Influence Of Velocity Profile Research Articles

Flow characteristics of the Rushton and pitched blade turbines in turbulent and laminar mixing

AbstractThe velocity field and concentration distribution of three radial and axial impellers were studied in miscible liquid blending in a stirred tank reactor. To obtain a better insight into the applicability of each impeller system, the influence of velocity profiles on the generated concentration profiles was studied in detail for each impeller. Particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) methods were used as the measurement techniques. In the turbulent regime, the Rushton turbine provided a homogeneous concentration field throughout the reactor by generating high radial and axial velocities in the bottom and upper zones of the tank. Operation comparisons of the up and down-pumping pitched blade turbines illustrated that the up-pumping turbine had a better performance in overall because of producing high turbulence in the upper half of the reactor. In this region, the radial concentration profile approached the final homogenized value in a shorter time. In the laminar regime, all three impellers acted in a similar way and produced a radial flow throughout the reactor.

Influence of velocity profile on the chip thickness and material removal rate in milling

In milling process, the tool path presents discontinuities in changing direction. The explicit form of the material removal rate was determined by the product of cross-section and the feed rate. This method was not accurate in the case of acceleration and deceleration process at the discontinuities. Based on the true trajectories, the cutter geometries and the velocity profiles, this paper present a method for determining the material removal rate of different end mills which considers the Acc/Dec process.

Influence of velocity profile and diffusion on residence time distributions: mesoscopic modeling and application to Poiseuille flow

Present knowledge regarding the link between processes inside a reactor and its residence time distribution is still unsatisfying. As a contribution to close this gap, a mesoscopic cell model is discussed and validated. Special regard is given to possible error sources. Comparison of computed results with analytical residence time distributions and with the Taylor dispersion model show good agreement for ratios of cell size to rms distance of diffusion of 1.5–1.6 (one-dimensional case) and 1.3 (two-dimensional case). Model application to Poiseuille flow leads to a discussion of various dimensionless parameters. The transition in the form of residence time distributions from Pe *= vd 2 D mol L =0.59−58.83 is discussed. Distributions in the case of Pe *>30 resemble the convection-only solution whereas cases with Pe *>3 have Gaussian distributions. Furthermore, distributions obtained from computation with radial diffusion only confirm that the neglect of axial diffusion leads to qualitatively correct results but reveal a quantitative disagreement in the residence time distribution's maxima.

Influence of the velocity profile on the heat transfer of a circular impact jet

The influence of the mean velocity profile in a round submerged jet on the heat transfer with a plane obstacle placed along the normal to the flow is investigated. A criterial relation for the heat transfer in the vicinity of the critical point is obtained.

Limiting Sherwood number of sphere packed beds by electrical method

An electrical method which applies the analogy between electric field and molecular diffusion has been utilized to measure the limiting Sherwood number of packed bed at zero flow rate. This limiting value appropriate to usual mass transfer operations is found 9·40 when expressed in terms of the hydraulic diameter and the area averaged mean concentration driving force. When the influence of velocity profile on the film coefficient is corrected, this Sherwood number compares favourably with the previously reported value of 7·87 which is based on the hydraulic diameter and the cup-mixing mean concentration driving force.