Researchers say mixer efficiency calculations can save power and cost

Researchers have incorporated TorqSense transducers into a test rig that is analyzing losses in in-line mixers.

Efficient production is fundamentally important to success in the process industries, and optimizing energy consumption is seen as essential because improvements will repay dividends over many years.

Developing new methods

The energy consumption involved in in-tank mixing processes is well researched, but with in-line rotor-stator mixers, the flow is often controled independently of the rotor speed, and collecting sufficient data to accurately model the process has to date required a large number of experiments.

Researchers Dr Mike Cooke and T. L. Rogers at Manchester University have developed two simplified methods for obtaining the necessary information for particular stator-rotor mixers: one uses torque measurements, the other heat balance.

Cooke said high shear rotor-stator mixers are widely used in process industries, including the manufacture of many foods. Rotor-stator devices provide a focused delivery of energy, power and shear to accelerate physical processes such as mixing, dissolution, emulsification and deagglomeration.

“To reliably scale-up these devices from laboratory size to industrial scale we need to understand the relationship between rotor speed, flow rate and the energy dissipated. The first step is to link the energy dissipation rate to desired process results,” ​Cooke said.

TorqSense used

The scientists created two mixing experiments and measured torque profile and heat balance. In the first experiment torque was measured by a Sensor Technology’s TorqSense in-line torque meter fitted to the drive shaft.

There are two main sources of potential error when measuring the torque on the rotor shaft: time-based zero-drift, and bending moments on the shaft, both of which are counteracted with the TorqSense.

Other corrections also have to be made for factors including bearing losses and temperature fluctuations.

TorqSense was chosen for the study, because its non-contact operation meant extra drag forces were not added to the system and also allowed rapid assembly and disassembly during the experiments, the researchers said. Sensor Technology did not fund the study.

Improving bottom line

The conclusion from Cooke’s experiments is that the performance characteristics of in-line mixers can be easily modelled, which lets industrial users calculate their optimum energy consumption and tune their mixer drives accordingly.

The researchers said power and cost savings will accrue during the whole production period, making a valuable contribution to the company’s bottom line and ‘green credentials.’