1,720,975 research outputs found
A model-based control system design for a coffee roasting process
Full text linkMEng (Chemical Engineering), North-West University, Potchefstroom Campus, 2018Coffee roasting is both a science and an art. Various models have been proposed in order to model the coffee roasting process. A model developed by Schwartzberg (2002) and validated by Vosloo (2016) is used in this study to develop a control strategy for a batch rotating-drum coffee roaster. The control strategy is based on experimentally determined parameters, and validated by simulated data. In addition to the control strategy the controllability of the process is investigated.
It was experimentally determined that there is an initial time frame (90 seconds) during the roasting process that is deemed uncontrollable, most likely due to evaporative cooling taking place during the initial drying phase of the roasting process.
The coffee roasting process was determined to be a lag-dominant first-order plus time delay process which may be approximated, and therefore modelled as a pure integrating system with an average dead-time of 20 seconds. This is in accordance with Hugo (2017) and Ruscio (2010). Initially a relative gain array (RGA) analysis was conducted based on simulated data to determine the best pairing of manipulated and controlled variables, in order to meet the control objective which is the recreating of a roast profile (i.e. the time vs. temperature plot of the roasted bean batch). The final control strategy is based on the RGA results recommending a single-input single-output (SISO) control system utilising the derivative of the roast profile as controlled variable, and the liquid petroleum gas (LPG) flow to the system as manipulated variable. A possible threshold control strategy to be used in combination with the developed control strategy is discussed qualitatively.
The control design methods used were the internal model control (IMC) (based on the pure integrating approximation of the process), the Cohen and Coon and integral of the time-weighted absolute error (ITAE) methods (based on the actual lag-dominant first-order plus time delay behaviour of the process).
The best performing controller was determined to be an IMC-based PI controller that utilises the average determined process parameters. This controller was fine-tuned in order to enhance its performance. The stability margins of the final controller were analysed using Bode plots.
Keywords: Model-based control, pure integrator, coffee roasting, roast profile, roast profile derivative, parameter scheduling.Master
Modelling the influence of physicochemical material feed properties on ammonium nitrate product quality
Full text linkMEng (Chemical Engineering, North-West University, Potchefstroom Campus, 2017In this study the effect of the physicochemical material feed properties of ammonium nitrate on the product granule quality in a fluidised bed granulator was investigated.
The effect of atomising air pressure, binder spray concentration, binder spray temperature, binder spray rate and feed particle size on the final particles’ abrasion resistance, size, shape, porosity and flowability was investigated on a production plant using a five factor, five level central composite design. The data obtained from the experimental work was then subjected to regression analysis, where multiple linear regression models with and without two-way interaction effects as well as a second order regression model was obtained for each of the quality parameters. The models obtained were evaluated by using the coefficient of determination (R2), the mean square error (MSr) and the F-test. The models deemed adequate were then validated using a different data set.
The abrasion resistance and particle shape was adequately described by multiple linear regression equations with two-way interactions. The identified physicochemical material feed properties of ammonium nitrate therefore successfully describes both the particles’ resistance to abrasion as well as the particle shape. The particle size was positively evaluated during the model development phase but proved to be inadequate during validation. The physicochemical material feed properties of ammonium nitrate and the experimental design alone were unable to describe the particle size adequately.
All the regression models obtained for both the particle porosity and flowability were deemed inadequate in describing these two quality parameters during both the model development and validation phases. Both quality parameters are associated with high measurement errors which could explain the complete inefficiency of the models obtained.
A further in-depth investigation of the particle size, particle porosity and flowability is needed to quantify the effect of the physicochemical material feed properties of ammonium nitrate on these quality parametersMaster
A statistical model of an ammonium nitrate fluidised bed granulator
No full textMEng (Chemical Engineering), North-West University, Potchefstroom Campus, 2017The inference modelling of a continuous industrial ammonium nitrate fluidised bed granulator was investigated. Fluidised bed granulators are difficult to model and control due to a large number of operating variables and long sample analysis time.
This study aims at developing inference models using the multiple linear regression (MLR) modelling technique to predict the output variables. These MLR models are qualitatively compared to the artificial neural network (ANN) modelling technique.
The granulation process starts with seed particles that are fluidised by air. These fluidised particles are sprayed with a solution of ammonium nitrate and water to induce granule growth. The final particles exit the granulator and are sieved to form the final product. Different literature sources obtained correlations between most of the operating variables concerning the output variables. Some authors obtained significant regression and ANN models that provided accurate predictions.
A screening phase is conducted to determine the significance of the chosen operating variables. The complete randomise experimental design is used where each operating variable is varied randomly from each run to produce unbiased data and lower the number of data points required for model development.
The input variables include the fluidising air flow rate, fluidising air temperature, spray liquid flow rate, spray liquid temperature, spray liquid concentration, seed particle size and the seed particle size distribution slope. The output variables consist of the production rate, recycle ratio, efficiency, product porosity, product circularity, product mean particle size, product particle size distribution slope, granulator mean particle size and granulator particle size distribution slope.
The correlations between the operating and output variables are determined using the Spearman’s rho correlation technique. It is concluded that the spray liquid variables had the strongest correlations with the output variables and are therefore important variables for the MLR main effect models.
Accurate main effects (MLR-M) and interaction effects (MLR-I) multiple linear regression models were developed with a fair performance. The addition of the two-way interactions increased the accuracy and performance of the MLR-I models. The adjusted coefficient of multiple determination was used to evaluate the addition of these variables. The MLR-I models were compared to the ANN models that included all the independent variables (ANN-
I). The MLR-I models performed in some cases better than the ANN-I due to undertraining from the ANN-I models.
The production rate, recycle ratio, efficiency and granulator particle slope models were accurate enough for prediction purposes. Future work can include the optimisation of the ANN models and the investigation of additional variables for inference modelling, e.g. the bed height, bed density and granulator humidity. A control system using the developed models can also be developed and evaluated on the plant.Master
CFD modelling of an ammonium nitrate fluidised bed: effect of distribution plate geometry
Full text linkMEng. (Chemical Engineering), North-West University, Potchefstroom CampusFluidisation, which is a process governed by the suspension of particles in a closed area by blowing air or another medium through the bed of particles, is gaining popularity in industries like pharmaceuticals and mining, to name a few. Contributing researchers developed theory and conducted experiments in an attempt to understand this concept of fluidisation. A wide range of investigations have been conducted, but according to current knowledge, no information was reported on the fluidisation of porous granular ammonium nitrate (PGAN). According to Geldart classification, PGAN falls under Group B particles therefore the behaviour of the particles are expected to be in agreement with that was observed for sand-like particles. The aim of this study is to investigate the effect of different distributor plates on bed hydrodynamics related to an ammonium nitrate fluidised bed in laboratory-scale and pilot-scale setup by: (i) obtaining the characteristics of different suggested distributor plates for use in the fluidisation of PGAN for modelling purposes in a CFD environment, (ii) generating a CFD model for PGAN granules fluidisation that can effectively reproduce the bed pressure drop versus superficial gas velocity curve for different distributor plates using PGAN granules with different particle sizes, and (iii) devising, using the CFD model, means to determine bed density and bed expansion for the (PGAN) fluidisation operation. The plate pressure drop against superficial gas velocity curve was plotted to calculate Darcy- Forchheimer coefficients which were used in the CFD model environment to characterise the distributor plates. The plate pressure drop was found to increase with increasing superficial gas velocity. In the laboratory-scale investigation, the behaviour of the distributor plates was investigated for both a straight duct configuration and bend duct configuration below the distributor plate, while cone-shaped and column-shaped ducts were used in the pilot-scale setup. The model provided a good representation of the experimental observations for both laboratory and pilot-scale fluidisation setups. The velocity profiles obtained from employing the porousSimpleFoam solver with porous media specified by the Darcy-Forchheimer coefficients were used to generate a polynomial function which was employed to specify the boundary conditions of air in the two-phase system. The bed pressure drop versus superficial gas velocity curves resulting from modelled data follow the trend proposed in the literature, therefore the model can be used to predict the bed pressure drop of a fluidised bed system. Fluidisation initialises quicker in the predictive model than in the experimental setups. The model overestimates the bed pressure drop for particles with small average particle diameters and underestimates the bed pressure drop for particles with higher average particle diameters. The model predicts the bed pressure drop accurately at low superficial gas velocities and the error increases with an increase in superficial gas velocity. The range of minimum fluidisation velocity for all particle sizes in the laboratory scale fluidised bed was found to be 0.3-0.6 m/s. Flow patterns were discussed for particles with an average particle diameter of 1.8 mm when fluidising with a superficial gas velocity of 1.1 m/s in a model for 2 seconds. The particles were specified as alpha.particles with a void fraction of 55%. Jetting was observed in a system with a straight duct configuration below the distributor plate. It was concluded that a preferential flow resulted when employing straight ducting configurations as well as bend ducting configurations in the air inlet duct below the distributor plates, both resulting in a high final particle content towards the walls of the duct after a running time of 2s. The fluidised bed expands in general quicker in the model compared to the experiments, but little to no correspondence in behaviour was observed for a bend ducting configuration system due to preferential flow patterns observed in the system. The bed expansion ratio was found to be directly proportional to superficial gas velocity up to a certain (maximum) extent. The bed pressure drop measured along the horizontal axis of the fluidised bed in the direction of the position of the air blower at three different probe positions above the perforated plate was used to calculate bed density across the bed. There was no significant correspondence observed between the experimental bed density and the modelled bed density using plates associated with either a straight duct configuration or a bend duct configuration. A higher bed density was observed when measuring directly above the plate due to high particle content at that position. For all the plates in the pilot-scale setup, the superficial gas velocity and probe position have influenced the bed density. An increase in e.g. the height of measurement above the plate resulted in a decrease in the measured fluidised bed density.Master
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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