CFD Simulation of Aerocyclone Hydrodynamics and Performance at Extreme Temperature

This work presents a Computational Fluid Dynamics calculation to predict and to evaluate the hydrodynamics and performance of a cyclone operating at extreme temperature. The numerical solutions were carried out using commercial CFD code FLUENT 6.1. The simulation was realised using a Reynolds stress model (RSM) for turbulent modelling and discrete phase model (DPM) for particle trajectories calculation. The kinetic theory was employed to predict the physical gas properties, i.e., ρ, Cp and μ as they vary with the operating temperature. The CFD simulations predict excellently the cyclone performance and gas properties at extreme operating conditions with a deviation of about 5% from the experimental data. The physical mechanism for cyclones operating under high temperature has been also successfully elucidated. Results obtained from the computer modelling exercise have demonstrated that CFD is a reliable method of modelling the cyclone performance at extreme temperature. Therefore, similar method can be applied to examine the effects of operating temperature on the cyclone performance. This method of analysis is almost certainly less expensive than experiment, and represents a cost-effective route for design optimisatio

Numerical Simulation of Cyclone Efficiency and Pressure Drop

The Department of Environment Malaysia (DOE) has been regulating particulate emission since the 1978. More stringent environmental regulations have resulted in considerable research into ways of reducing harmful and gloomy particulate emissions. Cyclones are probably the most commonly used means of separating dust from gases, controlling pollution, collecting particulate product or recovering catalyst particles from fluidised reactors. Their popularity is due to low maintenance and investment costs. Cyclone design maybe simple but models use to predict the cyclone efficiency and pressure drop are not always accurate. The objective of this study is to carry out simulation via a commercial spreadsheet, MS EXCEL and CFD code FLUENT 6.1, on cyclone design, efficiency, and pressure drop for particulate emission control. In this study, CFD code FLUENT and four cyclone collection models earlier developed by other researchers are used for prediction of cyclone efficiency. This study focuses on various operating conditions of cyclone and the simulation result is then verified via experimental data published in the literature. The model with the best prediction on experimental data is then used to evaluate the effects of cyclone configuration, dimension, and variable on its collection efficiency. The cyclone pressure drop calculations are performed using CFD and empirical models adopted from the literature. These four empirical models and CFD are compared with presented experimental data available in the literature.All the modelling and simulation of cyclone efficiency and pressure drop are proved to be satisfactory when compared with the presented experimental data. The CFD simulations and Li and Wang model predict excellently the cyclone cut-off size for all operating conditions with a deviation of 3 and 6% from the experimental data respectively. The CFD simulations also predict excellently the cyclone pressure drop under different temperature and inlet velocity with a maximum deviation of 3% from the experimental data. Specifically, results obtained from the computer modelling exercise have demonstrated that CFD and Li and Wang model is a best method of modelling cyclones collection efficiency and pressure drop. The result or finding obtained from the research work can be used to develop a cyclone with greater separation efficiency, which is capable of removing up to 99% of PM5. This cyclone can then be used for particulate pollutant control from industrial factory to the atmosphere

A CFD Study Of A Partial Combustion Lance

This paper presents a computational fluid dynamics (CFD) simulation of a partial combustion lance (PCL) aiming to evaluate the effect of oxygen flowrate on its performance. At first, the modelling strategy was developed by evaluating the effect of discretization, pressure interpolation scheme and turbulence models on the prediction accuracy. Three turbulence models namely standard kε (SKE), realizable k-ε (RKE) and renormalized (RNG) k-ε were used. Combustion was modelled using the species transport model, whereas the heat transfer was calculated by considering a combined convection-radiation boundary condition. The best CFD prediction was obtained using the thirdorder MUSCL, PRESTO pressure interpolation scheme and SKE, yielding an error of 4.79% from the experimentally measured temperature. It was found that 40% increase in oxygen flowrate increased the peak combustion temperature of the PCL by about 12%. Dual lance was found to be more effective than the single lance operating at a similar flowrate. The finding obtained from this work may be useful for design retrofits of a PCL

Mixing of EFB Fibre - Liquid in Stirred Tank Using Intermig Impellers

Mixing process involving palm oil empty fruit bunch (EFB) and liquid such as in production of the carboxyl methyl cellulose has never been studied. Better understanding of their mixing performance is of great interest in process design and scale-up. This paper presents mixing of palm oil empty fruit bunch (EFB) fibre-liquid in a stirred tank agitated by two Intermig impellers. The tank dimension was H=1.4T with the impeller diameter of 25.5 cm fixed at T/3 and 2T/3, respectively. Measurement of the power draw was carried out using an IKA Eurostar torque meter for a wide range of impeller speed. The result shows relative power draw increases as concentration of EFB fibre increases. The relative power draws increases as much as 5 times higher when concentration of EFB fibre increases from 1 wt.% w/w to 4 wt.%, which suggests higher operational power requirement. The result also suggests that a constant power number (desired mixing characteristic) can be achieved when the tank operates at Reynolds's number above 60000. The Intermig impellers are capable of handling up to 4 wt.% of EFB fibre, which is a significant improvement compared to conventional solid mixing impeller such as the pitched blade impeller which is limited to 2 wt.%. Results from this work might be useful for an efficient design of EFB-liquid mixer or reactor

Computational fluid mixing

Computational fluid dynamics (CFD) is an extremely powerful tool for solving problems associated with flow, mixing, heat and mass transfer and chemical reaction. Although the equations of motion for fluid flow were established in the first half of the nineteenth century (e.g. Navier, 1822; Stokes, 1845), it was not until the arrival of digital computers in the 1960s and 1970s that it became feasible to perform numerical simulations of complex engineering flows. In these early days, CFD was a very much a research tool and most of the early work was aimed at developing numerical methods, solution algorithms and Reynolds-averaged turbulence models. However, in the 1980s, the first commercial codes emerged — e.g. PHOENICS, FLUENT, FIDAP, Star-CD, FLOW3D (which later became CFX) — providing general purpose software packages for both academic and industry users. The aerospace and automotive industries were amongst the first to embrace the use of CFD in engineering design, but from the 1990s onwards commercial codes have found widespread applications, for example in: biomedical engineering, environmental and atmospheric modelling, meteorology, chemical reaction engineering and more recently in the food and beverage industries. This chapter will focus on mixing vessel applications for the last two of these industry sectors, where CFD is increasingly used to provide process understanding and semi-quantitative analysis. In their review, Norton and Sun (2006) presented a graph showing the very significant increase in the number of peer-reviewed papers related to CFD applications to food process engineering. Figure 0.1 is an updated version of this graph, containing more recent data and showing that the number of papers that specifically analyse food mixing operations using CFD is still relatively small. In contrast, there are a vast numbers of papers on CFD simulation of (i) other food process operations, (e.g. drying, sterilisation, thermal treatment and extrusion, many of which are described by Sun (2007)) and (ii) more conventional mixing operations in the chemicals and specialty product industries (see for example, Marshall and Bakker (2004)). This chapter will outline the background knowledge required for CFD studies, present some examples of CFD modelling of mixing vessel flows and finally will discuss the current difficulties in applying this approach to food mixing processes

Scale-up of gas-liquid stirred tanks using coupled computational fluid dynamics and population balance modelling

The main aim of the work was to produce scale-up methods for the design of aerated stirred tanks using a combined computational fluid dynamics (CFD) and population balance approach. First a modeling study of single phase stirred tanks was performed to evaluate the best model features (turbulence model, impeller's model, discretisation, grid etc). Good agreement was obtained between the CFD simulation and the LDA measurement on the time-averaged mean velocities and turbulence quantities. The angle-resolved mean velocities and turbulence quantities were also predicted very well as were the power number and the positions of the vortex cores. The next stage involved the development of a population balance model (PBM) which was carried out first using a well-mixed single compartment implemented in MATLAB to reduce the modeling complexity. The algorithm was validated for various mechanisms, namely breakage, aggregation, nucleation and growth which have an analytical solution available from literature. Tests using realistic models for bubble coalescence and breakage were also carried out with the results showing a reasonable agreement with the Sauter mean bubble sizes obtained from empirical correlations. The algorithm also responded well to changes in the turbulence dissipation rate, the initial bubble size distribution and the local gas hold-up, which suggest that the final bubble size is not affected by the initial bubble size. A fully predictive model must combine both the fluid mechanics and bubble dynamics models which can be performed either by a four-way or three-way coupling simulation. The disadvantage of the latter is that is does not consider the effect of the bubble dynamics in- the two-phase modelling. A four-way coupling (CFD-PBM) method was carried out by implementing the PBM within the CFD code. Various drag models which take into account the effect of distorted bubbles and dense gas dispersion are also considered. Mass transfer models are also implemented using the bubble sizes obtained from the PBM. The CFD-PBM model showed a reasonable prediction of the power number, local bubble sizes, gas hold-up, dissolved oxygen concentration and the mean velocities of the two-phase flow in comparison to experimental data taken from the literature. Finally, the CFD-PBM model was employed to evaluate the consequences of scale-up on the mass transfer rate in aerated stirred tanks agitated either by Rushton turbine or CD-6 impeller with operating volume ranged from 14L to 1500L. Three scale-up rules, namely a constant P IV combined with either constant Fig, Vg and VVM were studied. The simulation results suggest, that a successful scale-up may be achieved by keeping the P IV and VVM constant, which led to a slightly higher (kLa) representing a more conservative approach. In contrast, constant P/V and Vg led to a slight reduction in the rate of mass transfer at larger scale which is in agreement with experimental measurement . from the literature. Results from the CFD-PBM simulation also suggest a similar scale-up rule may be applicable for an advanced gas dispersion impeller such as the CD-6 which yielded a similar scale-up trend to that of a Rushton turbine.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Influence of Solvent Polarity and Conditions on Extraction of Antioxidant, Flavonoids and Phenolic Content from Averrhoa bilimbi

This paper presents the influence of solvent polarity and extraction conditions on the extraction of total flavonoid, total phenolic and antioxidants from Averrhoa bilimbi. The experiment was performed using a different solvent at different extraction conditions, including extraction time (15-240 min), temperature (30-70 °C) and agitation speed (50-300 rpm). Results showed that yields of extraction varies with solvent polarity. Extraction using 50% aqueous methanol gives the highest antioxidant activity and flavonoid content. The highest total flavonoid content (193.3 µg quercetin equivalent/g dry weight), total phenolic content (717.8 µg gallic acid equivalent/g dry weight) and antioxidant activity (77%) was achieved using 50% methanol, at 70 °C and agitation speed of 300 rpm. This work may be useful for obtaining higher bioactive compounds during the extraction process of A. bilimbi

Modelling of mass transfer in gas-liquid stirred tanks agitated by Rushton turbine and CD-6 impeller: a scale-up study

A combined computational fluid dynamics (CFD) and population balance model (PBM) approach has been applied to the simulation of gas-liquid stirred tanks agitated by (i) a Rushton turbine or (ii) a CD-6 impeller, operating at aeration numbers from 0.017 to 0.038. The multiphase simulations were realised via an Eulerian-Eulerian two-fluid model and the drag coefficient of spherical and distorted bubbles was modelled using the Ishii-Zuber equations. The effect of the void fraction on the drag coefficient was modelled using the correlation by Behzadi et al. (2004). The local bubble size distribution was obtained by solving the PBM using the quadrature method of moments (QMOM). The local kLa was estimated using both the Higbie penetration theory and the surface renewal model. The predicted gas-liquid hydrodynamics, local bubble sizes and dissolved oxygen concentration were in good agreement with experimental measurements reported in the literature. A slight improvement in the prediction of the aerated power number was obtained using the non-uniform bubble size distribution resulting from the coupled CFD-PBM simulation. Evaluation of the prospective scale-up approaches indicates a higher probability of maintaining a similar level of mass transfer in a larger tanks by keeping the Pg/V and VVM constant. Considering its predictive capability, the method outlined in this work can provide a useful scale-up evaluation of gas-liquid stirred tanks

Three-Dimensional CFD study of a Candle Ceramic Filter

Tightened environmental legislation enacted as a consequence of government policy has compelled industry to pay serious attention to air pollution issues. Gas cleaning with ceramic filters has proven to be the most important technology for removal of particulate emissions at high temperatures. This paper presents a computational fluid dynamics (CFD) investigation of a rigid candle ceramic filter. The aim is to examine numerically the pressure drop and velocity profile along the candle filter under a filtration mode. The filter element was modeled as a porous medium and the media resistance at x, y and z direction is assumed to be isotropic. The gas flow within the porous media (filter element) is also assumed to be a laminar flow. The CFD calculations show a good agreement with the experimental data, with an average discrepancy around 5%, which probably in the same magnitude of the experimental error. The modeling exercise presented in this study offers an alternative solution for examining a pressure drop in ceramic filter via computational method and may be useful in design of a ceramic filter

Characterization of Ag-promoted Ni/SiO2 Catalysts for Syngas Production via Carbon Dioxide (CO2) Dry Reforming of Glycerol

The carbon dioxide (CO2) dry reforming of glycerol for syngas production is one of the promising ways to benefit the oversupply crisis of glycerol worldwide. It is an attractive process as it converts carbon dioxide, a greenhouse gas into a synthesis gas and simultaneously removed from the carbon biosphere cycle. In this study, the glycerol dry reforming was carried out using Silver (Ag) promoted Nickel (Ni) based catalysts supported on silicon oxide (SiO2). The catalysts were prepared through wet impregnation method and characterized by using Bruanaer-Emmett-Teller (BET) surface area, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and Thermo Gravimetric (TGA) analysis. The experiment was conducted in a tubular reactor which condition fixed at 973 K and CO2: glycerol ratio of 1, under atmospheric pressure. It was found that the main gaseous products are H₂, CO and CH4 with H₂:CO < 1.0. From the reaction study, Ag(5)NiSiO2 results in highest glycerol conversion and hydrogen yield, accounted for 32.6% and 27.4%, respectively