New correlations for the prediction of incipient nucleate boiling in a one-side heated swirl tube

Future tokamak cooling systems should always be maintained in a single phase during operation to avoid po-tential hazards caused by vapor. To this end, a correlation to accurately predict sub-cooled flow boiling onset of nucleate boiling (ONB) under the one-side high heat load condition, which is the heat flux condition inside the tokamak, is required. According to this necessity, the ONB of a one-side heated swirl tube was experimentally explored in this study. The inserted swirl tape induces a secondary swirling flow, which causes ONB to occur at a higher heat flux condition than the smooth tube. As the twist ratio of the tape decreased, the ONB heat flux enhancement rate increased. Sub-cooling and mass flow rate have a proportional relationship with ONB heat flux, whereas pressure has an inverse relationship. The prediction accuracy of the existing ONB correlations was evaluated. However, most correlations tended to under-predict the experimental values. Because they were not developed for the purpose of predicting the ONB of the swirl tube under sub-cooled flow conditions, all system parameters and the effect of the swirl tape were not reflected. Therefore, we developed new correlations using Python combined with machine learning.