Experimental study on sub-cooled flow boiling heat transfer characteristics in non-uniform heating tube bundle channel

Since the primary coolant temperature decreases along the U-tube, so the secondary side fluid in the steam generator tubes will receive non-uniform heating (NUH) from the primary side. Compared with uniform heating (UH), NUH has a great influence on the heat transfer characteristics of the secondary side, especially in terms of the sub-cooled flow boiling, during which the heat transfer mechanism changes. In this paper, sub-cooled flow boiling in a tube bundle channel under NUH and UH conditions are performed experimentally. The results show that NUH makes the onset of nucleate boiling (ONB) occur ahead of time, and it also leads to a greater radial inhomogeneity of fluid temperature field than UH. Four Chen-type correlations were evaluated, and it is found that the Gungor-Winterton correlation is most suitable for experiments under UH condition. However, the Gungor-Winterton correlation has a relatively large deviation under NUH condition, and it is also difficult to capture the predicted trend, which means that it is not applicable to NUH conditions. Therefore, an improved Gungor-Winterton correlation is proposed for NUH conditions. Its average relative error is 8.02%, and less than 2.18% of data has larger deviation than 20%. (C) 2021 Elsevier Ltd. All rights reserved.