Mass transfer and particleinteractions in granular systems and suspension flows

The purpose of this study was to investigate some important features of granular flows and suspension flows by computational simulation methods. Granular materials have been considered as an independent state ofmatter because of their complex behaviors. They sometimes behave like a solid, sometimes like a fluid, and sometimes can contain both phases in equilibrium. The computer simulation of dense shear granular flows of monodisperse, spherical particles shows that the collisional model of contacts yields the coexistence of solid and fluid phases while the frictional model represents a uniform flow of fluid phase. However, a comparison between the stress signals from the simulations and experiments revealed that the collisional model would result a proper match with the experimental evidences. Although the effect of gravity is found to beimportant in sedimentation of solid part, the stick-slip behavior associated with the collisional model looks more similar to that of experiments. The mathematical formulations based on the kinetic theory have been derived for the moderatesolid volume fractions with the assumption of the homogeneity of flow. In orderto make some simulations which can provide such an ideal flow, the simulation of unbounded granular shear flows was performed. Therefore, the homogeneous flow properties could be achieved in the moderate solid volume fractions. A new algorithm, namely the nonequilibrium approach was introduced to show the features of self-diffusion in the granular flows. Using this algorithm a one way flow can beextracted from the entire flow, which not only provides a straightforward calculation of self-diffusion coefficient but also can qualitatively determine the deviation of self-diffusion from the linear law at some regions nearby the wall inbounded flows. Anyhow, the average lateral self-diffusion coefficient, which was calculated by the aforementioned method, showed a desirable agreement with thepredictions of kinetic theory formulation. In the continuation of computer simulation of shear granular flows, some numerical and theoretical investigations were carried out on mass transfer and particle interactions in particulate flows. In this context, the boundary element method and its combination with the spectral method using the special capabilities of wavelets have been introduced as theefficient numerical methods to solve the governing equations of mass transfer in particulate flows. A theoretical formulation of fluid dispersivity in suspension flows revealed that the fluid dispersivity depends upon the fluid properties and particle parameters as well as the fluid-particle and particle-particle interactions.

Diverse Routes from School, via Higher Education, to Employment. A Comparison of Nine European Countries

The central theme for this study is graduate employment and employability in European-wide discussion. In this study, the complex relationships between higher education and the world of work are explored from the vantage point of how individuals make use of the higher education system in their transition from education to employment. The variation among individual transition processes in nine European countries is analysed with the help of a comparable graduate survey. Countries in this study are Italy, Spain, France, Austria, Germany, the Netherlands, the United Kingdom, Finland, and Norway. The data used for the study is commonly known as the “CHEERS” or “Careers after Higher Education, A European Research Survey.” The data was collected in 1999. The study discusses the possibilities and limitations the higher education system has in supporting the initial education-to-work transitions of youth. The study also addresses problems with comparing national higher education systems in terms of enrolment and graduate employability. A central purpose for this study is to reflect on concerns about the prolongation of individual transitions with a framework that simultaneously considers both the graduate employability and the duration of the education-to-work transition process. The key concept for this study is the standard student/graduate; synonym concepts are the traditional and the conventional student/graduate. Standard graduates are relatively young individuals who are performing their initial transition from education to working-life and who complete the degree-earning process within the stipulated time frame. In all nine countries, standard graduates make up a considerable share of the student flow, passing from higher education to the labour markets. The share of standard graduates is by far the largest in France, where they comprise the overwhelming mass. The proportion of the standard graduates is the lowest in Italy, Finland, and Austria where approximately one in four graduates completed the process of higher education within the stipulated time frame. Of the nine countries compared, employability of the whole graduate population is the greatest in Norway, the UK, Finland, and the Netherlands. Compared with employability of the whole graduate population, variation among the countries is considerably reduced when reviewing the employability of only the standard graduates. Thereby, even though the ranking among countries remains largely unchanged, the variations among them are smaller when the duration of degree earning process is standardized. The study also discusses other ideal types of student careers (or transition processes) besides the standard student/graduate. Results of regression analyses indicate that that at the pan-European level analysis, the graduate labour markets are not heavily segmented in terms of the type of the individual transition process. When considering within-country differences between the graduates, the field of studies is clearly a more powerful explanatory variable than the type of the transition process. There are, nevertheless, clear indications that, irrespective of the country, chances of finding a high status job are, on the average, highest amongst those who graduate within the stipulated duration of the degree program and who thereby have experienced the standard student career, whereas, participating in working life while studying protects against unemployment after finishing one’s degree.

Competitor comparison: variable speed drives in pumping applications

As the world’s energy demand is increasing, a durable solution to control it is to improve the energy efficiency of the processes. It has been estimated that pumping applications have a significant potential for energy savings trough equipment or control system changes. For many pumping application the use of a variable speed drive as a process control element is the most energy efficient solution. The main target of this study is to examine the energy efficiency of a drive system that moves the pump. In a larger scale the purpose of this study is to examine how the different manufacturers’ variable speed drives are functioning as a control device of a pumping process. The idea is to compare the drives from a normal pump user’s point of view. The things that are mattering for the pump user are the efficiency gained in the process and the easiness of the use of the VSD. So some thought is given also on valuating the user-friendliness of the VSDs. The VSDs are compared to each other also on the basis of their life cycle energy costs in different kind of pumping cases. The comparison is made between ACS800 from ABB, VLT AQUA Drive from Danfoss, NX-drive from Vacon and Micromaster 430 from Siemens. The efficiencies are measured in power electronics laboratory in the Lappeenranta University of Technology with a system that consists of a variable speed drive, an induction motor with dc-machine, two power analyzers and a torque transducer. The efficiencies are measured as a function of a load at different frequencies. According to measurement results the differences between the measured system efficiencies on the actual working area of pumping are on average few percent units. When examining efficiencies at the whole range of different loads and frequencies, the differences get bigger. At low frequencies and loads the differences between the most efficient and the least efficient systems are at the most about ten percent units. At the most of the tested points ABB’s drive seem to have slightly better efficiencies than the other drives.

Poka-yoke for mass customization

Producing high quality products and services is one of the key concerns in order to keep up with the competition in the global markets. Companies are putting a great effort on preventing customers having faulty products and services by any means. However, the total elimination of mistakes in manufacturing processes has always been a great challenge for quality management. In this thesis the applicability of poka-yoke methodology in reducing the number of quality failures in the case company has been studied. Poka-yoke stands for the mistake-proofing and is mainly developed for the purpose of eliminating human errors in manufacturing processes. Inspection techniques; judgment, informative and source inspection are in the core of this methodology. Mass customization and large configurability of products leads to situation where the root causes of quality problems may vary a lot. To study the effects of these factors extensive analysis of quality failures was conducted. Recommendations and proposals for further actions regarding problem solving processes and utilization of mistake-proofing methods were provided on the basis of the analysis.

Developing of the Variable Speed Drive -control in simulated parallel pumping systems

This thesis presents briefly the basic operation and use of centrifugal pumps and parallel pumping applications. The characteristics of parallel pumping applications are compared to circuitry, in order to search analogy between these technical fields. The purpose of studying circuitry is to find out if common software tools for solving circuit performance could be used to observe parallel pumping applications. The empirical part of the thesis introduces a simulation environment for parallel pumping systems, which is based on circuit components of Matlab Simulink —software. The created simulation environment ensures the observation of variable speed controlled parallel pumping systems in case of different controlling methods. The introduced simulation environment was evaluated by building a simulation model for actual parallel pumping system at Lappeenranta University of Technology. The simulated performance of the parallel pumps was compared to measured values of the actual system. The gathered information shows, that if the initial data of the system and pump perfonnance is adequate, the circuitry based simulation environment can be exploited to observe parallel pumping systems. The introduced simulation environment can represent the actual operation of parallel pumps in reasonably accuracy. There by the circuitry based simulation can be used as a researching tool to develop new controlling ways for parallel pumps.

Effects of modern variable frequency drive on the reliability of an old crane induction motor

The work aims to analyze the possibilities of utilizing old crane driving AC induction motors in modern pulse-width-modulated variable frequency drives. Bearing currents and voltage stresses are the two main problems associated with modern IGBT inverters, and they may cause premature failure of an old induction motor. The origins of these two problems are studied. An analysis of the mechanism of bearing failure is proposed. Certain types of bearing currents are considered in detail. The most effective and economical means are chosen for bearing currents mitigation. Transient phenomena of cables and mechanism of over voltages occurring at motor terminals are studied in the work. The weakest places of the stator winding insulation system are shown and recommendations are given considering the mitigation of voltage stresses. Only the most appropriate and cost effective preventative methods are chosen for old motor drives. Rewinding of old motors is also considered.

Power line communication in motor cables of variable-speed electric drives − analysis and

Data transmission between an electric motor and a frequency converter is required in variablespeed electric drives because of sensors installed at the motor. Sensor information can be used for various useful applications to improve the system reliability and its properties. Traditionally, the communication medium is implemented by an additional cabling. However, the costs of the traditional method may be an obstacle to the wider application of data transmission between a motor and a frequency converter. In any case, a power cable is always installed between a motor and a frequency converter for power supply, and hence it may be applied as a communication medium for sensor level data. This thesis considers power line communication (PLC) in inverter-fed motor power cables. The motor cable is studied as a communication channel in the frequency band of 100 kHz−30 MHz. The communication channel and noise characteristics are described. All the individual components included in a variable-speed electric drive are presented in detail. A channel model is developed, and it is verified by measurements. A theoretical channel information capacity analysis is carried out to estimate the opportunities of a communication medium. Suitable communication and forward error correction (FEC) methods are suggested. A general method to implement a broadband and Ethernet-based communication medium between a motor and a frequency converter is proposed. A coupling interface is also developed that allows to install the communication device safely to a three-phase inverter-fed motor power cable. Practical tests are carried out, and the results are analyzed. Possible applications for the proposed method are presented. A speed feedback motor control application is verified in detail by simulations and laboratory tests because of restrictions for the delay in the feedback loop caused by PLC. Other possible applications are discussed at a more general level.

Modeling reaction kinetics and mass transfer in ozonation in water solutions

This dissertation is based on four articles dealing with modeling of ozonation. The literature part of this considers some models for hydrodynamics in bubble column simulation. A literature review of methods for obtaining mass transfer coefficients is presented. The methods presented to obtain mass transfer are general models and can be applied to any gas-liquid system. Ozonation reaction models and methods for obtaining stoichiometric coefficients and reaction rate coefficients for ozonation reactions are discussed in the final section of the literature part. In the first article, ozone gas-liquid mass transfer into water in a bubble column was investigated for different pH values. A more general method for estimation of mass transfer and Henry’s coefficient was developed from the Beltrán method. The ozone volumetric mass transfer coefficient and the Henry’s coefficient were determined simultaneously by parameter estimation using a nonlinear optimization method. A minor dependence of the Henry’s law constant on pH was detected at the pH range 4 - 9. In the second article, a new method using the axial dispersion model for estimation of ozone self-decomposition kinetics in a semi-batch bubble column reactor was developed. The reaction rate coefficients for literature equations of ozone decomposition and the gas phase dispersion coefficient were estimated and compared with the literature data. The reaction order in the pH range 7-10 with respect to ozone 1.12 and 0.51 the hydroxyl ion were obtained, which is in good agreement with literature. The model parameters were determined by parameter estimation using a nonlinear optimization method. Sensitivity analysis was conducted using object function method to obtain information about the reliability and identifiability of the estimated parameters. In the third article, the reaction rate coefficients and the stoichiometric coefficients in the reaction of ozone with the model component p-nitrophenol were estimated at low pH of water using nonlinear optimization. A novel method for estimation of multireaction model parameters in ozonation was developed. In this method the concentration of unknown intermediate compounds is presented as a residual COD (chemical oxygen demand) calculated from the measured COD and the theoretical COD for the known species. The decomposition rate of p-nitrophenol on the pathway producing hydroquinone was found to be about two times faster than the p-nitrophenol decomposition rate on the pathway producing 4- nitrocatechol. In the fourth article, the reaction kinetics of p-nitrophenol ozonation was studied in a bubble column at pH 2. Using the new reaction kinetic model presented in the previous article, the reaction kinetic parameters, rate coefficients, and stoichiometric coefficients as well as the mass transfer coefficient were estimated with nonlinear estimation. The decomposition rate of pnitrophenol was found to be equal both on the pathway producing hydroquinone and on the path way producing 4-nitrocathecol. Comparison of the rate coefficients with the case at initial pH 5 indicates that the p-nitrophenol degradation producing 4- nitrocathecol is more selective towards molecular ozone than the reaction producing hydroquinone. The identifiability and reliability of the estimated parameters were analyzed with the Marcov chain Monte Carlo (MCMC) method. @All rights reserved. No part of the publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of the author.

Power Consumption in Carbon Capture and Storage Systems (CCS) and Possibilities to Reduce Power Consumption with Variable Speed Drives

The aim of this master´s thesis is to study which processes increase the auxiliary power consumption in carbon capture and storage processes and if it is possible to reduce the auxiliary power consumption with variable speed drives. Also the cost of carbon capture and storage is studied. Data about auxiliary power consumption in carbon capture is gathered from various studies and estimates made by various research centres. Based on these studies a view is presented how the power auxiliary power consumption is divided between different processes in carbon capture processes. In a literary study, the operation of three basic carbon capture systems is described. Also different methods to transport carbon dioxide and carbon dioxide storage options are described in this section. At the end of the thesis processes that consume most of the auxiliary power are defined and possibilities to reduce the auxiliary power consumption are evaluated. Cost of carbon capture, transport and storage are also evaluated at this point and in the case that the carbon capture and storage systems are fully deployed. According to the results, it can be estimated what are the processes are where variable speed drives can be used and what kind of cost and power consumption reduction could be achieved. Results also show how large a project carbon capture and storage is if it is fully deployed.

Varioituvat moduulit liikuteltavissa murskauslaitoksissa

Tässä diplomityössä tutkitaan Metso Mineralsin moduuli- sekä tuoterakennemaailmaa. Työn tarkoituksena on löytää uusia mahdollisuuksia moduuli- ja tuoterakennemaailman kuvaamiseen sekä niiden hallitsemiseen. Työssä otetaan kantaa asioihin pääsääntöisesti moduulin näkökulmasta. Työssä määritellään kohdeyritystä parhaiten palveleva varioituvan moduulin periaatteellinen rakenne. Työssä annetaan moduulien uudelleenkäytön tehostamiseen sekä helpottamiseen tähtääviä ehdotuksia. Varioituvien moduulien näkökulmasta tarkastellaan nykyisiä tuoterakenneperiaatteita, ja ehdotetaan uutta tapaa lähestyä lopputuotteita. Varioituvien moduulien ja uusien tuoterakenteiden johtamiseen liittyvistä toimenpiteistä annetaan ehdotuksia, sekä määritellään niille omistajuudet. Työn lopputuloksena saadaan kokonaisvaltainen näkemys mahdollisesta tavasta nähdä ja hallita moduuli- ja tuoterakennemaailma.

Mass for the poor

Soitinnus: Kuoro, urut.

Energy efficiency parameters in variable speed drives

The main purpose of this thesis is to measure and evaluate how accurately the current energy saving calculation in ABB’s new variable speed drive ACS850 works. The main topic of this thesis is energy-efficiency parameters. At the beginning of this thesis centrifugal pump, squirrel cage motor and variable speed drive, including some equations related to them, are being introduced. Also methods of throttling control and variable speed drive control of centrifugal pumps are being introduced. These subjects are introduced because the energy saving calculation in ACS850 is related to the centrifugal pumps usually driven by squirrel cage motors. The theory also includes short section about specific energy of pumping. Before measurements the current energy saving calculation of ACS850 is being introduced and analyzed. The measurements part includes introduction of measuring equipment, measurement results, summary and analysis of the measurements. At the end of this thesis a proposal for an improvement to the current energy saving calculation is being introduced and few proposals are made for new energy-efficiency parameters, which could be added to variable speed drives. At the end are also thoughts

Active du/dt Filtering for Variable-Speed AC Drives

An oscillating overvoltage has become a common phenomenon at the motor terminal in inverter-fed variable-speed drives. The problem has emerged since modern insulated gate bipolar transistors have become the standard choice as the power switch component in lowvoltage frequency converter drives. Theovervoltage phenomenon is a consequence of the pulse shape of inverter output voltage and impedance mismatches between the inverter, motor cable, and motor. The overvoltages are harmful to the electric motor, and may cause, for instance, insulation failure in the motor. Several methods have been developed to mitigate the problem. However, most of them are based on filtering with lossy passive components, the drawbacks of which are typically their cost and size. In this doctoral dissertation, application of a new active du/dt filtering method based on a low-loss LC circuit and active control to eliminate the motor overvoltages is discussed. The main benefits of the method are the controllability of the output voltage du/dt within certain limits, considerably smaller inductances in the filter circuit resulting in a smaller physical component size, and excellent filtering performance when compared with typical traditional du/dt filtering solutions. Moreover, no additional components are required, since the active control of the filter circuit takes place in the process of the upper-level PWM modulation using the same power switches as the inverter output stage. Further, the active du/dt method will benefit from the development of semiconductor power switch modules, as new technologies and materials emerge, because the method requires additional switching in the output stage of the inverter and generation of narrow voltage pulses. Since additional switching is required in the output stage, additional losses are generated in the inverter as a result of the application of the method. Considerations on the application of the active du/dt filtering method in electric drives are presented together with experimental data in order to verify the potential of the method.