CFD Modelling and Experimental Validation of Emulsification Processes
Lead Research Organisation:
University of Manchester
Department Name: Chem Eng and Analytical Science
Abstract
This exciting joint project between the University of Manchester and Unilever will investigate mixing inside stirred tanks through a combination of predictive computational fluid dynamics (CFD) simulations, and simulation validation via experimental methods.
Oil in water emulsions are ubiquitous in consumer products. Emulsions are found in everyday consumer goods such as deodorants and ice creams. The emulsions are typically shear thinning non-Newtonian liquids. Oil droplet size distributions inside emulsions has a significant effect on emulsion stability and as well as on viscosity. Therefore, the ability to predict these droplet size distributions is highly desirable.
Many consumer goods involving oil in water emulsions are produced inside stirred tanks, where the ingredients are mixed to form an emulsion. The oil droplet sizes inside the emulsions are a function of mixing times, turbulent eddy dissipation rates, the type of stirred tank used, and other key variables.
The project requirement is to use CFD to perform simulations of oil in water emulsions as they are formed inside stirred tanks, and provide predictions of the oil droplet size distributions. A key part of the project will be to validate the CFD predictions against experimental data, where the data will be from power measurements and electrical tomography methods. The successful candidate will undertake the CFD simulations and experimental work.
The CFD simulations will be multiphase, involving population balance modelling coupled with breakup and coalescence kernels. CFD and experimental methods have been used previously with success to predict oil size distributions in high pressure homogenizers and Silverson high shear devices. Therefore, there is confidence that those models can be generalised to simulate oil droplet size distributions inside stirred tanks.
The student will benefit by undertaking an industrially relevant PhD, supported by Unilever, a leading consumer goods company. The student will receive close support from the academic and the industrial advisers. Continuing professional development is actively encouraged, such as charting progress towards chartered engineer (CEng) status or equivalent. There will be opportunities to attend renowned conferences (UK and overseas), and publish novel work in high impact factor journals.
Oil in water emulsions are ubiquitous in consumer products. Emulsions are found in everyday consumer goods such as deodorants and ice creams. The emulsions are typically shear thinning non-Newtonian liquids. Oil droplet size distributions inside emulsions has a significant effect on emulsion stability and as well as on viscosity. Therefore, the ability to predict these droplet size distributions is highly desirable.
Many consumer goods involving oil in water emulsions are produced inside stirred tanks, where the ingredients are mixed to form an emulsion. The oil droplet sizes inside the emulsions are a function of mixing times, turbulent eddy dissipation rates, the type of stirred tank used, and other key variables.
The project requirement is to use CFD to perform simulations of oil in water emulsions as they are formed inside stirred tanks, and provide predictions of the oil droplet size distributions. A key part of the project will be to validate the CFD predictions against experimental data, where the data will be from power measurements and electrical tomography methods. The successful candidate will undertake the CFD simulations and experimental work.
The CFD simulations will be multiphase, involving population balance modelling coupled with breakup and coalescence kernels. CFD and experimental methods have been used previously with success to predict oil size distributions in high pressure homogenizers and Silverson high shear devices. Therefore, there is confidence that those models can be generalised to simulate oil droplet size distributions inside stirred tanks.
The student will benefit by undertaking an industrially relevant PhD, supported by Unilever, a leading consumer goods company. The student will receive close support from the academic and the industrial advisers. Continuing professional development is actively encouraged, such as charting progress towards chartered engineer (CEng) status or equivalent. There will be opportunities to attend renowned conferences (UK and overseas), and publish novel work in high impact factor journals.
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/R512035/1 | 01/10/2017 | 31/12/2022 | |||
| 1918781 | Studentship | EP/R512035/1 | 01/10/2017 | 30/09/2021 | Thomas John |
| Description | The power number and flow number are two dimensionless numbers that are very useful for characterizing mixing devices. One of these devices is a rotor-stator mixer. From experimentation, it has been shown that there exists a linear relationship between the two numbers. The gradient and intercept of this relationship are functions of the exact design of the mixer. Typically these values are just found experimentally and then recorded in literature. In this project, we have used computational fluid dynamics to investigate how these values of gradient and intercept change with the design of the mixer. We have developed an empirical correlation which allows the prediction of the power and the flow numbers for a wide range of designs, something which has not been done before. The correlation has been shown to work for previous experimental data for mixers with very different designs. We have also shown that the relationship between the power number and flow number is independent of the mode of operation used, since these mixers can be used in batch or inline mode. Again this has not previously been shown before. We also propose a method to predict the flow number for a batch rotor-stator, something which is very challenging experimentally. We have also investigated the relationship between power, flow, and mixer geometry in stirred vessels with radial impellers. In stirred vessels, it is not easy to independently vary these parameters like it is in rotor-stator mixers, so a more theoretical approach was taken in order to develop useful correlations to predict the important characteristics of the mixer without having to perform complex and time-consuming experiments. An angular momentum balance on the impeller provides us with much insight into the relationship between power and flow, so that the correlations developed are not just purely empirical but have some physical meaning. It is most useful, however, when combined with accurate CFD data, as has been done in our study. Another specific type of mixing device is a Sonolator, a type of high pressure homogeniser. We have conducted an experimental study using this device, investigating how the operating conditions, such as flow rate and orifice size, affect the droplet size distributions of emulsions produced using the device. We were able to develop a model which is capable of predicting the entire droplet size distribution of the produced emulsions, rather than just a representative average size of the distribution, for a wide range of conditions. Discrepancies between theoretical predictions and experimental results have been validated using previous simulational studies which highlight errors in the theoretical predictions, which adds significant validation to our model. The model is especially useful as it is actually the drop size distribution which affects the quality and stability of emulsified products, rather than a representative average droplet size. This is especially the case when distributions are highly non-uniform. |
| Exploitation Route | The work we have performed on rotor-stator mixers used only single screen - single rotor configurations. Rotor stators are often double screen - double rotor configurations. Our results and findings provide a useful starting point for the development of similar research for dual screen dual rotor configurations. Our models can also be modified to account for changes in the design of the rotor, since ours focuses heavily on the design of the screen. This work will likely need to be performed simulationally, as was done in this work, since such experiments are costly and difficult to perform. For the work undertaken in stirred vessels, we have developed accurate and useful correlations that can be employed as they are, but the work in general also shows a novel methodology for studying power and flow in stirred vessels which can be used to study different types of impellers. The correlations could also be used to improve predictions of mixing time and mixing kinetics, since most previous work in this area assumes a proportionality between power and flow; our work shows this is not the case and so the models we have developed might be more useful in this respect. The models we have developed are able to predict the power and flow numbers for a wide range of designs of rotor-stator. The power number, in particular, is known to influence the droplet size of emulsions. Experimental studies of emulsification using rotor-studies with various screen designs could be performed to add further experimental validation to our models, and also develop further empirical models to predict droplet size across multiple designs of rotor-stator. These models could directly be used in industry as a method of product quality control. |
| Sectors | Agriculture, Food and Drink,Chemicals,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology |