Dimensional analysis on incipient flow instability in one-side high heat loaded rectangular flat heat sink under sub-cooled flow boiling conditions

The onset of flow instability (OFI) is a major threat to the operation of a fusion power plant. In particular, because the divertor is loaded with a high heat flux of up to 20 MW/m2, it may be vulnerable to OFI. Therefore, in this study, the OFI of a one-side heated flat heat sink was experimentally analyzed. When the effect of the system parameters on the OFI was analyzed, the faster the vapor inside the channel could be removed, the higher was the OFI that was experimentally recorded. As the flow rate and degree of subcooling increase, the OFI increases because it induces an enhancement of the forced convective heat transfer performance and a rapid coding rate, respectively. However, when the pressure is increased, the latent heat and liquid surface tension are reduced; thus, boiling occurs at a lower heat rate, which leads to a decrease in OFI. When the prediction performance of the existing OFI correlations developed under the subcooled flow boiling condition was evaluated, it showed a tendency to overpredict this experimental value significantly. This is because the evaluated correlations were developed based on relatively low heat flux conditions and narrow rectangular channels. Therefore, in this study, we developed a new OFI correlation optimized for experimental values using an artificial intelligence (AI) regression method. Because this correlation can be utilized under one-side high heat load conditions, it is expected that it will be especially useful when establishing the operation strategy of the cooling system of a fusion power plant.