Online Measurement Of Viscosity Research Articles

Measurement of viscosity and shear wave velocity of a liquid or slurry for on-line process control

An on-line sensor to measure the density of a liquid or slurry, based on longitudinal wave reflection at the solid–fluid interface, has been developed by the staff at Pacific Northwest National Laboratory. The objective of this research is to employ shear wave reflection at the solid–fluid interface to provide an on-line measurement of viscosity as well. Both measurements are of great interest for process control in many industries. Shear wave reflection measurements were conducted for a variety of liquids. By analyzing multiple reflections within the solid (only 0.63 cm thick––similar to pipe wall thickness) we increased the sensitivity of the measurement. At the sixth echo, sensitivity was increased sufficiently and this echo was used for fluid interrogation. Shear wave propagation of ultrasound in liquids is dependent upon the viscosity and the shear modulus. The data are analyzed using the theory for light liquids (such as water and sugar water solutions) and also using the theory for highly viscous liquids (such as silicone oils). The results show that, for light liquids, the shear wave reflection measurements interrogate the viscosity. However, for highly viscous liquids, it is the shear wave modulus that dominates the shear wave reflection. Since the density is known, the shear wave velocity in the liquid can be determined from the shear wave modulus. The results show that shear wave velocities in silicone oils are very small and range from 315 to 2389 cm/s. Shear wave reflection measurements are perhaps the only way that shear wave velocity in liquids can be determined, because the shear waves in liquids are highly attenuated. These results show that, depending on the fluid characteristics, either the viscosity or the shear wave velocity can be used for process control. There are several novel features of this sensor: (1) The sensor can be mounted as part of the wall of a pipeline or tank or submerged in a tank. (2) The sensor is very compact and can be located within the process stream. (3) The sensor can interrogate and characterize very attenuative liquids or slurries because the sensor operation depends upon reflection at the interface between the solid and the fluid, rather than on transmission through a liquid. (4) The sensor performance is not affected by fluid flow rate, entrained air, or vibration.

In-line use of near infrared spectroscopy to measure structure parameters of frozen model sorbet

In a continuous freezer/extrusion process on-line viscosity and conductivity measurements in frozen model sorbet were carried out. On-line viscosity measurements were based on the pressure difference in the extruder exit. Light-microscopy (off-line), conductivity (on-line), viscosity (on-line) and the measurement of exit temperature were used to calibrate an on-line NIR spectrometer with a light fibre probe introduced in the product flow. Based on these calibrations, on-line NIR measurements of viscosity and ice crystal size in continuously produced model sorbet were carried out. A first qualitative check of elaborated NIR-models has been carried out successfully.

On-line measurement of viscosity and determination of flow types for mineral suspensions

A viscometry system involving a vibrating sphere viscometer and a rotational viscometer has been developed for on-line measurement of viscosity, and for rheological characterization of mineral slurries into either Newtonian or non-Newtonian flows. Special precautions were taken to allow measurements of viscosity of rapidly settling mineral suspensions. Both the viscometers were able to measure viscosity as low as one centipoise, which is the approximate room temperature viscosity of water. Because the vibrating sphere viscometer operated at a much higher shear rate than the rotating viscometer, the two instruments together could determine the shear-rate dependency of the viscosity. Ground silica of 80% passing 65 μm size was suspended in water, and was used to prepare slurries at different percent solids. Viscosity of each slurry sample was measured simultaneously by both the viscometers, and the results were compared to determine the rheological characters of the slurries. With this technique, it was found that all the silica slurry samples (up to 70 wt% solids) at the given size distribution were in the Newtonian flow regime.