It is widely acknowledged that the spacer grid has great effect on heat transfer downstream of it. The conventional correlations to predict the augmentation of the spacer were carried out on high Reynolds numbers. However, recent studies have shown that Reynolds number on the heat transfer enhancement is not negligible when the Reynolds number is lower than about 10000. An experiment to investigate the single-phase convective heat transfer downstream of the spacer grid at low flow rate has been performed in a 5×5 rod bundle. The test section was uniformly heated by a DC power and cooled by water. The Reynolds number covered from about 2000 to 10000. The experiment showed that the existing correlations for heat transfer enhancement by a spacer grid underestimated the maximum enhancement at the grid exit of the spacer grid at low Reynolds numbers. As the Reynolds number decreases, the maximum enhancement increases, nevertheless, when Reynolds number decreases to about 4300, the maximum enhancement tend to converge at a certain value. A new correlation has been proposed to account for the Reynolds number effect on heat transfer enhancement downstream of the spacer grid at low Reynolds numbers and which gave good predictions.
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