Measurement of flow rate using straight pipes and pipe bends with integrated piezoelectric sensors

The original noninvasive method for measuring the flow rate of liquids proposed in this work relies on the ability of the piezoelectric sensors embedded into pipes or pipe bends to detect the pressure fluctuations of turbulent flow. As the pressure fluctuation is directly related to the flow velocity, the electric responses of the piezoelectric sensors are correlated to the flow rate. Plastic pipes and pipe bends of different curvature radius with embedded piezoelectric ceramics of lead zirconate titanate (PZT) were used for measuring the flow rate of water. The piezoelectric sensors are placed close to the inner surface of pipe to increase their sensitivity to the pressure fluctuations of turbulent flow. Measurements of pipe vibration with accelerometers were also performed for comparison purposes. Frequency domain analyses demonstrate that the response of the piezoelectric sensors is mainly related to the pressure fluctuation of turbulent flow. Preliminary results of tests with straight acrylic pipes and 90° pipe bends made of polyvinyl chloride (PVC) demonstrate the effectiveness of the proposed technique. An interesting sensing performance to flow was observed for the PZT sensors installed in bends of small curvature radius. The disturbances to flow generate high pressure fluctuations in short radius bends, consequently improving the sensitivity to flow rate of the PZT sensors. Volumetric flow rates lower than 0.1 l/s were detected using a 90° bend of r/d = 0.5, with inside diameter d = 21 mm and integrated PZT sensors. As the pressure fluctuation is responsible for the pipe bend vibration, the sensitivity to flow rate of the accelerometers was also significantly improved.