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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Striping on flexo post-printed corrugated board

Holmvall, Martin January 2007 (has links)
<p>Striping is the most common print non-uniformity on corrugated board. It is defined as periodic print density and/or print gloss variations parallel to the flutes. Corrugated boards are mainly printed with flexography, making striping a major concern for the flexographic post-printing industry. In spite of its long history, the basic mechanisms of striping have not been fully understood, and no concrete solution has been provided. The objective of this thesis is to obtain an understanding of the fundamental mechanisms behind and a solution to striping. Both experimental and numerical approaches have been taken in thiswork. Nonlinear finite element models have been constructed in both corrugated board and halftone dot scales to determine the pressure distributions in the printing nip. Ink transfer experiments have been performed to determine the print density vs. pressure relations. Parametric studies have been done for the effects of printing system variables and deformations. The results showed that striping is predominantly print density variations caused by pressure variations in the printing nip. The pressure variations are inherent to the corrugated board structure. Washboarding was shown to play a minor part in causing print density variations, but might contribute to gloss striping. A new printing plate design has been proposed to eliminate the pressure variations and hence the print density striping.</p>
2

Mass Transport and Kinetic Phenomena in Catalytic Polymerization of Olefins

Kittilsen, Pål January 2001 (has links)
Parts of this thesis have been rewritten and published in various journals. These parts are not included in the on-line version of the thesis.
3

Striping on flexo post-printed corrugated board

Holmvall, Martin January 2007 (has links)
Striping is the most common print non-uniformity on corrugated board. It is defined as periodic print density and/or print gloss variations parallel to the flutes. Corrugated boards are mainly printed with flexography, making striping a major concern for the flexographic post-printing industry. In spite of its long history, the basic mechanisms of striping have not been fully understood, and no concrete solution has been provided. The objective of this thesis is to obtain an understanding of the fundamental mechanisms behind and a solution to striping. Both experimental and numerical approaches have been taken in thiswork. Nonlinear finite element models have been constructed in both corrugated board and halftone dot scales to determine the pressure distributions in the printing nip. Ink transfer experiments have been performed to determine the print density vs. pressure relations. Parametric studies have been done for the effects of printing system variables and deformations. The results showed that striping is predominantly print density variations caused by pressure variations in the printing nip. The pressure variations are inherent to the corrugated board structure. Washboarding was shown to play a minor part in causing print density variations, but might contribute to gloss striping. A new printing plate design has been proposed to eliminate the pressure variations and hence the print density striping.
4

Mass Transport and Kinetic Phenomena in Catalytic Polymerization of Olefins

Kittilsen, Pål January 2001 (has links)
Parts of this thesis have been rewritten and published in various journals. These parts are not included in the on-line version of the thesis.
5

Minimum Energy Requirements in Complex Distillation Arrangements

Halvorsen, Ivar Johan January 2001 (has links)
<p>Distillation is the most widely used industrial separation technology and distillation units are responsible for a significant part of the total heat consumption in the world’s process industry. In this work we focus on directly (fully thermally) coupled column arrangements for separation of multicomponent mixtures. These systems are also denoted Petlyuk arrangements, where a particular implementation is the dividing wall column. Energy savings in the range of 20-40% have been reported with ternary feed mixtures. In addition to energy savings, such integrated units have also a potential for reduced capital cost, making them extra attractive. However, the industrial use has been limited, and difficulties in design and control have been reported as the main reasons. Minimum energy results have only been available for ternary feed mixtures and sharp product splits. This motivates further research in this area, and this thesis will hopefully give some contributions to better understanding of complex column systems.</p><p>In the first part we derive the general analytic solution for minimum energy consumption in directly coupled columns for a multicomponent feed and any number of products. To our knowledge, this is a new contribution in the field. The basic assumptions are constant relative volatility, constant pressure and constant molar flows and the derivation is based on Underwood’s classical methods. An important conclusion is that the minimum energy consumption in a complex directly integrated multi-product arrangement is the same as for the most difficult split between any pair of the specified products when we consider the performance of a conventional two-product column. We also present the V<sub>min</sub>-diagram, which is a simple graphical tool for visualisation of minimum energy related to feed distribution. The V<sub>min</sub>d-diagram provides a simple mean to assess the detailed flow requirements for all parts of a complex directly coupled arrangement.</p><p>The main purpose in the first part of the thesis has been to present a complete theory of minimum energy in directly coupled columns, not a design procedure for engineering purposes. Thus, our focus has been on the basic theory and on verification and analysis of the new results. However, based on these results, it is straightforward to develop design procedures including rigorous computations for real feed mixtures without the idealized assumptions used to deduce the analytic results.</p><p>In part 2 we focus on optimization of operation, and in particular the concept of self-optimizing control. We consider a process where we have more degrees of freedom than are consumed by the product specifications. The remaining unconstrained degrees of freedom are used to optimize the operation, given by some scalar cost criterion. In addition there will in practice always be unknown disturbances, model uncertainty and uncertainty in measurements and implementation of manipulated inputs, which makes it impossible to precalculate and implement the optimal control inputs accurately.</p><p>The main idea is to achieve <i>self-optimizing control</i> by turning the optimization problem into a constant setpoint problem. The issue is then to find (if possible) a set of variables, which when kept at their setpoints, indirectly ensures optimal operation.</p><p>We have used the ternary Petlyuk arrangement to illustrate the concept. It is a quite challenging case where the potential energy savings may easily be lost if we do not manage to keep the manipulated inputs at their optimal values, and the optimum is strongly affected by changes in feed composition and column performance. This also applies to the best control structure selection, and we believe that the reported difficulties in control are really a control structure problem (the task of selecting the best variables to control and the best variables to manipulate).</p><p>In this analysis we present in detail the properties of the Petlyuk arrangement, and show how important characteristics depend on the feed properties and product purity. We have used finite stage-by-stage models, and we also show how to use Underwood’s equations to compute the energy consumption for infinite number of stages for any values of the degrees of freedom. Such computations are very simple. The results are accurate and in terms of computation time, outperform simulations with finite stage-by-stage models by several magnitudes. The analysis gives a basic understanding of the column behaviour and we may select operating strategies based on this knowledge for any given separation case. In some cases there will be a quite flat optimality region, and this suggests that one of the manipulated inputs may be kept constant.We also show that the side-stream purity has strong impact on the optimality region. One observation is that a symptom of sub-optimal operation can be that we are unable to achieve high sidestream purity, and not necessarily increased energy consumption. </p><p>In summary, the presented results contribute to improved understanding and removal of some uncertainties in the design and operation of directly integrated distillation arrangements.</p>
6

Controllability analysis for process and control system design

Faanes, Audun January 2003 (has links)
<p>Controllability is the ability of a process to achieve acceptable performance, and in this thesis we use controllability analysis in the design of buffer tanks, feedforward controllers, and multivariable controllers such as model predictive control (MPC).</p><p>There is still an increasing pressure on the process industry, both from competitors (prize and quality) and the society (safety and pollution), and one important contribution is a smooth and stable production. Thus, it is important to dampen the effect of uncontrolled variations (disturbances) that the process may experience.</p><p>The process itself often dampens high-frequency disturbances, and feedback controllers are installed to handle the low-frequency part of the disturbances, including at steady state if integral action is applied. However, there may be an intermediate frequency range where neither of these two dampens the disturbances sufficiently. In the first part of this thesis we present methods for the design of buffer tanks based on this idea. Both mixing tanks for quality disturbances and surge tanks with “slow” level control for flow-rate variations are addressed.</p><p>Neutralization is usually performed in one or several mixing tanks, and we give recommendations for tank sizes and the number of tanks. With local PI or PID control, we recommend equal tanks, and give a simple formula for the total volume. We also give recommendations for design of buffer tanks for other types of processes. We propose first to determine the required transfer function to achieve the required performance, and thereafter to find a physical realization of this transfer function.</p><p>Alternatively, if measurements of the disturbances are available, one may apply feedforward control to handle the intermediate frequency range. Feedforward control is based mainly on a model, and we study the effect of model errors on the performance. We define feedforward sensitivities. For some model classes we provide rules for when the feedforward controller is effective, and we also design robust controllers such as μ -optimal feedforward controllers.</p><p>Multivariable controllers, such as model predictive control (MPC), may use both feedforward and feedback control, and the differences between these two also manifest themselves in a multivariable controller. We use the class of serial processes to gain insight into how a multivariable controller works. For one specific MPC we develop a state space formulation of the controller and its state estimator under the assumption that no constraints are active. Thus, for example the gains of each channel of the MPC (from measurements to the control inputs) can be found, which gives further insight into to the controller. Both a neutralization process example and an experiment are used to illustrate the ideas.</p> / Paper 4 reprinted with kind permission of the Research Council of Norway Paper 8 reprinted with kind permission of Elsevier Publishing, http://www.sciencedirect.com
7

Minimum Energy Requirements in Complex Distillation Arrangements

Halvorsen, Ivar Johan January 2001 (has links)
Distillation is the most widely used industrial separation technology and distillation units are responsible for a significant part of the total heat consumption in the world’s process industry. In this work we focus on directly (fully thermally) coupled column arrangements for separation of multicomponent mixtures. These systems are also denoted Petlyuk arrangements, where a particular implementation is the dividing wall column. Energy savings in the range of 20-40% have been reported with ternary feed mixtures. In addition to energy savings, such integrated units have also a potential for reduced capital cost, making them extra attractive. However, the industrial use has been limited, and difficulties in design and control have been reported as the main reasons. Minimum energy results have only been available for ternary feed mixtures and sharp product splits. This motivates further research in this area, and this thesis will hopefully give some contributions to better understanding of complex column systems. In the first part we derive the general analytic solution for minimum energy consumption in directly coupled columns for a multicomponent feed and any number of products. To our knowledge, this is a new contribution in the field. The basic assumptions are constant relative volatility, constant pressure and constant molar flows and the derivation is based on Underwood’s classical methods. An important conclusion is that the minimum energy consumption in a complex directly integrated multi-product arrangement is the same as for the most difficult split between any pair of the specified products when we consider the performance of a conventional two-product column. We also present the Vmin-diagram, which is a simple graphical tool for visualisation of minimum energy related to feed distribution. The Vmind-diagram provides a simple mean to assess the detailed flow requirements for all parts of a complex directly coupled arrangement. The main purpose in the first part of the thesis has been to present a complete theory of minimum energy in directly coupled columns, not a design procedure for engineering purposes. Thus, our focus has been on the basic theory and on verification and analysis of the new results. However, based on these results, it is straightforward to develop design procedures including rigorous computations for real feed mixtures without the idealized assumptions used to deduce the analytic results. In part 2 we focus on optimization of operation, and in particular the concept of self-optimizing control. We consider a process where we have more degrees of freedom than are consumed by the product specifications. The remaining unconstrained degrees of freedom are used to optimize the operation, given by some scalar cost criterion. In addition there will in practice always be unknown disturbances, model uncertainty and uncertainty in measurements and implementation of manipulated inputs, which makes it impossible to precalculate and implement the optimal control inputs accurately. The main idea is to achieve self-optimizing control by turning the optimization problem into a constant setpoint problem. The issue is then to find (if possible) a set of variables, which when kept at their setpoints, indirectly ensures optimal operation. We have used the ternary Petlyuk arrangement to illustrate the concept. It is a quite challenging case where the potential energy savings may easily be lost if we do not manage to keep the manipulated inputs at their optimal values, and the optimum is strongly affected by changes in feed composition and column performance. This also applies to the best control structure selection, and we believe that the reported difficulties in control are really a control structure problem (the task of selecting the best variables to control and the best variables to manipulate). In this analysis we present in detail the properties of the Petlyuk arrangement, and show how important characteristics depend on the feed properties and product purity. We have used finite stage-by-stage models, and we also show how to use Underwood’s equations to compute the energy consumption for infinite number of stages for any values of the degrees of freedom. Such computations are very simple. The results are accurate and in terms of computation time, outperform simulations with finite stage-by-stage models by several magnitudes. The analysis gives a basic understanding of the column behaviour and we may select operating strategies based on this knowledge for any given separation case. In some cases there will be a quite flat optimality region, and this suggests that one of the manipulated inputs may be kept constant.We also show that the side-stream purity has strong impact on the optimality region. One observation is that a symptom of sub-optimal operation can be that we are unable to achieve high sidestream purity, and not necessarily increased energy consumption. In summary, the presented results contribute to improved understanding and removal of some uncertainties in the design and operation of directly integrated distillation arrangements.
8

Controllability analysis for process and control system design

Faanes, Audun January 2003 (has links)
Controllability is the ability of a process to achieve acceptable performance, and in this thesis we use controllability analysis in the design of buffer tanks, feedforward controllers, and multivariable controllers such as model predictive control (MPC). There is still an increasing pressure on the process industry, both from competitors (prize and quality) and the society (safety and pollution), and one important contribution is a smooth and stable production. Thus, it is important to dampen the effect of uncontrolled variations (disturbances) that the process may experience. The process itself often dampens high-frequency disturbances, and feedback controllers are installed to handle the low-frequency part of the disturbances, including at steady state if integral action is applied. However, there may be an intermediate frequency range where neither of these two dampens the disturbances sufficiently. In the first part of this thesis we present methods for the design of buffer tanks based on this idea. Both mixing tanks for quality disturbances and surge tanks with “slow” level control for flow-rate variations are addressed. Neutralization is usually performed in one or several mixing tanks, and we give recommendations for tank sizes and the number of tanks. With local PI or PID control, we recommend equal tanks, and give a simple formula for the total volume. We also give recommendations for design of buffer tanks for other types of processes. We propose first to determine the required transfer function to achieve the required performance, and thereafter to find a physical realization of this transfer function. Alternatively, if measurements of the disturbances are available, one may apply feedforward control to handle the intermediate frequency range. Feedforward control is based mainly on a model, and we study the effect of model errors on the performance. We define feedforward sensitivities. For some model classes we provide rules for when the feedforward controller is effective, and we also design robust controllers such as μ -optimal feedforward controllers. Multivariable controllers, such as model predictive control (MPC), may use both feedforward and feedback control, and the differences between these two also manifest themselves in a multivariable controller. We use the class of serial processes to gain insight into how a multivariable controller works. For one specific MPC we develop a state space formulation of the controller and its state estimator under the assumption that no constraints are active. Thus, for example the gains of each channel of the MPC (from measurements to the control inputs) can be found, which gives further insight into to the controller. Both a neutralization process example and an experiment are used to illustrate the ideas. / Paper 4 reprinted with kind permission of the Research Council of Norway Paper 8 reprinted with kind permission of Elsevier Publishing, http://www.sciencedirect.com
9

Vätgasutvecklande nickelelektroder : Vätningens inverkan vid beläggning med metallkloridbaserad lösning på nickelytor. / Hydrogen producing nickel electrodes - The effect of wetting when coating with metal chloride based solution on nickel surfaces

Haeggström, Marcus January 2020 (has links)
The production of hydrogen gas might be a part of the transition towards renewable fuels. Hydrogen can be used as fuel, electricity or heat with the help of an energy converter. In the production of hydrogen gas, electrolysis is usually used, which means that water is split into hydrogen and oxygen. Permascand AB in Ljungaverk is one of the world leaders in the production of electrodes and equipment for the electrochemical process industry and water treatment. One product that Permascand produces is hydrogen-developing cathodes, which is a nickel substrate coated with a metal chloride-based solution. In order for these cathodes to have long a service life and as uniform a quality as possible on the finished metal oxide coating, the coating solution must wet the substrate sufficiently. The purpose of the study is to investigate how different pre-treatments of the substrate affect the wetting of the surface. The wetting is measured with contact angle measurements and the various pre-treatments are pickling with HCl, blasting and pre-oxidation in the oven. These pre-treatments are varied and combined to see how they affects wetting.   The results show that with pickling alone, the temperature of the pickling bath has the greatest effect on the contact angle compared to the concentration and time. Combining pickling and blasting gives a contact angle of over 120 ° which is not desirable for coating work. Pre-oxidizing a sample in 30 or 60 was found to be able to lower the contact angle from 120 ° for a sample that was both blasted and worked to a contact angle of 82 ° and 73 °, respectively.   Pre-treated samples are also affected by a time aspect from the time the sample is processed until it is coated. The result of a completed time study shows that the contact angle of a sample deteriorates at most for the first eight hours. / Produktionen av vätgas kan vara en del av dagens omställning från fossila bränslen till förnyelsebara bränslen. Vätgas kan användas som bränsle, el eller värme med hjälp av en energiomvandlare, bränslecell. Vid tillverkningen av vätgas används vanligen elektrolys, vilket innebär att vatten spjälkas till vätgas och syrgas. Permascand AB i Ljungaverk är ett av de världsledande företag som tillverkar elektroder och utrustning till elektrokemisk processindustri och vattenrening. En av produkterna Permascand idag producerar är vätgasutvecklande katoder vilket är ett nickelsubstrat belagt med en metallkloridbaserad lösning. För att dessa katoder ska få en så lång livslängd samt en så jämn kvalitet som möjligt på den färdiga metalloxidbeläggningen krävs bland annat beläggningslösningen väter substratet tillräckligt. Studiens syfte är att undersöka hur olika förbehandlingar av substratet påverkar vätningen av ytan. Vätningen mäts med kontaktvinkelmätningar och de olika förbehandlingarna är betning med HCl, blästring samt föroxidering i ugn. Dessa förbehandlingar varieras och kombineras för att se hur det påverkar vätningen.   Resultaten visar att vid enbart betning har betbadets temperatur störst inverkan på kontaktvinkeln jämfört med koncentrationen och tiden. Att kombinera betning och blästring ger en kontaktvinkel på över 120° vilket inte är önskvärt vid beläggningsarbeten. Att föroxidera ett prov i 30 eller 60 visade sig kunna sänka kontaktvinkeln från 120° för ett prov som både var blästrad och betad till en kontaktvinkel på 82° respektive 73°.   Förbehandlade prover påverkas även av en tidsaspekt från det att provet behandlats till dess den beläggs. Resultatet av en genomförd tidsstudie visar att ett provs kontaktvinkel försämras som mest de först åtta timmarna.
10

Diffusive properties of granitic rock as measured by in-situ electrical methods

Löfgren, Martin January 2005 (has links)
<p>Diffusion into the rock matrix has been identified as one of the most important retention mechanisms for dissolved contaminants in fractured crystalline rock. In this thesis the diffusive properties of granitic rock, described by the formation factor, have been investigated by electrical methods. These methods are based on the Einstein relation between diffusivity and ionic mobility. Formation factors have been obtained both in the laboratory and in deep lying rock in-situ. </p><p>At present, two locations in Sweden, Forsmark and Oskarshamn, are undergoing site investigations for the siting of a repository for spent nuclear fuel. As a part of these investigations, the formation factor of the rock surrounding five, 1000 m deep boreholes has been investigated. More than 250 rock samples, taken from the bore cores, have been investigated in the laboratory and around 50 000 formation factors have been obtained in-situ. The results have been treated statistically and it appears that the formation factor is lognormally distributed. The mean and standard deviation of the obtained log-normal distributions vary from site to site, depending on the geology. For intact granitic rock, the obtained formation factors range between 2.2·10-7 and 2.5·10-2. </p><p>The results suggest that diffusion into open, but hydraulically non-conductive fractures may have a significant influence on radionuclide retention by way of increasing it. Therefore, the fractured rock formation factor was introduced in addition to the traditional rock matrix formation factor. The retardation capacity of crystalline rock is strongly associated with the pore connectivity. In this thesis, it is shown that the micropore network of granitic rock is connected on, at least, a metre scale in-situ.</p>

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