Description of the reagent turbulent mixing process on the basis of the equation of the scale probability density

1984 ◽  
Vol 46 (2) ◽  
pp. 159-164
Author(s):  
V. A. Sosinovich ◽  
V. A. Tsyganov
Keyword(s):  
Probability Density ◽  
Turbulent Mixing ◽  
Mixing Process ◽  
Scale Probability

Review of theoretical modelling approaches of Rayleigh–Taylor instabilities and turbulent mixing

2010 ◽  
Vol 368 (1916) ◽  
pp. 1809-1828 ◽  
Author(s):  
Snezhana I. Abarzhi
Keyword(s):  
Turbulent Mixing ◽  
Statistical Properties ◽  
Momentum Transport ◽  
Theoretical Modelling ◽  
Theoretical Studies ◽  
Mixing Process ◽  
Physical Intuition ◽  
New Ideas ◽  
Theoretical Developments ◽  
Modelling Approaches

We review the theoretical developments in the field of Rayleigh–Taylor instabilities and turbulent mixing, discuss what is known and what is not known about the phenomenon, and outline the features of similarity of the turbulent mixing process. Based on the physical intuition and on the results of rigorous theoretical studies, we put forward some new ideas on how to grasp the essentials of the mixing process and consider the influence of momentum transport on the invariants and on scaling and statistical properties of the unsteady turbulent mixing.

Numerical Simulation of Turbulent Mixing for Dislocated Blades in a Stirred Tank

2011 ◽  
Vol 354-355 ◽  
pp. 559-563
Author(s):  
Lei Shi ◽  
Shen Jie Zhou ◽  
Feng Ling Yang ◽  
Fan Jin Hu
Keyword(s):  
Numerical Simulation ◽  
Turbulent Mixing ◽  
Stirred Tank ◽  
Industrial Processes ◽  
Mixing Efficiency ◽  
Mixing Process ◽  
Flow Number ◽  
Stirred Tanks ◽  
Calculation Results ◽  
Better Than

Mixing efficiency is an important parameter in the design of many industrial processes in stirred tanks. In this study, CFD technology was used to simulate the mixing process inside the stirred tank with dislocated blades and standard turbine. Calculations were performed to study the effects of agitator speed and the configuration of impellers on mixing efficiency. The results showed that the flow field in the stirred tank with the dislocated blades is better than the standard turbine, and the flow number of the dislocated blades had been improved while the power number had been reduced. According to calculation results of Wr, we found the mixing efficiency of the dislocated blades had been improved about 4 times than that of standard turbine.

Experimental Measurement of the Vortex Development Downstream of a Lobed Forced Mixer

1992 ◽  
Vol 114 (1) ◽  
pp. 63-71 ◽  
Author(s):  
W. A. Eckerle ◽  
H. Sheibani ◽  
J. Awad
Keyword(s):  
Secondary Flow ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Velocity Ratio ◽  
Mixing Process ◽  
Mixing Processes ◽  
Design Variables ◽  
Secondary Motion ◽  
The Mean

An experimental study was conducted to investigate the mixing processes downstream of a forced mixer. A forced mixer generates large-scale, axial (stirring) vorticity, which causes the primary and secondary flow to mix rapidly with low loss. These devices have been successfully used in the past where enhanced mixing of two streams was a requirement. Unfortunately, details of the mixing process associated with these lobed forced mixers are not well understood. Performance sensitivity to design variables has not been documented. An experiment was set up to investigate the mixing processes downstream of a mixer. Air flow was independently supplied to each side of the forced mixer by separate centrifugal blowers. Pressures were measured at the entrance to the lobes with a pitot-static probe to document the characteristics of the approaching boundary layer. Interior mean and fluctuating velocities were nonintrusively measured using a two-component laser-Doppler velocimetry (LDV) system for velocity ratios of 1:1 and 2:1. The wake structure is shown to display a three-step process where initially secondary flow was generated by the mixer lobes, the secondary flow created counterrotating vortices with a diameter on the order of the convolute width, and then the vortices broke down resulting in a significant increase in turbulent mixing. The results show that the mean secondary motion induced by the lobes effectively circulated the flow passing through the lobes. This motion, however, did not homogeneously mix the two streams. Turbulent mixing in the third step of the mixing process appears to be an important element in the enhanced mixing that has been observed with forced mixers. The length required for the flow to reach this third step is a function of the velocity ratio across the mixer. The results of this investigation indicate that both the mean secondary motion and the turbulent mixing occurring after vortex breakdown need to be considered for prediction of forced mixer performance.

A probability density function method for turbulent mixing and combustion on three-dimensional unstructured deforming meshes

2000 ◽  
Vol 1 (2) ◽  
pp. 171-190 ◽  
Author(s):  
S Subramaniam ◽  
D. C. Haworth
Keyword(s):  
Probability Density Function ◽  
Probability Density ◽  
Density Function ◽  
Turbulent Mixing ◽  
Three Dimensional ◽  
Quantitative Agreement ◽  
Particle Number Density ◽  
Time Dependent ◽  
Ic Engine ◽  
Density Control

A hybrid Lagrangian-Eulerian methodology is developed for numerical simulation of turbulent mixing and combustion in arbitrary three-dimensional time-dependent geometric configurations. The context is a probability density function (PDF) based approach intended for modelling in cylinder processes in reciprocating piston internal combustion (IC) engines. Issues addressed include mean estimation, particle tracking and particle number-density control on three-dimensional unstructured deforming meshes. The suitability of the methodology for statistically time-dependent three-dimensional turbulent flow with large density variations is demonstrated via simulations of turbulent freon vapour/air mixing on an unstructured deforming mesh representing an idealized IC engine [13]. Computed profiles of mean and r.m.s. freon mole fractions show good quantitative agreement with measurements. Moreover, inherent advantages of the Lagrangian-Eulerian PDF approach are demonstrated, compared to Eulerian finite volume solutions of an (approximately) equivalent set of moment equations. The new approach is, by design, compatible with existing computational fluid dynamics codes that are used for multidimensional modelling of in-cylinder thermal fluids processes. This work broadens the accessibility of PDF methods for practical turbulent combustion systems.

Numerical study on turbulent mixing process in cross-flow type T-junction

2015 ◽  
Author(s):  
Azzi Abbes ◽  
Nemdili Fadéla ◽  
Ahmed Zineddine Dellil
Keyword(s):  
Turbulent Mixing ◽  
Numerical Study ◽  
Cross Flow ◽  
Mixing Process ◽  
Flow Type

Experimental Measurement of the Vortex Development Downstream of a Lobed Forced Mixer

1990 ◽  
Author(s):  
Wayne A. Eckerle ◽  
Hamdi Sheibani ◽  
Jean Awad
Keyword(s):  
Secondary Flow ◽  
Turbulent Mixing ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Velocity Ratio ◽  
Mixing Process ◽  
Mixing Processes ◽  
Design Variables ◽  
Secondary Motion ◽  
The Mean

An experimental study was conducted to investigate the mixing processes downstream of a forced mixer. A forced mixer generates large scale, axial (stirring) vorticity which causes the primary and secondary flow to mix rapidly with low loss. These devices have been successfully used in the past where enhanced mixing of two streams was a requirement. Unfortunately, details of the mixing process associated with these lobed forced mixers are not well understood. Performance sensitivity to design variables has not been documented. An experiment was set up to investigate the mixing processes downstream of a mixer. Air flow was independently supplied to each side of the forced mixer by separate centrifugal blowers. Pressures were measured at the entrance to the lobes with a pitot-static probe to document the characteristics of the approaching boundary layer. Interior mean and fluctuating velocities were nonintrusively measured using a two-component Laser Doppler Velocimetry (LDV) system for velocity ratios of 1:1 and 2:1. The wake structure is shown to display a three step process where initially secondary flow was generated by the mixer lobes, the secondary flow created counter-rotating vortices with a diameter on the order of the convolute width, and then the vortices broke down resulting in a significant increase in turbulent mixing. The results show that the mean secondary motion induced by the lobes effectively circulated the flow passing through the lobes. This motion, however, did not homogeneously mix the two streams. Turbulent mixing in the third step of the mixing process appears to be an important element in the enhanced mixing that has been observed with forced mixers. The length required for the flow to reach this third step is a function of the velocity ratio across the mixer. The results of this investigation indicate that both the mean secondary motion and the turbulent mixing occurring after vortex breakdown need to be considered for prediction of forced mixer performance.

Numerical Mixing Analysis of a Vaned Circular Micromixer

2006 ◽  
Author(s):  
Richard Bergman ◽  
Alexander Efremov ◽  
Pierre Woehl
Keyword(s):  
Numerical Analysis ◽  
Turbulent Mixing ◽  
Parametric Study ◽  
Large Scale ◽  
Acceptable Level ◽  
Mixing Efficiency ◽  
Mixing Process ◽  
Mixing Performance ◽  
Numerical Mixing ◽  
Cutting And Stacking

Mixing of fluids is a common and often critical step in microfluidic systems. In typical large scale processes turbulence greatly speeds the mixing process. At the mini and micro-scales, however, the flow is laminar and the benefits of turbulent mixing are not present. Mixing at the mini- and micro-scales tends to become a more highly engineered process of bringing fluids together in predictable ways to achieve a predetermined and acceptable level of mixing. This paper summarizes a numerical analysis of the mixing performance of a vaned circular micromixer. A newly developed mixing metric suitable for reacting fluids is developed for this study. Applying the basic steps of stretching, cutting, and stacking to effect mixing, a useful micromixer is analyzed numerically for its mixing efficiency. A parametric study of flow and viscosity indicate that a flow Re of 12 or higher is sufficient to achieve effective and rapid mixing in this device.

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