Temperature corrections for coaxial cylindrical viscosity measurement method on molten salt

Abstract

Modern industrial applications often require accurate measurements of high temperature fluids such as molten salts. However, the commonly used coaxial cylindrical viscosity measurement method has an intrinsic bias when the calibration fluid and test fluid are run at significantly different temperatures due to the thermal expansion of solid container materials. In this study, we take a novel approach by deriving and quantifying the thermal expansion bias, β, for various common container materials using fluid dynamics arguments, thermal expansion data, and empirical methods. To the best knowledge of the authors, this work represents the first quantification of the thermal expansion bias and fills a significant gap in the current understanding. To validate our findings, we conducted an experiment on solar salt and applied the derived thermal expansion correction to the results, comparing them to independent studies. The results highlight the importance of the thermal expansion correction, which increases with rising temperature, particularly in high thermal expansion materials such as stainless steel, which has a bias of ∼6 % at 1000 °C. Our contribution provides valuable insights into the accurate measurement of high temperature fluids and offers a substantial advancement in addressing the thermal expansion bias, setting a new standard for future research in this field.