11 research outputs found
Non-Gaussian statistics for the motion of self-propelled Janus particles: Experiment versus theory
The influence of Saffman lift force on nanoparticle concentration distribution
The lift force on a spherical nanoparticle near a wall in micro/nanofluidics has not received sufficient attention so far. In this letter the concentration of 200 nm particles is measured at 0.25–2.0 m to a wall in a microchannel with pressure-driven de-ionized water flow pressure gradient 0–2000 kPa/m . The measured data show the influence of the lift force on the nanoparticle concentration distribution. By introducing the Saffman lift force into the Nernst–Planck equation near a wall, we find that the lift force is dominant at the range of 2</p
Discussions on slip length measurements by microPIV/PTV in microchannels
Fluid transportation in microfluidic system
could be benefit from the slip on solid-liquid
interface. Slip length on many kinds of
hydrophilic/hydrophobic surfaces have been
measured recently. The two common-used
experimental methods for boundary slip
measurement include: (1) surface force
measurement, such as surface force
apparatus (SFA), atom force microscope
(AFM), and (2) velocity measurement, like
microPIV/PTV (Particle image velocimetry /
Particle tracking velocimetry), total internal
reflection velocimetry (TIRV). However, the
measured results are rather scattered, larger
measured slip lengths were reported by
microPIV/PTV experiments. In this paper,
we will investigate the deviations of the
measured slip length on smooth hydrophilic
surface. After measuring detailed velocity
profiles very close to hydrophilic glass wall,
we give a discussion on the effects
influencing the slip measurements
The near wall velocity measurements in microchannels with different diameter particles by microPIV/PTV. 8th International symposium on PIV
In near wall measurements with microPIV/PTV, whether seeding particles can be effectively used to detect local fluid velocity is a
crucial problem. This talk presents our recent measurements in microchannels [1][2]. Based on measured velocity profiles with 200nm
and 50nm in pure water, we found that the measured velocity profiles are agreed with the theoretical values in the middle of channel,
but large deviations between measured data and theoretical prediction appear close to wall (0.25mm <z<1.5mm). Moreover, these
deviations depend on the particle sizes. Considering the volume illumination [3] and particle physical behavious [4], we try to analysis
the influence of focal plane thickness and particle concentration distribution near wall on the velocity deviation appeared in shear
flows
Measurement of velocity profiles in a rectangular microchannel with aspect ratio α = 0.35
In this work, we measured 14 horizontal velocity profiles along the vertical direction of a rectangular microchannel with aspect ratio alpha = h/w = 0.35 (h is the height of the channel and w is the width of the channel) using microPIV at Re = 1.8 and 3.6. The experimental velocity profiles are compared with the full 3D theoretical solution, and also with a Poiseuille parabolic profile. It is shown that the experimental velocity profiles in the horizontal and vertical planes are in agreement with the theoretical profiles, except for the planes close to the wall. The discrepancies between the experimental data and 3D theoretical results in the center vertical plane are less than 3.6%. But the deviations between experimental data and Poiseuille's results approaches 5%. It indicates that 2D Poiseuille profile is no longer a perfect theoretical approximation since a = 0.35. The experiments also reveal that, very near the hydrophilic wall (z = 0.5-1 mu m), the measured velocities are significantly larger than the theoretical velocity based on the no-slip assumption. A proper discussion on some physical effects influencing the near wall velocity measurement is given.</p