Reza Sadr

An experimental study of electro-osmotic flow in rectangular microchannels

Experimental studies were carried out on fully developed and steady electro-osmotic flow in a rectangular channel where the channel height

Scaling the near-wall axial turbulent stress in the zero pressure gradient boundary layer

h

Diffusion-induced bias in near-wall velocimetry

is comparable to its width and the thickness of the electric double layer characterized by the Debye length is much less than

An experimental investigation of the near-field flow development in coaxial jets

h

Velocity measurements inside the diffuse electric double layer in electro-osmotic flow

. The nano-particle image velocimetry technique was used to measure the two components of the velocity field parallel to and within about 100 nm of the channel wall for

Surface shear stress measurement system for boundary layer flow over a salt playa

h\,{\leq}\,25\,\umu

Characteristics of surface layer turbulence in coastal area of Qatar

m. The mobility of the particle tracers was calculated from averaged velocity data for various electric field strengths. The experimentally determined mobility values are compared with analytical predictions for dilute aqueous solutions of sodium tetraborate.

Theoretical Prediction of Laminar Burning Speed and Ignition Delay Time of Gas-to-Liquid Fuel

Based upon high resolution LDA measurements over a range of momentum deficit thickness Reynolds numbers (Rθ=U∞θ/ν) from 1430 to 31 000, DeGraaff and Eaton [J. Fluid Mech. 422, 319 (2000)] propose a new mixed scaling for the near-wall region profile of the axial turbulent stress, u2¯. The present results support the validity of this scaling over an extended Reynolds number range 1000⩽Rθ⩽5×106.

nPIV velocity measurement of nanofluids in the near-wall region of a microchannel

The Brownian fluctuations of the colloidal tracers often used in microscale velocimetry are typically isotropic in the bulk. In the near-wall region, however, these fluctuations are strongly affected by the hydrodynamic interaction with the wall and by the no-flux condition imposed by the wall. These wall effects can, under appropriate conditions, bias measurements based on colloidal tracers, potentially leading to significant overestimation of near-wall velocities. We use a Fokker–Planck description to generate probability density functions of the distances from a single wall sampled by the matched particles that are present in the same window at both the start and end of a time interval. The importance of the resulting bias for experimental parameters is then quantified in terms of the size of the imaged region and measurement interval. We conclude with a brief discussion of the implications for near-wall velocimetry measurements.

Effects of surface forces and non-uniform out-of-plane illumination on the accuracy of nPIV velocimetry

The near-field region of a coaxial jet having inner to outer diameter ratio di/do=0.39 is investigated experimentally for four ratios of annular to central jet velocities of η=0.18, 0.48, 0.8, and 1.11. Measurements were acquired nonintrusively using molecular tagging velocimetry at downstream distances up to six inner jet diameters. High spatial-resolution profiles of mean axial velocity, axial turbulent intensity, skewness, kurtosis, radial gradients of mean velocity, and velocity gradient fluctuations are presented and discussed. In the near-exit region of the inner mixing layer, evidence suggests the existence of two trains of vortices shed from the inner jet wall for velocity ratios η>0.18. The results also indicate that for the flow configuration examined the length of the annular potential core is a function of the velocity ratio. Turbulence characteristics of the flow appear to be influenced by both the velocity ratio and absolute velocity of the annular jet. Integral length and Taylor microscales...