Licentiatavhandling (sammanfattning) Stockholm : Kungliga Tekniska högskolan, 2009. / Härtill 3 uppsatser.

The Yankee cylinder is used in most of Metso Paper's machines. It is used in the drying and creping process. Since the outcome of these processes largely affect the paper's final quality it is important that the Yankee cylinder behaves in a controlled fashion. One important parameter affecting the behaviour of the Yankee cylinder is its surface temperature. The objective of this thesis was to search for and evaluate methods for measuring the surface temperature of a Yankee cylinder during operation. Metso Paper is looking for a method having an accuracy of ΔT = 1°C, a response time of t<10 ms, and being portable. Three different instruments were tested during the thesis: Thermophone, a contact measurement device currently used by Metso Paper. RAYNGER MX4, a pyrometer from Raytek. FLIR P640, a thermographic camera with a 640x480 focal plane array from FLIR. The instruments were tested by performing measurements on Metso Paper's pilot machine in Karlstad during operation. The measurements revealed drawbacks for all three instruments. The biggest drawbacks of the Thermophone was its response time, t~5 min, and its dependence on the frictional heating of the teflon cup. The frictional heating causes the measured temperature to increase even after 15 min making it hard to know when to stop the measurement. How much the frictional heating affects the measured temperature was difficult to analyse, making it a suggestion for future studies. The biggest drawback of the pyrometer and the thermographic camera is the measurement error due to emissivity errors. Since the Yankee cylinder have a varying surface finish the emissivity varies a lot along the surface introducing temperature errors as large as ΔT=30°C. Two methods that claim to be emissivity independent were investigated; double-band and gold cup pyrometers. Double-band pyrometers require the target to be a grey body and for it to have large temperatures, T>300°C, making this method unsuitable for measuring the surface temperature of the Yankee cylinder. Gold cup pyrometers require the gold hemisphere to have a reflectance of ρ=1. Because of the environment surrounding the Yankee cylinder it would be difficult keeping the gold hemisphere as clean as required making this method unsuitable as well.

This thesis concerns the analytical and numerical analysis of the water vapour condensation from the multicomponent mixture of condensable and noncondensable gases in the area of the nuclear reactor thermal-hydraulic safety. Following an extensive literature review in this field three aspects of the condensation phenomenon have been taken into consideration: a surface condensation, a liquid condensate interaction with gaseous mixtures and a spontaneous condensation in supersaturated mixtures. In all these cases condensation heat and mass transfer rates are significantly dependent on the local mixture intensive parameters like for example the noncondensable species concentration. In order to analyze the multicomponent mixture distribution in the above-mentioned conditions, appropriate simplified physical and mathematical models have been formulated. Two mixture compositions have been taken into account: a binary mixture of water vapour with heavy noncondensable gas and a ternary mixture with two noncondensable gases with different molecular weights. For the binary mixture a special attention has been focused on the heavy gas accumulation in the near-interface region and the influence of liquid film instabilities on the interface heat and mass transfer phenomena. For the ternary mixture of gases a special attention has been paid to the influence of the light gas and induced buoyancy forces on the condensation heat and mass transfer processes. Both analytical and numerical methods have been used in order to find solutions to these problems. The analytical part has been performed applying the boundary layer approximation and the similarity method to the system of film and mixture conservation equations. The numerical analysis has been performed with the in-house developed code and commercial CFD software. Performing analytical and CFD calculations it has been found that most important processes which govern the multicomponent gas distribution and condensation heat transfer degradation are directly related to the interaction between interface mass balances and buoyancy forces. It has been observed that if the influence of the liquid film instabilities is taken into consideration the heat transfer enhancement due to the presence of different types of waves is directly related to the internal film hydrodynamics and shows up in the mixture-side heat transfer coefficient. The model developed for the dispersed phase growth shows that degradation of the condensation heat transfer rate, which is a consequence of degradation of the convective mass flux, should be taken into account for highly supersaturated gaseous mixtures and can be captured by combination with the mechanistic CFD surface condensation model. Keywords: condensation, noncondensable gases, CFD simulation, boundary-layer approximation, binary and ternary mixtures / <p>QC 20100623</p>

<p>The Yankee cylinder is used in most of Metso Paper's machines. It is used in the drying and creping process. Since the outcome of these processes largely affect the paper's final quality it is important that the Yankee cylinder behaves in a controlled fashion. One important parameter affecting the behaviour of the Yankee cylinder is its surface temperature.</p><p>The objective of this thesis was to search for and evaluate methods for measuring the surface temperature of a Yankee cylinder during operation. Metso Paper is looking for a method having an accuracy of ΔT = 1°C, a response time of t<10 ms, and being portable.</p><p>Three different instruments were tested during the thesis:</p><ul><li>Thermophone, a contact measurement device currently used by Metso Paper.</li><li>RAYNGER MX4, a pyrometer from Raytek.</li><li>FLIR P640, a thermographic camera with a 640x480 focal plane array from FLIR.</li></ul><p>The instruments were tested by performing measurements on Metso Paper's pilot machine in Karlstad during operation. The measurements revealed drawbacks for all three instruments. The biggest drawbacks of the Thermophone was its response time, t~5 min, and its dependence on the frictional heating of the teflon cup. The frictional heating causes the measured temperature to increase even after 15 min making it hard to know when to stop the measurement. How much the frictional heating affects the measured temperature was difficult to analyse, making it a suggestion for future studies.</p><p>The biggest drawback of the pyrometer and the thermographic camera is the measurement error due to emissivity errors. Since the Yankee cylinder have a varying surface finish the emissivity varies a lot along the surface introducing temperature errors as large as ΔT=30°C.</p><p>Two methods that claim to be emissivity independent were investigated; double-band and gold cup pyrometers. Double-band pyrometers require the target to be a grey body and for it to have large temperatures, T>300°C, making this method unsuitable for measuring the surface temperature of the Yankee cylinder.</p><p>Gold cup pyrometers require the gold hemisphere to have a reflectance of ρ=1. Because of the environment surrounding the Yankee cylinder it would be difficult keeping the gold hemisphere as clean as required making this method unsuitable as well.</p>

Light scattering in turbid media is essential for such diverse application areas as paper and print, computer rendering, optical tomography, astrophysics and remote sensing. This thesis investigates angular variations of light reflected from plane-parallel turbid media using both mathematical models and reflectance measurements, and deals with several applications. The model of most widespread use in industry is the Kubelka-Munk model, which neglects angular variations in the reflected light. This thesis employs a numerical solution of the angle resolved radiative transfer problem to better understand how the angular variations are related to medium properties. It is found that the light is reflected anisotropically from all media encountered in practice, and that the angular variations depend on the medium absorption and transmittance and on the angular distribution of the incident light. If near-surface bulk scattering dominates, as in strongly absorbing or highly transmitting media or obliquely illuminated media, relatively more light is reflected in large polar (grazing) angles. These results are confirmed by measurements using a set of paper samples. The only situation with isotropic reflectance is when a non-transmitting, non-absorbing medium is illuminated diffusely. This is the only situation where the Kubelka-Munk model is exactly valid. The results also show that there is no such thing as an ideal bulk scattering diffusor, and these findings can affect calibration and measurement procedures defined in international standards.The implications of the presented results are studied for a set of applications including reflectance measurements, angle resolved color and point spreading. It is seen that differences in instrument detection and illumination geometry can result in measurement differences. The differences are small and if other sources of error - such as fluorescence and gloss - are not eliminated, the differences related to instrument geometry become difficult to discern. Furthermore, the angle resolved color of a set of paper samples is assessed both theoretically and experimentally. The chroma decreases and the lightness increases as the observation polar angle increases. The observed differences are clearly large, and it is an open issue how angle resolved color should be handled. Finally, the dependence of point spreading in turbid media on the medium parameters is studied. The asymmetry factor is varied while maintaining constant the optical response in a standardized measurement geometry. It is seen that the point spreading increases as forward scattering becomes more dominant, and that the effect is larger if the medium is low-absorbing with large mean free path. A generic model of point spreading must therefore capture the dependence on all of these medium parameters.This thesis shows that turbid media reflect light anisotropically, and angle resolved radiative transfer models are therefore necessary to capture this. Using simplified models can introduce errors in an uncontrolled manner. The results presented potentially have consequences for all applications dealing with light scattering, some of which are studied here.

Materials with biotechnological applications and materials that interact with the biological environment play an ever increasing role in our lives and society. In order to be able to tailor specific properties of these materials to suit their intended applications, it is important to gain a deeper understanding of the relationship between the material structure and its function. This thesis contributes to the goal of achieving a better understanding of the functional properties of materials through the development of novel characterizing methods as well as the analysis of such materials. Electrodynamic and mechanical spectroscopy methods are developed or employed in the characterization of three classes of materials, namely, pharmaceutical, biomedical and biological materials. Two electrodynamic methods utilizing conductivity measurements were developed for the investigation of drug release from pharmaceutical dosage forms, particularly in low liquid volumes. Furthermore, a mechanical spectroscopy method based on the split Hopkinson pressure bar setup was developed for the viscoelastic characterization of pharmaceutical compacts. It was shown that this method is a valuable complement to other methods of characterization. Dielectric spectroscopy was integrated with microfabrication techniques to create a method for bacteria detection in a biotechnological application. As well, dielectric spectroscopy was used in the characterization of a novel biomimetic ionomer and was demonstrated to be a powerful tool for studying the bulk molecular dynamics of this functional material. The work presented in this thesis not only provides an enhanced understanding of materials and their functional properties, but also presents new methods that should be useful for the future characterization of such materials.

Electroacoustic technology has in many ways revolutionised the wireless telecommunication industry. The IC compatible fabrication technique of thin film electroacoustic devices has so far provided a considerable increase in device performance and reduction in size. At the moment, new areas where this technology can be of use is under investigation. In particular, thin film bulk acoustic wave resonators are promising candidates for biochemical and gravimetric sensor applications. For bulk acoustic waves, the thesis addresses a number of aspects in the design, fabrication, characterisation, and integration of thin film electroacoustic devices. The object of the studies conducted in the thesis has been to improve on design and thereby optimise the performance of the device to fit a particular application of interest. For high frequency and high power applications, a conceptually new design of the solidly mounted resonator has been investigated. A 1 GHz plate wave resonator with a much higher Q factor than its surface acoustic counterpart have also been fabricated. A multi-chip-module 2 GHz microwave oscillator featuring a monolithically integrated solidly mounted resonator and a flip chip transistor have been fabricated and characterised with a phase noise of -125 dBc/Hz at 100 kHz. For sensor applications, the fabrication of shear mode solidly mounted resonators featuring c-axis inclined AlN films has been studied. A process for the bonding of a microfluidic system on top of the resonator has been realised. Further, the effect of conductive liquids on the resonator performance has been investigated.For surface acoustic wave devices, acoustic manipulation of particles in microfluidic channels has been studied. Two functional devices have been fabricated by bonding piezoelectric substrates to glass or fused silica superstrates. By generating an interface acoustic wave, that propagates along the bonded interface, manipulation of sub-micrometer particles was realised. / wisenet

<p>The power quality of modern society relies on the electrical properties of the dielectric insulators used in the power industry. Much research work has been conducted with an aim to understand and predict the insulating behaviour of such materials under different kinds of atmospheric conditions, but still there are many unsolved problems. In particular, there is a lack of knowledge concerning the electrohydrodynamic and electrophysical processes at the insulator surface and the surrounding medium. No detailed knowledge exists at present of the processes governing the development of electrical discharges along the surface of insulators.</p><p>With an aim to enhance the knowledge in this field in general and on the electrical performance of outdoor insulators in particular a detailed study of the positive streamer discharges in air and along dielectric surfaces was conducted. The study was also extended to gain more knowledge on the water drop initiated electrical discharges in air and the attachment of natural lightning flashes to a Franklin conductor.</p><p>In the first phase, the study was focused on positive streamer discharges propagating in air. The spatial distribution of the charge of a branched streamer discharge was obtained and the charge contained in a single streamer branch was quantified. In the second phase measurements and simulations of streamer discharges propagating along insulating surfaces were conducted with an aim to understand how the insulating surfaces interact with streamer discharges. In addition to quantifying the parameters of streamer discharges propagating along insulating surfaces, the results of these studies made it possible to separate and quantify the effects of the dielectric constant and the surface properties on the streamer discharges. In the third phase a comprehensive computer algorithm was developed to simulate 3-dimensional propagation of positive streamer discharges in air and along dielectric surfaces taking into account the branching effect. </p><p>The conditions necessary for the initiation of streamer discharges were applied to obtain the minimum strength of the background electric field required to initiate electrical discharges in the presence of water drops. In particular the study provided an explanation of how lightning flashes are initiated in thunderclouds in background electric fields as low as 200 kV/m. Finally, the study was extended to understand the performance of lightning conductors paying special attention to the influence of conductor radius and the streamer inception criterion.</p>

<p>The optical properties of electrochromic materials can be changed by application of an electrical voltage. The conventional electrochromic device consists of several thin films of electrochromic materials and layers for electron- and ion conduction. The ion conductor in devices intended for applications using visible light is often a polymer electrolyte that is used to laminate two half-cells together. The miniaturization of satellites has led to reduced mass and volume available for systems to handle temperature variations onboard. The satellite will be submitted to large variations in the radiating environment in an earth bound orbit. An electrochromic device could provide adaptable radiation exchange due to its variable infrared optical properties. The polymer electrolyte is not a desirable component in the space environment, but it can be replaced by an inorganic thin film so that an all-thin-film (ATF) device is obtained. </p><p>This thesis investigates the optical properties of amorphous and crystalline WO₃, as well as the performance of ATF devices with sputtered ZrO₂ as the ion conductor. The infrared reflectance for Li-intercalated WO₃ has been measured in the wavelength range 2-50 mm. The near infrared absorption for low intercalation levels showed good agreement with large polaron theory. The infrared reflectance increased with higher intercalation levels and exhibited a free-electron behaviour. The infrared reflectance of a laminated device with polymer electrolyte was measured, and the calculated emittance varied between 0.56 and 0.65. The ATF device consisted of thin films of WO₃, ZrO₂ and NiV_xO_yH_z, as well as evaporated Al top contacts. The substrates were commercial ITO on glass. The emittance for different device designs was calculated from reflectance measurements, and could be varied between 0.33 and 0.59. This makes them strong contenders to other contemporary emittance modulating devices.</p>

<p>In this thesis permanent magnet direct drive generator for power conversion from water currents is studied. Water currents as a power source involves a number of constrains as well as possibilities, especially when direct drive and permanent magnets are considered. The high power fluxes and low current velocities of a water current, in combination with its natural variations, will affect the way the generator is operated and, flowingly, the appearance of the generator. The work in this thesis can, thus, be categorized into two general topics, generator technology and optimization. Under the first topic, fundamental generator technology is used to increase the efficiency of a water current generator. Under the latter topic, water current generators are optimized to a specific environment. The conclusion drawn from this work is that it is possible to design very low speed direct drive generators with good electromagnetic properties and wide efficiency peak.</p>