Lenterra, Inc., Newark, N.J., is displaying at its booth (#644) what it claims are the first commercially available sensors for direct measurement of wall shear stress. The so-called RealShear F-Series sensors provide inline continuous real-time measurements as often as 1,000 times/second without disrupting process flow. They also can be used to compute viscosity and to characterize multiphase flow (such as to warn of aeration in a fluid).
The sensor can be used with high-shear and conventional mixers as well as in pipelines. The regular cleaning done to batch equipment should suffice to keep the sensor clean, says the company. It also can be used in continuous processes, Lenterra adds.
The sensors rely on micro-optical resonators to detect minute lateral displacements on the sensor's face, which is flush-mounted with the surface of a vessel or pipe. The displacements cause a shift in the resonant spectrum of the resonators. A ruggedized optical cable with a water- and dust-proof connector transmits the data to a controller, which then can be connected to a PC or, optionally, can provide a 4–20-mA output. The sensor/controller package costs a little over $20,000.
Lenterra now offers five RealShear models, with shear stress measurement ranges from ±400 Pa (with a resolution of 0.4 Pa) to ±100 kPa (with a resolution of 100 Pa), with custom sensitivity ranges also available. They boast chemical-resistant construction and can handle temperatures from -30°C to 200°C. The sensor has a ¼-80 threaded housing to ease installation but custom adapters also are available.
At present, the sensor is undergoing trials at a major consumer products maker, where it is being used to measure the viscosity of a fluid after a powder thickener has been added via a high shear mixer.
Lenterra also is in preliminary discussions with vendors of both high shear and conventional mixers about having them offer the sensors as a turnkey package with their mixers.