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  • 1.
    Altorkmany, Lobna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Kharseh, Mohamad
    Civil Environmental Engineering Department, Chalmers University of Technology, Sweden.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effect of Working Parameters of the Plate Heat Exchanger on the Thermal Performance of the Anti-Bact Heat Exchanger System to Disinfect Legionella in Hot Water Systems2018In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 141, p. 435-443Article in journal (Refereed)
    Abstract [en]

    The objective of the current study is to analyze the effect of different working parameters on the thermal performance of the Anti-Bact Heat Exchanger system (ABHE). The ABHE system is inspired by nature and implemented to achieve continuous disinfection of Legionella in different human-made water systems at any desired disinfection temperature. In the ABHE system, most of the energy is recovered using an efficient plate heat exchanger (PHE). A model by Engineering Equation Solver (EES) is set-up to figure out the effect of different working parameters on the thermal performance of the ABHE system. The study shows that higher supplied water temperature can enhance the regeneration ratio (RR), but it requires a large PHE area and pumping power (PP) which consequently increase the cost of the ABHE system. However, elevate temperature in use results in a reduced PHE area and PP, which accordingly reduce the cost of the ABHE system. On the other hand, the EES-based model is used to study the effect of the length and the width of the plates used in the PHE on the RR and the required area of the PHE. Finally, taking into account the geometrical parameters, flow arrangement and the initial operating conditions of the PHE, the EES-based model is used to optimize the PHE in which its area is minimized, and the RR of the ABHE system is maximized.

  • 2.
    Altorkmany, Lobna
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Kharseh, Mohamad
    Civil Environmental Engineering Department, Chalmers University of Technology.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental and Simulation Validation of ABHE for Disinfection of Legionella in Hot Water Systems2017In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 116, p. 253-265Article in journal (Refereed)
    Abstract [en]

    The work refers to an innovative system inspired by nature that mimics the thermoregulation system that exists in animals. This method, which is called Anti Bacteria Heat Exchanger (ABHE), is proposed to achieve continuous thermal disinfection of bacteria in hot water systems with high energy efficiency. In particular, this study aims to demonstrate the opportunity to gain energy by means of recovering heat over a plate heat exchanger. Firstly, the thermodynamics of the ABHE is clarified to define the ABHE specification. Secondly, a first prototype of an ABHE is built with a specific configuration based on simplicity regarding design and construction. Thirdly, an experimental test is carried out. Finally, a computer model is built to simulate the ABHE system and the experimental data is used to validate the model. The experimental results indicate that the performance of the ABHE system is strongly dependent on the flow rate, while the supplied temperature has less effect. Experimental and simulation data show a large potential for saving energy of this thermal disinfection method by recovering heat. To exemplify, when supplying water at a flow rate of 5 kg/min and at a temperature of 50 °C, the heat recovery is about 1.5 kW while the required pumping power is 1 W. This means that the pressure drop is very small compared to the energy recovered and consequently high saving in total cost is promising.

  • 3.
    Burström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Liepaja University .
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, B. Daniel
    LKAB, Kiruna.
    Modelling heat transfer during flow through a random packed bed of spheres2018In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 54, no 4, p. 1225-1245Article in journal (Refereed)
    Abstract [en]

    Heat transfer in a random packed bed of monosized iron ore pellets is modelled with both a discrete three-dimensional system of spheres and a continuous Computational Fluid Dynamics (CFD) model. Results show a good agreement between the two models for average values over a cross section of the bed for an even temperature profiles at the inlet. The advantage with the discrete model is that it captures local effects such as decreased heat transfer in sections with low speed. The disadvantage is that it is computationally heavy for larger systems of pellets. If averaged values are sufficient, the CFD model is an attractive alternative that is easy to couple to the physics up- and downstream the packed bed. The good agreement between the discrete and continuous model furthermore indicates that the discrete model may be used also on non-Stokian flow in the transitional region between laminar and turbulent flow, as turbulent effects show little influence of the overall heat transfer rates in the continuous model.

  • 4.
    Burström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    LKAB.
    Discrete and continuous modelling of convective heat transport in a thin porous layer of mono sized spheres2017In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 1, p. 151-160Article in journal (Refereed)
    Abstract [en]

    Convective heat transport in a relatively thin porous layer of monosized particles is here modeled. The size of the particles is only one order of magnitude smaller than the thickness of the layer. Both a discrete three-dimensional system of particles and a continuous one-dimensional model are considered. The methodology applied for the discrete system is Voronoi discretization with minimization of dissipation rate of energy. The discrete and continuous model compares well for low velocities for the studied uniform inlet boundary conditions. When increasing the speed or for a thin porous layer however, the continuous model diverge from the discrete approach if a constant dispersion is used in the continuous approach. The new result is thus that a special correlation must be used when using a continuous model for flow perpendicular to a thin porous media in order to predict the dispersion in proper manner, especially in combination with higher velocities.

  • 5.
    Burström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Liepaja University.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    LKAB Research and Development.
    Grate aerodynamic: Model strategies for gas flow through a 2D iron ore pellet bed2014Conference paper (Refereed)
  • 6. Eriksson, Martin
    et al.
    Lucchese, Riccardo
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Gustafsson, Jonas
    RISE - Swedish Institute of Computer Science.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mousavi, Arash
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Monitoring and Modelling Open Compute Servers2017In: Proceedings IECON 2017: 43rd Annual Conference of the IEEE Industrial Electronics Society, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 7177-7184Conference paper (Refereed)
    Abstract [en]

    Energy efficient control of server rooms in modern data centers can help reducing the energy usage of this fast growing industry. Efficient control, however, cannot be achieved without: i) continuously monitoring in real-time the behavior of the basic thermal nodes within these infrastructures, i.e., the servers; ii) analyzing the acquired data to model the thermal dynamics within the data center. Accurate data and accurate models are indeed instrumental for implementing efficient data centers cooling strategies. In this paper we focus on a class of Open Compute Servers, designed in an open-source fashion and currently deployed by Facebook. We thus propose a set of methods for collecting real-time data from these platforms and a control-oriented model describing the thermal dynamics of the CPUs and RAMs of these servers as a function of both manipulable and exogenous inputs (e.g., the CPU utilization levels and the air mass flow produced by the server's fans). We identify the parameters of this model from real data and make the results available to other researchers.

  • 7. Hellström, J. Gunnar I.
    et al.
    Ljung, Anna-Lena
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Flow through a hexagonal array of perturbed spheres at low to high Reynolds number2007In: Abstracts of the Second International Conference on Porous Media and its Applications in Science, Engineering and Industry, Engineering Conferences International , 2007Conference paper (Refereed)
    Abstract [en]

    When performing numerical simulations of fluid flow through porous media it is necessary to know when to switch from a creeping flow formulation to a more elaborate laminar description. In the creeping flow regime the Darcy law is sufficient while when inertia-effects become significant it is necessarily to use the full Navier-Stokes equations or at least add a non-linear term to Darcy's law as done in the empirically derived Ergun equation. The latter equation has also turned out to be valid for turbulent flows. It is however not obvious which equation to use at a certain Reynolds number. In order to solve this problem Computational Fluid Dynamics is used to derive the apparent permeability of a hexagonal packed array of spheres. In addition the forces acting on the spheres are derived when a perturbation in the form of a spherically shaped particle is introduced in the pore space. Then simulations are performed at various Reynolds number ranging from the creeping flow region to moderate Reynolds number flows. The simulations are carried out with the commercially available software, ANSYS CFX 11.0, with a particular effort on grid refinement and numerical iteration in order to secure that the errors are sufficiently small. One result is that inertia effects become important already at Reynolds number about 5 for as well the array as the perturbed geometry. As the particle radius increases the shear and normal forces per unit area decreases. In general, these forces increase with Reynolds number. The simulations however show that for some cases the normal forces per unit area decreases and even change sign as Reynolds number increases.

  • 8.
    Hellström, J. Gunnar I.
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Lundström, Staffan
    Forces on grains located in model geometry with application to internal erosion in embankment dams2007In: International Symposium on Modern Technology of Dams: The 4th EADC Symposium, 2007, p. 375-386Conference paper (Refereed)
    Abstract [en]

    For a comprehensive understanding of internal erosion in embankment dams it is necessary to elucidate the detailed seepage flow. A neat tool that can be used for this purpose is Computational Fluid Dynamics. With such a tool forces on individual particles can be derived and means to decide when to switch from a creeping flow formulation to a more elaborate laminar description for macroscopic flow simulations can be derived. It can even be decided when the transition from a laminar formulation to a fully turbulent description should take place. In the creeping flow regime a Darcy law formulation is sufficient while when inertia-effects become significant it is necessary to use the Navier-Stokes equations or at least add a non-linear term to Darcy's law as done in the empirically derived Ergun equation. It is, however, not obvious which equation to use at a certain Reynolds number. Hence, Computational Fluid Dynamics is here used to derive the apparent permeability of a hexagonal packed array of spheres. Then, grains are introduced in the pore space between the spheres and forces acting on the grains are derived. It will then be possible to decide at what conditions such particles will start to move, due to flow induced forces, and thereby initiating internal erosion. The simulations are performed at various Reynolds number ranging from the creeping flow region to the transition regime. The software ANSYS CFX 11.0 is applied with particular effort on grid refinement and numerical iteration in order to secure that the numerical errors are sufficiently small. One result is that inertia-effects become important already at a Reynolds number of 10. Another is that the forces acting on the grains can decrease as a function of Reynolds number and can as well be dependent on the geometry of the grains, even though the force per unit area on the array of spheres increases. Interestingly, the direction of the forces on the grains can even be opposite to the main flow direction.

  • 9. Högberg, Sofie
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Velaga, Sitaram
    Luleå University of Technology, Department of Health Sciences, Medical Science.
    Ljung, Anna-Lena
    Fluid mechanics of particle deposition in human lungs2005In: Contributed paper abstracts / American Association of Pharmaceutical Scientists: annual meeting and exposition, 2005Conference paper (Other academic)
    Abstract [en]

    Aim: To develop an ideal Computational Fluid Dynamic (CFD) model, which provides knowledge of fundamental characteristics of particles and their eventual deposition patterns in the respiratory system, to design an effective formulation for a specific therapeutic application (local or systemic) Methods: The whole flow field was measured in a single measurement using Particle Image Velocimetry (PIV). The concept was to add small sized particles to the flow. These particles were then illuminated by a thin laser-layer in the region of interest and the motion of the formed speckle pattern was captured by a CCD-camera. Results: In a preliminary study, the flow in the uppermost three generations of airways, with a focus on branches of rectangular cross-sections, has been investigated. This geometry was easily built from blocks of PMMA. The model captured the main flow features. A qualitative agreement between experiments and simulations was obtained as shown in Figure 1, a snap-shot taken during inhalation. The experiments further enable a more detailed study of the quality and trust of the simulations. The result of this is then applied on a more realistic model of the uppermost airways and the particle deposition simulated (Figure 2). Fig 1 Fig 2 Figure 1: PIV-measurements showing the velocity field, the upper CFD-graph is obtained for a k-? turbulent flow and the lower graph shows the field for a laminar; Figure 2: Virtual model of the upper part of the air-ways. Please notice that the grid was refined for the initial simulations Conclusions: Preliminary studies were initiated with an ultimate aim of developing a complete lung model. Our efforts so far yielded a good understanding of experimental and numerical visualisation of the flow in the uppermost airways and we are currently engaged in quantifying the results.

  • 10.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The impact of a fixed contact angle on a freezing water droplet2015Conference paper (Refereed)
  • 11.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The influence of a fixed contact angle on a freezing water droplet2015Conference paper (Refereed)
  • 12.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of internal natural convection on water droplets freezing on cold surfaces2014Conference paper (Refereed)
  • 13.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of internal natural convection on water droplets freezing on cold surfaces2014Conference paper (Refereed)
  • 14.
    Karlsson, Linn
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modelling the dynamics of the flow within freezing water droplets2018In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181Article in journal (Refereed)
    Abstract [en]

    The flow within freezing water droplets is here numerically modelled assuming fixed shape throughout freezing. Three droplets are studied with equal volume but different contact angles and two cases are considered, one including internal natural convection and one where it is excluded, i.e. a case where the effects of density differences is not considered. The shape of the freezing front is similar to experimental observations in the literature and the freezing time is well predicted for colder substrate temperatures. The latter is found to be clearly dependent on the plate temperature and contact angle. Including density differences has only a minor influence on the freezing time, but it has a considerable effect on the dynamics of the internal flow. To exemplify, in the vicinity of the density maximum for water (4 C) the velocities are about 100 times higher when internal natural convection is considered for as compared to when it is not.

  • 15. Kluge, Jimmy
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Nyman, Tony
    Saab Aeronautics, SE-582 54 Linköping, SWEDEN.
    An Experimental Study of Temperature Distribution in an Autoclave2016In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 35, no 7, p. 566-578Article in journal (Refereed)
    Abstract [en]

    In this work, the temperature distribution on an industrial mold tool is monitored during autoclave runs with three settings. In one of the settings, the temperature and pressure follow a scheme used in real moldings, while in the other two cases, the temperature is increased as fast as possible with and without an applied pressure. The temperature difference over the tool is relatively large and varies between 29℃ and 76℃ validating a detailed investigation of the temperature at different points. Two results of this are that positions on the up-stream side of the tool are heated faster than positions down-stream and the heating over the tool is symmetric while that within is asymmetric. Roughly estimated heat transfer coefficients reveal that the temperature ramping has no significant effect on the local heat transfer coefficients while the applied pressure more than doubled them. In addition flow field measurements with particle image velocimetry are performed, revealing a very slow flow near the roof of the autoclave and a velocity peak near the floor of it, indicating that the flow profile within the autoclave and variation in heat transfer coefficients should be considered in autoclave simulations.

  • 16.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Drying of iron ore pellets: analysis with CFD2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Iron ore pellets are a highly refined product and for companies such as LKAB it is important to constantly improve the pelletization in order to enhance production and improve product quality. A long term goal has been established to develop and considerably refine tools and techniques with which the drying zone of a pelletizing plant can be optimized. The aim with this research project is to numerically investigate how material and processing parameters influence the drying. This will be applied to several scales: i) The constituents of the pellets and their properties and geometry. ii) The geometry of the pellet, their permeability and size distribution. iii) The geometry of the bed and the processing conditions including the state of the air (ex. humidity, temperature and velocity). To start with, a pellet bed model of velocity and temperature distribution in the up-draught drying zone without regard to moisture transport is developed with aid of Computational Fluid Dynamics (CFD). Results from simulations show a rapid cooling of air due to the high specific surface area in the porous material. Following this work, heat and mass transport within a single pellet during drying is modeled. Heat transfer and convective transport of water and air through the capillaries of the porous media is computed and vaporization by boiling is taken into account. A sensitivity analysis shows that it is important to use a realistic value of the convective heat transfer coefficient when the vaporization of water is a dominating drying mechanism while the temperature of the solid and capillary movement of water is not influenced to the same extent. The derived model is applicable to a number of numerical set up such as a single pellet placed in infinite space. To further develop a single pellet model, forced convective heating of a porous media with surrounding flow field taken into account must first be examined. Therefore, a two dimensional model with properties similar to that of an iron ore pellet is numerically investigated. With interface heat transfer condition provided by CFD, the heat transfer and fluid flow around and within a porous cylinder is examined. The results lay foundation of future development of a single pellet drying model where heat and mass transfer models are combined and coupled to the surrounding flow field.

  • 17.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modeling drying of iron ore pellets2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Iron ore pellets are a highly refined product supplied to the steel making industry for use in blast furnaces or direct reduction processes. The use of pellets offers many advantages such as customer adopted products, transportability and mechanical strength yet the production is time and energy consuming. Being such, there is a natural driving force to enhance the pelletization in order to optimize production and improve quality. The aim with this thesis is to develop numerical models with which the drying zone of an induration furnace can be examined and optimized. To start with, a continuous model of velocity and temperature distribution in the up-draught drying zone, without regard to moisture transport, is developed with aid of Computational Fluid Dynamics (CFD). The results show a rapid cooling of air due to the high specific surface area in the porous material. With the global model an overall understanding of heat transfer is gained, but the heat and moisture transport should also be investigated on a smaller scale in order to account for small scale phenomena such as turbulence and dispersion. Drying of a bed of iron ore pellets is therefore considered by modeling a two-dimensional discrete system of round pellets. The system is divided by modified Voronoi diagrams and the convective heat transfer of hot fluid flow through the system including dispersion due to random configuration of the pellets is modeled. The results show that the temperature front advances much faster in the gaps between pellets than in the interior of the pellets even if all the heat energy of the air goes in heating of the pellets initially. Decrease of temperature is possible for low dew points of the input air due to evaporation. If the dew point temperature is higher than the temperature of the pellets on the other hand, there is slight condensation of the steam at the beginning of the process and the temperature increases faster than it would for pure thermal heating. An uneven distribution in temperature and moisture content between pellets is furthermore displayed in the discrete system. This phenomenon is related to the natural dispersion occurring in random system of pellets.To further investigate drying of individual pellets, forced convective heating of a cylindrical porous pellet with surrounding flow field taken into account is first examined. A model with properties similar to that of an iron ore pellet is numerically investigated and with interface heat transfer condition provided by CFD, the simulations show an increased heating rate for the porous cylinder when compared to a solid. The most plausible explanation to this is that there is less solid to heat up for the porous medium since the porous cylinder behaves as if it was impermeable from a fluid flow point of view. With diffusive liquid transport inside the two-dimensional pellet and corresponding evaporation at the surface, simulations of drying show an initial warm up phase with a succeeding constant rate drying phase. Constant drying rate will only be achieved if the surface temperature is constant, i.e. if it has reached the wet bulb temperature. The falling rate period will subsequently start at the forward stagnation point when the local moisture content approaches zero, while other parts of the surface still provide enough moisture to allow surface evaporation. The phases will thus coexist for a period of time. Experiments are carried out in order to examine the drying behavior of a single iron ore pellet with main goal to retrieve data for validation of the computational drying models. The experiments are performed with two inlet temperatures and one pellet from the experiments is scanned by an optical scanning equipment. In order to investigate the influence of surface irregularities and overall geometry on drying, simulations of the first drying period are compared for: 1) a scanned pellet 2) an oval pellet resembling the experimental one with equivalent volume 3) a spherical pellet with equivalent volume. The results show that the local moisture content at the surface is influenced by both surface irregularities and overall geometry. A smooth surface will decrease the local variation of moisture while a spherical geometry will, compared to an oval, increase the difference. A diffusive model taking into account capillary flow of liquid moisture and internal evaporation is developed to account for the whole drying process and simulations of the scanned pellet are validated with good agreement. The result clearly shows four stages of drying; i) evaporation of liquid moisture at the pellet surface, ii) surface evaporation coexisting with internal drying as the surface is locally dry, iii) internal evaporation with completely dry surface and iv) internal evaporation at boiling temperatures. A moisture front moving towards the core of the pellet will start to develop at the second drying stage and the results show that the front will have a non-symmetrical form arising from the surrounding fluid flow. With the developed drying model, simulations are then carried out on a spherical pellet with aim to investigate how the inlet air humidity affects drying. The results indicates that the effect of air dew point arise from the start of the first drying period, i.e the surface evaporation period, while the difference is reduced at the end of the period due to a prolonged stage of constant rate drying attained at high dew points. The wet-bulb temperature is increased with humidity and condensation will occur if the pellet surface temperature is below the dew point. Furthermore it is found that the moisture gradients at the surface and inside the pellet are increased with drying rate.

  • 18.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    铁矿石颗粒干燥数值模型2013In: Drying Technology & Equipment, ISSN 1727-3080, Vol. 11, no 3, p. 57-59Article in journal (Refereed)
  • 19.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Robin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Andersson, Anders G.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Eriksson, Mats
    Relitor Engineering AB.
    Modelling the Evaporation Rate in an Impingement Jet Dryer with Multiple Nozzles2017In: International Journal of Chemical Engineering, ISSN 1687-806X, E-ISSN 1687-8078, Vol. 2017, article id 5784627Article in journal (Refereed)
    Abstract [en]

    Impinging jets are often used in industry to dry, cool, or heat items. In this work, a two-dimensional Computational Fluid Dynamics model is created to model an impingement jet dryer with a total of 9 pairs of nozzles that dries sheets of metal. Different methods to model the evaporation rate are studied, as well as the influence of recirculating the outlet air. For the studied conditions, the simulations show that the difference in evaporation rate between single- and two-component treatment of moist air is only around 5%, hence indicating that drying can be predicted with a simplified model where vapor is included as a nonreacting scalar. Furthermore, the humidity of the inlet air, as determined from the degree of recirculating outlet air, has a strong effect on the water evaporation rate. Results show that the metal sheet is dry at the exit if 85% of the air is recirculated, while approximately only 60% of the water has evaporated at a recirculation of 92,5%

  • 20.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Endimensionell bäddmodell för simulering av torkning av järnmalmspellets2011Conference paper (Refereed)
    Abstract [sv]

    Järnmalmspellets är en högt förädlad produkt utvecklad av gruvindustrin för användning iexempelvis masugnar. För ett bandugnsverk sker pelletsprocessen huvudsakligen i fyra steg då en kontinuerlig bädd av pellets transporteras på rosterband genom torkzon, förvärmningzon,brännzon och kylzon. Genomströmmande luft används för att torka, sintra och kyla materialet ide olika zonerna. Då produktionen av järnmalmspellets är tids- och energikrävande finns deten naturlig drivkraft att förbättra processen så att produktionen kan optimeras medbibehållen produktkvalitet.För att i detalj studera torkzonen har en modell för konvektiv torkning av en enskildpellet tidigare tagits fram. Resultat från simuleringarna visar tydligt fyra torkningsfaser; i)förångning av vätska från pelletens yta, ii) förångning av vätska vid ytan samtidigt som vissinre förångning sker då ytan lokalt är torr, iii) torkning enbart på grund av inre förångningoch iv) kokning av vatten inuti pelleten [1]. Den framtagna torkningsmodellen har ävenapplicerats på en sfärisk geometri med syfte att undersöka hur fukthalten i inloppsluftenpåverkar torkningen [2]. Simuleringar visar att effekten av luftfuktighet främst uppkommeri början av den första torkningsfasen medan skillnaderna minskar i slutet av perioden då ettförlängt stadie av konstant torkhastighet fås vid höga luftfuktigheter.Ovanstående resultat visar att det är av stort intresse att även undersöka hur pellets i enpelletbädd påverkas av omgivande lufttemperatur och luftfuktighet. En endimensionellbäddmodell har därför utvecklats som ett komplement till enkulemodellen för attundersöka hur våttemperatur, pellettemperatur, torkhastighet etc. varierar som funktion avbäddhöjd i den första torkningsfasen. I modellen beräknas förångning från pelletsens ytamed motsvarande fukttransport genom den porösa bädden och det är därmed möjligt attutreda vilka områden i bädden som påverkas av eventuell återkondensation.

  • 21.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Frishfelds, Vilnis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    Discrete and continuous modelling of heat and mass transport in drying of a bed of iron ore pellets2012In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 30, no 7, p. 760-773Article in journal (Refereed)
    Abstract [en]

    Drying of a porous bed of iron ore pellets is here considered by modeling a discrete two-dimensional system of round pellets. As a complement to the two-dimensional model, a continuous one-dimensional model enabling fast calculations is developed. Results from the discrete model show that the temperature front advances faster in areas with large distances between the pellets. In areas with low flow speed, the temperature of the pellets increases with a relatively slow rate. The water inside these pellets will therefore remain for a long time. The continuous model fits the discrete model very well for a regular distribution of equal-sized particles. A discrete model with irregular packing will, compared to the continuous model, show a larger variation in the distribution of temperature and moisture content in the final phase of drying.

  • 22.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lindmark, Elianne M.
    AB Electrolux.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of plate size on the evaporation rate of a heated droplet2015In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 33, no 15-16, p. 1963-1970Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to numerically investigate how the width of a plate influences natural convection around a droplet. Droplets evaporating on hot surfaces has many applications including drying of dishes and paint. Evaporation rate and deposition of particles withheld in the fluid is of great importance in both cases. As a first step to investigate how the drying rate and deposition mechanisms can be controlled, this work aims to investigate how the external flow around a water droplet influences the evaporation rate. Natural convection caused by the hot plate on which the droplet rests is considered and the effect of different widths is examined. Results show that an extension of the plate past the droplet will increase the maximum velocity in the domain due to natural convection while the flow close to the surface is decreased due to the no slip condition and temperature gradient. A decrease of the evaporation rate is therefore observed when the plate is extended past the droplet as compared to the case when the plate and droplet have the same diameter. Simulations furthermore show that the results from the heat and mass transfer analogy only compare well to the results of Fick's law when the droplet and plate has the same width.

  • 23.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lindmark, Elianne M.
    AB Electrolux.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of plate size on the evaporation rate of a heated droplet2014Conference paper (Refereed)
    Abstract [en]

    Droplets evaporating on hot surfaces has many applications including drying of dishes and paint. Evaporation rate and deposition of particles withheld in the fluid is of great importance in both cases. As a first step to investigate how the drying rate and deposition mechanisms can be controlled, this work aims to investigate how the external flow around a droplet influences the evaporation rate. Natural convection of the surrounding fluid caused by heated plates of different widths is considered and the effect of the heat and mass transfer mechanisms on the evaporation rate is investigated.

  • 24.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Heat and mass transfer boundary conditions at the surface of a heated sessile droplet2017In: Heat and Mass Transfer, ISSN 0947-7411, E-ISSN 1432-1181, Vol. 53, no 12, p. 3581-3591Article in journal (Refereed)
    Abstract [en]

    This work numerically investigates how the boundary conditions of a heated sessile water droplet should be defined in order to include effects of both ambient and internal flow. Significance of water vapor, Marangoni convection, separate simulations of the external and internal flow, and influence of contact angle throughout drying is studied. The quasi-steady simulations are carried out with Computational Fluid Dynamics and conduction, natural convection and Marangoni convection are accounted for inside the droplet. For the studied conditions, a noticeable effect of buoyancy due to evaporation is observed. Hence, the inclusion of moisture increases the maximum velocities in the external flow. Marangoni convection will, in its turn, increase the velocity within the droplet with up to three orders of magnitude. Results furthermore show that the internal and ambient flow can be simulated separately for the conditions studied, and the accuracy is improved if the internal temperature gradient is low, e.g. if Marangoni convection is present. Simultaneous simulations of the domains are however preferred at high plate temperatures if both internal and external flows are dominated by buoyancy and natural convection. The importance of a spatially resolved heat and mass transfer boundary condition is, in its turn, increased if the internal velocity is small or if there is a large variation of the transfer coefficients at the surface. Finally, the results indicate that when the internal convective heat transport is small, a rather constant evaporation rate may be obtained throughout the drying at certain conditions.

  • 25. Ljung, Anna-Lena
    et al.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Strömningsmekaniken för torkning av järnmalmspellets2007In: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, p. 80-Conference paper (Other academic)
  • 26.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Sjöström, Ulf
    Swerea MEFOS AB.
    Marjavaara, Daniel
    LKAB.
    Lindblom, Bo
    LKAB.
    Tano, Kent
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Drying of an iron ore pellet: investigation of the influence of surface irregularities and overall geometry2010In: Proceedings of the 3rd International Conference on Porous Media and its Applications in Science and Engineering, ICPM3, 2010Conference paper (Refereed)
    Abstract [en]

    In this paper, simulations of the first drying period of a single iron ore pellet are compared for: i) a scanned pellet from experiments ii) an oval pellet resembling the experimental one with equivalent volume iii) a spherical pellet with equivalent volume. The comparison provides information on how simplifications of an actual geometry might affect the result. The simulations are carried out with the commercial software ANSYS CFX 12.0 and the model is validated against experimental results with good agreement. The results show that the local moisture content at the surface is influenced by both surface irregularities and overall geometry. A smooth surface will decrease the local variation of moisture while a spherical geometry will, compared to an oval, increase the difference.

  • 27.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan T.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Evaporation of a sessile water droplet subjected to forced convection in humid environment2018In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300Article in journal (Refereed)
    Abstract [en]

    The evaporation of a sessile droplet is here investigated numerically with a design of experiment approach. Boundary conditions are chosen based on forced convection in humid air, i.e., mimicking the conditions inside a dishwasher. Computational fluid dynamic simulations of an axisymmetrical droplet placed on a heated plate show that relative humidity, initial contact angle, plate temperature, and temperature difference between plate and air all have significant effect on the initial evaporation rate. For the studied conditions, relative humidity is the most significant factor while the magnitude of the velocity and type of internal flow are insignificant within a 95% confidence interval.

  • 28.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Tano, Kent
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Enkulemodell för torkning av järnmalmspellets2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 104-Conference paper (Other academic)
  • 29.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Tano, Kent
    Fluid flow and heat transfer within and around a porous iron ore pellet placed in infinite space2008In: Proceedings of the 19th International Symposium on Transport Phenomena (ISTP-19): Reykjavik, Iceland, August 17-21, 2008 / [ed] Sigurdur Brynjolfsson; Olafur Petur Palsson; Jong H. Kim, University of Iceland, Faculty of Industrial Engineering, Mechanical Engineering and Computer Science , 2008Conference paper (Refereed)
    Abstract [en]

    The forced convective heating of a porous cylinder with properties similar to an iron ore pellet is here numerically investigated. The numerical setup is based on a two dimensional microporous model with surrounding flow field taken into account. The simulations are carried out with special attention directed towards minimizing numerical errors. With interface conditions provided by CFD, simulations show an increased heat transfer rate for the porous cylinder when compared to a solid.

  • 30.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Tano, Kent
    LKAB.
    Heat and mass transfer in a single iron ore pellet during drying2009In: Proceedings of 4th ICAPM: August 10-12, 2009, Istanbul, Turkey, 2009Conference paper (Refereed)
  • 31.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Tano, Kent
    Heat, mass and momentum transfer within an iron ore pellet during drying2008In: Proceedings of CHT-08 ICHMT International Symposium on Advances in Computational Heat Transfer, International Centre for Heat and Mass Transfer , 2008Conference paper (Refereed)
    Abstract [en]

    Iron ore pellets is one of the most refined products for mining industry. Being such, there is a natural driving force to enhance the pelletization in order to optimize production and improve quality especially since the process is time and energy consuming. In order to be successful it is of highest importance that the pelletization process is known in detail. Following this demand, heat and mass transport within a single pellet during drying is modeled with aid of Computational Fluid Dynamics. A two dimensional rectangular domain is chosen to represent the porous media within the pellet and the governing equations are set up for one directional flow through it. Convective transport of water and air through the capillaries of the porous media is computed from Darcy's law being adapted to a two-fluid system. Vaporization by boiling is taken into account and two energy equations are used to calculate the temperature distribution, one for the liquid and solid, and one for the gas. To start with, iteration errors and discretization errors are found to be negligible. Following this a sensitivity analysis shows that it is important to use a realistic value of the convective heat transfer coefficient when the vaporization of water is the dominating drying mechanism while the temperature of the solid and capillary movement of water is not influenced to the same extent. The derived model can be applied to a number of numerical set-ups such as a single pellet in an infinite space.

  • 32.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Tano, Kent
    Simulation of convective drying of a cylindrical iron ore pellet2011In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 21, no 6, p. 703-716Article in journal (Refereed)
    Abstract [en]

    Purpose – The purpose of this paper is to numerically model convective drying of a two-dimensional iron ore pellet subjected to turbulent flow.Design/methodology/approach – Simulations of the iron ore pellet drying process are carried out with commercial computational fluid dynamics software. The moisture distribution inside the pellet is calculated from a diffusion equation and drying due to evaporation at the surface is taken into account.Findings – The results show an initial warm up phase with a succeeding constant rate drying period. Constant drying rate will only be achieved if the surface temperature is constant. The falling rate period will subsequently start at the forward stagnation point when the minimum moisture content is reached, while other parts of the surface still provide enough moisture to allow surface evaporation. The phases will thus coexist for a period of time.Research limitations/implications – Owing to the complex physical processes involved in iron ore pellet drying, some parameters in the model are based on estimations. The effective diffusivity should, for example, in the future be investigated more thoroughly. It is also important to extend the model so that the falling rate drying period is also included. The model is at present undergoing further validation.Practical implications – The simulations can provide detailed information on some key fluid dynamics and physical processes that an iron ore pellet undergoes during drying.Originality/value – The simulations enhance the understanding of iron ore pellet drying and the model provides a complement to experimental investigations when optimizing the drying process.

  • 33.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Tano, Kent
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Simulation of heat transfer and fluid flow in a porous bed of iron ore pellets during up-draught drying2006In: Proceedings of the Fifth International Conference on CFD in the Process Industries: Hilton on the Park, Melbourne, Australia, 13-15 December 2006 / [ed] P.J. Witt, Melbourn: CSIRO Publishing, 2006Conference paper (Refereed)
    Abstract [en]

    Iron ore pellets is one of the most refined products for companies such as LKAB and it is therefore a global need for research in the area in order to optimize the production and improve quality. This work aim at modelling and optimizing the drying zone of a travelling grate pelletizing plant and to start with, a model of velocity and temperature distribution in the up-draught drying zone is developed with aid of computational fluid dynamics. The velocity distribution in the porous bed is described by laws of fluid dynamics in porous media. The dominating heat transfer mechanism is convection and two energy equations are required since the porous media region contains both fluid and solid. Result from simulations show a rapid cooling of air due to the high specific surface area in the porous material. Conclusions are that it is possible to simulate convective heat transfer within a porous media in ANSYS CFX 10.0. There are however some limitations when using the diffusive transport equation as the solid phase energy equation that need further investigation. Moisture content and condensation in the bed are not included in the present model and is therefore subject to future work

  • 34.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Influence of sample temperature on drying of individual porous spheres2011Conference paper (Refereed)
    Abstract [en]

    Heat and mass transport within a porous sphere during drying is here modeled and simulations of the surface evaporation period are carried out with aim to investigate the influence of the initial temperature on the drying time. A three dimensional spherical domain is formed and governing equations are set up for the flow past it. The local heat and mass transfer at the surface is determined from simulations of the surrounding fluid flow with aid of Computational Fluid Dynamics. For the studied conditions, the results show that increasing the initial temperature will decrease the drying time in a rather linear manner. There is also a distinct reduction in drying time if the humidity of the surrounding air is lowered. Increasing the initial temperature could thus be an effective way to reduce problems due to condensation and to decrease the drying time.

  • 35.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Modeling evaporation of droplets on a heated plate2014Conference paper (Refereed)
  • 36.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Numerical study of the heat and mass transfer conditions at the surface of a heated droplet2014Conference paper (Refereed)
    Abstract [en]

    This work aims to numerically investigate how the heat and mass transfer boundary conditions at a droplet surface should be presented in order to fully represent the surrounding fluid flow. With aid of Computational Fluid Dynamics, a numerical study is carried out to investigate the validity of the heat and mass transfer analogy at the droplet surface. Natural convection in the air surrounding the droplet, arising from the heated surface below the droplet, is considered. The heat and mass transfer analogy needs to be deliberated when the evaporation is dominated by density differences rather than temperature differences and the numerical results show this transition in detail.

  • 37.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    The flow field within a droplet located on a flat heated surface -Influence of the heat transfer boundary conditions2013Conference paper (Other academic)
    Abstract [en]

    Evaporation of droplets on heated surfaces is important in a number of applications including the drying of paint and cooling of electronics. Questions are addressed both towards increasing the drying rate as well as on how to control the deposition of particles suspended in the fluid. This work aims to numerically investigate how the heat and mass transfer boundary condition at the droplet surface should be presented in order to fully represent the surrounding fluid flow. With aid of Computational Fluid Dynamics, a numerical study is therefore carried out to determine the general consequence of using a local heat transfer coefficient and how it affects the separate mechanisms of the internal flow in particular. Results show that the application of a local heat transfer boundary condition is important only if the internal velocity of the fluid inside the droplet is small. If the surface tension is high, i.e. if the flow is dominated by Marangoni convection, the surface temperature is instead controlled by the internal mixing rather than the local heat transfer. For the conditions studied, Marangoni convection is dominating and will enhance the drying rate when compared to the influence of conduction and natural convection.

  • 38.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Marjavaara, Daniel
    LKAB.
    Tano, Kent
    LKAB.
    Convective drying of an individual iron ore pellet: Analysis with CFD2011In: International Journal of Heat and Mass Transfer, ISSN 0017-9310, E-ISSN 1879-2189, Vol. 54, no 17-18, p. 3882-3890Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to model convective drying of an individual iron ore pellet placed in a free stream of air with the aim to clarify the different stages of drying. A numerical model taking into account capillary flow of liquid moisture and internal vapor flow is developed and implemented in a commercial available software for Computational Fluid Dynamics where also the flow around the pellet is simulated, yielding heat- and mass transfer coefficients as a function of position. A real pellet is optically scanned for its geometry and simulations of the drying are compared to experiments with very good agreement. The result clearly shows four stages of drying; (i) evaporation of liquid moisture at the pellet surface, (ii) surface evaporation coexisting with internal drying as the surface is locally dry, (iii) internal evaporation with completely dry surface and (iv) internal evaporation at boiling temperatures. A moisture front moving towards the core of the pellet will start to develop at the second drying stage and the results show that the front will have a non-symmetrical form arising from the surrounding fluid flow.

  • 39.
    Ljung, Anna-Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Marjavaara, Daniel
    LKAB.
    Tano, Kent
    Influence of air humidity on drying of individual iron ore pellets2011In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 29, no 9, p. 1101-1111Article in journal (Refereed)
    Abstract [en]

    The influence of air humidity on drying is investigated at four inlet air dew points; T dp = 273, 292, 313, and 333 K. A numerical model taking into account capillary transport of liquid and internal evaporation is applied to a spherical geometry representative for an individual iron ore pellet. Drying simulations are carried out with commercial computational fluid dynamic (CFD) software and the boundary conditions are calculated from the surrounding fluid flow. The results indicate that the effect of air humidity arises from the start of the first drying period, that is, the surface evaporation period, whereas the difference is reduced at the end of the period due to a prolonged stage of constant rate drying attained at high saturations. At low saturations, there is no constant drying stage because the surface becomes locally dry before the pellet temperature has stabilized at the wet bulb temperature. The magnitudes of the drying rates and moisture contents are rather similar at the time when internal drying becomes dominating (i.e., when the total surface evaporation rate is zero) for the respective dew points, yet the drying time is increased at high saturations. It was also found that the moisture gradients at the surface and inside the pellet increased with drying rate.

  • 40.
    Lucchese, Riccardo
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Olsson, Jesper
    Luleå University of Technology.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Garcia-Gabin, Winston
    ABB Corporate Research, Västerås.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Energy savings in data centers: A framework for modelling and control of servers’ cooling2017In: IFAC-PapersOnLine, ISSN 1045-0823, E-ISSN 1797-318X, Vol. 50, no 1, p. 9050-9057Article in journal (Refereed)
    Abstract [en]

    Aiming at improving the energy efficiency of air cooled servers in data centers, we devise a novel control oriented, nonlinear, thermal model of the servers that accounts explicitly for both direct and recirculating convective air flows. Instrumental to the optimal co-design of both geometries and cooling policies, we propose an identification methodology based on Computational Fluid Dynamics (CFD) for a generic thermal network of m fans and n electronic components. The performance of the proposed modelling framework is validated against CFD measurements with promising results. We formalize the minimum cooling cost control problem as a polynomially constrained Receding Horizon Control (RHC) and show, in-silico, that the resulting policy is able to efficiently modulate the cooling resources in spite of the unknown future computational and electrical power loads.

  • 41.
    Lundström, T. Staffan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Rahkola, Mattias Brynjell
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hellström, J. Gunnar I.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Green, Torbjörn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Evaluation of Guiding Device for Downstream Fish Migration with In-field Particle Tracking Velocimetry and CFD2015In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 8, no 3, p. 579-589Article in journal (Refereed)
    Abstract [en]

    The performance of a fish guiding device located just upstream a hydropower plant is scrutinized. The device is designed to redirect surface orientated down-stream migrating fish (smolts) away from the turbines towards a spillway that act as a relatively safe fishway. Particles are added up-stream the device and the fraction particles going to the spillway is measured. A two-frame Particle Tracking Velocimetry algorithm is used to derive the velocity field of the water. The experimental results are compared to simulations with CFD. If the smolts move passively as the particles used in the study the guiding device works very well and some modifications may optimize its performance. In-field Particle Tracking Velocimetry is a suitable technique for the current case and the results compare well with numerical simulations.

  • 42.
    Pavasson, Jonas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Larsson, Sofia
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Johansson, Simon
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, T. Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Challenges and opportunities within simulation-driven functional product development and operation: Special Session: Product Development for Through-Life Engineering Services2014In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 22, p. 169-174Article in journal (Refereed)
    Abstract [en]

    The product development process at industrial companies has traditionally focused on hardware-oriented solutions. Business strategies strive towards more service-oriented solutions e.g., functional product business models. In this paper two case studies are developed and the objective is to highlight important challenges and opportunities by implementing a simulation-driven strategy in functional product development and operation. It can be concluded that challenges and opportunities within simulation-driven functional product development and operation are related to both quality and management of the simulations. With the proposed strategies for validation and coupling of the simulations, some of the challenges within functional product development can be overcome.

  • 43.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Xiong, Damiano
    Sveriges Lantbruksuniversitet.
    Nilsson, Michael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Distance- Spanning Technology.
    A modelling methodology for assessing use of datacenter waste heat in greenhouses2017Conference paper (Refereed)
    Abstract [en]

    In Sweden, the number of datacenters establishments are steadily increasing thanks to green, stable and affordable electricity, free air cooling, advantageous energy taxes and well-developed Internet fiber infrastructures. Even though datacenters use a lot of energy, the waste heat that they create is seldom reused. A possible cause is that this waste heat is often low grade and airborne: it is therefore hard to directly inject it into a district heating system without upgrades, which require additional energy and equipment that generate extra costs. One option for reusing this heat without needs for upgrades is to employ it for heating up greenhouses. But assessing the feasibility of this approach by building physical prototypes can be costly, therefore using computer models to simulate real world conditions is an opportunity. However, there is a lack of computer modelling methodologies that can assess the possibility of using waste heat from datacenters in greenhouses in cold climates.

    The objective of this paper is therefore to propose such a methodology and discuss its benefits and drawbacks in comparison with other research studies. This methodology combines computational fluid dynamics, process modelling and control engineering principles into a computer model that constitutes a decision support system to study different waste heat and greenhouse or mushroom house scenarios.

    The paper validates the strategy through a case study in northern Sweden, where we assess the amount of produced waste heat by collecting temperature, relative humidity, and fan speed data for the air discharged from the datacenter.

    The resulting methodology, composed by conducting measurements and computer models, calculations can then be used for other datacenter operators or greenhouse developers to judge whether it is possible or not to build greenhouses using datacenter waste heat.

  • 44.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    CFD Simulations Comparing Hard Floor and Raised Floor Configurations in an Air Cooled Data Center2016In: 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malaga, Spain, 11-13 July 2016, s. 450-455, 2016Conference paper (Refereed)
    Abstract [en]

    An increasing number of companies and organisations have started to outsource their data storage. Although the potential of future investments in data centers is prosperous, sustainability is an increasingly important factor. It is important to make sure that the server racks in data centers are sufficiently cooled whereas too much forced cooling leads to economical losses and a waste of energy. Computational Fluid Dynamics (CFD) is an excellent tool to analyze the flow field in data centers. This work aims to examine the performance of the cooling system in a data center using ANSYS CFX. A hard floor configuration is compared to a raised floor configuration. When a raised floor configuration is used, the cold air is supplied into an under-floor space and enters the room through perforated tiles in the floor, located in front of the server racks. The flow inside the main components and the under-floor space is not included in the simulations. Boundary conditions are applied to the sides where the flow goes out of or into the components. The cooling system is evaluated based on a combination of two different performance metrics. Results show that the performance of the cooling system is significantly improved when the hard floor configuration is replaced by a raised floor configuration. The flow field of the air differs in the two cases. It is considered to be improved when the raised floor configuration is used as a result of reduced hot air recirculation around the server racks.

  • 45.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Comparison of turbulence models when modeling the airflow in a data center2016Conference paper (Refereed)
  • 46.
    Wibron, Emelie
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Lundström, Staffan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Computational Fluid Dynamics Modeling and Validating Experiments of Airflow in a Data Center2018In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 11, no 3, article id 644Article in journal (Refereed)
    Abstract [en]

    The worldwide demand on data storage continues to increase and both the number and the size of data centers are expanding rapidly. Energy efficiency is an important factor to consider in data centers since the total energy consumption is huge. The servers must be cooled and the performance of the cooling system depends on the flow field of the air. Computational Fluid Dynamics (CFD) can provide detailed information about the airflow in both existing data centers and proposed data center configurations before they are built. However, the simulations must be carried out with quality and trust. The k–ɛ model is the most common choice to model the turbulent airflow in data centers. The aim of this study is to examine the performance of more advanced turbulence models, not previously investigated for CFD modeling of data centers. The considered turbulence models are the k–ɛ model, the Reynolds Stress Model (RSM) and Detached Eddy Simulations (DES). The commercial code ANSYS CFX 16.0 is used to perform the simulations and experimental values are used for validation. It is clarified that the flow field for the different turbulence models deviate at locations that are not in the close proximity of the main components in the data center. The k–ɛ model fails to predict low velocity regions. RSM and DES produce very similar results and, based on the solution times, it is recommended to use RSM to model the turbulent airflow data centers.

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