Numerical Investigation on Heat Transfer Characteristics of High Pressure Boiling Water in Vertical Internally-Ribbed Tubes

Heat transfer characteristics of high pressure boiling water flowing in vertical internally-ribbed tubes are numerically investigated with the RPI wall boiling model. Specifically, Tolubinsky’s bubble departure diameter model is applied in the present study. The numerical results indicate that the value of d_ref in Tolubinsky’s bubble departure diameter model needs to be modified at high pressures so that reasonable wall temperature values can be obtained. A recommended value of d_ref is achieved for the cases at 14.2 MPa in the present paper, and the simulated value of wall temperature is in good agreement with the corresponding experimental data collected from the published literature. Based on the present modified RPI wall boiling model, the effects of rib geometries on heat transfer characteristics of high pressure boiling water in internally-ribbed tubes are investigated. The numerical results show that the heat transfer capability of high pressure boiling water in internally-ribbed tubes increases with the increase in rib heights or the number of ribs, but decreases with the increase in helix angle of the rib. Meanwhile, the increase in rib width has little influence on the heat transfer of boiling flow in the internally-ribbed tube. The results obtained in this study will be helpful for optimizing the rib geometries of internally ribbed tubes.