Heat transfer characteristics of supercritical pressure water in vertical upward annuli

Abstract

Heat transfer characteristics of supercritical pressure water in vertical-upward annuli with annular gaps of 4mm and 6mm were investigated experimentally. The inner heated rod has an outer diameter of 8mm with an effective heated length of 1400mm. Experimental parameters covered the pressures of 23–28MPa, mass fluxes of 350–1000kg/m2s, heat fluxes of 200–1000kW/m2 and inlet bulk temperature up to 400°C. According to the experimental data, the effects of heat flux and mass flux on heat transfer of supercritical water were analyzed. Experimental results showed that heat transfer of various heat fluxes and mass fluxes in annuli are similar with those in tubes. Compare the heat transfer differences in the two annular gaps, it was found that heat transfer in 6mm gap channel is better than that in 4mm gap channel, especially in the pseudo-critical enthalpy region. Experimental results also showed that the spiral spacer, which was arranged on the outer surface of the heated rod, has a positive effect on enhancing local heat transfer. However, this enhanced phenomenon seems stronger in 4mm gap compared to that in 6mm gap. The criterion of Jackson–Hall was selected to distinguish the effect of buoyancy in annular channels. Predicted results demonstrated that this criterion achieves good agreements against the experimental data at various mass fluxes and pressures. The present paper compared the experimental data with eight heat transfer correlations for supercritical pressure water. It was found that the correlations of Jackson, Bishop and Cheng are most close to the test data for normal heat transfer region, whereas only the correlation of Cheng seems acceptable when heat transfer deterioration occurs.