Experimental and numerical study on the enhanced effect of spiral spacer to heat transfer of supercritical pressure water in vertical annular channels

Heat transfer characteristics of supercritical pressure water in annular channel have been investigated experimentally and numerically. The gap of the annular channel was 6 mm and a spiral spacer with a length of 100 mm was arranged on the inner test section. Experimental parameters included pressures of 23–28 MPa, mass fluxes of 350–1000 kg/m2 s and heat fluxes up to 1000 kW/m2. Special attention has been focused on the effect of spacer on heat transfer characteristics of water. In the experiments, an enhanced effect of the spiral spacer on heat transfer has been observed. It was found that the affected distance of the spacer depends strongly on flow conditions. Moreover, it was also observed that the spiral spacer has a positive effect on eliminating heat transfer deterioration which occurred at high ratios of heat flux to mass flux. Numerical simulation was carried out with a Computational Fluid Dynamics (CFD) method to obtain a deep insight of how the spiral spacers affect heat transfer. Calculated heat transfer coefficients captured the experimental data pretty well, with a largest deviation of 14.33% shows up at the vicinity of the pseudo-critical temperature. The mechanisms for the enhanced effect of spacer on heat transfer have been discussed based on the physical profiles obtained from numerical results. ► Enhanced effects of spacer to heat transfer of water were investigated. ► Spiral spacer has local and global effects on heat transfer. ► Spiral spacer has positive effect on eliminating heat transfer deterioration. ► The mechanisms for the enhanced effect of spacer were obtained.