Vibrational process viscometers have been known for nearly 60 years but have found only modest application in food manufacturing processes, where control of product consistency is a high priority. This is due to the ingrained belief on the part of process operators that only measurements defined shear are capable of predicting the behavior of the usually non-Newtonian, often inhomogeneous products that they manufacture. A new instrument, the Rheonics SRV process viscometer, is descended from a line of vibrational viscometers that have found wide acceptance in the food process industry because they have proven themselves to be capable of controlling consistency in complex processes such as batter mixing, cheese coagulation, and beer mashing. The SRV builds on this heritage and adds to it a novel balanced resonator structure that makes it compact, simple to install, and free from the sensitivity to mounting conditions that has plagued earlier designs that lack its symmetric structure. Since vibrational viscometers function by measuring the rate of energy loss of a resonator immersed in the fluid under test, any additional energy losses due to vibrations transferred to surrounding structures place limits on the stability and reproducibility of the instrument’s measurements. The Rheonics balanced resonator (patent pending) ensures the highest possible reproducibility and stability in a resonant instrument by eliminating transmission of the resonator’s vibrations to surrounding structures. Further improvements to traditional vibrational viscometers include patented systems for rejection of ambient vibration due to pumps and other process machinery, as well as advanced electromagnetic transducers with unprecedented rejection of magnetic interference from neighboring machinery. The Rheonics SRV has already proven itself in a complex slurry-coating process line for which the operator initially believed that only a rheologically accurate instrument could bring the process under control. The operator found that the high sensitivity and stability of the SRV enabled control of the process by a single point measurement, whereas a battery of other instruments capable of measuring density and solids content were not sufficiently sensitive to measure the small variations in the process stream that were crucial to a uniform, adherent coating.

The SRV can be used wherever one-point measurements of apparent viscosity are required, whether in Newtonian or non-Newtonian fluids.

Applications include:

• Batter mixing
• Heavy fuel oil viscosity control
• Slurry coating process monitoring and control
• Pumping optimization
• Polymerization monitoring

• Vibrational viscometer seems like an unlikely candidate for rheological measurements:
  • Shear takes place in a thin boundary layer around the probe, rather than in the bulk fluid
  • Shear is oscillatory, changing direction with the frequency of the probe’s vibration – roughly 7.4 kHz. for the Rheonics SRV.
  • Sensor is effectively immersed in a semi-infinite volume of fluid, so that the velocity gradients are undefined.
• On the positive side:
  • They are very stable
  • Although the shear rate is unknown and unknowable, it is repeatable, so that vibrational viscometers are good for keeping the flow properties of a fluid constant in a process environment

• Observation: When a vibrational sensor such as the SRV is placed in a highly shear rate-sensitive material like tomato ketchup, its indicated viscosity fluctuates strongly as the probe is moved through the material.
• This suggests that if the sensor were placed in a uniform, controllable shear field, changing its shear rate could give information about shear-sensitive properties of the fluid.

To explore more about our solutions for food industry, please visit the solutions page.