<p>Soot and radiation play an important role when designing practical combustion devices, and great efforts have been put into developing models which describe soot formation and oxidation. The Eddy Dissipation Concept (EDC) has proven to describe turbulent combustion well, and has the flexibility to describe chemical kinetics in a detailed manner. The aim of this work is to study how the EDC handles soot models based on a detailed representation of the gas-phase chemical kinetics.</p><p>Two versions of a semi-empirical soot model is used in conjunction with the EDC. Concentrations of various intermediate species are used as input to the soot models.</p><p>The implementation of the new soot models is discussed in relation to the previous implementation of a less detailed soot model. To assure that the interaction between soot and the gas-phase species is represented correctly, the soot models are implemented with a two-way coupling of soot and gas-phase kinetics.</p><p>Soot is a good radiator. In a sooting flame a substantial amount of energy will be transferred to the surroundings by thermal radiation. This transfer of energy will alter the temperature field of the flame and the change in temperature will affect the kinetics of soot and gas-phase chemistry. To simulate sooting flames correctly, it was therefore necessary to include a radiation model.</p><p>To validate the coupled models of turbulence, combustion, soot, and radiation two different turbulent flames were simulated. One turbulent jet flame of methane and one turbulent jet flame of ethylene. For both flames the computed results were compared with measured values.</p><p>Several aspects of the simulations are studied and discussed, such as the effect of the two-way coupling of soot and gas-phase kinetics on both soot yield and gas-phase composition, and the importance of a suitable radiation model.</p><p>The two-way coupling of soot and gas phase kinetics is shown to have a positive effect on the computed soot volume fractions, and the results are considered to be encouraging. The work has demonstrated that the EDC has the capacity to handle different types of chemical reaction mechanisms, such as mechanisms for gas-phase combustion and soot kinetics, without modification.</p>

Soot and radiation play an important role when designing practical combustion devices, and great efforts have been put into developing models which describe soot formation and oxidation. The Eddy Dissipation Concept (EDC) has proven to describe turbulent combustion well, and has the flexibility to describe chemical kinetics in a detailed manner. The aim of this work is to study how the EDC handles soot models based on a detailed representation of the gas-phase chemical kinetics. Two versions of a semi-empirical soot model is used in conjunction with the EDC. Concentrations of various intermediate species are used as input to the soot models. The implementation of the new soot models is discussed in relation to the previous implementation of a less detailed soot model. To assure that the interaction between soot and the gas-phase species is represented correctly, the soot models are implemented with a two-way coupling of soot and gas-phase kinetics. Soot is a good radiator. In a sooting flame a substantial amount of energy will be transferred to the surroundings by thermal radiation. This transfer of energy will alter the temperature field of the flame and the change in temperature will affect the kinetics of soot and gas-phase chemistry. To simulate sooting flames correctly, it was therefore necessary to include a radiation model. To validate the coupled models of turbulence, combustion, soot, and radiation two different turbulent flames were simulated. One turbulent jet flame of methane and one turbulent jet flame of ethylene. For both flames the computed results were compared with measured values. Several aspects of the simulations are studied and discussed, such as the effect of the two-way coupling of soot and gas-phase kinetics on both soot yield and gas-phase composition, and the importance of a suitable radiation model. The two-way coupling of soot and gas phase kinetics is shown to have a positive effect on the computed soot volume fractions, and the results are considered to be encouraging. The work has demonstrated that the EDC has the capacity to handle different types of chemical reaction mechanisms, such as mechanisms for gas-phase combustion and soot kinetics, without modification.

<p>Micro Electro Mechanical Systems (MEMS) produced to date include IR detectors, accelerometers, pressure sensors, micro lenses, actuators, chemical sensors, gear drives, RF devices, optical processor chips, micro robots and devices for biomedical analysis. The track for tomorrow has already been set and products like 3D TV, physician on a chip, lab on a chip, micro aircraft and food safety sensors will be developed when the technology matures and the market is ready.</p><p>Todays MEMS fabrication is typically based around a silicon substrate and borrow batch fabrication processes from the IC industry. Many of the developed MEMS products have never left a laboratory environment because they are fragile in the macro environment. The way to deal with this is to provide proper packaging so that they can be handled. This poses one of the major challenges in the MEMS industry. Not many packaging techniques have been commercially developed for MEMS and companies that have overcome the packaging problems very seldom reveal their packaging techniques. Functional problems that could be associated with a MEMS structure are often amplified by the package. The reason for this is often associated with packaging stress. Packaging stress related problems is what has kept many promising products from emerging on the market. Even the commercially available pressure sensors and accelerometers have packaging stress problems, but most of them have been overcome. A first step towards solving these challenges is to localise, quantify and understand the critical packaging stresses that act in a packaged MEMS device.</p><p>The goal of this work was to understand how packaging stresses act in a plastic moulded MEMS chip. The work has been threefold; simulation of transfer moulding, static stress analysis of the plastic capsule after moulding and modelling of the piezo-resistive behaviour of a MEMS pressure sensor.</p><p>This dissertation is divided into 9 chapters. Chapter 1 introduces the concept of level-0 and level-1 packaging and looks at different techniques of obtaining the different packaging levels. It introduces the Small Outline Package (SOP) which is the package that has been simulated in this dissertation.</p><p>Chapter 2 gives the background in the theory that has been used to complete this work. It starts by discussing the chemistry and mechanics of thermosetting polymers. Then the rheological behaviour of Epoxy Moulding Compounds (EMC) in a transfer moulding process is discussed. </p><p>The experimental results from the thermomechanical material characterisation of the EMC are presented in Chapter 3. The material was found to have a Tg of 130^oC and coefficient of linear expansion of /oC and /oC below and above Tg respectively. It was further found that the material showed linear viscoelastic behaviour. Stress relaxation tests were run to obtain the relaxation coefficients needed for accurate modelling. The material was found to behave in a thermo rheologically simple manner and the WLF shift function was used to describe the time-temperature superposition principle.</p><p>Chapter 4 addresses the applicability of the plastic processing simulation code, C-Mold, for simulations of MEMS packaging in a SOP. It was found that the 2.5D simulation technique used by the software was inadequate for simulating the polymer filling of the SOP in question. This conclusion was drawn because 3D flow effect were observed in the moulding cavities. The cause for the 3D flow effect was the height of the SOP which was relatively large in order to accommodate for the MEMS device. However, the software proved to be very useful for balancing the runner system.</p><p>Chapter 5 starts with the development of a novel method for calculating the accurate piezoresistance for implanted silicon piezo-resistors. The method let each finite element in a piezoresistor region represent one resistor in a resistor network. The total resistance was then found by simple resistor summation. This method was then utilized on a silicon diaphragm pressure sensor, which had four piezo-resistors implanted into the top surface. The resistors on the diaphragm formed a Wheatstone bridge and the change in piezo-resistance, as a result of applied pressure and hence change in the stress field, was transformed into an electrical signal by proper post processing. The model was built from the design specifications of a commercially manufactured die. The results were compared to the production measurements and matched the data within one standard deviation. It was found that the level-0 package had an effect on the output signal. This work is believed to be the first to report an estimation of the distortion effect that a level-0 package has on a sensor signal with temperature.</p><p>Chapter 6 presents the model of the complete MEMS pressure sensor component encapsulated by EMC in a SOP. The EMC was treated as being elastic and temperature dependent. The method that was developed and calibrated in Chapter 5 was used as an indirect measure of the accuracy of the FEM model. It was evident that the package had a profound effect on the sensor signal. This was consistent with the actual measured data. The match of the signal data was not satisfactory. The signal values for two of the four service temperatures lay outside 3 standard deviations of the experimentally measured results. The estimated sensitivity of the die also fell outside 3 standard deviations for three of the four service temperatures.</p><p>A special vector plot was developed to understand how the pressure, or packaging stress, from the EMC effected the signal and sensitivity of the sensor die. The numerical simulations were done assuming a stress free temperature of 175^oC, the moulding temperature. The packaging stress was found to increase with decreasing temperature. This was the effect of the subsequent increase in ΔT as the service temperature decreased.</p><p>The signal at zero pressure was found to shift as a function of temperature. This was caused by the packaging stress and a corresponding stress-field-shift on the diaphragm. The origin for this shift was an uneven packaging stress between the front and the back side of the sensor die. At -7^oC, the pressure on the front and the back was 30 and 20MPa respectively. This caused an uneven bending moment on the membrane long sides and resulted in a shift in the stress field.</p><p>Chapter 7 elaborated the model one step further by treating the EMC as a viscoelastic material. The result of using the viscoelastic material model showed a reduction in the packaging stress due to stress relaxation. Viscoelastic materials are temperature and strain-history dependent. It was therefore necessary to run the model through the same processes posed by the manufacturing of the MEMS and SOPs. These included a set of thermocycles between -40^oC and 125^oC before the signals as a function of temperature and pressure were taken. The thermocycles were found to have a positive effect on signal shifting. Less signal distortion was seen with more cycles. The estimated and measured signal- vs. temperature-values matched within two standard deviations. The estimated sensitivities did not match the experimental measurements any better than those obtained for the elastic case. It was also found that sensitivity was nearly independent on packaging stress, but significantly dependent on pressure loading conditions.</p><p>The use of the viscoelastic model gave an improvement in simulated signal accuracy over the elastic model. It became clear that the EMC had to be treated as a viscoelastic material.</p><p>Chapter 8 concerned the change in material properties of the EMC and the impact this had on the FEM results. It was found that the behaviour of the MEMS pressure sensor was greatly affected by such changes.</p><p>Chapter 9 present the concluding remarks of this study.</p>

<p>The current study has investigated two-phase refrigerant flow distribution in heat exchange manifolds. Experimental data have been acquired in a heat exchanger test rig specially made for measurement of mass flow rate and gas and liquid distribution in the manifolds of compact heat exchangers. Twelve different manifold designs were used in the experiments, and CO² and HFC-134a were used as refrigerants. </p>

<p>The presence of deposits in the honing grooves in diesel engine cylinder liners can cause a severe increase in the consumption of lubricating oil. These deposits may appear amber in which case they may be referred to as 'liner lacquerer' or be nearly invisible in which case they are often referred to as 'transparent glaze' or 'bore glaze' in the marine sector. The formation of these deposits is believed to be influenced by engine design, engine load, fuel composition and lubricating oil composition. This relationship has, however, not been well understood and little material has been published on this subject. This thesis describes an investigation of this phenomenon. The problem has been approached by studying the composition of deposit samples, studying cases of deposit formation in the field and through experimental work.</p><p>As a result of this work, it is hypothesized that the root cause of the deposit formation is a mismatch between the rate of formation of oil insoluble material on or within the oil film and the oil film dispersing power and exchange rate. A large number of parameters will affect this balance which explains the sliding shift in appearance and composition of 'liner lacquer' and 'bore glaze' and the difficulty in identifying the cause of this problem.</p><p>A combined mass balance and chemical kinetics approach is used to bridge the gap between fundamental deposit theory and tangible engine related parameters. It is thus possible to rationalize the formation of deposits on cylinder liners. This understanding is sufficient to point out which factors should be considered in terms of the prevention of deposit formation and to present a viable hypothesis on the reason for the deposit formation in the engines that have been investigated in the course of this work as summarized in the following paragraph.</p><p>The presence of deposit indicates that the dispersing power and transport rate of the oil film is insufficient to deal with the deposit precursors being formed. This is believed related to extensive low load operation which is associated with both low liner temperatures and low nominal oil consumption in these engines. Low liner temperatures will encourage the formation of insoluble material due to condensation of sulphuric acid precursors, while low oil consumption is believed to indicate low oil film exchange which reduces the transport of matter and also contributes to oil film oxidation by prolonging the exposure to combustion gases.</p>

<p>Frequency and amplitude dependency of velocity distribution and head loss of oscillatory flow in a rectangular duct have been studied experimentally with a model tunnel system.</p><p>Tests were carried out with the duct of both smooth and rough walls. The smooth wall was made of Plexiglas. Sand roughness was used for the rough wall. Velocity, pressure and differential pressure of stationary flow, pure oscillatory flow and combined oscillatory flow were measured. The combined oscillatory flow was classified as oscillation dominant flow, stationary dominant flow, and oscillation-and-stationary balanced flow. Various oscillating frequencies, amplitudes and steady flow percentages were tested for oscillatory flows. The oscillating frequencies tested were varied from 0.01 Hz to 1.00 Hz. Oscillatory amplitude and stationary part were varied from 10 to 100%. Velocity of the flow was measured with a 2D PIV (Particle Image Velocimetry) and a 2D LDV (Laser Doppler Velocimetry) respectively at different test stages. The maximum mainstream velocity was ranged from 0.05 m/s to 1.1 m/s. Data of pressure variations along the tunnel were collected with differential pressure sensors. Flow rate and instant wall pressures at multiple points along the test tunnel were measured simultaneously. The static pressure in the test tunnel was about 1.0 mWC. The differential pressure along the tunnel was less than 20 mmWC per meter.</p><p>Examples of velocity distribution in the test rig from LDV measurement are presented, for both stationary flow and oscillatory flow. The dimensionless velocity distributions of stationary flow are in good agreement with the universal velocity distribution law. Deviations are obvious between the velocity distributions of oscillatory flow and the universal velocity distribution law, when the measured velocity is scaled to dimensionless by friction velocity from Clauser chart. Examples of PIV velocities of different flow regimes are presented in the forms of velocity profile and velocity waveform. Generally, the velocity distributions are in good agreement with the results from LDV, in agreement with the normal turbulent velocity distribution in a duct, if the velocity magnitude is not too small. Dimensionless velocity profiles at various phase angles of the same oscillatory flow regime have quite consistent distribution. The annular effect is observed in some cases. Its occurrence depends on the complex actions of oscillating frequency, amplitude and stationary flow percentage. The velocity waveform confirms the characteristics of mass oscillation of the flow. No significant phase shift is displayed between the velocity waveform of the boundary and centreline in most cases tested. The vertical velocity, which is normal to the mainstream, is quite small and has similar features to the mainstream velocity.</p><p>The velocity profiles got from both LDV and PIV show that the flows in the test tunnel were typical turbulence, with typical velocity distribution of turbulence. No transition between laminar and turbulence is observed even at the turning point of oscillation.</p><p>Pressure variations measured along the tunnel of different flow regimes are presented. The accelerative heads of oscillatory flow are calculated. The friction head losses along the tunnel are evaluated. The dependencies of pressure variation and friction head loss on oscillatory frequency and amplitude are investigated for both pure oscillatory flow and combined oscillatory flow. It is proven that the friction head loss of oscillatory flow increases along with the increase of frequency if the mean flow rate is kept constant. The peak friction head loss increases along with the increase of oscillatory amplitude. Comparison of pressure variation and friction head loss between stationary flow and oscillatory flow shows that the friction head loss of unsteady flow is much bigger than that of steady flow. This is in good agreement with the expectancy based on the experimental results of laminar flow. The head loss of pure oscillatory flow was greater than that of the stationary flow for dozens or more times for various flow regimes running at equivalent flow rate. The ratio of head loss of combined oscillatory flow to stationary flow running at equivalent flow rate is smaller than that of pure oscillatory flow to stationary flow, several times to dozen times. In general, the frequency dependency of head loss on oscillatory frequency and amplitude is clear, though the measuring length is only 9 metres and the absolute magnitude of pressure variation is less than 0.20 mWC.</p>

<p>More than forty years has passed since the start of the North Sea oil and gas developments. On the managerial side of the projects there have been large cost overruns, project planning and control measures developed to avoid these, initiatives to improve the industry’s competitiveness in the North Sea, as well as measures to improve the supply chains contribution in the projects. We have seen a focus first and foremost on the CAPEX side of the projects, which still is the public measure of a ‘project’s’ success as seen in medias coverage. However, the operation side of the project has been given extended focus, especially through life-cycle cost measures, and life cycle value measures trying to balance out the CAPEX, OPEX and income sides of the project to obtain the most commercial value enhancement from each project. At the same time there has been an increasing focus on the core business among the project demand and supply chain actors in this industry as in most other industries.</p><p>Our belief is that this necessitates an enhanced focus on the project demand and supply chains of the industry, both for the projects development and operations phases. A question is whether the project demand and supply chain developments are approached appropriately according to the characteristics of the industry’s project context?</p>

<p>Carbon dioxide (CO₂, R-744) has been identified as a promising alternative to conventional working fluids in a number of applications due to its favourable environmental and thermophysical properties. Previous work on residential CO₂ heat pumps has been dealing with systems for either space heating or hot water heating, and it was therefore considered interesting to carry out a theoretical and experimental study of residential CO₂ heat pump systems for combined space heating and hot water heating – so-called integrated CO₂ heat pump systems. The scope of this thesis is limited to brine-to-water and water-to-water heat pumps connected to low-temperature hydronic space heating systems..</p>

<p>A major part of the national and county road network in Norway consists of two-lane roads with relatively narrow shoulders. The width of the roadway is limited, forcing heavy trucks to drive close to the pavement edge. This represents a considerable deteriorating effect on these pavements, which typically consist of granular base materials and thin asphalt surfacing. The result is often premature cracking and deformations along the pavement edge. </p><p>Despite the fact that pavement edge damages represent a great problem for the Norwegian road network, little research has been performed on this topic. This is the main background for the present thesis work to focus on pavement edge damages and load responses towards the pavement edge.</p><p><i>Chapter 2</i> gives a brief presentation of the basic theory of continuum mechanics together with some elastic constitutive material models. The general elasto-plastic theory is also described. Further, methods and programs based on elastic layer theory developed for structural analysis of pavements are presented. Finally, advantages and basic principles for the finite element method are discussed.</p><p>In <i>Chapter 3</i> the different types of pavement edge damages are described. Further, the factors influencing the strength of the pavement edge and damage development are discussed. To get information of the variation of bearing capacity over the cross section of existing roads, own FWD measurements are performed at different sites in Sør-Trøndelag county. As expected, a considerable decrease in bearing capacity towards the pavement edge was found. Also a minor field study on the effect of varying side slope is accomplished. The structural effect of gradually steepening the side slope is measured by FWD and plate loading tests. Chapter 3 also contains the findings from a literature review on measurement and calculation of pavement edge effects. Only a small number of articles on these subjects were found.</p><p>A full-scale pavement test has been performed at Sandmoen near Trondheim. Two pavements with different subbase materials were constructed, one of them instrumented for the measurement of stresses and strains in the base and subbase layers at different offsets from the pavement edge. The construction work, materials, sensor types and positions are thoroughly described in <i>Chapter 4</i>.</p><p>Results from Sandmoen test field are presented in <i>Chapter 5</i>. Responses to three different types of loading have been measured. These are controlled wheel loading, FWD and plate loading. Vertical stresses have been successfully measured at the bottom of both the base and the subbase layers. Independent of loading type, the results show increasing vertical stresses as loads are applied closer to the pavement edge. This effect is evident at the bottom of the base layer for load positions closer than approximately one meter from the edge. Increasing horizontal stress is recorded at the bottom of the base layer when a load is applied on the pavement surface. Deformation measurements show large plastic strains in granular materials, especially for load application close to the pavement edge. Parts of these strains recover when the load position is changed.</p><p>Theoretical modelling and analysis of the Sandmoen test field are dealt with in <i>Chapter 6</i>. Both multilayered elastic and three dimensional finite element analyses are performed. In all calculations, the load is modelled as a uniformly distributed vertical pressure over a circular area, and all materials are modelled as linear elastic with material parameters found from laboratory testing. When linear elastic material models are used, the three dimensional finite element calculations show only insignificant differences in stresses, strains and deformations as the load is moved towards the pavement edge. Best correlation between measured and calculated load responses are found for vertical stress and strain in the base layer for the case of static plate loading being applied in the inner wheel path. Beyond this, the comparisons of measured and calculated load responses show considerable discrepancies.</p>

<p>This thesis focuses on three main areas within the field of SOFC/GT-technology:</p><p>• Development of a dynamic SOFC/GT model</p><p>• Model calibration and sensitivity study</p><p>• Assessment of the dynamic properties of a SOFC/GT power plant</p><p>The SOFC/GT model developed in this thesis describes a pressurised tubular Siemens Westinghouse-type SOFC, which is integrated in a gas turbine cycle. The process further includes a plate-fin recuperator for stack air preheating, a prereformer, an anode exhaust gas recycling loop for steam/carbon-ratio control, an afterburner and a shell-tube heat exchanger for air preheating. The fuel cell tube, the recuperator and the shell-tube heat exchanger are spatially distributed models. The SOFC model is further thermally integrated with the prereformer. The compressor and turbine models are based on performance maps as a general representation of the characteristics. In addition, a shaft model which incorporates moment of inertia is included to account for gas turbine transients.</p><p>The SOFC model is calibrated against experimentally obtained data from a single-cell experiment performed on a Siemens Westinghouse tubular SOFC. The agreement between the model and the experimental results is good. The sensitivity study revealed that the degree of prereforming is of great importance with respect to the axial temperature distribution of the fuel cell.</p><p>Types of malfunctions are discussed prior to the dynamic behaviour study. The dynamic study of the SOFC/GT process is performed by simulating small and large load changes according to three different strategies;</p><p>• Load change at constant mean fuel cell temperature</p><p>• Load change at constant turbine inlet temperature</p><p>• Load change at constant shaft speed</p><p>Of these three strategies, the constant mean fuel cell temperature strategy appears to be the most rapid load change method. Furthermore, this strategy implies the lowest degree of thermal cycling, the smoothest fuel cell temperature distribution and the lowest current density at part-load. Thus, this strategy represents the overall lowest risk with respect to system malfunctions and degradation. In addition, the constant mean fuel cell temperature strategy facilitates high efficiency part-load operation. The constant turbine inlet temperature strategy proved to lead to unstable operation at low load, and thus it is considered to be the least adequate method for load change. For both the constant mean fuel cell temperature strategy and the constant TIT strategy, surge might be a problem for very large load reductions. The slowest response to load changes was found for the constant shaft speed strategy. Furthermore, this strategy leads to very low fuel cell temperatures at low loads. This in combination with a possible higher degradation rate makes the constant shaft speed strategy unsuited for large load variations. Nevertheless, operation at constant shaft speed may be facilitated by air bypass, VIGV or compressor blow off.</p> / Paper I is published with kind permission of Elsevier, Sciencedirect.com