Free-flow fluids

Researchers at the University College of Dublin are claiming that real time process control for food manufacturers - and more specifically the confectionery sector - has been advanced thanks to pioneering work into viscosity measurement techniques for characterising the flow and mixability of highly non-Newtonian fluids.

At the heart of the researchers' experiments is the Torqsense transducer made by Sensor Technology in Oxon, UK, which monitors the constantly changing flow characteristics of materials as diverse as tomato ketchup, chocolate, pasta sauce and chicken tikka massala as they are mixed.

Ireland's national economy has always had a strong agricultural element and more recently considerable value has been added to this by becoming one of Europe's foremost manufacturers of processed ingredients and ready meals.

Many foods and confectioneries are presented in a sauce or as what physicist could describe as a neo-liquid and can be produced in a process-type environment. But to date real time control has been virtually impossible due to the non-uniform nature of the food, which may contain particulates, fibres, vegetables, meat, nuts, raisins, biscuits etc.

"Real time process control is vital if food processors are to achieve the ultimate in product quality,"​ said PJ Cullen, who leads the research team. "To achieve this the sensor has to be pretty special to detects the changes with sufficient sensitivity, yet be robust enough for regular wash-downs and general industrial abuse. Of course it must not compromise hygiene standards and regimes either.​

We tried a number of sensors and Torqsense stood out as by far the best at meeting all our needs."​

Torqsense uses Surface Acoustic Waves techniques to provide non-contact monitoring of instantaneous rotary torque, allowing what the researchers say is accurate modelling of the instantaneous load changes. It is in effect a frequency dependent strain gauge operating at ultrasound frequencies and consists of a transducer mounted on the mixer's rotating shaft to monitors variations in its resonance frequency as the torsional load varies. An RF (radio frequency) link is used for wireless transmission of signals to an adjacent pick up so that rotation is unhindered.

The researchers have simulated food processing techniques in a number of different laboratory rigs, one of the most used being a helical ribbon mixer similar to those employed by manufacturers for mixing ingredients together. Often the key requirement is to mix sufficiently to achieve a uniform dish, but not to waste time and energy by over-mixing.

"We do this by monitoring the torque on the mixer's shaft, as it will move to a steady state (within the characteristics of the given recipe) once fluid uniformity is achieved,"​ said Cullen.

Torqsense is said to embrace all the advantages of SAW technology, including no load imparted to the drive mechanism under investigation, a broader signal bandwidth than other analogue based technologies and elimination of electronic interference.