Characterization of Thermal Striping in Liquid Sodium With Optical Fiber Sensors

Abstract

This study characterized the magnitude, spatial profile, and frequency spectrum of thermal striping at a junction using a novel sodium-deployable optical fiber temperature sensor. Additionally, this study revealed for the first time the capability of performing cross correlation velocimetry (CCV) with an optical fiber to acquire fluid flow rates in a pipe. Optical fibers were encapsulated in stainless steel capillary tubes with an inert cover gas for high-temperature sodium deployment. Plots of temperature oscillation range as a function of two-dimensional space highlighted locations prone to mechanical failure for particular flow momentum ratios. The effect of inlet sodium temperature differential and bulk flow rate on thermal striping behavior was also explored. The power spectral density (PSD) revealed that the striping temperature oscillations occurred at frequencies ranging from 0.1 to 6 Hz. Finally, the bulk flow rate of liquid sodium was calculated from thermal striping's periodic temperature oscillations using cross correlation velocimetry for flow rates of 0.25–5.74 L/min.