Ronnie Yip

Development of Carbon Nanotube-Based Sensors—A Review

Carbon nanotubes (CNTs) have shown great promise as sensing elements in nanoelectromechanical sensors. In this review paper, we discuss the electrical, mechanical, and electromechanical properties of CNTs that are used in such applications. This investigation indicates which nanotube properties should be carefully considered when designing nanotube-based sensors. We then present the primary techniques that have been used for the integration of nanotubes into devices and proceed to give a description of sensors that have been developed using CNTs as active sensing elements

Calibrating the X-ray attenuation of liquid water and correcting sample movement artefacts during in operando synchrotron X-ray radiographic imaging of polymer electrolyte membrane fuel cells

Synchrotron X-ray radiography, due to its high temporal and spatial resolutions, provides a valuable means for understanding the in operando water transport behaviour in polymer electrolyte membrane fuel cells. The purpose of this study is to address the specific artefact of imaging sample movement, which poses a significant challenge to synchrotron-based imaging for fuel cell diagnostics. Specifically, the impact of the micrometer-scale movement of the sample was determined, and a correction methodology was developed. At a photon energy level of 20 keV, a maximum movement of 7.5 µm resulted in a false water thickness of 0.93 cm (9% higher than the maximum amount of water that the experimental apparatus could physically contain). This artefact was corrected by image translations based on the relationship between the false water thickness value and the distance moved by the sample. The implementation of this correction method led to a significant reduction in false water thickness (to ∼0.04 cm). Furthermore, to account for inaccuracies in pixel intensities due to the scattering effect and higher harmonics, a calibration technique was introduced for the liquid water X-ray attenuation coefficient, which was found to be 0.657 ± 0.023 cm(-1) at 20 keV. The work presented in this paper provides valuable tools for artefact compensation and accuracy improvements for dynamic synchrotron X-ray imaging of fuel cells.

Slow flow of Boger fluids through model fibrous porous media

The flow of viscoelastic fluids through square arrays of parallel cylinders was investigated experimentally by measuring the pressure drop and flow rate and by mapping the velocity field using particle image velocimetry. The arrays had solid volume fractions of 2½%, 5%, and 10% and the fluids were Boger fluids—specifically, two solutions of polyisobutylene in polybutene. With Reynolds numbers less than 0.1, viscosity and elasticity were the only relevant fluid properties. Measurements were made first with a glycerol/water mixture to establish an inelastic baseline. For the three arrays and two viscoelastic fluids, elastic effects started consistently at a Deborah number (De) of 0.5. For De up to 4, the flow resistance due to elasticity was up to several times that due to viscosity, which is comparable to previous findings with much higher volume fractions. But, unlike prior flows, the present ones were steady. Particle image velocimetry measurements revealed unit-cell velocity profiles, which became progr...