A team of researchers from The University of Sheffield, Sheffield, U.K., has developed a non-invasive device that enables real-time monitoring of how viscosity of liquids changes during a production process. The device can be used for determining not just the viscosity, but the full rheometric characterization as well, making it easier, quicker and cheaper to control the properties of the liquid, say the researchers.
The University's Department of Chemical and Biological Engineering, in a joint effort with the School of Mathematics and Statistics (SoMaS), developed the sensor system in which the liquid flows through microchannels (Figure 1). The sensor sends data to an electronic device that calculates likely behaviors of the liquid.
For complex fluids, Dr. Julia Rees, who's at SoMaS, explains the rheology is influenced by several parameters, one of them being the shear rate.
"By designing an experiment in which a range of shear rates co-exist (e.g., by forcing the fluid to flow around a corner) we effectively remove this as one of the variables when using inverse methods to determine the other parameters controlling the rheology. We measure global flow statistics at two or three key positions (one position for each parameter we wish to determine). These measures could be pressure or flow rate, for example." Rees notes that the accuracy of the device depends on the sensitivity of the sensors. "At the moment we are using cheap sensors as we are still proving the concept. Some of our intermediate parameters are estimated to within 0.05%. Viscous parameters are estimated to within 3%."
While the rheometer is customizable to the viscosity of the test fluid, and suitable for viscosities in the range of 0.0001 Pa.s (water) up to 10 Pa.s, the team is working on prototypes with wider channels to handle more viscous fluids. This also will help prevent fouling in the channels.
"Fouling … depends on the consistency of the material. Some complex fluids have big inclusions, such as proteins, which have long macromolecules that would block microchannels. However, we also have a prototype rheometer with channels on the millimeter scale, and will soon be constructing a prototype with channel widths on the centimeter scale. We can also clean the channels between cycles," says Rees.
The prototype is currently undergoing laboratory testing.
"This [prototype] potentially enables us to test a wider range of fluids that are commonly used in production process (e.g. ketchup, mayonnaise, cosmetics). Benchmarking statistics could be obtained using cheap sensors, rather than expensive optical techniques such as micron resolution particle image velocimetry…. Consequently we can deal with opaque fluids," Rees further explains.
The next steps will focus on product design and packaging to ease commercial implementation. The team is also working on an upgraded electronic control system that is suitable for an industrial plant.
Four end users have expressed serious interest in cooperating on the development says Rees.
If all goes as hoped, she expects a commercial sensor to be available by 2013.
A recent paper published in the journal Measurement Science and Technology provides more details.