Numerical study of the influence of rolling condition on the spacer effect of convective heat transfer at low-flow-rates

A numerical study of spacer effect at low-flow-rates under rolling condition was conducted. The rolling model was validated based on experimental data, and computational fluid dynamics (CFD) method based on the SST k-ω turbulence model was established. The results show: 1) For circumferential mean time-averaged heat transfer, it is enhanced in the downstream of spacer for low-flow-rates conditions. However, in mixed convective heat transfer recovery and free convective regions, spacer effect still has damping oscillation attenuation whose amplitude decreases along flow direction. 2) For local time-averaged heat transfer, hot spots always lie in the direction of vertical rolling axis, where the heat transfer is weakened under rolling condition. 3) For instantaneous heat transfer at hot spots, the maximum weakening degree of the instantaneous heat transfer coefficient in the computing condition can reach 40 % compared with fully developed steady-state, which needs to be paid attention to in safety analysis. 4) With the decrease of rolling period, circumferentially averaged time-averaged heat transfer in the downstream of the spacer and instantaneous transfer at hot spots fluctuate more violently in mixed convective and free convective regions. 5) With the increase of maximum rolling angle, the enhancement of circumferential average time-averaged heat transfer increases in the far away from the spacer. But instantaneous heat transfer oscillation is more severe at hot spots. The local material life needs to be considered in detail in safety analysis.