HTC of water in the spirally-ribbed tubes were evaluated with the test data collected from open literatures and obtained in this experiment. On the basis of experimental results of flow boiling heat transfer from open literature and internal report, a new universal correlation for the flow boiling HTC of subcritical pressure water was developed for spirally-ribbed tubes with different rib structures, by introducing suitable dimensionless quantities of the spirally-ribbed tube structures to the existing empirical correlations. It was shown that the values calculated by the new correction are in good agreement with the experimental data for the two new-type spirally-ribbed tubes, indicating that the newly proposed universal correlation could provide good support for the application of the vertically-upward spirally-ribbed tubes.
