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A Chance Discovery Could Reduce the Cost of Expensive Fluid Flow Sensors

Image Credit: Princeton University

What started as a happy accident and an odd measurement could lead to a new, cost-effective way of measuring fluid flow. 

Often the course of science doesn’t run smooth and happy accidents can lead to major findings and discoveries. From Michelson and Morley’s failure to detect the ether  —  a mysterious substance through which light was thought to propagate  —  arose Einstein’s theory of special relativity, for example. That’s a lesson that researchers at Princeton University also recently learned.

When they set about to test a high-resolution temperature sensor in water, Marcus Hultmark and three Ph.D. students discovered something remarkable. The sensor initially appeared to be displaying some weird ‘back to front’ readings. 

What the team actually found, was rather than measuring temperature, their sensor was detecting an altogether different quality of the fluid. They were actually capturing readings of the water’s fluid velocity, something far trickier to measure than temperature. Even more excitingly for the team, the sensor was measuring flow velocity in a completely new way. 

The researchers studied the measurement technique and its mechanics. The device, which uses Elastic Filament Velocimetry (EFV)¹ has been patented by the team  —  Hultmark, Clayton Byers, Matt Fu, and Yuyang Fan  — who plan to distribute it widely.

Of broader significance is the fact that utilizing this different detection method makes for a much cheaper sensor, especially when flow rates are low.

“This is a great example of a fundamental research project leading to an unexpected discovery,” says Hultmark. “It was not planned for, it just happened.”

Sensing Low Flow Rates is High Cost

The EFV sensor employs fine filaments called nanoscale ribbons that are stretched across anchoring points in a manner reminiscent of a suspension bridge across a river. Unlike most successful suspension bridges, of course, the fluid flows directly over the nanoribbons. 

The real revelation for the team was discovering how the flow was affecting these nanoribbons. As the fluid passes the ribbons  —  with a width equivalent to about a 1000th of a human hair  —  it further stretches them. This stretching changes the ribbon’s electrical properties, and by monitoring these changes, the sensor can tell how fast the fluid is moving. 

The beauty of the system is that it works well in extreme viscous fluids with very low-flow rates. “You can put it in honey, in water, in air, and the same sensor does a very good job in all of them,” Hultmark comments. “On top of that, because of the mechanical behavior, you can tailor it very well to whatever application you have.”

The use of these nanoribbons results in a sensor with a lightweight sensing element, meaning the device can be manufactured much more cheaply than current, often expensive, flow rate detector technology.

Even though the team knew that their chance discovery was important, Hultmark remarks that initially, they weren’t quite sure about how to apply it best and indeed, who might need it. 

Programs provided by the National Science Foundation (NSF) and Keller Center for Innovation in Engineering Education enabled the team to investigate gaps in the market in which the EFV sensor could fit nicely. 

Stretching the Uses of Elastic Filament Velocimetry

The Princeton researchers opted to focus their attention on potential consumer devices that could benefit from the EFV sensor. The device adapts itself well to a wide range of applications thanks to the fact that EFV can be used to measure the flow rate of gases and liquids and across a range of viscosities running from honey to air.

Thus, as well as medical devices such as injection devices and respirators, the EFV sensor could find its way into industrial processes in which fluids have to be measured by automated systems. The team now markets the device and its applications as Tendo Technologies, a knowing wink to the technology’s origins as ‘Tendo’ is Latin for stretch. 

But just because it has made the transition from the lab to the commercial market, that doesn’t mean that the EFV sensor is done in the field of research. The sensor and its related technology are still employed in Hultmark’s lab by his students to measure fluids' flow rate. In particular, Katie Wu, a graduate student in Fast Lab is currently using the EFV sensor to measure flows in fluids that have parameters dependant on both time and position. 

Recalling the moment that Clayton Byers discovered that the sensor was registering hot water as cold and cold water as hot, and the year other researchers spent figuring out why, Hultmark remarks how fun the process was. And how their achievements arose from what some teams may have just written off as a mistake. 

One could have said, 'No, this is wrong. We should measure temperature. Go back and measure temperature'. But instead we were able to discover a new mode of sensing, and the knowledge we gained also allowed us to improve the temperature sensor for temperature measurements in liquids.

Marcus Hultmark, Associate Professor, Princeton University


¹ Fu. M. K., Fan. Y., Byers. C. P., Arnold. C. B., Hultmark. M. N., [2017], ‘Elastic filament velocimetry (EFV),’ Measurement Science and Technology, [10.1088/1361–6501/28/2/025301]

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Robert Lea

Written by

Robert Lea

Robert is a Freelance Science Journalist with a STEM BSc. He specializes in Physics, Space, Astronomy, Astrophysics, Quantum Physics, and SciComm. Robert is an ABSW member, and aWCSJ 2019 and IOP Fellow.


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