Ultrasonic Guided Waves for Liquid Water Localization in Fuel Cells: An Ex Situ Proof of Principle

Abstract

Water management is a key issue in the design and operation of proton exchange membrane fuel cells (PEMFCs). For an efficient and stable operation, the accumulation of liquid water inside the flow channels has to be prevented. Existing measurement methods for localizing water are limited in terms of the integration and application of measurements in operating PEMFC stacks. In this study, we present a measurement method for the localization of liquid water based on ultrasonic guided waves. Using a sparse sensing array of four piezoelectric wafer active sensors (PWAS), the measurement requires only minor changes in the PEMFC cell design. The measurement method is demonstrated with ex situ measurements for water drop localization on a single bipolar plate. The wave propagation of the guided waves and their interaction with water drops on different positions of the bipolar plate are investigated. The complex geometry of the bipolar plate leads to complex guided wave responses. Thus, physical modeling of the wave propagation and tomographic methods are not suitable for the localization of the water drops. Using machine learning methods, it is demonstrated that the position of a water drop can be obtained from the guided wave responses despite the complex geometry of the bipolar plate. Our results show standard deviations of 4.2 mm and 3.3 mm in the x and y coordinates, respectively. The measurement method shows high potential for in situ measurements in PEMFC stacks as well as for other applications that require deposit localization on geometrically complex waveguides.

P66 - Ultrasonic Sensor System for Water Localization in Fuel Cells: Investigation of Operational Conditions

“…This measurement principle has been demonstrated in ex-situ experiments on a single bipolar plate in a temperature-controlled lab environment [2]. For an integration of the sensor system in an operating PEMFC, the changing environmental and operational conditions must be considered.…”

“…The resulting difference signal is divided into 500 windows before calculating the normalized signal energy Ed for each window. It has been shown that the resulting signal feature vector is suitable to localize single water drops on the bipolar plate using data-driven modelling [2]. Here, the same signal feature is used to quantify the influence of different conditions on the measurement.…”

A Water Monitoring System for Proton Exchange Membrane Fuel Cells Based on Ultrasonic Lamb Waves: An Ex Situ Proof of Concept

“…a droplet, will lead to reflection or attenuation of the incident wave [29]. In a recent work, a tomographic water droplet localization scheme is implemented using Lamb waves crossing the entire flow field in different directions [30], in which a localization precision of approx. 4 mm in case of a single 5 µL droplet was realized.…”