Abstract
Ultrasonic oscillating rod probes have recently been used by researchers to measure viscosity and/or density in fluids. However, in order to use such probes to characterise the rheological properties of fluids, it is necessary to define the shear rate produced by the probe. This paper proposes an analytical solution to estimate the shear rate of ultrasonic oscillating rod viscosity probes and a method to measure their maximum operational shear rate. A relationship is developed which relates the torsional surface velocity of an oscillating cylindrical rigid body to the rate of shear in its vicinity. The surface displacement and torsional surface velocity of a torsional probe of length 1000mm and diameter 1mm were measured over the frequency range from 525 to 700kHz using a laser interferometer and the maximum shear rate estimated. The reported work provides the basis for characterising shear rate for such probes, enabling their application for rheological investigations.
Highlights
The rheological characteristics of fluids influence many aspects of their performance, such as pumpability, droplet breakup in spray drying, emulsion formation, flow into moulds, formability and so forth, and qualities such as stability during and after processing
The results show that the shear rates (62500 sÀ1) generated by the 1 mm diameter carbon steel ultrasonic oscillating rod viscosity probe are within the range of the shear rates (1–20,000 sÀ1 [17]) that conventional rotational viscometers can generate
This paper has described the theory for shear rate estimation for ultrasonic oscillating rod viscosity probes
Summary
The rheological characteristics of fluids influence many aspects of their performance, such as pumpability, droplet breakup in spray drying, emulsion formation, flow into moulds, formability and so forth, and qualities such as stability during and after processing. Among the rheological properties of fluids, viscosity is an integral component of a large number of quality control procedures in the processing of complex liquids [1]. Viscosity can be expressed as the proportionality of the force (the shear stress) to the relative rate of movement (the rate of shear strain or shear rate). This proportionality can be independent of shear rate, in the case of Newtonian fluids, or vary with shear rate for non-Newtonian fluids. Knowledge of the shear rate is of paramount importance in the study of fluids and their rheological characteristics such as viscosity
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