Near-Wall Velocity and Temperature Measurements in the Meniscus Region for Staggered Glass Beads

Velocity and temperature fields in the meniscus are crucial for the heat transfer mechanism in porous medium. The meniscus zone, however, is narrow so that it is difficult for observation. The velocimetry and thermometry in the near-wall region of the surface provide possible measurement methods with the development of micro/nanotechnology. Being exponentially decay in the intensity, the evanescent-wave illumination has the advantage of high spatial resolution and non-intrusion for these measurement methods. The multilayer nano-particle image velocimetry (MnPIV) uses the evanescent-wave illumination, decayed exponentially with the wall-normal distance, to obtain near-wall velocity data at different distances from the wall. The thermometry in the meniscus region could also use the evanescent-wave to illuminate the fluorescence dye, the emitted intensity of which changes with temperature. In this paper, these techniques are employed to measure the near-wall velocity and temperature between the porous media and the ITO heater, in order to explore the role of meniscus during convection of water. Near-wall velocity and temperature of the deionized water, seeded with 100 nm fluorescent colloidal tracers and flow in the staggered glass beads with diameters ranging from 2 mm to 6 mm, are obtained and discussed.