<p>This review summarizes and evaluates an in situ process viscometry technique for the direct estimation of the viscosity of non-Newtonian fluids inside an agitator equipped with an impeller during operation. Conventional viscosity measurements of non-Newtonian fluids rely on rheometers. However, in actual mixing processes, flow fields and shear conditions vary continuously across both space and time, making it difficult to accurately represent in-process viscosity behavior using laboratory measurements alone. To address this limitation, the Metzner–Otto correlation has been applied in previous studies using torque measured at the agitator shaft and impeller rotational speed to determine effective shear rate and effective viscosity, enabling quantitative assessment of viscosity changes under actual operating conditions. This review focuses on two agitator systems with different impeller configurations: one used for experimental verification of the feasibility of process viscosity measurement, while the other combined experimental data with simulation results to rigorously verify the reliability of the proposed approach. Experiments were performed using representative non-Newtonian fluids, including Carbopol solutions, xanthan gum solutions, and bentonite-based drilling muds, from which torque responses were acquired and converted into shear rate–viscosity relationships. The results were then compared with rheometer data. In addition, simulations were conducted to predict internal flow behavior and torque, and the results were in close agreement with experimental results, confirming the physical validity of the method. The reviewed studies demonstrate that the technique enables reasonably accurate estimation of viscosity changes under real mixing conditions without requiring sample extraction or offline analysis. The proposed approach is therefore expected to serve as a practical diagnostic tool for real-time process monitoring and operational optimization in a wide range of industrial applications involving high-viscosity non-Newtonian fluids, including mixing, dispersion, slurry preparation, and drilling mud management.</p> Graphical Abstract <p>In situ process viscometry using a flat-bladed turbine (FBT) agitator accurately reconstructs the shear-rate-dependent viscosity of non-Newtonian fluids, showing close agreement with rheometer measurements and numerical simulations (adapted from Ref. [<CitationRef CitationID="CR10">10</CitationRef>]).</p>

A review of in-situ viscometry using agitators in mixing processes

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发表日期：

2026年7月7日

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Hae Jin Jo,
Young Ju Kim,
Wook Ryol Hwang

摘要

This review summarizes and evaluates an in situ process viscometry technique for the direct estimation of the viscosity of non-Newtonian fluids inside an agitator equipped with an impeller during operation. Conventional viscosity measurements of non-Newtonian fluids rely on rheometers. However, in actual mixing processes, flow fields and shear conditions vary continuously across both space and time, making it difficult to accurately represent in-process viscosity behavior using laboratory measurements alone. To address this limitation, the Metzner–Otto correlation has been applied in previous studies using torque measured at the agitator shaft and impeller rotational speed to determine effective shear rate and effective viscosity, enabling quantitative assessment of viscosity changes under actual operating conditions. This review focuses on two agitator systems with different impeller configurations: one used for experimental verification of the feasibility of process viscosity measurement, while the other combined experimental data with simulation results to rigorously verify the reliability of the proposed approach. Experiments were performed using representative non-Newtonian fluids, including Carbopol solutions, xanthan gum solutions, and bentonite-based drilling muds, from which torque responses were acquired and converted into shear rate–viscosity relationships. The results were then compared with rheometer data. In addition, simulations were conducted to predict internal flow behavior and torque, and the results were in close agreement with experimental results, confirming the physical validity of the method. The reviewed studies demonstrate that the technique enables reasonably accurate estimation of viscosity changes under real mixing conditions without requiring sample extraction or offline analysis. The proposed approach is therefore expected to serve as a practical diagnostic tool for real-time process monitoring and operational optimization in a wide range of industrial applications involving high-viscosity non-Newtonian fluids, including mixing, dispersion, slurry preparation, and drilling mud management.

Graphical Abstract

In situ process viscometry using a flat-bladed turbine (FBT) agitator accurately reconstructs the shear-rate-dependent viscosity of non-Newtonian fluids, showing close agreement with rheometer measurements and numerical simulations (adapted from Ref. [10]).