Phenomenological Investigation and Numerical Simulation of Gas Bubble Behaviors in the Vicinity of Mixing Vane of Spacer Grid

Abstract

The presence of spacer grid with mixing vane in fuel assemblies has obvious influence on two phase flow. However, it is always difficult to obtain clear image of bubbles in the vicinity of mixing vane due to non-transparent fuel rods and interface overlapping in fuel assemblies. Hence, the understanding of bubble behaviors in that area is still insufficient. In this paper, phenomenological technique and interface tracking method were used to study the gas bubble behaviors in the vicinity of mixing vane of spacer grid in a 3×3 rod buddle under ambient temperature and atmospheric pressure. With the application of injecting rod, which produced bubble locally, and application of transparent rods, which eliminated interface distortion and discontinuity between rods and fluid, available photographs of bubble movement were obtained, and it was found that bubble stagnation occurred at the leeward of mixing vane. As increasing the liquid flow rate and volume fraction, stagnated bubble size increased and the size of bubble, broke up from the stagnated bubble , decreased. In the numerical simulation, VOF model was implemented to tracking bubble interface in a typical subchannel with spacer grid. Good agreement of bubble behavior in the vicinity of mixing vane was found between phenomenological experiment and numerical simulation. The influence of bubble behavior on flow pressure drop was also investigated.