Numerical Investigations of the Helium Flow in Mini-Scale Gaps

Abstract

According to the loose body structure design of the high temperature gas-cooled reactor (HTGR), narrow gaps between the graphite and carbon blocks are widely distributed in the reactor core and become possible bypass flow paths. Related to the effective cooling flow rate in the primary loop, the bypass flow distribution is important to the thermal hydraulic design and safety analyses of the HTGR. Typical gaps of bypass flow paths are mini-scale rectangular gaps with small height/width ratio of the cross section, and their sizes are about 1.0 mm. Due to non-circular cross section, small height/width ratio and mini-scale sizes, helium flow in those gaps may be laminar, transient, or turbulent so that the resistance performance of each gap is difficult to predict and is crucial to analyze the bypass flow distribution in the reactor core. In this paper, commercial Computational Fluid Dynamic (CFD) software ANSYS Fluent was utilized to simulate helium flow in mini-scale gaps to investigate the reasonable models for predicting the resistance performances. Two-dimensional simulation results were compared with experimental data conducted in South Africa. The RNG k-ε model with enhanced wall treatments was more appropriate to simulate flows with Reynolds number up to 2  × 10⁴ in mini-scale gaps. Based on the CFD models validated by the pressurized helium flow experiments, they can be further used to study more complex bypass flows in the HTGR.