Abstract
The in-situ characterization of soft deposits in liquid media is important in several scientific and industrial applications but presents substantial technological challenges. Nevertheless, fluid dynamic gauging (FDG), which is based on the principle of fluid flow through a nozzle that is in close proximity to a wall, can be used to estimate the thickness of wet deposits but its uncertainty analysis has not been rigorously addressed in the literature. This paper reports the development of a comprehensive device-agnostic methodology that can be used to characterize the uncertainty of FDG instruments. Furthermore, the uncertainty analysis of a calibrated instrument that has a horizontal configuration, in which the flow rate is controlled but the pressure drop is measured, is presented. The results indicate that the calibrated instrument can be used to estimate the thickness of deposits to ±81 μm at a 95% confidence. In addition, the uncertainty in thickness was found to be dependent on the confidence level of the expanded uncertainty coefficient, magnitude of the estimated thickness, and final clearance or height of the nozzle from the wall. The highest sensitivities of the instrument to the systematic uncertainties in the flow rate and pressure drop were observed at relatively low and high thickness estimates, respectively. An important contribution of the paper is the introduction of an uncertainty component from external mechanisms that may be used for independent displacement measurements or position control in the course of operating FDG instruments.
