Flow and heat transfer of supercritical water in a rifled tube with axially non-uniform heating

Abstract

Flow and heat transfer of supercritical water through a four-head rifled tube with axially non-uniform heating was numerically investigated. After preliminary validation against experimental data, numerical runs were performed for operating pressure of 22.6–27.3 MPa, mass flux G of 350–800 kg/(m2·s) and heat flux q of 215–600 kW/m2. Results showed that at low q/G wall temperature distribution was highly dependent on the axial heat flux distribution. The location of maximum wall temperature varied with the heat flux curve. Operating parameters such as inlet temperature, mass flux and pressure had similar influence on heat transfer to supercritical water under axially uniform and non-uniform heating. Consequently, Nusselt correlations which were originally developed under uniform heating also showed acceptable performance under non-uniform heating. On the other hand at high q/G, flow and heat transfer was significantly affected by the axial heating mode due to strong buoyancy influence. Wall temperature peaks occurred earlier in non-uniform heating cases, and wall temperature at the location of maximum heat flux could be remarkably lower than the globally maximum wall temperature. However, the minimum heat transfer coefficient seemed less sensitive to the heat flux profile, and can’t be improved by delaying the appearance of maximum heat flux. Axial heating mode only affected local heat transfer coefficients when forced and natural convection shared competing roles. Finally, an empirical correlation for estimation of heat transfer under axial non-uniform heating was developed.