Browsing by Author "Papadikis, Konstantinos"

Now showing 1 - 5 of 5
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    Application of a high density ratio lattice-Boltzmann model for the droplet impingement on flat and spherical surfaces
    (Elsevier, 2014-06-06) Zhang, Duo; Papadikis, Konstantinos; Gu, Sai
    In the current study, a 3-dimensional lattice Boltzmann model which can tolerate high density ratios is employed to simulate the impingement of a liquid droplet onto a flat and a spherical target. The four phases of droplet impact on a flat surface, namely, the kinematic, spreading, relaxation and equilibrium phase, have been obtained for a range of Weber and Reynolds numbers. The predicted maximum spread factor is in good agreement with experimental data published in the literature. For the impact of the liquid droplet onto a spherical target, the temporal variation of the film thickness on the target surface is investigated. The three different temporal phases of the film dynamics, namely, the initial drop deformation phase, the inertia dominated phase and the viscosity dominated phase are reproduced and studied. The effect of the droplet Reynolds number and the target-to-drop size ratio on the film flow dynamics is investigated.
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    CFD modelling of particle shrinkage in a fluidized bed for biomass fast pyrolysis with quadrature method of moment
    (Elsevier, 2017-05-08) Liu, Bo; Papadikis, Konstantinos; Gu, Sai; Fidalgo, Beatriz; Longhurst, Philip J.; Li, Zhongyuan; Kolios, Athanasios
    An Eulerian-Eulerian multi-phase CFD model was set up to simulate a lab-scale fluidized bed reactor for the fast pyrolysis of biomass. Biomass particles and the bed material (sand) were considered to be particulate phases and modelled using the kinetic theory of granular flow. A global, multi-stage chemical kinetic mechanism was integrated into the main framework of the CFD model and employed to account for the process of biomass devolatilization. A 3-parameter shrinkage model was used to describe the variation in particle size due to biomass decomposition. This particle shrinkage model was then used in combination with a quadrature method of moment (QMOM) to solve the particle population balance equation (PBE). The evolution of biomass particle size in the fluidized bed was obtained for several different patterns of particle shrinkage, which were represented by different values of shrinkage factors. In addition, pore formation inside the biomass particle was simulated for these shrinkage patterns, and thus, the density variation of biomass particles is taken into account.
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    Micro-scale CFD modeling of reactive mass transfer in falling liquid films within structured packing materials
    (Elsevier, 2015-02) Sebastia-Saez, Daniel; Gu, Sai; Ranganathan, Panneerselvam; Papadikis, Konstantinos
    Post-combustion carbon capture in structured packing columns is considered as a promising technology to reduce greenhouse gas (GHG) emissions because of its maturity and the possibility of being retrofitted to existing power plants. CFD plays an important role in the optimization of this technology. However, due to the current computational capacity limitations, the simulations need to be divided into three scales (i.e. micro-, meso- and macro-scale) depending on the flow characteristics to be analyzed. This study presents a 3D micro-scale approach to describe the hydrodynamics and reactive mass transfer of the CO2-MEA chemical system within structured packing materials. Higbie's penetration theory is used to describe the mass transfer characteristics whereas enhancement factors are implemented to represent the gain in the absorption rate attributable to the chemical reaction. The results show a detrimental effect of the liquid load on the absorption rate via a decrease in the enhancement factor. The evolution of the wetted area for MEA solutions is compared to the case of pure water highlighting the differences in the transient behavior. The CO2 concentration profiles are examined showing the capability of the model to reproduce the depletion of the solute within the bulk liquid ascribed to the high value of the Hatta number. Also, several approaches on the reaction mechanism such as reversibility and instantaneous behavior are assessed. The results from micro-scale are to be used in meso-scale analysis in future studies to optimize the reactive absorption characteristics of structured packing materials.
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    Micro-scale CFD study about the influence of operative parameters on physical mass transfer within structured packing elements
    (Elsevier Science B.V., Amsterdam, 2014-09-01T00:00:00Z) Sebastia-Saez, Daniel; Gu, Sai; Ranganathan, Panneerselvam; Papadikis, Konstantinos
    In this work a VOF-based 3D numerical model is developed to study the influence of several operative parameters on the gas absorption into falling liquid films. The parameters studied are liquid phase viscosity, gas phase pressure and inlet configuration, liquid-solid contact angle and plate texture. This study aims to optimize the post-combustion CO2 capture process within structured packed columns. Liquid phase viscosity is modified via MEA (i.e. monoethanolamine) concentration. The results show that an increase in liquid viscosity reduces the diffusivity of oxygen within the liquid film thus hindering the efficiency of the process. Higher pressure carries an absorption improvement that can be attractive to be applied in industry. The simulations show that enhanced oxygen absorption rates can be achieved depending on the velocity of the gas phase and the flow configuration (i.e. co- and counter-current). Also, the importance of wetting liquid-solid contact angles (i.e. less than 90°) is highlighted. Poor liquid-solid adhesion has similar effects as surface tension in terms of diminishing the spreading of the liquid phase over the metallic plate. Finally the influence of a certain geometrical pattern in the metallic surface is also assessed.
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    A numerical model for the fractional condensation of pyrolysis vapours
    (Elsevier, 2015-01-20) Palla, V. S. Kiran Kumar Palla; Papadikis, Konstantinos; Gu, Sai
    Experimentation on the fast pyrolysis process has been primarily focused on the pyrolysis reactor itself, with less emphasis given to the liquid collection system (LCS). More importantly, the physics behind the vapour condensation process in LCSs has not been thoroughly researched mainly due to the complexity of the phenomena involved. The present work focusses on providing detailed information of the condensation process within the LCS, which consists of a water cooled indirect contact condenser. In an effort to understand the mass transfer phenomena within the LCS, a numerical simulation was performed using the Eulerian approach. A multiphase multi-component model, with the condensable vapours and non-condensable gases as the gaseous phase and the condensed bio-oil as the liquid phase, has been created. Species transport modelling has been used to capture the detailed physical phenomena of 11 major compounds present in the pyrolysis vapours. The development of the condensation model relies on the saturation pressures of the individual compounds based on the corresponding states correlations and assuming that the pyrolysis vapours form an ideal mixture. After the numerical analysis, results showed that different species condense at different times and at different rates. In this simulation, acidic components like acetic acid and formic acids were not condensed as it was also evident in experimental works, were the pH value of the condensed oil is higher than subsequent stages. In the future, the current computational model can provide significant aid in the design and optimization of different types of LCSs.