Progress 10/01/03 to 09/30/11
Outputs
OUTPUTS: PI has left the University. No progress to report. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
No outcomes to report
Publications
- No publications reported this period
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Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: The project to extend the fundamental study of the mixing of viscous, viscoelastic materials to the simple but relevant vane rheometer geometry is ongoing. The approach is to combine the use of classical rheological techniques to characterize and model the viscoelastic responses of the materials studied, computational fluid dynamics using commercially available finite element method techniques for viscoelastic constitutive models to simulate the flow and mixing, and experimental torque measurement and flow visualization to validate and improve the simulations. The results are expected show the effect of a wider range of realistic viscoelastic responses on mixing in a relevant geometry. Currently, simulations using a fixed top surface boundary with generalized Newtonian models and simple viscoelastic fluid models have been run. Experimental validation by using a high speed digital video camera to capture tracer paths and surface shapes, as well by measuring the torque generated will be completed in the next couple months. This work will better define mixing behavior of complex fluids with validated simulation results, thus increasing understanding of mixing and building trust in CFD simulation results. Results of the CFD mixing study of the Mixograph planetary pin mixer were presented at the International Symposium on Mixing in Industrial Processes - ISMIP VI, Aug 17-21, 2008, Niagara Falls, Ontario, Canada. PARTICIPANTS: This project has been used to train 2 graduate and 2 undergraduate food engineering students to better understand mixing processes and to use computational fluid dynamics simulation as a research and problem solving tool. TARGET AUDIENCES: Food engineers in the food industry, government agencies and academia. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
Mixing is an important process in the production of most biological materials, but it is difficult to experimentally evaluate due to the opacity and complexity of most biological materials. The use of CFD simulation in combination with validation using high speed digital photography in this work is leading to a better understanding of the flow and mixing character in a range of realistic food mixing geometries. It is providing a means for determining the source of differences between the mixers that will allow for better design of mixing processes.
Publications
- Connelly, R.K. and Valenti-Jordan, J.B. 2008. Mixing analysis of a Newtonian fluid in a 3D planetary pin mixer. Chem. Engr. Res. and Design, 86(12):1434-1440.
- Connelly, R.K. 2008. Going with the flow: computational fluid dynamics simulation of dough testing mixers. Cer. Foods World, 53(4):186-192.
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Progress 01/01/07 to 12/31/07
Outputs
A recently begun project in this category is to extend the fundamental study of the mixing of viscous, viscoelastic materials to the simple but relevant vane rheometer geometry. The approach is to combine the use of classical rheological techniques to characterize and model the viscoelastic responses of the materials studied, computational fluid dynamics using commercially available finite element method techniques for viscoelastic constitutive models to simulate the flow and mixing, and experimental torque measurement and flow visualization to validate and improve the simulations. The results are expected show the effect of a wider range of realistic viscoelastic responses on mixing in a relevant geometry. Currently, geometry input is complete and initial simulations using a fixed top surface boundary with generalized Newtonian models have been run. Work is ongoing to use a deformable top surface and planned to extend the simulations to simple viscoelastic fluid models
based on real materials. We also expect to do experimental validation by using a high speed digital video camera to capture tracer paths and surface shapes, as well by measuring the torque generated. This work will better define mixing behavior of complex fluids with validated simulation results, thus increasing understanding of mixing and building trust in CFD simulation results. Results of the CFD mixing study of the Mixograph planetary pin mixer were presented at the 2007 IFT annual meeting. Publications, including a paper to be presented at the International Symposium on Mixing in Industrial Processes - ISMIP VI, Aug 17-21, 2008, Niagara Falls, Ontario, Canada, are in the final stages of preparation for submission. The CFD study of in-line static mixers with collaborative NMR validation by Kathryn McCarthy at UC-Davis under the umbrella of the multi-state project NC1023 "Improvement of thermal and alternative processes for foods" is on-going.
Impacts
Mixing is an important process in the production of most biological materials, but it is difficult to experimentally evaluate due to the opacity and complexity of most biological materials. The use of CFD simulation in this work is leading to a better understanding of the flow and mixing character in a range of realistic food mixing geometries. It is providing a means for determining the source of differences between the mixers that will allow for better design of mixing processes.
Publications
- Connelly, R.K. and Kokini, J.L. 2007. Analysis of Mixing Processes Using CFD. Chapter 23, pgs. 555-588 in Computational Fluid Dynamics in Food Processing, Da-Wen Sun (ed.), Taylor and Francis Group, LLC, Boca Raton, FL.
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Progress 01/01/06 to 12/31/06
Outputs
The Mixograph is a planetary pin mixer that has been used for decades to evaluate the hydration of flour. In the past, the response curve has been studied as a source of more information about the strength and development rate of the dough. These studies have recently shifted to evaluating the dynamics of the mixer itself, rather than the response curve. Computational Fluid Dynamics (CFD) can be used to gain greater understanding about a mixer by evaluating both local and global measures of dispersive and distributive mixing, such as mixing index and efficiency. CFD results are known to be subject to several types of error, such as discretization error, if not properly guarded against. In this study, a basic Newtonian corn syrup is used so that the approach and methodology of meshing the Mixograph may be evaluated without complex results from more difficult fluids. The 3D mesh of the Mixograph is built as an extension of a 2D mesh, so the 2D mesh is first optimized
with respect to pin movement simulation, mesh discretization, and time step size. Several methods of qualitative and quantitative analysis are used to resolve differences between the different proposed meshes. Once optimized for minimizing error and required calculation resources, the 2D mesh is expanded into 3D for observance of local and bulk mixing properties. It is shown that the Mixograph does not experience as much vertical mixing as cross-sectional mixing over the same time span. Additionally, it is observed that different pin positions are more efficient than others. These meshes and results will be used to develop future studies around more complex fluids. These results will be presented at the 2007 IFT annual meeting. A new short term project looking at the simulation of mixing in a simple in-line mixer, which is being collaboratively validated using NMR by Kathryn McCarthy at UC-Davis, was begun. This project is under the umbrella of the multi-state project NC1023
"Improvement of thermal and alternative processes for foods". Mixing is a universal unit operation addressed within this project that impacts a wide range of food processing issues but is poorly understood. The multistate project is an opportunity to bring together these two different sets of expertise to better define and validate these results in order to increase understanding of mixing and build trust in the simulation results.
Impacts
Mixing is an important process in the production of most biological materials, but it is difficult to experimentally evaluate due to the opacity and complexity of most biological materials. This work will lead to a better understanding of the flow and mixing character in a planetary pin mixer, which will then be available for comparison with the simulation results for mixers used for the same purpose generated previously. It provides a means for determining the source of differences between the two mixers. The new short term project is an additional opportunity to increase understanding of mixing and build trust in simulation results.
Publications
- Jordan, J.B., Simulation development and mixing analysis of a Newtonian fluid in a 3D mixograph-style mixer. Masters Thesis, University of Wisconsin-Madison, December, 2006.
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Progress 01/01/05 to 12/31/05
Outputs
2-D mesh development for a pin mixer was undertaken using a rotating reference frame approach to limit the area that is covered by the pin paths. The pin paths were then meshed in such a way that the shape and area of the pins was closely preserved at each position of the pins, thus reducing the error generated by variability of the pin shape inherent in the way the mesh superposition technique generates the flow domain with moving parts. Meshes of increasing density were created in such a way as to allow checks for mesh independence and convergence with mesh refinement. Initial 2-D simulations were undertaken with Newtonian fluid models and simulations with shear thinning fluid models based on real fluids are planned. 3-D mesh development is underway. 3-D simulations with a series of Newtonian and shear thinning fluids based on real fluids as well as experiments to gather torque readings in the actual mixer being modeled are planned. Results will be presented at the
2006 IFT annual meeting.
Impacts
This work will lead to a better understanding of the flow and mixing character in this mixer, which will then be available for comparison with the simulation results for a similar mixer used for the same purpose generated previously and provide a means for determining the source of differences between the two mixers.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
In order to test the ability of the commercial CFD code Fluent to model the crystallization behavior of sugars, a collaboration was formed between Richard Hartel and Robin Connelly in the Department of Food Science and Kumar Dhanasekharan of Fluent, Inc. to develop a numerical simulation of lactose crystallization in a labscale mixed suspension, with mixed product removal crystallizer based on that used by Shi, Liang and Hartel (1990). The fruit of this initial collaborative effort was presented at the Institute of Food Technologists Annual meeting in July of 2004. The geometry of the crystallizer was recreated as exactly as possible and meshed with 114,374 hexahedral and tetrahedral elements, where the density of mesh elements was increased near the impeller. The boundary conditions included no slip at the walls, the impeller in a local rotating reference frame full slip with no normal force at the top, outer walls at the coolant temperature of 40C, an impeller speed
of 800 rpm and fluid parameters for a supersaturated lactose solution at 40C, as well as inlet conditions for the supersaturated lactose solution coming in at 45C for run 7 from Shi, Liang and Hartel (1990). This mesh and boundary set were combined with k-epsilon turbulence model to produce the steady-state, non-isothermal, single-phase result flow field results. The final stage involved the coupling of the multiphase mixture model that incorporated conservation of mass and momentum for each species and phase as well as the population balance equation that was transformed to a transport equation using the method of moments (Randolph & Larson, 1988) with user defined functions to incorporate the lactose crystallization kinetics to the single phase results to determine the CSD. When compared with the model of Shi, Liang & Harte (1990), the results were similar although curvature indicating a departure from straight logarithmic behavior was evident in the simulation results and likely
indicated some short circuiting or preferential removal of small crystals in the crystallizer. In addition, gradients in the total number density and volume fraction of crystals showed where the perfect mixing assumption was less accurate, with this seen especially near the inlet and behind the baffles. The net result of the preliminary work is proof that the concept of combining population balance theory with CFD is viable for use with sugar crystallization and can be used as a tool to investigate the effects of mixing and the configuration of the crystallizer on the CSD. Over the course of the next year, this preliminary project will be further refined, and run under a range of conditions, with particular attention paid to the effect of moving the inlet and also to the effect of changing from using a local rotating reference frame to a sliding mesh around the impeller.
Impacts
Facilitating collaborations between experienced process researchers and the commercial software application specialists allows the development of simulated mixing solutions with the highest possible degree of reliability and applicability to real systems. The simulation results can then be applied to increasing the efficiency of real mixing processes, as well as improving the quality and yield of the final product.
Publications
- No publications reported this period
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