Characteristics of bubble behavior in petal-shaped fuel rod bundle channels under different flow conditions

Abstract

The petal-shaped fuel element is a novel type of fuel element suitable for small-scale reactors. The motion of bubbles in the rod bundle channel has a significant impact on the surrounding flow and temperature fields, thereby influencing the two-phase flow and heat transfer characteristics. To investigate the dynamics of bubbles in the rod channel of the petal-shaped fuel rod, we simulated the rising motion of bubbles with different inlet flow rates using the volume of fluid method (VOF). We obtained the trajectory, rising speed, and shape changes of the bubbles with varying initial sizes, and analyzed the flow field around the bubbles. Our results indicate that the transverse displacement of bubbles in the radius range of 0.5 mm–1.25 mm increases gradually with their initial size, and the degree of deformation and maximum rising velocity of the bubbles also increase. However, bubbles with a radius of 1.5 mm experience less transverse displacement due to their larger size and contact with multiple fuel rods during the ascent process. Furthermore, the transverse displacement distance of the bubble increases and then decreases with the increase of fluid flow rate in the channel, while the aspect ratio of the bubble remains unaffected by the inlet flow rate. The study of bubble behavior sheds light on the mechanism of bubble motion in the channel of petal-shaped rod bundles, and provides a foundation for the study of two-phase flow and heat transfer in the channel.