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- Post1D Modeling and Simulations of Soot Oxidation in Diesel Particulate Filters and Monoliths using GT-POWER(2016) Lerdmaleewong, Chanin; Luong, Staffan; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsDiesel particulate filter (DPF) is part of the exhaust aftertreatment system for diesel engines. The DPF’s main function is to trap particulate matter (soot) from the exhaust stream. The trapped soot is removed by regeneration of the filter. The regeneration process involves soot oxidation via oxygen and nitrogen dioxide. Simulations on kinetics and pressure drop are widely used in the assessment of the DPF. In this work detailed kinetic models of soot oxidation (by oxygen) were investigated and implemented in a flow-through monolith model and also in a DPF model using GT-POWER. The detailed kinetic models and data origins from previously published data. The DPF model consists of a number of interrelated sub-models soot oxidation by NO2 , NO oxidation and pressure drop. These sub-models were developed by using semi-steady state and transient engine data on a catalyzed DPF. Kinetics and pressure drop analysis were found to be the key in finding parameters for the models. The implementation of these models into GT-POWER required some special techniques due to rigid built-in model structure. The detailed kinetics was adequate to predict the low temperature experiment, in general, the detailed kinetic model was able to reduce the residual by approximately 25% compared to global kinetics model.
- PostCFD simulation of a large-scale VAWT- Evaluation of the rotor performance for a gradient wind profile(2019) Boberg, Mikaela; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime SciencesSeaTwirl is a developer of a large-scale vertical axis wind turbine and in previous aerodynamic studies of the rotor performance a uniform wind profile have been used. However, the characteristics of the landscape result in friction for the wind flow and the shear stresses generates a gradient wind profile. Hence, this study aims to investigate how the velocity gradients affect the rotor performance and how the efficiency may be increased by alternating the rotor design such as elevating the rotor position or the blade height. The numerical domain consisted of a 2D horizontal cross-section of three airfoils, the tower and struts were excluded. The k-! SST turbulence model was used to solve the unsteady RANS equations. The result showed that the difference in estimated power generation between the usage of a uniform compared to a gradient wind profile deviated with 5%. The result also indicated that it was more beneficial to increase the rotor swept area instead of increasing the rotor position. The study showed that the tip-speed-ratio drastically affected the forces acting on the blades and that these effects are prominent for large-scale vertical axis wind turbines due to the fixed blade configuration. This method was a good implement to obtain a deeper knowledge of the forces acting over the whole blade length. However, performing a full 3D model of the wind turbine would be desirable to validate the 2D method.
- PostCFD Simulation of Flow and Temperature inside a monolith of an Exhaust After-Treatment System (EATS)(2019) Duong, Victor; Khan, Mohammed Afzal; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Sjöblom, Jonas; Nygren, AndreasInternal Combustion Engine is the most popular and efficient types of engine used in the transport sector. On the other hand, it has serious downside in degrading the environmental stability as well. The exhaust gases after the combustion of fuel contain emissions which are harmful for human health and responsible for the climate change. Treating the exhaust gases of an Internal Combustion Engine is a major operation in the vehicle. Exhaust After Treatment System engineering simply known as EATS, can treat and remove these substances from the engine exhaust. Although the applied technology in EATS engineering are already very efficient, it is of interest to gather more knowledge about the velocity and temperature distributions inside the monolith of the reactor during transient operation to further improve the efficiency. By using computer aided simulations to capture the fine details, CFD has become a vital part to gain high resolution data in the monolith channels inside an EATS with the single channel approach. However, due to the computational cost, solving for a complete EATS with high resolution is not yet a possibility. The idea behind this research is to find a small set of channels which can be modelled to represent a complete EATS. Hence, using the single channel approach on the selected channels, these can represent a high resolution EATS simulation. The goal of this project was mainly focusing on obtaining high detailed simulations of ow and temperature for a specially designed monolithic catalytic reactor in transient state. A range of air ow and temperatures were tested in a laboratory, where the ow and temperatures in the inlet and outlet of monolith were recorded. The same ow conditions were reproduced with CFD simulations and a verification for the CFD model was done by comparing these results. A D-optimal algorithm was used on the outlet data of simulated ow tests, to find the optimal four locations for the different cases. Finally, a weighting model was developed where the four locations represent the complete outlet.
- PostCombined Empirical and 1D Modeling Approach for Exhaust Aftertreatment System for Heavy Duty Diesel Engines(2017) Almqvist, Frida; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsThe aim of this project was to develop a model for the first part of the exhaust aftertreatment system including diesel oxidation catalyst (DOC) and diesel particulate filter (DPF). The model would then be tested against test cell data to evaluate if it could be used in a virtual test rig. The model consists of two individual models one for DOC and one for DPF respectively, which were later linked together. The software used was GT-SUITE and the models were constructed as 1D single channel ow and tested against test cell data provided by Volvo Penta. The key parameters of investigation were concentration of CO, HC and NO, temperature and pressure drop. The reaction kinetics and properties of the substrate were optimized to get the best fit to data. The activation energy and the pre-exponent multiplier for the reaction rate expressions were optimized based on values for an entire cycle. A major error in the model is due to inconsistent degree of conversion at high temperatures (CO, HC). So at high temperatures the model predicted high conversion (100%) and the sensitivity of the parameters decreased, however, there were also come CO slip in this region which also caused problems in the model. The model should have been optimized towards the last part of the test data, where the conversion is lower than 100%. This was out of the scope for this thesis and therefore the model includes inaccurate optimized parameters for the low temperature region of the cycle. The lower conversion in test cell data might be due to a bend in the inlet pipe causing non-uniform inlet gas ow and non-uniform temperature and a ow of reactant were the model predicts almost full conversion. Another source of inaccuracy was the unknown initial soot loading of the DPF, causing errors in pressure drop simulation. Nevertheless, the models can give a good approximation to what happens in the DOC and DPF, especially when using PLM and NRTC cycles.
- PostEffect of Different Oil Droplet Sizes in a Flow of Natural Gas around a Compressor Blade. Numerical Simulations of Multiphase Flow using Computational Fluid Dynamics.(2015) Nohlås, Kajsa; Tryggvadóttir, Signý; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsSubsea is a term that refers to drilling and processing of gas and oil in underwater locations. One example of a subsea technology is a wet gas compressor which is used to compress fluids that consists of multiple phases. By compressing the wet gas the recovery of unprocessed streams can be increased and the investment cost reduced. The Norwegian company OneSubsea has designed and manufactured a wet gas compressor, first of its kind, and is developing the next generation of the compressor with assistance from the technical consultancy company ÅF. At ÅF’s department for technical analysis in Gothenburg simulations of the compressor with pure gas flow are performed. To compliment these simulations a separate project is performed to evaluate the effects of a flow that is multiphase. Therefore the aim of this project is to study the effect of different droplet sizes on a gas flow around a compressor blade in a wet gas compressor. Multiphase flow, consisting of natural gas and oil droplets, around one blade in the first step of the wet gas compressor is considered. Computational fluid dynamic simulations of one way coupled multiphase flow are solved using the conservation equations of mass and momentum, Lagrangian particle tracking and the k −! SST turbulence model. The range of the droplet size and volume fraction evaluated are 1-200 μm and 1-2%, respectively. Several different studies were performed. The results are characterised by flow properties outputted just after the blade, at the start of the next blade row, and with visualisations of the particle tracks around the blade. The main study, the Base case, consisted of 22 different case studies where the droplet size was held constant for each case, but varied within the size range between the cases. A coefficient of restitution (COR) was used to model the droplet wall interaction and the results showed that the droplets have an effect on the outflow from the first compressor step. The droplets decrease the average velocity angle at the axial clearance for all droplet sizes. The decrease is low, at a relatively constant value, for droplet sizes up to around 80 μm. For droplets larger than 80 μm, velocity angle decreases with increasing droplet size. By studying the particle tracks around the blade the droplet flow could be divided into three characteristic regions, according to the importance of wall interaction and effect of gas flow on the droplet. v After analysing the results from the Base case the importance of wall interaction was studied further. Simulations showed that the majority of the droplets are colliding with the wall. A sensitivity study for the COR was performed which showed that the droplet flow is independent of COR for droplet sizes up to 50 μm, almost independent up to 100 μm, and strongly dependent for the rest of the size range. A case study where the droplets were trapped at the wall was performed, but the reliability of these results are questionable since the data is based on a small fraction of droplets that pass the blade. For the final wall interaction study a liquid wall film at the blade was modelled. According to the theory this should be the most realistic way to model a droplet wall interaction. Due to lack of time this case study could not be fully completed and only an idea of the result is presented. The result shows that a thin film will cover the blade which has an effect on the particle tracks. The conclusion from this project is that the droplets will effect the flow around the blade by decreasing the average velocity angle for the flow entering the next blade row; the magnitude of the effect is increasing with increased droplet size. The droplet wall interaction is important for the particle tracks, thus it is recommended to further evaluate this aspect.
- PostEstimation of the temperature field in an industrial bubbling fluidised bed Development of a diffusion-type reduced-order model with input from Eulerian-Eulerian multiphase simulation(2019) Gustafsson, Gabriel; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime SciencesFluidised bed reactors are widely used in industry today, not at least in the energy sector. A common use case is the combustion and gasification of solid fuels such as coal, but also waste and biomass. Recently, a design proposing a fluidised bed divided into two chambers was presented. The proposed design could be beneficial for processes such as gasification where the residence time of fuel and char should be controlled. This work investigates the feasibility of the proposed design. The main point of investigation is whether the heat transfer between the two chambers will be sufficient as well as whether any gas leakage between the two chambers will occur. As a step in the investigation, a design tool to estimate the average temperature differences in the fluidised bed is developed. In addition, the effective conductivity of such a fluidised bed is investigated by means of Eulerian-Eulerian multiphase simulation. The results indicate that any eventual gas leakage would be minor and that the heat transfer might very well be enough, however further work is needed.
- PostExperimental and Computational Characterization of a Novel In-Situ Reactor(2015) Gustafson, Pontus; Malmström, Emil; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsOver the last years, the concern for environmental effects of different industrial applications has gained a great importance. One explanation for contributing to the global warming and air pollution is the release of particulate matter (PM) and carbon dioxide (CO2) from the increasing amount of vehicles that are serving our roads. New efficient engines are under constant development to utilize the fuels in a more efficient way. This also includes the exhaust aftertreatment system (EATS) that cleans the gases from the engine exhaust. Reducing the amount of released PM is of great importance to avoid contamination of our cities and avoid health problems such as cardiovascular diseases and lung cancer. This thesis aims to gain knowledge in the soot oxidation process to reduce release of PM to our environment. A unique In-Situ reactor from Chalmers, designed for detailed studies of soot oxidation, has been studied both with experiments and simulations using computational fluid dynamics (CFD). An iterative method has been applied between the experiments and the simulations were the outcome from the result is trying to improve the next setup. Experiments have been performed to study the oxidation process and simulations have been executed to study the behavior of the heat and fluid flow in the reactor to improve the reactor design and the way the reactor is operated. The results gave a good descriptions and understanding of the reactor behavior and its performance. The results include the obtained pressure drop and temperatures needed for reaction at different flow rates. As soot oxidation experiments have been executed, several conclusions have been drawn on the reaction dependencies of different temperature levels and oxidants, such as nitrogen dioxide (NO2) and oxygen levels (O2). Multiphase simulations have also been performed to study the effect of thermophoresis on the deposition of particles in the reactor. The results show that the particles follow the continuous phase well and that only a small effect of thermophoresis is obtained when the reactor is used with a continuous flow of air as the heat source as in the original design. The small effect of thermophoresis indicates that particle deposit on the glass tube won’t decrease the possibility to use the reactor In-Situ
- PostModeling of Hydrogen-Peroxide Films for Aseptic Processing Applications- A Parameter Study on Hydrogen-Peroxide Exposure to Internal Surfaces of mm-wide Slits(2019) Eriksson, Jesper; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Sasic, Srdjan; Sasic, SrdjanDisinfection methods are used within many fields to keep equipment and environments free from harmful biological agents such as fungi, bacteria, viruses and spore forms. Within the food and drug industry, aseptic processing refers to a process chain in which sterilized products are filled into sterilized containers. Aseptic processing brings benefits such as improved quality and increased shelf life of a product, which in turn leads to less waste due to the expiration of products. The benefits of aseptic processing introduce a demand for the development of effective disinfection methods. A common chemical disinfection method is the usage of hydrogen-peroxide to kill bacteria. One way to perform hydrogen-peroxide disinfection is to spray a vapor containing air, water and hydrogen-peroxide which is allowed to condense on cold surfaces forming a liquid film of water and hydrogen-peroxide which conducts the desired bacteria killing. It is important that all surfaces have been exposed to a hydrogen-peroxide film to ensure a rapid disinfection. This project aims to investigate the process of hydrogen-peroxide film condensation to evaluate the degree of liquid film coverage and gas hydrogen-peroxide exposure within mm-wide slits. The investigation was carried out using Computational Fluid Dynamics (CFD). The process of hydrogen-peroxide gas disinfection is well understood, but the process of liquid film formation and dynamics is more complex and many challenges remain within this field. In particular, there are no previous studies investigating film formation within small slits. A parameter study was performed to evaluate how the characteristic width of a slit h and the external gas flow velocity v influence the degree of liquid film coverage on the inside surfaces of a slit. The results suggest that the critical value of h as a function of v to ensure full surface film coverage follow hcrit(v) = 6.44v−0.2838−1.84, which is valid within the range v = [0.5, 2.0]. Expressed in terms of the dimensionless mass transfer Péclet number Peh, the criteria for full surface film coverage is according to the results Peh > 97. The results remove the need of having a high spatial resolution around mm-narrow spaces. Instead the developed macro-scale model can be used to predict the degree of hydrogen-peroxide exposure within the slit only with the knowledge of gas velocity external to the slit.
- PostModeling of multiphase flows in a spray dryer(2021) Vasudevan, Sindhuja; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Srdjan, Sasic; Niklasson Björn, IngelaSpray drying is a robust and popular unit operation in the pharmaceutical industry. One of the many applications of this unit operation is the manufacture of dry dosage formulations for nasal or pulmonary delivery. It is important that the generated particles from the spray drying process have certain attributes such as flowability, dispersibility and suitable aerodynamic properties, which depend on the particle design. In order to obtain a suitable particle design, a sound understanding of the particle formation process, which includes the physical and chemical mechanisms that control the drying process, is required. In this thesis, the drying process is studied by modeling with the commercial computational fluid dynamics (CFD) code ANSYS Fluent. This multiphase system which includes a gaseous continuous phase and droplet/particle as the dispersed phase is modeled using an Euler-Lagrangian approach. In Euler-Lagrangian modeling, the fluid phase is modeled as a continuum while for the dispersed phase a large number of individual particles is modeled. The different phases are said to be coupled when there is exchange of momentum, mass and energy between them. The significant presence of exchange of mass and heat between the continuous and dispersed phase indicates that the phases are two-way coupled, i.e., the continuous phase transfers mass and heat to dispersed phase and vice-versa. The effect of turbulence on the dispersed phase is accounted through a turbulent dispersion model. The choice of characteristic parameter of the turbulent dispersion model, i.e., the ’number of tries’ is decided based on a sensitivity analysis. This is done by analysing its effect on the residence time distribution of the dispersed phase. Analysis of the drying data obtained from the simulation reveals that the rate of drying of droplets of same initial diameter is different since they follow different trajectories. That is, for droplets of the same initial diameter, the drying rate varies in such a way that the maximum value is around 50% higher than the minimum value. Hence, this implies corresponding variation in solute concentration profile in the droplet and hence, particle structure for particles obtained from droplets of same initial diameter. Additionally, the impact of process operating conditions, especially the mass flow rate of the solution, on the drying rate and hence, the corresponding particle structure is indicated.
- PostNew generation of industrial crystallizers Numerical simulation of a bubble growth induced by laser(2015) Gheisi, Mohammad; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsProduction of crystals of different chemicals with the desired properties is a not trivial task and great number of studies have been carried out in order to understand the crystallization kinetics. Notwithstanding all these efforts, further investigation is needed to understand the underlying physics and the sequence of events that leads to crystallization. Moreover, introduction of novel technologies that facilitate the crystallization process and, as a result, produces crystals with the desired and controlled quality are essential. In this thesis, several technologies such as the laser-induced crystallization, ultrasound-induced crystallization, air-lift crystallization, oscillatory baffled crystallization and the high-gravity crystallizer have been studied and their main features are presented. In particular, the study focuses on the laser-induced crystallization or, more specifically, on the growth of a bubble that is induced by laser irradiation in an aqueous solution of ammonium sulfate. The numerical part of study is based on the volume of fluid (VOF) framework and the Schnerr and Sauer cavitation model (G.H.Schnerr, A.J.Sauer, F.I.C.M.F, 2001) to model the bubble growth. The simulations consider mass and energy transfer during the phase change in a stagnant ammonium solution. The simulation results show that the mass fraction of ammonium sulfate increases as a result of evaporation of solvent from liquid into the bubble. The increase of solute concentration during the expansion of a bubble is recognized as a driving force for nucleation. In the same time, it also increases the probability of formation of stable clusters.. The predicted values for the bubble radius as a function of flow time are found to be lower than the experimental data and the maximum predicted bubble radius is higher than the maximum bubble size in another sudy (A. Soare et.al, Cryst. Growth Des, 2011).
- PostParticulate matter removal in automotive after-treatment systems(2013) Ojagh, Houman; Kannan, Ananda Subramani; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsThere is growing concern in the world with regard to pollution and climate change. The relation between air pollution and climate change in particular is strong and complex. There is thus a shift towards greener technologies and a large amount of resources have been allocated for the research and development of such technologies. As emission regulations are becoming stricter, there is a concerted effort from all fronts in the EU to design and develop an optimal exhaust after-treatment system which would concur with current emission regulations imposed by Euro V and Euro VI (0.005 g/km of particulate matter (PM) and particulate number (PN) 6.0×1011) for both gasoline and diesel powered drives). Open channel substrates (described in this work) are used for the removal of particulate matter from exhaust. Such substrates are made of channels (arranged in a honeycomb structure) which permit the flow of exhaust through them. The PM is ultimately trapped on the wall of these channels. Over the past decade there has been a substantial increase in the computational power available to researchers. This increase of available computational resources has shifted the prime focus of research from time-consuming and expensive construction of pilot-scale prototypes towards simulation-driven development of new after treatment solutions. The current work aims to describe such a feedback between experiments and simulations in order to describe the capture of an inert particle (sodium chloride - NaCl) in an open substrate (monolith channel). The experiments and simulations are done in conjunction and such a systematic approach improves the quality of the experimental evaluation. This congruence is evident throughout this work, with the simulations generally, corresponding to the experimental results (simulations results are within the error limit of the experimental results). Both temperature and residence time have a significant impact on the capture efficiency due to Brownian deposition along an open channel. In addition the general trends with variation in residence time (flow conditions) and temperature are noticeably similar in both experiments and simulations. This indicates that the theory behind the description of capture efficiency in open channels (Brownian deposition in open substrates) is able to explain the capture phenomena of inert particulates accurately.
- PostParticulate matter removal in automotive aftertreatment systems(2013) Kannan, Ananda Subramani; OJAGH, HOUMAN; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsThere is growing concern in the world with regard to pollution and climate change. The relation between air pollution and climate change in particular is strong and complex. There is thus a shift towards greener technologies and a large amount of resources have been allocated for the research and development of such technologies. As emission regulations are becoming stricter, there is a concerted effort from all fronts in the EU to design and develop an optimal exhaust after-treatment system which would concur with current emission regulations imposed by Euro V and Euro VI (0.005 g/km of particulate matter (PM) and particulate number (PN) 6.0×1011) for both gasoline and diesel powered drives). Open channel substrates (described in this work) are used for the removal of particulate matter from exhaust. Such substrates are made of channels (arranged in a honeycomb structure) which permit the flow of exhaust through them. The PM is ultimately trapped on the wall of these channels. Over the past decade there has been a substantial increase in the computational power available to researchers. This increase of available computational resources has shifted the prime focus of research from time-consuming and expensive construction of pilot-scale prototypes towards simulation-driven development of new after treatment solutions. The current work aims to describe such a feedback between experiments and simulations in order to describe the capture of an inert particle (sodium chloride - NaCl) in an open substrate (monolith channel). The experiments and simulations are done in conjunction and such a systematic approach improves the quality of the experimental evaluation. This congruence is evident throughout this work, with the simulations generally, corresponding to the experimental results (simulations results are within the error limit of the experimental results). Both temperature and residence time have a significant impact on the capture efficiency due to Brownian deposition along an open channel. In addition the general trends with variation in residence time (flow conditions) and temperature are noticeably similar in both experiments and simulations. This indicates that the theory behind the description of capture efficiency in open channels (Brownian deposition in open substrates) is able to explain the capture phenomena of inert particulates accurately.
- PostPrediction of High-Speed Planing Hull Resistance and Running Attitude - A Numerical Study Using Computational Fluid Dynamics(2015) Frisk, David; Tegehall, Linda; Chalmers tekniska högskola / Institutionen för sjöfart och marin teknik; Chalmers University of Technology / Department of Shipping and Marine TechnologyAccurate predictions of the resistance and running attitude are key steps in the process of hull design and manufacturing. The predictions have traditionally relied on model testing, but this technique is both expensive and time consuming. In this study, the performance of CFD simulations of planing hulls is evaluated using two commercial software: ANSYS FLUENT, developed by ANSYS, Inc., and STAR-CCM+, developed by CD-adapco. This was done by predicting the steady resistance, sinkage and trim angle of one semi-planing and one planing hull in calm, unrestricted water. The Reynolds averaged Navier-Stokes equations with the SST k-! turbulence model was used along with the volume of fluid method to describe the two-phase flow of water and air around the hull. Furthermore, a two degrees of freedom solver was used together with dynamic mesh techniques to describe the fluid-structure interaction. The simulations were performed with both fixed and free sinkage and trim to make careful comparisons of the software and with experimental data. The results from the fixed sinkage and trim simulations of the planing hull in FLUENT and STAR-CCM+ show a good consistency. However, there is a significant difference in the pressure resistance obtained from the two codes that could not be explained. The free sinkage and trim simulations were mainly conducted in STAR-CCM+ due to problems with obtaining a stable solution in FLUENT. Froude numbers between 0.447 and 1.79 were simulated and the results follow the same trends as what is seen in the experimental data. The calculated resistance, sinkage and trim angle show good correspondence to experimental data in the planing region, where the errors of the predicted values are below 10%.
- PostReal Time Modeling of Engine Coolant Temperature(2016) Palm, Caroline; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsAn engine with double cooling circuits operating at two temperature levels has been developed at Volvo Cars. In this thesis the cooling circuit at the lower temperature level is studied and a model estimating the coolant temperature in this circuit has been developed in Simulink/TargetLink. The model is to be implemented in the engine control unit and used for function based diagnosis of the cooling system. The cooling system consists of the following components: a water cooled air cooler which is used to cool the charged air entering the engine, turbochargers in two-stages with cooled bearings systems and a cooled compressor house in one of the turbochargers, an inlet throttle (ETM) cooled for component protection, an SCR injector also cooled for component protection, and a radiator used to cool the coolant. After an investigation of the average heat transfer rate from each component, the ETM was excluded from the model. The SCR injector was also excluded since this component had not yet been installed in the studied engine. The model was formulated with a physical foundation, using energy balances of the system as well as experimentally obtained heat transfer relationships. An overall energy balance was used to calculate the coolant temperature in each discrete time step, based on heat transfer from the modeled components in the system (the water cooled air cooler, turbochargers and radiator). Model evaluation was performed using vehicle data obtained from real time measurements in a four cylinder diesel engine with extra measurement sensors installed in the air system and cooling system. The developed model estimates the temperature with a total mean error of −0.2 C. The 95 th and 5 th percentile for all simulated data is 1.4 C respectively −2.8 C. The model was also shown to be robust against input errors in a sensitivity analysis done for a representative test case.
- PostSand erosion in dilute and dense mixtures. An Eulerian and Lagrangian CFD-study of wear correlations.(2012) Hybert, Martin; Granberg, Oscar; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsSand erosion is the cause of widespread structural damage in offshore pipe systems and it is often associated with large costs. Correlative and empirical methods are often used to predict erosion rates. Such procedures, however, tend to yield overly conservative estimates. In this thesis, a Lagrangian CFD model has been compared with some of the main correlative methods for predicting erosion in gas streams for pipe bends and blinded tees. It is found that the correlative methods differ by several orders of magnitude. The DNV RP O501 correlation under-predicts erosion by more than one order of magnitude for low density fluid mixtures at velocities below 10 m/s. Maximum erosion rates are obtained at intermediate sand particle diameters both for the pipe bend and blinded tee. Furthermore, an Eulerian model for high particle loadings, derived for use in fluidized-bed combustors, has been adapted to predict erosion on steel grades. The model reproduces similar erosion patterns, as well as velocity and particle diameter dependencies, as correlative methods suggest. The magnitude of erosion has not been reproduced, presumably due to an erroneous proportionality constant. Eulerian methods are associated with inherent losses of vital information, such as the particle impingement angle and impact phenomena. We believe that the outlook is generally poor for accurate wear predictions in the Eulerian framework and capturing of effects such as lowered erosion efficiency in dense mixtures.
- PostSemi-Physical Modelling Approach for Exhaust Aftertreatment System of Heavy Duty Diesel Engines(2018) Narayanan, Badhri; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime SciencesThe aim of this thesis work was to establish a kinetic and heat transfer model for the Diesel Oxidation Catalyst (DOC) using GT-Suite. The kinetic model was calibrated using a transient Part Load Map (PLM) driving cycle. The inhibition functions of the reactions were tuned to obtain a good curve fitting of reaction species. When a different drive cycle was applied, the model predictability was poor. The result demands a requirement for better heat transfer modelling. Adetailed external Heat transfer model was set up for this purpose. The results were better and the model was found to account for thermal mass variations in the system. The flow along the DOC was non-uniform, a 2 DOC model was established to account for the unequal inlet flow split and improved thermal mass understanding of the model. The results of the 2 DOC model however were inferred to be the same as 1 DOC. A discussion of results and a future outlook are presented.
- PostThermal control of a lab-scale in-situ reator for soot oxidation(2016) Biro, Annika; Eriksson, Rebecka; Chalmers tekniska högskola / Institutionen för tillämpad mekanik; Chalmers University of Technology / Department of Applied MechanicsCFD simulations were coupled with lab-scale experiments to study steep temperature increases (thermal fronts) during thermal regeneration of a diesel particulate filter (DPF) via soot oxidation. The study investigated the conditions under which these fronts appear. A more well-defined open-flow system in contrast to a wall-flow system as in DPFs was used for practicality reasons. An open-flow reactor was developed and soot oxidation experiments were carried out, using Printex-U and a synthetic gas mixture. Different operating conditions were used to provoke thermal fronts in the reactor. A peak of high temperature was observed, which is dependent on the conditions used. Input data from the experiments was used to develop a 2D CFD model and verification was done via comparison with a numerical study. The validity of the model was assessed via the ability of the model to predict the temperature profile obtained from the experiments. Kinetic expressions for non-catalytic oxidation for both diesel soot and Printex-U were evaluated. The soot reaction rate in the simulations is found to be very sensitive to kinetic parameters. The obtained CFD model is able to predict soot oxidation at low reaction rates. However, at high reaction rates numerical instabilities occur due to large gradients in the domain. Reasons for this can be oversimplification of the soot layer, but also the use of a very large time step. A thermal front that moves across the substrate during soot oxidation as reported by other studies (numerical and experimental) could not be obtained. It is found that oxygen depletion or soot depletion is needed in order to observe a moving thermal front which was not achieved under the experimental conditions used in this work. Mass transfer simulations suggest that mass transfer limitations are the main reason for this. Through coupling of the experimental and numerical results the placement of the thermocouples in the reactor is found to be very important to get a representative temperature measurement. It is finally concluded that the open-flow configuration cannot be used to predict the behavior of a DPF configuration.
- PostWater contamination of a side view camera monitoring system. Understanding how driving conditions and design features affect dynamics of airborne droplets using CFD and experiments(2023) Hamidi, Oskar; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Ström, Henrik; Eidevåg, TobiasEvery year, an estimated 1.3 million lives are lost in traffic collisions. To make driving safer, hazard detecting safety technology is continuously developed, relying on sensors such as cameras to monitor the road. A side view Camera Monitoring System is a tech nology that enables wider rear view vision, revealing the driver’s blind-spot and overall increases visibility in dusk and dawn glaring-conditions. However, the camera is suscep tible to soiling by water droplets, obstructing its lens and hindering its function. This project aimed to increase the understanding of airborne water droplet contamination of a prototype Camera Monitoring System, designed specifically for the project. The theoreti cal droplet dynamics were used to derive a computational model capable of simulating the problem in Simcenter STAR-CCM+ using an Eulerian-Lagrangian approach on a simpli fied aerodynamic body in different driving conditions. Design features of the prototype were evaluated by altering the shape of its glareshield, adding a drainage groove and streamlining the flow at its arm. The designs and bluff body were all tested in Volvo Cars Aerodynamic Wind Tunnel to produce comparable results to the simulations. The project concluded that majority of airborne droplets within the camera’s wake region de form, with some fragmenting into smaller droplets. Subsequently, the droplet drag force would be underestimated if deformation was excluded from the drag model. Drag was also the most significant droplet force, although both gravity and pressure gradient forces became significant for larger droplets, with the latter increasing their response to the flow. Few of the smallest droplets from the primary road spray would soil the prototype, instead airborne droplets would mostly originate from rupturing films of accumulated water at the face’s circumference. Most of the larger droplets would not reach the lens, but deposition size would increase with driving velocity. Grounded droplets were observed migrating to the camera face instead of rupturing in experiments, where they could coalesce with other deposited droplets to form a self-cleaning mechanism, although the likelihood of favoring film ruptures would increase with driving velocity. The simulated ideal drainage groove only permitted the smallest droplets to soil the camera, whilst the real groove would overflow which would permit larger droplets to reach the face, but it did also prevent the migrations. A deeper or wider glareshield would reduce soiling, but when slanted the glareshield would be more susceptible to soiling in both experiments and simulations. Finally, the size of the camera’s wake would decrease when flattening its arm, leading to a reduction in contamination.
- PostWurster fluidized bed coating: Integrative validation of coarse-grained CFD-DEM(2023) Kjaer Jepsen, Philip; Chalmers tekniska högskola / Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Sasic, Srdjan; Martin De Juan, Luis