Scale-Resolving Simulation of the Flow in Next Generation Nuclear Power Plant Helical Coil Steam Generator

Abstract

The helical coil steam generator (HCSG) is a specific type of shell-and-tube heat exchanger known for having a higher heat transfer coefficient than similar straight tube designs. Because of its compactness and higher heat transfer coefficient than many other designs, they are considered in a small modular reactor (SMR) and high-temperature reactor designs. Another advantage of HCSGs is that the helical coil bundle design has a high resistance to flow-induced vibrations (FIV), which is the important driver of tube ruptures. Investigation of flow behavior in HCSGs is essential for a safe nuclear reactor design.

The present study focuses on the analysis of the flow in the shell side of a 24- degree cut helical coil steam generator (HCSG) with large eddy simulation (LES). In the study, the open-source, high-order spectral element CFD code Nek5000 was employed for numerical simulation. LES was performed at a Reynolds number of 9000 based on the inlet velocity and tube diameter. Spectral analysis was carried out along the tube bundle to investigate the vortex shedding and to reveal shedding frequencies in HCSGs. Wavelet analysis was carried out to determine the time-frequency information of the fluctuating velocities in the domain. The flow was decomposed into modes with proper orthogonal decomposition, which revealed the most energetic coherent structures in the flow and evolution of the modes in time. Multi-resolution dynamic mode decomposition (mrDMD) was employed for the wavelet-inspired analysis of the coherent structures in the domain. For the validation of Nek5000 in complex geometries, results from the numerical simulation were compared with experiments conducted at Texas A&M University.