Parabolic Flow Velocity Research Articles

Explicit role of ionic strength in retention behavior of polystyrene latex particles in sedimentation field-flow fractionation: Slip boundary model

We investigate an explicit role of the ionic strength in the retention behaviors of polystyrene (PS) latex particles in sedimentation field-flow fractionation (SdFFF) by hinging upon the retention theory recently developed [1] asR=(Ro+vb*)/(1+vb*). Here R is an experimental retention ratio, and Ro is the analytical expression of the standard retention theory based on the parabolic flow velocity. The reduced boundary velocityvb* is expressed in terms of the ionic strength I of the carrier liquid as vb*=vb,o*/(1+εI), where vb,o*=0.070and ε=60 mM−1 for all the PS latex systems under investigation. We then apply this to study the explicit ionic strength effect on the retention behaviors of PS beads of 200, 300, 400, and 500nm, respectively. As a primary result, the strong dependence of the retention ratio on the ionic strength can be quantitatively accounted for in an excellent accuracy: The slip effect at the channel surface is significant, particularly when I≲0.5mM, without showing any distinguishable dependence on the specific additives to control I, such as FL-70, SDS, NaNO3, and NaN3. Based on the present study, we put forward an experimental means to estimate the ionic strength of an aqueous solution using an FFF technique.

Multidimensional Effects on Structure and Extinction Process of Counterflow Nonpremixed Hydrogen - Air Flames

The axisymmetric Navier-Stokes model together with detailed chemical kinetics and variable transport properties has been applied to analyze the effects of the multidimensional flow on the flame characteristics in the nitrogen-diluted hydrogen counterflow nonpremixed flame. Computations are carried out for the laminar counterflow hydrogen-air flames with two fuel dilutions. In order to investigate the effects of the jet exit velocity profiles on the hydrogen-air diffusion flame structure, computations are made for two boundary conditions simulating the plug-flow and parabolic-flow velocity profiles at nozzle exit. In case of the highly diluted hydrogen flames, the near-extinction flame structure and extinction flame process are numerically studied for two nozzle exit area-averaged velocities based on the plug-flow profile. Numerical results indicate that the jet exit profiles significantly influence the flame structure in terms of strain rate, flame thickness, peak temperature, overlap of fuel and air, and differential diffusion. Effects of multidimensional flow and strain rate on the near-extinction structure of the highly diluted hydrogen flames are also discussed in detail.