Rheological characterisation of highly concentrated mineral suspensions using an ultrasonic velocity profiler

Abstract

The rheological behaviour of non-Newtonian, highly concentrated and non-transparent fluids used in industry have so far been analysed using commercially available instruments, such as conventional rotational rheometers and tube viscometers. When dealing with the prediction of non-Newtonian flows in pipes, pipe fittings and open channels, most of the models used are empirical in nature. The fact that the fluids or slurries that are used normally are opaque, effectively narrows down the variety of applicable in-line rheometers even further, as these instruments are normally based on laser or visible light techniques, such as Laser Doppler Anemometry. Electrical Resistance Tomography is a non-invasive method used to look into opaque suspensions during pipe flow, but cannot be used to measure in-line rheometry. In this research, an Ultrasound Pulsed Echo Doppler Velocity Profile technique (UVP), in combination with a pressure difference (PD) was tested to provide in-line measurement of rheological parameters. The main objective ofthis research was to evaluate the capabilities of the UVP-PD technique for rheological characterisation of different concentrations of non-transparent non-Newtonian slurries. A unique pipe viscometer was designed and constructed. It consisted of four pipes, one of stainless steel and three of PVC, linked to an in-line mass-flow meter and equipped with two different ranges of pressure transducers on each pipe. The stainless steel pipe, with an inner diameter of 16 mm, was equipped with a specially designed flow adapter for in-line rheological characterisation using the UVP-PD method. The three PVC pipes with different diameters of 9 mm, 13 mm and 16 mm served as a tube viscometer for in-line rheological characterisation of mineral suspensions.