Robust processing of capillary velocimetry data via stress-rescaled velocity functions

A method is presented to obtain rheological information from capillary velocimetry experiments coupled with pressure drop measurements. The method is based on rescaling the velocity profile with the wall shear stress. The stress-rescaled velocity curve generated depends only on the rheological properties of the fluid, and not on other experimental variables such as tube dimensions, flow rates or pressure drops employed, thus providing a direct means for rheological characterization. We also present transformed functions of the rescaled velocity that facilitate the interpretation of the rheological information via plots that resemble conventional rheograms. In contrast with previous data processing methods that require differentiation, model fitting, or smoothing, the proposed rescaling approach does not require the introduction of additional data processing parameters, such as smoothing factors, that may affect reproducibility of the results. The rescaling method should be useful for robust measurements in low signal-to-noise conditions such as rapid measurements required for process control.