For further information

you can contact

Robert S. Brodkey at

(614) 292-2609;

brodkey.1@osu.edu

Many present and former students and friends have asked about the status of our research on turbulence, mixing, and reactor design and on our future plans.  This summary is meant for you. There are four key elements that are fundamental to the experimental and computational work underway: 

• Research on both opposed-jet mixers and mixing vessels with rotating impellers is underway.  The former shape is that found in injection reaction molding used in polymer processing and the latter is the most common mixing type used in industry today for chemical reactions and blending operations.   
• Experimental measures that involve full-field, time-resolved, velocity vector measurements in both stationary and convective frames of reference are being obtained.
• Integration of dynamic ideas where a superimposed non-periodic motion can enhance mixing is also being considered.   
• Parallel computational efforts are also underway. The opposed-jet experimental mixing data is being used as a definitive validation for the parallel numerical results.  The second, and more difficult effort, is to extend the approach to mixing vessels. 

The work involves a unique combination of these points. Use of a convective view allows measurement of time-resolved, three-dimensional velocity vectors in a mixing vessel (a synchronized view with the mixer turbine) even at high Reynolds numbers.  More fundamental and local parameters (e.g., local turbulent kinetic energy) can be obtained that describe inhomogeneities that are of importance in mixing vessels and can be used to describe trailing impeller vortex structures, baffle-fluid interactions, etc.  Such measures can be contrasted with overall global parameters such as the power per unit volume.  Local motions must be used to allow prediction of mixing, especially where selectivity is of importance. These measurements must be made under true dynamic conditions where superimposed larger scale motions can influence finer scale mixing processes.   

The ultimate goal is to model mixing so that computational approaches can make experimental measurements unnecessary.  The view must be well based in fundamentals, but at the same time be clearly directed to solving real world engineering problems. To contribute to the solution of this problem, attention is focused on the opposed-jet system. This simple system of industrial importance is key to the validation of computational results.  Computationally, it is a fixed system that does not require moving coordinates.  The opposed-jet inlets can be laminar and well defined, thus eliminating cyclic boundary conditions, while the flow within the mixing region is highly turbulent.  Finally, the initial conditions can be taken from the actual three-dimensional experimental results. There are no free parameters in the numerical calculations and thus the comparison with experiments should be definitive.  

Significance 

• This study is the first time-resolved, full-field, systematic examination of three-dimensional flows for the full mixing flow range. The measurement technique allows characterization of the local flow field so that critical measures of the flow (such as details of vortical structures, local dissipation, extension etc.) can be made.  It is our intent to expand on what is already known about turbulent mixing.  We need to establish the nature of and the range of scales of turbulence; especially those associated with the vortical motions.  Such motions help diffusion by increasing area, but we also need to understand the initial mixing that breaks down the large scale so that the mixing cascade process can occur to obtain grossly uniform conditions so that the mixing process between smaller elements can proceed. 
• Stirred tanks are the most common type of equipment used in industrial operations.  By measuring the detailed performance of such realistic mixing devices, the work will provide the data needed for validation of theory and be an incentive for extending theories into the turbulent flow regime.  The work is a direct application of a very fundamental approach to the industrial important mixing problem.
• Dynamic motion methods for enhancing mixing require simple and relatively inexpensive retrofits, and therefore they have considerable probability of being implemented, leading to substantial process improvement and pollution prevention.  Recent industrial trends have been for the chemical industries to be more competitive. 

One example of the potential value to industry is the mixing requirements needed for polymerization reaction operations.  The monomers and catalyst may at the very beginning be of low viscosity and the flow can be turbulent; however, as the polymerization proceeds, the viscosity increases, the mixing Reynolds number decreases, as does the mixing.  It is, however, necessary to achieve good mixing over the entire process cycle to satisfy polymer reaction requirements, since it is often necessary to continuously add monomer, chain terminators, other additives, and control temperature. Enhancing such mixing operations could be a significant contribution leading to better quality and control, faster processing and lower cost. Improved mixing could lead to the use of increased levels of solid concentration in polymerization reactions. 

Objectives

• The opposed jet measurements are now complete.
• Mixing will be investigated experimentally using both qualitative tracer visualization techniques and quantitative particle-tracking velocimetry.  A rotating frame of reference view will be used for mixing vessels.  This sometimes is referred to as a view phase-locked to the impeller rotation. 
• Time-dependent rates of stirring and transverse flows with time-dependent intensities will be used to enhance mixing by either radial or axial flow impellers.   
• The flow-field data-base obtained will be used to validate existing theoretical and computational efforts.   By focusing on realistic case studies, the impact of this project will contribute to the development of concrete applications. 

Plan 
Rather than repeating material already on the web, if you want more detailed information on the plan you should go to a review of The Current Mixing Problem.  This link is from my home page, and at the end it is “Current Research on Mixing.” 

Impact of the Proposed Work
To summarize the impact of the work, by focusing on realistic case studies, we hope to contribute to the development of concrete applications. What we want to accomplish is 

• A set of well-developed experimental techniques for characterizing and improving mixing processes for well-defined mixing flow cases.  It is our intent to investigate two or three impeller geometries that are in current use today.  The rapidity of our data acquisition by our PTV technique and the automated data reduction steps we have developed lend themselves to the reduction of massive data bases as demonstrated by the opposed-jet work.  
• The performance of the dynamically perturbed stirred tank-mixing vessel will be examined for a limited set of experiments. Conditions leading to improved mixing will be identified for several common systems and translated into heuristic tools useful for achieving optimal performance in other systems. 
• The proposed work should lead to improved reactor technology, based on dynamically stirred tanks, which could be easily implemented in production operations simply by retrofitting existing equipment. This new reactor technology could increase the efficiency and reduce the adverse environmental impact of many reactive flow processes.