Title : Wall shear sensor development for taylor-couette flow
Abstract:
Understanding and assessing how fluids behave is a critical function across a variety of industries. While manufacturing inputs are known and outputs are often characterized, actual industrial processes are not well monitored due to limitations in commercial probe technology and environmental conditions. Ignorance of how fluid materials behave can lead to manufacturing deficiencies and impede the maturation of new materials. While knowledge of the flow environment is critical to successful operation, it is equally important that the measuring apparatus does not impact the flow. As such, non-intrusive methods such as optical diagnostics are an attractive option and are widely used in research environments. However, such methods require a significant amount of support infrastructure, including specialized modifications for optical access, dedicated acquisition and processing hardware/software, and frequent maintenance to ensure accurate results. Moreover, there is significant interest in incorporating flow monitoring hardware into existing infrastructure, but integrating complicated indirect measurement systems into existing industrial installations is impractical.
Ahmic has recently developed and tested a new harsh-environoment sensor technology that can directly measure wall shear in a variety of common industry fluids and manufacturing processes. A flush-mounted sensing element, located atop the probe, directly measures the tangential frictional forces imparted by the moving flow. The displacement of the element is sensed through a network of transducers, which is proportional to the wall shear acting upon its face. Coupled with an integrated temperature measurement, the sensor enables the user to infer additional critical flow parameters, such as phase changes, mass flow, velocity, and turbulence intensity. The design of the gage is such that it can be easily integrated into existing hardware with minimal effort by the end-user.
To assess the performance of the wall shear sensors and apply the sensors in a canonical flow environment, a Taylor-Couette flow apparatus was utilized with distilled water as the primary working fluid. The apparatus features a stationary outer cylinder with a variable speed, a rotating inner cylinder, and a small gap where the working fluid interacts with the concentric cylinders. This setup has long been used as a method for characterizing the viscosity of fluids in the liquid state using the basic Couette flow case. The present work expands the use of Ahmic’s sensors to direct shear measurements of not only Couette flow, where fluid motion is sufficiently slow to prevent unsteadiness, but also to Taylor-Couette flow in which velocity is sufficient to induce Taylor vortices and eventually turbulence.
Audience Take away:
The audience will be introduced to the fundamentals of direct wall shear stress measurement in fluids, which will contribute to an understanding within the industry of how direct shear measurement is beneficial to understanding flow conditions in real time. The addition of wall-shear measurement to any flow chain is beneficial for ensuring the accuracy of predictions and can inform design decisions to mitigate surface erosion, alter surface roughness, and modify flow parameters to achieve desired process conditions.
