Doctor of Philosophy
Mechanical and Nuclear Engineering
ROBERT M. SEXTON
Structural non-destructive evaluation techniques are applied to viscous flows to detect fluid property changes. The main operating principle consists of an actuator which provides a stimulus, and a sensor to receive a signal traveling to a fluid domain. The main challenge of the operating principle consists of investigating waves traveling in a viscous flow. Traveling waves utilizing a piezoelectric actuator-sensor pair are modeled and the results are validated experimentally. ANSYS models, coupled with a two-way fluid-solid interaction model, are built to investigate how far a signal travels and what frequency ranges are of interest. The numerical model includes modeling three different geometries (square, circular, triangular) for the actuator-sensor pair manufactured with three different piezoelectric materials (PZT4, PZT5A, PMN32). Numerical work is validated with experimental work using a pair of circular actuator-sensors manufactured with PZT5A and immersed in a large container of water and glycerin. Furthermore, in order to establish mesh independence of the results, three mesh refinement levels (coarse, medium and fine) were utilized with different materials, geometries and fluid viscosity values.
The actuator receives a 0.5 VAC signal ranging from 100 Hz to 40 MHz. The sensor records the signal at varying distances from the actuator, and the result is labeled as the gain or the ratio of received to send wave magnitude. The pattern of decay for both numerical and experimental results are in close agreement (the numerical decay are 10.825 and 11.4 for water and glycerin, respectively, while the experimental are 11.254 and 14.48 for water and glycerin, respectively). Numerically, the results show that the maximum acoustic pressure can be obtained by using a square piezoelectric actuator- sensor pair fabricated with PMN32. Numerically, the results show that the maximum acoustic pressure can be obtained by using a square piezoelectric actuator- sensor pair fabricated with PMN32.
A viscosity probe for medical applications is developed using a piezoelectric actuator-sensor pair. The design constraints were size and cost. The actuator-sensor pair is manufactured with PZT5A with a rectangular shape to fit a 3 mL vacutainer. The actuator is excited by 0.5 VAC sinusoidal waves with varying frequencies ranging from 100Hz to 40 MHz. The sensor will detect the produced wave in the fluid. Also, the phase shift is recorded for different concentrations of glycerin and water to simulate different viscosities ranging from 1 to 1600 cP. The numerical analysis, a modal analysis, of the probe was performed and the results showed that the first, second and third modes of the device were in the range of 684–2358 Hz for air, 500–1080 Hz for water, and 469–625 Hz for glycerin. From the harmonic acoustic analysis, the results showed that the highest phase shifts, and maximum gain, occurs at the ultrasonic frequency range, 6 to 9 MHz. Hence, there is no relation between the natural frequencies of the probe and the ultrasonic frequency for the phase shift. Most importantly, a correlation between the phase shift and viscosity is found, making the probe a feasible device for measuring viscosity in an inexpensive, small, and disposable way.
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