| dc.description.abstract | A very high-temperature, test facility was designed and constructed at the Thermal-Hydraulic Research Laboratory of Texas A&M University (TAMU) to conduct two-phase flow visualization experiments in molten salt. A stainless-steel 316 (SST316) test apparatus equipped with a clear quartz section was designed to conduct visualization experiments of single helium bubbles rising in fluoride salt within a temperature range of 460 – 650 °C. The fluoride-salt chosen for this research was a eutectic mixture of LiF- NaF-KF (46.5-11.5-42%), also known as FLiNaK. A set of helium bubble tests were conducted at 550 - 600 °C, and Particle Image Velocimetry (PIV) technique was successfully applied to estimate velocity fields. The analysis conducted helped to understand the effects of bubble size and shape on the helium bubble terminal velocity in FLiNaK. Each bubble varied in shape and trajectory throughout rising in the test section. The bubble shapes observed were ellipsoidal, wobbling, and spherical cap; and the bubble motions observed were helical, zigzag, and rectilinear. The helium bubbles were measured and had an aspect ratio range of 0.363 – 0.681 ± 10%, an equivalent bubble diameter range within 2.96 – 6.47 ± 12% mm, and an experimental terminal velocity range of 208.41 - 268.82 ± 3% mm/s. Non-dimensional numbers were calculated with liquid and gas thermophysical properties evaluated from 550-600°C and atmospheric pressure. The non-dimensional number ranges in this study were determined as 243 < Re < 759, 0.940 < Eo < 4.54, 1.59 < We < 4.36, 39323 < Ar < 622809, and 7.63x10-10 < Mo < 2.41x10-10. The experimental terminal velocities were
compared to two contaminated liquid terminal velocity correlations for gas bubbles rising in liquid. The experimentally determined terminal velocities agreed with two terminal velocity empirical correlations chosen for this study. The experimental terminal velocities differed by an average of 2.17% with a standard deviation of ±12.8% for the first correlation, and by an average of 13.21% with a standard deviation of ± 7.18% for the second correlation. | en |
