Numerical investigation on heat transfer of supercritical fluid in a vertical 7-rod bundle

• The ωω type turbulence models predict the heat transfer deterioration.
• Strong non-uniform circumferential temperature distribution is observed.
• The mass flux distribution shows significant non-uniformity among sub-channels.
• The impact of secondary flow structure on rod wall temperature is negligible.
• The flow direction shows crucial impact on mass flux and wall temperature distribution.

Thermal–hydraulic behaviors in fuel assemblies of supercritical water-cooled reactor (SCWR) have been investigated worldwide since the SCWR was selected as a candidate of the Generation IV nuclear reactors for further development. However, the understanding of thermal–hydraulic behavior of supercritical fluids is still insufficient and a well prediction model has not been established, especially in rod bundles. In this paper, four turbulence models are assessed for simulating the Freon R12 flowing through a 7-rod bundle vertically and the simulated results are validated with experimental data. It is shown that the predicted results by all the turbulence models match the experimental data well in the region far from the pseudo-critical temperature. The ωω type turbulence models predict the heat transfer deterioration qualitatively in the near-critical region. Strong non-uniform circumferential temperature distribution is observed in the vicinity of pseudo-critical temperature. The anisotropic turbulence models show that secondary flow structure has little impact on rod wall temperature while the mass flux distribution is non-uniform greatly among different sub-channels. It is interesting that the flow direction exhibits crucial impact on the mass flux distribution as well as the wall temperature distribution which is valuable for future experimental study and fuel assembly design.

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