The original work of Kang et al (2004 Meas. Sci. Technol. 15 1104–12) presents a scheme for correcting optical distortion caused by the curved surface of a droplet, and illustrates its application in PIV measurements of the velocity field inside evaporating liquid droplets. In this work we re-derive the correction algorithm and show that several terms in the original algorithm proposed by Kang et al are erroneous. This was not evident in the original work because the erroneous terms are negligible for droplets with approximately hemispherical shapes. However, for the more general situation of droplets that have shapes closer to that of a sphere, with heights much larger than their contact-line radii, these errors become quite significant. The corrected algorithm is presented and its application illustrated in comparison with that of Kang et al.
Two-phase air-water flow in an experimental model of a polymer electrolyte membrane fuel cell (PEMFC) gas distribution channel is investigated using quantitative flow imaging of the liquid phase. A rectangular gas channel model was fabricated from polydimethylsiloxane (PDMS), glass and carbon paper. A micro-digital-particle-image-velocimetry (micro-DPIV) technique was used to provide qualitative and quantitative visualizations of flow inside a water droplet adhering to the bottom wall of a gas channel and exposed to an air flow within the channel. Velocity measurements in a central cross-sectional plane inside a droplet placed in the channel are reported for a range of air flow rates. The relationships between air velocity in the channel, secondary rotational flow inside a droplet, droplet deformation and contact angle hysteresis are examined. The resulting flow fields provide insight into the interactions between the air and water flows that occur at the gas-liquid interface.
Harmonic forced vibration of thick viscoelastic hollow cylinders of infinite extent is considered. The cylinder is excited by stresses applied at the inner and outer boundaries. The governing equation of motion is developed by utilizing three dimensional theory of elastodynamics. The material damping is allowed using complex elastic moduli for the viscoelastic medium. Modal displacements and stresses at any point in the medium are formulated in terms of boundary stresses. Frequency responses for radial, tangential and axial displacements are computed for different circumferential and axial wave numbers. The effect of different material loss factors on the frequency responses is examined for axial and nonaxisymmetric modes. The dimensionless resonant frequencies for zero loss factor are compared with dimensionless natural frequencies available for elastic material. Comparison indicates excellent agreement between the results.
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