| 1. |
- Skoglund, Tomas
(författare)
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Dynamic Modelling and Simulation of Liquid Food Process Lines
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the present work a dynamic model library of components for process lines was developed. The analysis addressed characteristic aspects of liquid food process lines, and new models were developed for fluid transitions, dispersion, mixing zones and first-order chemical reactions in pipes and heat exchangers. The computational efficiency and accuracy of the models were analysed. It was demonstrated that classical models of fluid propagation in process lines could be combined with modern numerical methods to obtain computationally efficient dynamic models for the simulation of dispersed convective flow, with and without chemical reactions. In particular it was demonstrated that a transport delay model was well suited for the simulation of thermal transients due to fluid transitions in heat exchangers. It was shown that the model could be extended to account for dispersion with a method that, although classical in approach, enables a certain freedom in the choice of degree of discretization depending on the demand for accuracy vs. computational speed. Further extension of the model with first-order chemical reactions to account for microbial deactivation was demonstrated. The usefulness of the dispersed-convection model to predict the extent of mixing zones and the amount of product rejects in continuous processing was demonstrated. The relevance concerning product traceability is discussed and the concept ?fuzzy traceability? introduced.
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| 3. |
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| 4. |
- Olsson, E E M, et al.
(författare)
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Flow and heat transfer from multiple slot air jets impinging on circular cylinders
- 2005
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774 .- 1873-5770. ; 67:3, s. 273-280
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Tidskriftsartikel (refereegranskat)abstract
- This study presents flow and heat transfer predictions of multiple slot air jets impinging on circular cylinders using CFD (computational fluid dynamics). The distribution of Nusselt numbers around the cylinders for different Reynolds numbers (23,000-100,000), distances between the jets, and openings between them was determined for two and three jets and compared to simulations of a single jet. The flow characteristics and the heat transfer distribution around the cylinders are found to be dependent on the distance and the opening between the jets. The interaction between two jets is found to be most advantageous. The heat transfer increases for higher Reynolds number in general; for two jets the heat transfer in the stagnation point is Nu(s) = 0.20Re(0.68). For three jets, the heat transfer distribution is different on the outer cylinders, as compared to the cylinder in the centre. (C) 2004 Elsevier Ltd. All rights reserved.
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| 5. |
- Risman, PO, 1943, et al.
(författare)
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Retro-modelling of a dual resonant applicator and accurate dielectric properties of liquid water from −20 °C to +100 °C
- 2007
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Ingår i: Measurement Science and Technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 18, s. 959-966
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Tidskriftsartikel (refereegranskat)abstract
- A critical analysis is made of literature reports on the dielectric properties of pure water from liquid water supercooled at −20 ◦C, to +100 ◦C, in principle in the frequency range 0 to 3 GHz. Measurements using completemulti-step numerical modelling of a dual resonant cavity at about 920 MHz and 2230 MHz are presented. The measured data at about +20 ◦C are used as reference for the calculation of data at other temperatures. Due to the high resolution and considerations of various error sources, the resultingaccuracy becomes high and allows the construction of improved empiricalformulae for the Debye relaxation behaviour.
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| 6. |
- Olsson, Eva
(författare)
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Jet Impingement and Infrared Heating of Cylindrical Foods. Flow and Heat Transfer Studies
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rapid heat transfer methods such as jet impingement and infrared radiation can be used to speed up thermal processing in the food industry. The heating rate affects important food characteristics, such as colour. Jet impingement consists of directed jets of air with a high velocity that impinge on the food surface, which reduces the velocity boundary layer between the air and surface and gives a fast heat transfer. Infrared heating is a radiative heat transfer method with instant and effective heating of the food product, without heating the surrounding air. Flow and heat transfer from single and multiple jets impinging on a circular cylinder placed on a flat surface were studied numerically by computational fluid dynamics (CFD) simulations using the k-? SST and RSM models. The results concerning velocity obtained by CFD were generally in good agreement with experimental measurements using particle image velocimetry (PIV). The heat transfer distribution on the cylinder surface, expressed as local heat transfer coefficients, was non-uniform due to air flow characteristics that influenced the boundary layer thickness. The heat transfer was highest on the top of the cylinder, and lower close to the separation point and on the back of the cylinder. In addition to making CFD simulations, the local heat transfer coefficients were determined by an inverse heat transfer method, including a sensitivity analysis, using temperature profiles in the cylinder at different positions. The heat transfer coefficients were generally higher than what was predicted by CFD. The interaction between multiple jets strongly affected the heat transfer around the cylinder. The distance and opening between the jets were found to be important to achieving a high and even heat transfer rate using multiple jets. Jet impingement and infrared heating simultaneously was studied using CFD, which showed that there is a synergistic effect when the two heating methods are combined. A higher heat transfer was achieved by combining the methods than by using each method separately. The effect of impingement and infrared heating on colour and crust formation on partially baked baguettes was investigated experimentally. Impingement and infrared heating gave different temperature profiles in the crust, which resulted in different colour development and crust formation. A rapid heating increased the rate of colour development and shortened the total heating time, which resulted in a thin crust and reduction in the total moisture loss. The combination of jet impingement and infrared made it possible to create product properties that cannot be achieved by use of the heating methods alone. A thicker crust and better heating in the centre of the bread could only be achieved by combining infrared and impingement. For industrial thermal processes, prediction of flow and heat transfer with CFD can be used to design equipment and processes that offer optimal heat transfer to the product, thus resulting in high and even product quality.
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| 7. |
- Innings, Fredrik, et al.
(författare)
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Dynamic modelling of the deformation of a drop in a four-roll mill
- 2005
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 60:17, s. 4771-4779
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Tidskriftsartikel (refereegranskat)abstract
- The deformation of a drop flowing along the centre streamline of a four-roll mill (4RM) has been investigated. The velocities and elongation rates along the centre streamline in the 4RM were measured using particle tracking velocimetry. The deformation and position of the deforming drops were photographed with a video camera. A dynamic, one-dimensional, analytical simulation model describing the drop deformation has been developed. The model is based on Taylor's [1964. International Congress on Applied Mechanics, vol. 11, 790-796] static conical drop shape model, but has been extended to include elliptic drops undergoing rapid deformation. The model was incorporated into a numerical scheme using Matlab and the drop deformation in the 4RM was simulated. The simulations were compared with the results of the experiments with the help of a dynamic Weber number incorporating the exact effect of the continuous phase stress on the deformation of the drop. With a dynamic Weber number of 0.42 the agreement between the experiments and the simulations along the whole deformation process was excellent for all three drop diameters studied. With this model the deformation of drops of all sizes in different elongation fields can be calculated, for example sub-micron-sized drops in a high-pressure homogeniser. (c) 2005 Elsevier Ltd. All rights reserved.
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| 8. |
- Roos, H, et al.
(författare)
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Evaluation of new methods and measuring systems for characterisation of flow behaviour of complex foods
- 2006
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Ingår i: Applied Rheology. - 1430-6395. ; 16:1, s. 19-25
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Tidskriftsartikel (refereegranskat)abstract
- Conventional methods often impose difficulties when measuring the viscosity of fluids containing particles or fibres, e.g. tomato paste or fruit preparations, mainly due to the narrow gaps of the viscometer. In order to solve these problems different geometries have been developed, e.g. different mixer systems and wide gap double concentric cylinders. However, these can not be evaluated assuming a constant shear rate throughout the fluid. In this study, three different kinds of mixer systems have been studied; a small and a large paddle and a helix. For the mixer systems an average shear rate must be determined and a quotient between torque and shear stress must be found. in addition, a wide gap double concentric cylinder (DCC) was examined and evaluated using two different methods. When evaluating the mixer systems a method based on the Couette analogy has been used successfully for a number of complex fluids, including prepared sauces and fruit samples containing particles of different size. The DCC has been evaluated using a numerical as well as an approximate method, both giving results of good accuracy. All systems had the limitation that no consistent results were obtained for tomato paste. However, when starch was added to the diluted tomato paste dispersion, satisfying results were once again obtained.
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| 9. |
- Johansson, Erika, 1969, et al.
(författare)
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Towards Sustainable Conservation and Use of Materials in Built Environments : Summary from the FORSCENE workshop: Industry/Economy, Vienna, October 23-24, 2006
- 2007
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Ingår i: Giljum, S., Hinterberger, F., Hammer, M. (Eds.), Report from the FORSCENE workshop Industry-Environment, Sustainable Europe Research Institute (SERI), Vienna, October 2006, Part 2..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Up until today, no comprehensive efforts have been made, and principles are yet to be established for the ‘sustainable conservation’ of the built environment – in an inter- and transdisciplinary manner, including systematic integrative modelling and an appreciation of the inherent values of already existing structures and ambiences. Existing built structures and environments are still often seen as obstacles for sustainable development. It may be argued that a more preventive and integrated approach, i.e. an early estimation and a meta-level understanding of the built environment and its processes; its critical loads, inherent qualities, values, threats, life cycles, production chains, recyclability and quantities etc., would rather promote any kind of planning for a sustained future and the proper use of materials by hindering unnecessary material flows - i.e. through their unnecessary/unsympathetic production, exploitation and/or use, that would minimise their negative impact on peoples lives and the environment. This alternative and more preventative approach - earlier the predominant way of handling urban planning, construction and development (i.e. the production and utilisation of both existing and planned for resources, e.g. by the use of high quality production technologies and crafts, processes and skills), was historically much based on the valorisation of costs of manpower, materials, traditional knowledge, techniques and low-energy modes of transportation, compared to modern circumstances. There was also a profound knowledge of economics in more general terms and a well-developed forecasting of future scenarios. Given the demands for a sustained future, it would be reasonable to assume that this knowledge and approach would have a great deal to offer also to the planning and epistemological modelling of our times.
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| 10. |
- Johansson, Erika, 1969, et al.
(författare)
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Towards Sustainable Conservation and Use of Materials in Built Environments
- 2007
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Ingår i: Giljum, S., Hinterberger, F., Hammer, M. (Eds.), Report from the FORSCENE workshop Industry-Environment, Sustainable Europe Research Institute (SERI), Vienna, October 2006, Part 2..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Up until today, no comprehensive efforts have been made, and principles are yet to be established for the ‘sustainable conservation’ of the built environment – in an inter- and transdisciplinary manner, including systematic integrative modelling and an appreciation of the inherent values of already existing structures and ambiences. Existing built structures and environments are still often seen as obstacles for sustainable development. It may be argued that a more preventive and integrated approach, i.e. an early estimation and a meta-level understanding of the built environment and its processes; its critical loads, inherent qualities, values, threats, life cycles, production chains, recyclability and quantities etc., would rather promote any kind of planning for a sustained future and the proper use of materials by hindering unnecessary material flows - i.e. through their unnecessary/unsympathetic production, exploitation and/or use, that would minimise their negative impact on peoples lives and the environment. This alternative and more preventative approach - earlier the predominant way of handling urban planning, construction and development (i.e. the production and utilisation of both existing and planned for resources, e.g. by the use of high quality production technologies and crafts, processes and skills), was historically much based on the valorisation of costs of manpower, materials, traditional knowledge, techniques and low-energy modes of transportation, compared to modern circumstances. There was also a profound knowledge of economics in more general terms and a well-developed forecasting of future scenarios. Given the demands for a sustained future, it would be reasonable to assume that this knowledge and approach would have a great deal to offer also to the planning and epistemological modelling of our times.
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