Non-invasive inline rheometry for fluid foods containing millimeter-sized ingredients

In this study, we propose a non-invasive inline rheometry based on spatiotemporal velocity distribution measurements within a circular pipe to monitor the rheological properties of fluid products. Pulsatile flow in the pipe is measured using an ultrasonic velocity profiler (UVP), and the phase analysis of the velocity fluctuations is employed to convert radial phase shifts of the pulsatile flow into the spatial distribution of the effective viscosity. Compared to conventional methods, this approach employing the velocity fluctuations demonstrates significant robustness against UVP measurement noise and obtains more than tenfold higher precision. As a demonstration of this method, measurements were conducted on a Newtonian fluid (silicone oil) and a shear-thinning fluid (carboxymethyl cellulose aqueous solution). Results consistent with offline evaluations were achieved, validating the proposed method. Additionally, as an application to complex fluids with time-dependent properties, measurements were conducted on rice porridge containing millimeter-sized ingredients. By adding water, thickening agents, and amylase to alter the flowability of the porridge, the proposed phase analysis successfully captured the changes in rheological properties, demonstrating its effectiveness for monitoring rheology in food manufacturing processes.