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  • 1.
    Bel Fdhila, Rebei
    et al.
    Mälardalen University, School of Business, Society and Engineering. ABB AB, Corporate Research, SE - 721 78, Västerås, Sweden.
    Rahmani, Mohamed Ali
    ABB AB, Corporate Research, SE - 721 78, Västerås, Sweden.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering.
    PREDICTION AND MEASUREMENTS OF THE GAS BUBBLES INDUCED MIXING IN A BIO-REACTOR WATER MODEL2013Conference paper (Other academic)
    Abstract [en]

    Biogas is a fuel gaining increased interest. To be commercially viable the biogas production process needs to be further improved with advanced industrial standards where the technical, economic and environmental aspects are fully considered.

    Understanding fluid dynamics and the microbial reactions in the digestion process is necessary to accurately model and predict the biogas production. In connection with the Swedish company SvenskVäxkraft AB we focus on reactors where part of the produced gas is re-injected at the bottom to generate a strong recirculation with a gas-lift effect with a rising flow in the core. The mixture motion in this type of bio-reactors is entirely induced by the gas.

    Computational fluid dynamics (CFD) is used to study the effect of gas plumes of bubbles in the range smaller than 10mm with a maximum local gas volume fraction lower than 10%. This study shows that considering the appropriate models to account for the added agitation and turbulence by the bubbles improves the prediction of the liquid flow characteristics. Neglecting the induced bubble effect leads to erroneous results where the radial dispersion of the gas concentration, the liquid velocity and the turbulence are significantly underestimated.

    To validate the model we performed local measurements in an experimental facility where a laboratory water-model is equipped with advanced instruments to measure the gas volume fraction as well as the liquid and gas vertical velocities.

    It was found that using the bubble induced turbulence model by Sato et al. [8] with the Tomyami models for the drag and lift forces [3-6], provides predictions in good agreement with the measured quantities.

    This study shows that for such processes where the flow is mainly created by the bubbles presence, the pseudo-turbulence (the turbulence induced by the bubbles) and the bubble size distribution need to be properly considered.

  • 2.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Air-Gap Heat Transfer in Rotating Electrical Machines: A Parametric Study2017In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 142, p. 4176-4181Article in journal (Refereed)
    Abstract [en]

    More than half of all electrical energy is consumed by motors and generators in an industrialized country. About 5-25% of this energy is lost and converted to heat. This heat produced by the losses has adverse effect on the lifetime and performance of a machine. A machine has to be operated at a given temperature to achieve maximum efficiency, therefore heat transfer study of machines is of special interest to rotating machines manufacturers. In this paper we investigate the heat transfer in the air-gap between the rotor and the stator of a simplified induction motor using Computational Fluid Dynamics. We consider three different air-gap widths and rotation speeds to explore the change in air-gap heat transfer when changing the air-gap width and the rotation speed. The simulated average heat transfer coefficients for all the models are in good agreement with the correlations from published literature. The Taylor-Couette vortical flow pattern is observed in the air-gap in our simulation results for the models with large air-gaps. The numerical results show that the presence of Taylor-Couette vortices in the air-gap enhance the heat transfer. The heat transfer coefficient increases with the increase in the rotation speed and decreases with the decrease in the air-gap width. 

  • 3.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Daneryd, Anders
    ABB AB, Corporate Research, Västerås, Sweden.
    Heat transfer by liquid jets impinging on a hot flat surface2016In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 164, no 15, p. 934-943Article in journal (Refereed)
    Abstract [en]

    Runout Table (ROT) cooling is one of the most important factors for controlling quality of hot rolled steel. ROT cooling uses large quantities of water to cool the steel plate. Optimizing heat transfer in the ROT would reduce the amount of water used, which will lower the amount of energy needed for pumping, filtering, storage and use of water. Optimization will therefore result in a direct energy saving as well as increasing the product quality.

    This study investigates heat transfer by turbulent water jets impinging on a hot flat steel plate at temperatures below the boiling point in order to understand convection heat transfer phenomena. This is an important stage that precedes the boiling and addresses the applicability of the heat transfer correlations available in the literature.

    A single axisymmetric jet and a pair of interacting jets are simulated using Computational Fluid Dynamics (CFD). The Reynolds Averaged Navier Stokes (RANS) model under steady and transient conditions and the kɛ turbulence model are used in both 2D axisymmetric and 3D simulations. We investigate the influence of the water flow rate on the jet cooling characteristics and develop a correlation for the radial position of the maximum Nusselt number based on numerical results.

    Two sets of boundary conditions – constant temperature and constant heat flux – are applied at the surface of the steel plate and evaluated. The single jet numerical results compare favourably with published data based on measurements and analytical models. The thermal performance of a two-jet system was found to be no better than a single jet because the jets were too far from each other to generate any additional thermal interaction.

  • 4.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Daneryd, Anders
    ABB, Sweden.
    Multi-Jet Impingement Cooling of a Hot Flat Steel Plate2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 61, p. 1835-1839Article in journal (Refereed)
    Abstract [en]

    One of the most important steps to control the quality in steel hot rolling is the Runout Table (ROT) Cooling. In this investigation, the heat transfer of water jets impinging on a hot flat steel plate was studied under temperatures below the boiling point to understand the convection heat transfer phenomena which is a major step preceding the boiling. Single axisymmetric jet and a pair of interacting jets are simulated using Computational Fluid Dynamics (CFD). The RANS model under steady and transient conditions as well as the k-Ɛ turbulence model are used for both 2D axisymmetric and 3D simulations. The water flow rate influence on the jets cooling characteristics is investigated.Two sets of boundary conditions, constant temperature and constant heat flux were applied at the surface of the steel plate and evaluated. The single jet numerical results are successfully compared to published data based on measurements and analytical models. The two jets thermal performance was found to be unaffected because the jets are too far from each other to generate any additional thermal interaction.

  • 5.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Kristian, Rönnberg
    ABB AB, Corporate Research, Sweden.
    Taylor-Couette flow and transient heat transfer inside the annulus air-gap of rotating electrical machines2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 207, p. 624-633Article in journal (Refereed)
    Abstract [en]

    Losses in an electric motor amount to between 4–24% of the total electrical power, and are converted to heat. The maximum hot spot temperature is one of the design constraints of thermal and electrical performance. Several studies have explored flow and thermal characteristics inside the air-gap between two concentric rotating cylinders such as those found in electric motors, however the transient flow and thermal effects still remain a challenge. This study uses Computational Fluid Dynamics to predict the thermal behaviour of a machine rotating at the kind of speed usually encountered in motors. The Reynolds Averaged Navier-Stokes model together with the realizable k-ε turbulence model are used to perform transient simulations. Velocity profiles and temperature distribution inside the air-gap are obtained and validated. The transient flow features and their impact on thermal performance are discussed. The numerical results show turbulent Taylor vortices inside the air-gap that lead to a periodic temperature distribution. When compared to correlations from published literature, the simulated average heat transfer coefficient at the rotor surface shows overall good agreement. The transient effects introduce local impacts like oscillations to the Taylor-Couette vortices. These flow oscillations result in oscillations of the hotspots. However, this transient oscillatory behaviour does not show any additional impact on the global thermal performance.

  • 6.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Kyprianidis, Konstantinos
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Simulation and validation of flow and heat transfer in an infinite mini-channel using Smoothed Particle Hydrodynamics2018In: Energy Procedia, Elsevier, 2018Conference paper (Refereed)
    Abstract [en]

    Fluid flow and heat transfer in small channels have a wide range of engineering and medical applications. It has always been a topic of numerous theoretical, numerical and experimental studies. Several numerical methods have been used to simulate such flows. The most common approaches are the finite volume method (FVM) and the direct numerical simulation (DNS), which are numerically expensive to solve cases involving complex engineering problems. The main purpose of this work is to investigate the usability of the mesh-free particle based Smoothed Particle Hydrodynamics (SPH) method to simulate convective heat transfer. To validate our approach, as a starting point, we choose to solve a simple well-established problem which is the laminar flow and heat transfer through an infinitely long mini-channel. The solution obtained from SPH method has been compared to the solution from FVM method and analytical solution with good accuracy. The results presented in this paper show that SPH is capable to solve laminar forced convection heat transfer, however, turbulent flow cases need to be considered to be able to utilize the SPH method for engineering thermal applications.

  • 7.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Sweden.
    Domínguez, J. M.
    EPHYSLAB Environmental Physics Laboratory, Universidade de Vigo, Spain.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Kyprianidis, Konstantinos
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Smoothed particle hydrodynamics modeling of industrial processes involving heat transfer2019In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 252, article id 113441Article in journal (Refereed)
    Abstract [en]

    Smoothed Particle Hydrodynamics (SPH) is a mesh-free particle method that has been widely used over the past decade to model complex flows. The method has mainly been used to investigate problems related to hydrodynamics and maritime engineering, in which heat transfer does not play a key role. In this article, the heat-conduction equation is implemented in the open-source code DualSPHysics, based on the SPH technique, and applied to different study cases, including conduction in still water in a cavity, laminar water flow between two infinite parallel plates and tube bank heat exchanger. The thermal solutions obtained from SPH are benchmarked with the solutions from Finite Volume Method (FVM) and validated using available analytical solutions. DualSPHysics results are in good agreement with FVM and analytical models, and demonstrate the potential of the meshless approach for industrial applications involving heat transfer.

  • 8.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Domínguez, José
    University of VIGO, Spain.
    Crespo, Alejandro
    University of VIGO, Spain.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Kyprianidis, Konstantinos
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Smoothed Particle Hydrodynamics modeling of transient conduction and convection heat transferManuscript (preprint) (Other academic)
    Abstract [en]

    Smoothed Particle Hydrodynamics (SPH) is a mesh-free particle method that has been widely used in the last years to model some complex flows. SPH was mainly used to investigate problems related to hydrodynamics and maritime engineering where heat transfer is of no importance. Thermal problems have seldom been addressed due to the limitation of the main commercial and open-source SPH codes.

    In this article, the energy equation is implemented in the SPH based open-source code DualSPHysics to solve conduction and forced convection heat transfer problems. Laminar flow cases are simulated as the first validation cases of the implemented model. The studied cases include conduction in an aluminum block, conduction in still water in a cavity, laminar water flow between two infinite parallel plates and tube bank heat exchanger. The thermal solutions obtained from SPH are benchmarked with the solutions from Finite Volume Method (FVM) and also validated using available analytical solutions. The obtained results are in good agreement with FVM and available analytical models, which combined with the advantages of the meshless approach, show the high potential for industrial heat transfer applications.

    This development is an important step towards thermal optimization of several industrial applications that can’t benefit from the conventional FVM approach due to geometry or process complexities. The demonstrated SPH simulation and visualization capabilities contribute to build the future reliable energy-saving solutions.

  • 9.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB Corp Res, Sweden.
    Fdhila, Rebei Bel
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB Corp Res, Sweden.
    Literature Review of accelerated CFD Simulation Methods towards Online Application2015In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 75, p. 3307-3314Article, review/survey (Refereed)
    Abstract [en]

    Engineering advanced methods for example Computational Fluid Dynamics (CFD) are heavily used to solve, design and model complex industrial applications. They provide high accuracy however, the simulation time is too long and this limit its generalized use dramatically as for control purposes. CFD tools and methods are often used to analyze the energy distribution and management in different industrial processes like hot rolling industries, furnaces and boilers as well as a number of areas where mixing and thermal management are of importance. Huge amounts of energy are often fed into such processes. A small amount of optimization can provide a very large energy saving. It is now an urgent need to have a tool like real-time CFD to analyze, control and optimize on-line various industrial processes. This tool or method can contribute to build efficient and sustainable energy systems. The scope of this work is to find alternative simulation techniques that can also address industrial applications and provide solutions within a decent accuracy and resolution. In this paper we provide a literature review of those methods that can be categorized as mesh based, mesh free and hybrid that are capable of providing appropriate results in some key areas of interest. As a next step one of these methods will be implemented and coupled to CFD simulation of cooling impinging jets used to control the heat transfer and temperature behavior of a hot flat surface in a hot rolling process where thermal energy and cooling water are used with excess. (C) 2015 The Authors. Published by Elsevier Ltd.

  • 10.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Fdhila, Rebei Bel
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås, Sweden.
    Rönnberg, Kristian
    ABB AB, Corporate Research.
    Air-Gap Flow and Thermal Analysis of Rotating Machines using CFD2017In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 105, p. 5153-5159Article in journal (Refereed)
    Abstract [en]

    Thermal management of the rotating electrical machines is a very challenging area which needs appropriate solutions for each machine and operating condition. The heat is generated by the electromagnetic losses and the mechanical friction during the rotation. Computational Fluid Dynamics (CFD) is used in this study to predict and analyze the thermal performance of a rotating electrical machine where high speed rotation is coupled with small flow gaps. The investigation presented in this paper is based on a geometry used for model assessment and verification purposes. However, the approach outlined and the observations made are transferrable to other geometries. ANSYS Fluent has been used to perform CFD simulation where both the air velocity field and the temperature distribution are obtained. The results are qualitatively highly interesting to understand the thermal behavior within an electrical machine operations. The results show a periodic temperature distribution on the stator surface with similar periodic pattern for the heat transfer coefficient on the rotor surface. The simulated average heat transfer coefficient at the rotor surface is compared with the correlations from published literature with an overall good agreement.

  • 11.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Rönnberg, Kristian
    ABB AB, Corporate Research.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Air Flow inside Rotating Electrical Machines: A Comparison between Finite Volume and SPH Method2017In: Conference Proceedings of NAFEMS World Congress 2017 (NWC17), 2017Conference paper (Refereed)
    Abstract [en]

    A general, sufficiently accurate, applicable and reasonably fast approach to thermal analysis of rotating electrical machines is of high interest for motor and generator developers and manufacturers. The thermal performance and the lifetime of a machine is limited by the temperature distribution and the hot spot temperature. The most commonly encountered cooling medium is air and the temperature distribution is driven by the air flow pattern inside the machine. Two different Computational Fluid Dynamics methods, the mesh based Finite Volume Method (FVM) and the mesh free particle based Smoothed Particle Hydrodynamics (SPH) method are employed in this paper to model the airflow inside a rotating machine. Mesh based methods are quite robust, however, they are very expensive in terms of meshing effort and CPU time to be used extensively in R&D. Analysing and optimizing products with complex geometrical shapes need mesh generation for every specific design change and this may be the major part of the modelling process. This challenging task is not necessary for the SPH method. SPH method can also provide high quality 3D visualization that can improve the design process.

    This work investigates the usability of the SPH method when applied to rotating machinery for rotor speeds normally encountered in motors and generators. A comparison with an FVM based approach is also performed. Both the FVM and the SPH solvers show good agreement for the overall flow pattern inside the machine with some disagreement for the airflow inside the air-gap between the rotor and the stator. The FVM solver successfully captures the Taylor vortex flow inside the annulus air-gap which is in general a great modelling challenge. The SPH solver on the other hand shows great capability to couple rotation of the rotor and well represent the overall flow pattern inside the machine. However, the 3D SPH solver could not capture the complex Taylor vortices inside the air-gap which may be due to the limited number of particles used for the simulation. An increase in the number of particles would certainly improve the accuracy of the results as confirmed by the 2D SPH simulation. The present study shows that the SPH solver can be used to predict the air flow pattern inside rotating machines within an acceptable accuracy.

  • 12.
    Hosain, Md Lokman
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Sweden.
    Sand, U.
    ABB AB, Corporate Research, Sweden.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Sweden.
    Numerical Investigation of Liquid Sloshing in Carrier Ship Fuel Tanks2018In: IFAC-PapersOnLine, ISSN 2405-8963, Vol. 51, no 2, p. 583-588Article in journal (Refereed)
    Abstract [en]

    Liquid sloshing inside a partially filled tank has a great impact on the fragile internal tank coating and also on the stability of carrier ships. Several studies highlighted the challenges encountered due to the sloshing and proposed anti-sloshing tank structures. However, sloshing of liquefied natural gas fuel in high pressure vessels during transportation still remain a challenge. In the present numerical study we consider a downscaled 2D geometry to investigate the sloshing. Non-dimensional numbers are used to downscale the geometry. The purpose is to understand the flow structures and validate the downscaling approach based on the similarity scale laws. In the present work, Computational Fluid Dynamics (CFD) based on the Reynolds Averaged Navier-Stokes equations (RANS) with the Volume of Fluid (VOF) method in one hand and the Smooth Particle Hydrodynamics (SPH) method in the other hand, are used to simulate the downscaled model. The results from both methods are compared and validated using experimental data. A full scale model have also been simulated using SPH to verify the applicability of the scaling laws. The SPH model shows the capability to efficiently capture the sloshing phenomena. The VOF and SPH provide similar results in terms of flow dynamics, pressure and forces. The overall numerical results agree with the measurements and show that SPH can be an efficient tool to be used in modelling sloshing phenomena, compared to the RANS-VOF approach which is expensive in terms of CPU time. However, features like turbulence need to be further investigated. 

  • 13.
    Lindmark, Johan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Bel Fdhila, Rebei
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Thorin, Eva
    Mälardalen University, School of Sustainable Development of Society and Technology.
    ON MODELLING THE MIXING IN A DIGESTER FOR BIOGAS PRODUCTION2009In: / [ed] I. Troch, F. Breitenecker, 2009Conference paper (Other academic)
    Abstract [en]

    At the Vaxtkraft biogas plant the mixing is produced by pumping in biogas and releasing it at the bottom. The mixing inside the digester of a biogas plant is important for good biogas production and since it is complicated to study the mixing inside the digester while it is in operation, this study is based on numerical simulations using a computational fluid dynamic finite volume code. To study the mixing dynamics, five different flow rates of gas (air) injections ranging from 0.1 to 0.6kg/s were simulated. These gas flow rates produced an average liquid speed in the digester between 0.10 and 0.22 m/s. The liquid recirculation impact on the mixing was investigated through the simulation of a case where it is combined with the lowest gas injection flow rate. The results from the simulation suggest that the liquid outlet is situated too close to the gas injection, resulting in energy losses in form of diminished mixing of the digester. A complete redesign of the digester is needed to seriously overcome the mixing limitation.

  • 14.
    Lindmark, Johan
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Thorin, Eva
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center. ABB AB, Corporate Research, Västerås.
    Dahlquist, Erik
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Effects of mixing on the result of anaerobic digestion: Review2014In: Renewable & Sustainable Energy Reviews, ISSN 1364-0321, Vol. 40, p. 1030-1047Article in journal (Refereed)
    Abstract [en]

    Mixing in an anaerobic digester keeps the solids in suspension and homogenizes the incoming feed with the active microbial community of the digester content. Experimental investigations have shown that the mixing mode and mixing intensity have direct effects on the biogas yield even though there are conflicting views on mixing design. This review analyzes and presents different methods to evaluate the mixing in a digester (chemical and radioactive tracers and laboratory analysis), tools for digester design (computational fluid dynamics and kinetic modeling) and current research on the effects of mixing on the anaerobic digestion process. Empirical data on experiments comparing different mixing regimes have been reviewed from both a technical and microbial standpoint with a focus both on full scale digesters and in lab-scale evaluations. Lower mixing intensity or uneven mixing in the anaerobic digestion process can be beneficial during the startup phase to allow for methanogenic biomass growth and alleviate process instability problems. Intermittent mixing has been shown to be able to yield a similar gas production as continuous mixing but with the possibility to reduce the maintenance and energy demands of the process. Problems often experienced with experimental design include the effect of mixing on the solids retention time, and measurement of steady state gas production because of startup instabilities. Further research should be aimed at studying the effects of mixing on a chemical and microbial level and on the different stages of anaerobic digestion (hydrolysis, acidogenesis, acetogenesis and methanogenesis). The focus should be on the effects of mixing on a multiple stage digestion process and also finding new methods to evaluate the effects of mixing in the one stage digestion process rather than evaluating a wider range of mixing modes, intensities and substrates.

  • 15.
    Lindmark, Johan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Thorin, Eva
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Bel Fdhila, Rebei
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    PROBLEMS AND POSSIBILITIES WITH THE IMPLEMENTATION OF SIMULATION AND MODELING AT A BIOGAS PLANT2012Conference paper (Refereed)
    Abstract [en]

    Advanced models are being developed for the anaerobicdigestion (AD) process. These models can be used to control and optimize industrial size biogas plant to reach their full potential. There are many models available for different types of implementations. However, many of the published models demands extensive chemical analysis that might not be practically and economically viable in industry. Sampling routines at six Swedish biogas plants was compiled for comparison with the demand of input in published modeling approaches. The gap between the models and practices in industry has to come together through model simplification and extended sampling routines. Chemical oxygen demand (COD) for example is not a commonly used analysis in Swedish biogas plants but which is regularly used to model the AD. Knowledge of the biochemical processes in AD built in to a model can help operators increase the biogas yield of the plant without jeopardizing the production. There is a lack of robust online measurement equipment today to be able to have reliable online models for operational support but near infrared spectroscopy (NIR) is a promising technology for online measuring of a series of different characteristics that could make modeling more interesting for the AD industry. The mixing has as of yet not been devoted much attention to when modeling the process.

  • 16.
    Md Lokman, Hosain
    et al.
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Sand, U.
    Engdahl, J.
    Dahlquist, Erik
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Li, Hailong
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    CFD Modeling of Real Scale Slab Reheating FurnaceConference paper (Refereed)
  • 17.
    Rahmani, M. A.
    et al.
    ABB AB, Corporate Research, Västeras, Sweden .
    Bel Fdhila, Rebei
    Mälardalen University, School of Business, Society and Engineering, Future Energy Center.
    Grönqvist, A.
    ABB AB, Västerås, Sweden .
    Tysell, M.
    ABB AB, Västerås, Sweden .
    Persson, T. L.
    ABB AB, Västerås, Sweden .
    Benendo, M.
    ABB AB, Västerås, Sweden .
    Uvgard, Z.
    ABB AB, Västerås, Sweden .
    Thermal management and design optimization of heatsink for cooling performance improvement during transient heat generation2014In: Energy Procedia, ISSN 1876-6102, E-ISSN 1876-6102, Vol. 61, p. 1665-1668Article in journal (Refereed)
    Abstract [en]

    Heatsinks have long been used for cooling of electronic components to maintain them under the maximum allowed operational temperature. Forced air cooling with heatsink is suitable and enough efficient for low power applications cooling. Varieties of heatsinks are proposed by specialized industries to cool different kinds of electronic components. However, in most cases we need the appropriate heatsink to each specific case and particularly under transient heat generation that can be caused by many electronic or power electronic devices. The heat transport and evacuation process is tightly related to the heatsink performance. This paper examines the cooling characteristics of a heatsink used in a specific industrial application. The investigation is performed using Computational Fluid Dynamics (CFD) and the heat transfer performance of the heatsink is mainly determined by the Nusselt number which can be calculated from the numerical results. Analysis and discussion of the numerical results and especially the level of Nusselt number obtained at the contact surface of the heatsink with the surrounding cooling air allow optimization of the industrial heatsink shape to meet the requested cooling performance. Comparison of cooling performance before and after heatsink design optimization showed noticeable improvement.

  • 18.
    Sand, U.
    et al.
    Mälardalen University, Department of Public Technology.
    Bel Fdhila, Rebei
    Mälardalen University, Department of Public Technology.
    Numerical Modelling of Wood Particle Pyrolysis2009In: CONV-09. Proceedings of International Symposium on Convective Heat and Mass Transfer in Sustainable Energy, 2009Conference paper (Refereed)
    Abstract [en]

    This article provides a description of the modelling and simulation of the pyrolysis process of a small wood cylinder of 5.4mm height and diameter in a heating chamber containing nitrogen gas. The model considers forced and free convection inside and outside the particle. Convective, conductive and radiative heat transfer modes are included in this approach. The conversion from wood to char, tar and pyrolysis gas is modelled using a two-step reaction scheme.This approach offers a novel analysis advantage by involving simultaneously the particle and the surrounding atmosphere. This allows for a realistic prediction of the strong coupling between the inside and the outside of the particle. Earlier numerical works on pyrolysis of wood particles are generally considering the surrounding gas through the boundary conditions of the particle. Numerical results are successfully compared with measurements of the particle surface temperature profiles and the mass depletion rate at quiescent external flow. The influence of free and forced convection (0 ≤ ReD ≤ 135) on the overall pyrolysis time is investigated and a Nusselt number correlation is proposed. Based upon the results of the present investigation, a Nusselt number correlation accounting for the pyrolysis effects is proposed. The pyrolysis gas plumes can reach 0.1 m s−1. This is the same magnitude as the wood particles slip velocity in industrial applications. This reveals that in complex process situations as gasification or fluidized beds, the gas released by many small wood particles can strongly influence the dispersion characteristics. However, this study shows that the rocket force magnitude is significantly smaller than the drag and buoyancy forces.

  • 19. Sand, U.
    et al.
    Bel Fdhila, Rebei
    Pyrolysis of Short Wood Cylinders: Local Heat Transfer Investigation2009In: Pyrolysis:  Types, Processes, and Industrial Sources and Products / [ed] Walker S. Donahue, Jack C. Brandt, Nova Science Publishers , 2009Chapter in book (Other (popular science, discussion, etc.))
  • 20. Sand, U.
    et al.
    Bel Fdhila, Rebei
    Yang, H.
    Eriksson, J-E.
    Control of gas bubbles and slag layer in a ladle furnace by electromagnetic stirring2008Conference paper (Refereed)
  • 21.
    Sand, U.
    et al.
    ABB AB Västerås.
    Bel Fdhila, Rebei
    ABB AB Västerås.
    Yang, H.
    ABB AB Västerås.
    Eriksson, J-E.
    ABB AB Västerås.
    Control of Gas Bubbles and Slag Layer in a Ladle Furnace by Electromagnetic Stirring2009In: Iron & Steel Technology, ISSN 1547-0423, Vol. 6, no 7, p. 49-59Article in journal (Refereed)
    Abstract [en]

    A study was conducted to present the numerical model and simulation results of electromagnetic and gas stirring (EMGAS) and compare with that of a water model. The new features of EMGAS regarding the gas plume, stirring energy, velocity, and mixing time were introduced. Fluent© was employed to develop the numerical modeling of the system and model the melt, slag, and gaseous atmosphere in the ladle top was conducted using the Volume of Fluid (VOF) approach. The turbulence of the flow system was modeled using the Reynolds stresses model that accounted for six equations, including one for each Reynolds stress component and the turbulent dissipation equation. The water model investigations were based on visualization using an advanced video camera. The model cases were designed to be analogous with the corresponding simulated cases. The visualization investigations focused mainly on the flow pattern and the gas plume structure.

  • 22.
    Sand, U.
    et al.
    ABB AB Västerås.
    Bel Fdhila, Rebei
    ABB AB Västerås.
    Yang, H.
    ABB AB Västerås.
    Eriksson, J-E.
    ABB AB Västerås.
    Numerical and Experimental Study on Fluid Dynamic Features of Combined Gas and Electromagnetic Stirring in Ladle Furnace2009In: Steel Research Int., Vol. 80, no 6, p. 441-449Article in journal (Refereed)
    Abstract [en]

    Basic fluid dynamic features of combined electromagnetic stirring, EMS, and gas stirring (EMGAS) have been studied In the present work. A transient and turbulent multiphase numerical flow model was built. Simulations of a real size ladle furnace were conducted for 7 cases, operating with and without combined stirring and varying the argon gas inlet plug position. The results of these simulations are compared considering melt velocity, melt turbulence, melt/slag-interface turbulence and dispersion of gas bubbles. An experimental water model was also built to simulate the effects of combined stirring. The water model was numerically simulated and visual comparison of the gas plume shape and flow pattern in the numerical and in the experimental model was also done for 3 flow situations. The results show that EMGAS has a strong flexibility regarding the flow velocity, gas plume, stirring energy, mixing time, slag layer, etc.

  • 23. Sand, U.
    et al.
    Bel Fdhila, Rebei
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Yang, H.
    Eriksson, J-E.
    Study on Fluid Dynamic Features of Combined Gas and Electromagnetic Stirring in Ladle Furnace2008Conference paper (Refereed)
  • 24. Sand, U.
    et al.
    Sandberg, J.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Larfeldt, J.
    Bel Fdhila, Rebei
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Numerical prediction of the transport and pyrolysis in the interior and surrounding of dry and wet wood log2008In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 85, p. 1208-1224Article in journal (Refereed)
    Abstract [en]

    The numerical simulation of the pyrolysis process of a dry and wet birch wood log in a cylindrical heating chamber is preformed. The model includes the flow inside and outside the porous wood log and accounts for convective, conductive and radiative heat transfer. A two-step pyrolysis reaction scheme is used to model the conversion from wood to tar. gas and char. The results of the simulations compare well with the authors experimental data which are presented in terms of radial temperature distribution and mass reduction, for both dry and wet cases. Our transient simulations provide us with the detailed flow field inside and outside the wood log. It clearly shows not only the existence but also the structure of the Pyrolysis gas plumes leaving the wood. These plumes have only been visualised experimentally by few authors [Brackmann C et al. Optical and mass spectroscopy study of the pyrolysis gas of wood particles. Appl Spectros 2003:57(2):216-22, [12]] without any quantitative Measurements and the present investigation gives a realistic estimation that we presently use to evaluate its impact on the heat and mass transfer, and on the momentum balance and the particle dispersion in a near future work. The gas plumes have a maximum velocity magnitude ranging between 0.1 and 0.2 m s(-1) and vanish when all the wood gas is produced. It is shown that increasing the convective flow around the wood log do not significantly modify the pyrolysis gas plume structure and seems to have small effect on the overall heating and the pyrolysis process which are mainly controlled by the thermal radiation from the hot surrounding walls.

  • 25.
    Sand, Ulf
    et al.
    Mälardalen University, Department of Public Technology.
    Sandberg, Jan
    Mälardalen University, Department of Public Technology.
    Bel Fdhila, Rebei
    Mälardalen University, Department of Public Technology.
    Two-phase transport model for the pyrolysis process of a vertical dry wood cylinder, including the surrounding flow field2006In: International Journal of Green Energy, ISSN 1543-5075, Vol. 3, no 1, p. 63-78Article in journal (Refereed)
    Abstract [en]

    This paper describes a mathematical model for the pyrolysis of a small dry pine wood cylinder. The computational domain is axisymmetric and involves the heating chamber, with the wood cylinder vertically situated in the centre of the chamber. The model simulates the laminar flow around the particle and the laminar flow inside the wood/char matrix by applying a two-phase transport model where the solid wood/char matrix acts as one phase and the various gases produced from the pyrolysis process is assembled in the other phase.

    Convective, conductive and thermal radiation transfer modes are included in the model. A two-step pyrolysis reaction scheme is used for the modelling of the conversion from wood to tar and gas. Both the thermal conductivity and the permeability of the wood/char matrix are modelled anisotropically in order to capture the directional differences in heat and mass transport, existing in real wood.

    Results from simulations are compared with measurements from literature for the centre core solid temperature and the conversion from wood to char, tar and pyrolysis gas in the particle during heating. The results show very good agreement with the measured temperature profile. The simulated conversion profile shows an overall good agreement with the measurements, however with discrepancies in the early stage of the process. Besides the successful validation with the experimental data, it provides us with all the details of the distribution of the migrating pyrolysis gas and tar, the temperature, the velocity flow field and pressure in the wood/char cylinder.

  • 26.
    Sandberg, Jan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Fdhila, Rebei Bel
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Avelin, Anders
    Mälardalen University, School of Business, Society and Engineering.
    Dynamic simulation of fouling in a circulating fluidized biomass fired boiler2011In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 5, p. 1813-1824Article in journal (Refereed)
    Abstract [en]

    A dynamic model is presented for a biomass-fired circulating fluidized bed boiler. The model is based on energy and mass balances for the components in the boiler and on a combustion model for the fluidized bed. The main purpose of the model is to simulate how deposits affect the boiler efficiency and performance. The model is verified against the municipal circulating fluidized bed boiler in Vasteras, Sweden, which produces 157 MW. The distribution of deposits on the surfaces in the boiler is well known from inspections. These observations are used as inputs to the model to simulate their effects on boiler performance. The heat exchanger most affected by fouling is Superheater 2, which is the first heat exchanger in the flue gas channel. Deposits typically reduce the heat transfer rate by half over a season despite soot blowing. This and other fouling scenarios are simulated and presented in this article. The simulations show that fouling on superheaters redistributes the heat transfer rate from the superheaters to Reheater 1 and partially redistributes turbine power from the high pressure turbine to the intermediate pressure turbine. If the boiler is running at maximum load, water injection to Reheater 1 has to increase to maintain temperatures below the permitted limit. The dynamic effects of fouling are small and the total efficiency of the boiler is only marginally affected. Fouling on evaporating surfaces has major dynamic effects and dramatically decreases the boiler efficiency. A decrease in fuel rate flow is needed to maintain temperatures in the fluidised bed and in the flue gas channel within acceptable limits.

  • 27.
    Sandberg, Jan
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Karlsson, Christer
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Fdhila, Rebei Bel
    Mälardalen University, School of Sustainable Development of Society and Technology.
    A 7 year long measurement period investigating the correlation of corrosion, deposit and fuel in a biomass fired circulated fluidized bed boiler2011In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 88, no 1, p. 99-110Article in journal (Refereed)
    Abstract [en]

    The present investigation involves a unique, 7 year (2001-2007) long study of corrosion and deposits on superheater tubes in a biomass fired circulated fluidized bed boiler. These measurements are correlated against the different fuels used over this period. In the earlier years, the boiler was run with a mixture of different biomass fuels and peat. In later years, recycled wood was introduced into the fuel mix. The deposit growth rate approximately doubled when the recycled wood content of the fuel was increased to 10-20%. Small amounts of chlorine and zinc were found both in the recycled wood and in the deposit layer. These elements together with alkali metals from the biomass, have the potential to form sticky compounds that increase the deposit growth rate. The corrosion rate of the superheater tubes varied over the study period. A number of possible explanations for this phenomenon are discussed.

  • 28.
    Sandberg, Jan
    et al.
    Mälardalen University, Department of Public Technology.
    Sand, Ulf
    Mälardalen University, Department of Public Technology.
    Bel Fdhila, Rebei
    Mälardalen University, Department of Public Technology.
    Long time investigation of the effect of fouling on the super-heaters in a circulating fluidised biomass boiler2006In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 30, no 13, p. 1037-1053Article in journal (Refereed)
    Abstract [en]

    The present investigation involves measurements and theories on the mechanisms of the forming of deposit layers on super-heater tubes in a biomass-fired CFD boiler. The deposit layer thickness and the soot-blowing frequency effect on the super-heaters heat transfer are the main subject of the study that has been conducted over a 3-year period. The measurements show a deposit growth rate on the super-heaters of approximately 4 g m−2 h−1. The distribution of the deposit material varies significantly between the windward and the leeward side of the tubes, with the thickest layers on the windward side. Further down stream of the first super-heater, the fouling problem on the super-heater and re-heater tubes are not so severe. A theoretical model shows that a deposit layer of 20 mm will decrease the heat transfer rate of the first super-heater by nearly 40%. The soot-blowing system shows a strong positive effect on the heat transfer rate of the super-heater a few hours after a soot-blowing sequence has been completed. However in the long run, the varied soot-blowing frequency does not have a significant influence on the deposit layer growth rate.

  • 29.
    Sandberg, Jan
    et al.
    Mälardalen University, Department of Public Technology.
    Sand, Ulf
    Bel Fdhila, Rebei
    Measurements, theories and simulations of particle deposits on super-heater tubes in a CFB biomass boiler2006In: International Journal of Green Energy, ISSN 1543-5075, E-ISSN 1543-5083, Vol. 3, no 1, p. 43-61Article in journal (Refereed)
    Abstract [en]

    The present investigation involves theories, simulations and experiments on deposit layers on super-heater tubes in a circulating fluidised bed in Vdsteras in Sweden. Simulation of particle trajectories in the vicinity of two super-heater tubes is conducted in a Eulerian-Lagrangian mode for the flue gas and the ash particles from the combustion process. Particle impingements on the tubes are investigated for different particle sizes. Measurements of the buildup of deposit layers in the super-heater environment are conducted using a deposit probe. Deposit layer growth and growth rate is analysed for different probe temperatures, as well as the aspect of sintering on the probe ring surface. Analysis of the probe deposit material and deposits from the super-heaters and from textile filters are chemically analysed. The temperature dependence of the deposit materials viscosity is predicted from the chemical analysis of the samples. A model is included to simulate the effect of the deposit layer thickness on the tube heat exchange. The results from the particle trajectory simulations show that particle larger than 10 mu m will mainly impinge on the front of the first tube and that smaller particles are more dispersed due to turbulence and thermophorectic forces, enabling a more even impingement on the whole surface of the tubes. The probe deposit layer growth measurements show significant temperature dependence. The deposit material sintering and distribution is proven to be dependent on; temperature, particle size and exposure time. The stickiness of the deposit material is shown to be dependent on the SiO2 and alkali relation in the samples, estimated through a viscosity model.

  • 30.
    Sandberg, Jan
    et al.
    Mälardalen University, Department of Public Technology.
    Sand, Ulf
    Bel Fdhila, Rebei
    Numerical simulation of fouling on super-heater tube walls2002In: Proceedings of the 10th workshop on two-phase flow predictions, Merseburg, April 9 - 12, 2002Conference paper (Refereed)
  • 31.
    Thorin, Eva
    et al.
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Nordlander, Eva
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Lindmark, Johan
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Dahlquist, Erik
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Yan, Jinyue
    Mälardalen University, School of Sustainable Development of Society and Technology.
    Bel Fdhila, Rebei
    Mälardalen University, School of Sustainable Development of Society and Technology.
    MODELING OF THE BIOGAS PRODUCTION PROCESS- A REVIEW2012Conference paper (Refereed)
    Abstract [en]

    Production of biogas by digestion of organic wastes and other feedstock is one of the important technical solutions that contribute to the transform of the energy system from being fossil fuel dependent to renewable energy originated. To be fully commercial and competitive, the production of biogas needs to be further developed and optimized based on the technical, economic and environmental aspects. Thus, comprehensive understanding of fluid dynamics and microbial reactions in the digestion process is necessary to accurately and robustly model, predict and control the biogas production.

    In this paper possible pathways for modeling the biogas reactor is discussed based on previous work on anaerobic digestion modeling and modeling of the fluid flow in reactors. Important parameters for modeling biogas production, with a focus on processes using waste as feedstock, are considered. Identification of knowledge gaps for the modeling of the biogas process is performed and how to overcome the obstacles is addressed.

1 - 31 of 31
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