1 

Verification of the FET Object Model: Implementation of Reactors and Separation Processes
The Front End Tools (FET) Project's goal is to create a software application which should aid the process engineer in creative design of process plants. Since this application will be written using objectoriented techniques, an object model has been designed by AkzoNobel Engineering. This document describes the verification procedure of this object model, which should be able to contain chemical engineering process design data and methods. During this verification (which included examining separation processes and reactors as well as writing two C++ applications) several elements of the original model have been modified. The conclusions made at the end of the project state that the currently developed object model can be used for its intended purpose. Apart from this conclusion, several concepts were proposed for further development in conjunction with the FET project.

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2 

Modeling of Complex Reaction Systems: Steam Cracker
Steam pyrolysis of ethane and naphtha is an important chemical bulk process. It produces ethylene and propylene, which are important base chemicals. In order to be competitive, crackers have to be operated at near optimal conditions. Hence, a simulation program of the process, particularly of the pyrolysis is very helpful. KTI uses and licenses such a program called SPYRO*. Development of this program has started over 20 years ago. Consequently, it uses a closed model.
It has been the objective of this study to investigate the feasibility of the development of an open version of SPYRO. Here open means that the equations are written in residual form .This enhances the flexibility of the program very much. For our studies we have used the model of Froment for ethane cracking because the documentation to make an open SPYRO model was insufficient. This Froment model has been modified as to improve the modeling of the bends. It has been checked, whether the solution of this model would pose any problems. It was found that the index might become more than 1 during integration. As yet no sound physical explanation has been found for this phenomena.
It also follows from investigation of the index that a startup problem of the numerical integration exists for the original set of differential equations. We have found a more elegant method to circumvent this problem than Froment. Moreover, we were able to solve the set of equations for bad initial conditions (equal to the boundary conditions).
The ordinary differential equations of the model are turned into algebraic equations using orthogonal collocation on finite elements. This allows the model to be solved with an equation solver. The results were compared with various commercial numerical integrators. Excellent agreement was found for limited numbers of sections and collocation points. The speed of solution of the linearized set of modal equations depends on the size, the sparsity and structure of the Jacobian. The latter has an enormous effect on the fillin of the L and U decomposition matrices. We found a very satisfying structure by modification of the equations and proper arrangement in the Jacobian.
On the basis of the above results we may draw the following conclusions regarding the feasibility of the development of an Open SPYRO model. Unfortunately we had to use a simple model of Froment rather than the SPYRO equations themselves. Nevertheless, we have concluded that such a development is feasible. Within a reasonable time an accurate solution will be found even with bad starting values. The computation time can be further reduced with a smart initialization procedure.

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3 

The assembly of flexible polystyreneblockpoly(ethylene oxide) wormlike micelles from chloroform droplets by the ‘emulsification and solvent evaporation’ method
Flexible wormlike micelles show promising results in their application as drug carriers in the field of targeted drug delivery. A method introduced to produce wormlike micelles is the ‘emulsification and solvent evaporation’ method, but the formation mechanism behind this method is not yet fully understood. The aim of this work is to study whether the lengths of the wormlike micelles formed depends on the size of the droplets in the emulsion. Wormlike micelles were formed by dissolving polystyreneblockpoly(ethylene oxide), or PSPEO, in chloroform, and mixing this into an emulsion with water containing NaCl through vigorous stirring. Interfacial instabilities between the water and chloroform phase caused by increased concentrations of polymer lead to the formation of wormlike micelles. Effects of varying stirring rates and times on the size of the chloroform droplets in the emulsion as well as the lengths of wormlike micelle sizes were studied by analysis through optical and fluorescence microscopy. The droplets were found to be polydisperse and stable for timescales up to a few minutes, but the diameters decrease during the course of mixing the emulsion. Wormlike micelles start to form directly when the chloroform and water phases are brought in contact. When mixing occurs more vigorously the average length of wormlike micelles increases and their distributions becomes broader. Interestingly, wormlike micelles produced using this method grow to lengths up to 1 mm.

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4 

Predicting the diffusivity of CO2 in substituted amines
The experimental determination of the diffusivity of carbon dioxide (CO2) in an amine solvent is difficult as the CO2 diffuses and reacts simultaneously when absorbed into an amine solvent. As the knowledge of the diffusivity and solubility of CO2 is essential to design the absorption units based on amine solvents, the nitrous oxide (N2O) analogy is used in practice to estimate them. It consists of evaluating those physical properties by substituting the reacting CO2 with an inert gas of a similar structure, N2O. The diffusion of CO2 in amine solvents is investigated using molecular dynamics (MD) simulation. Unlike experiments, MD simulation allows a direct measurement of the CO2 diffusivity. In MD simulations, the reaction between CO2 and the amine can be switched off. The Fick diffusion coeffcients are derived from the MaxwellStefan diffusivities and the thermodynamic factors. Different amine solvents like monoethanolamine, diethanolamine, methyldiethanolamine and ethylamine are investigated. The N2O analogy in the monoethanolaminewater solution has been validated.

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5 

Numerical modeling of heat transfer and fluid flow in welding with a moving heat source
Worldwide, welding is a multi billiondollar fabrication technology used extensively in construction and industry. The final quality of a weld is known to be dependent on the hydrodynamics in the liquid region and the energy transfer in the surrounding heat affected zone. Understanding of these processes is therefore vital in improving weld quality.

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6 

Experimental determination of the bubble size in foam created in gasliquid flow with surfactants
In the gas industry there is a common problem during the production of gas, which is called liquid loading. This is the accumulation of water and condensed gas at the bottom of the pipe, through which gas is produced. This occurs when the gas velocity becomes insufficient to drag the liquid to the surface. From experience they know in the gas industry that by adding surfactants to the water at the bottom of the well, liquid loading can be postponed to a lower reservoir pressure. The water will start to form foam, which changes the flow in the well as foam is easier to drag upwards. But the precise effect of the surfactant on the flow is still unclear. By gaining more knowledge, it may be possible to make a model of the flow with surfactant , to predict e.g. the optimal production conditions, like the amount of surfactant that should be used.

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7 

Numerical Studies on Phase Field Diffusion and Flow Solvers
The goal of this project is to validate and evaluate developed numerical solvers that solve both the CahnHilliard diffusion equation and the CahnHilliardNavierStokes coupled equations. The solvers are written for the implementation in the open source CFD software platform, OpenFOAM.

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8 

Numerical Study of Wetting of a 2D Cylinder by an Impacting Jet
In many processes, for example tricklebed reactors, it is important to completely wet small spheres, or particles. (Baussaron, et al., 2007) Ideally, a small stream of liquid on such a particle would create a film around the particle, completely wetting it. It is therefore interesting to investigate which factors influence the formation of this film and to what effect. To this end, a simpler 2D case is investigated in this project: a small cylinder.

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9 

Development of a small scale shaking test to evaluate foamability
The lifetime of a gas well is significantly influenced by the liquids present in the well. These liquids can be found along the walls in an annular flow and is carried up along with the gas as a result of the relatively high gas pressure in the early stages of the well. As time goes on the gas pressure decreases, thus the well’s ability to drag up the liquids with the gas also decreases. As a result the liquids start to accumulate in the tubing and bottom of the well. This severely limits or even halts the gas production. This phenomena is known as liquid loading.

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10 

Large Eddy Simulations of Electromagnetic Control of a Quasi2D Jet
This research aims to accurately predict the flow of electromagnetically conducting liquids liquid steel in a thin cavity. A thin cavity, with a thickness « width, is relevant as a model for a continuous steel caster mould. A turbulent jet flow enters the cavity, leading to a quasitwodimensional flow. Using large eddy simulations with the dynamic Smagorinsky model with cell faceaveraging the filtered velocity field is solved. The model is validated using experimental data before the flow of liquid steel is
simulated.

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11 

Experimental studies on heat transfer in thermomagnetic onvection for para and diamagnetic fluids
In industrial heat transfer processes, natural convection enters in various forms. One form of natural convection is thermomagnetic convection. Besides gravitational force, magnetic force causes warmer fluid to rise or fall dependent on the fluids magnetic susceptibility and direction of magnetic field gradient. Magnetic susceptibility is a material property which indicates a degree of magnetization in a material. For paramagnetic fluids magnetic susceptibility depends on temperature, is positive and therefore attracted by magnetic field. Magnetic susceptibility of diamagnetic materials is independent on temperature, is negative and hence repelled by magnetic field. Magnetic force can be used to enhance or suppress gravity. This phenomena is widely investigated for many materials, magnetic field strengths and setup geometries.
In this research thermomagnetic convection and the effect it has on internal heat transfer is experimentally investigated for para diamagnetic fluids. Making use of a 10 Tesla superconducting magnet, which can generate field gradients up to 870 T2/m, steady, oscillating and turbulent flow regimes can be observed. I performed the experiments at the AGH University of Science and Technology in Krakow, Poland. A small cubical enclosure filled with para or diamagnetic fluid is placed at different positions in the magnet to get enhancement or suppression of internal heat transfer. Enclosure is heated from below and top is kept at constant temperature. Temperature of the fluid is measured with thermocouples at six different positions inside the enclosure. From these temperaturetime measurements a power spectrumis obtained to determine the characteristic flow regime. Internal heat transfer is investigated by measuring different variables and calculate thermomagnetic Rayleigh and Nusselt numbers.
As paramagnetic fluid a 40% waterglycerol solution is used and gadoliniumnitrate is added to create a higher magnetic susceptibility. Enclosure was placed above the magnet centre which should give a magnetic force that enhances gravitational buoyancy. Temperature difference between the hot and cold plate of the enclosure is 5 and 11±C, respectively case G5A and G11A. Case G5A shows transition in the flow regime from steady to oscillating to turbulent with increasing of magnetic field. Case G11A shows turbulent regime for each measurement. Nusselt number calculations for glycerol solution measurements show an increase, up to 2.5 times, in internal heat transfer. Turbulence causes better mixing and hence better heat transfer. Relation between RaTM and Nu are compared with previous (experimental) relations and show good agreement.
Pure water is used as diamagnetic fluid. First enclosure is placed below magnet centre and temperature difference is 5 and 1 ±C, respectively case W5B and W1B. Here magnetic force should enhance internal heat transfer. Case W5A and W3A are measured above the magnet centre and have respectively a temperature difference of 5 and 3 ±C. Case W5B and W5A both show turbulent flow regime for all measurements. Internal heat transfer is about the same for both cases but show a slight increase for W5B and decrease for W5A. There can be concluded that for turbulent flow regimes magnetic force direction has no significant influence on internal heat transfer. For smaller temperature differences, case W1B and W3A, magnetic force does influence measurements. CaseW1B shows steady flow regime first and for higher magnetic field strengths fluid plumes start to rise and sink due to magnetic force. Case W3A shows a very clear transition from turbulence to oscillating flow. Small temperature differences cause large measurement errors and internal heat transfer is assumed to be constant.
Recommendations for further research is to get a better impression of fluid structures and temperatures in the enclosure. Fluid behaviour can be visualized with liquid crystals and velocity fields can be determined by using PIV on these visualizations. The velocities can be compared to simulations. To get realistic simulations, fluid properties need to be measured for different temperatures and if necessary differentmagnetic field strengths.

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12 

Magnetic Drug Targeting in Human Airway Geometry
Patient specific drug delivery may improve the efficiency of the medicine and reduce the sideeffects. In addition to different medicines and dosages, the target site of the medicine can differ from patient to patient. By using drug particles with a magnetic core, and under the influence of a magnetic field, the particles may be steered towards the point of interest.
In the present study, computational fluid dynamics is used to study air flow and particle deposition in human airway geometry. In the first case study, passive particle deposition was carried out in a 90◦ bend to represent a simplified throat. Randomuniform and deterministicuniform particle inlet distributions were used. Both the total and cumulative deposition efficiencies showed good agreement with literature.
The second case study is again a 90◦ bend simulation but this time represents a simplified artery.
Although the curvature ratio was the same the dimensions of the geometry were much smaller. In addition to passive particle deposition, magnetically enhanced particle deposition was studied and good agreement was obtained with both reference cases.
The third case study features a simplification of the conducting airways: a triple bifurcation geometry.

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13 

Experimental study of fluid flow in the bifurcation of a patient specific carotid artery, with severe stenosis: comparing PIV, PCMRI and CFD
Magnetic Drug Targeting is a relatively new technique whereby chemotherapeutic agents are attached to
magnetic particles that will be injected in an artery upstream of an affected area. By exerting an external
magnetic field an internal magnetic field gradient will be induced that will entrap the particles that contain the drugs in the affected region. By doing so only the affected region will be treated, leaving the rest of the body free from drugs and therefore the side effects are reduced as the total dose of the drugs is much lower than when more conventional procedures are used. Clinical trials have been performed using this technique on various types of cancer with promising results.

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14 

Assessing the performance of ground source heat pumps in neighboring mediumsize households
The Master's programme Industrial Ecology is jointly organised by Leiden University and Delft University of Technology.
This research project was done during an internship of 8 months completed with Royal Dutch Shell within the department of Future Energy Technologies of The Netherlands. It is focused on a case study of a medium size house (2202) situated in The Hague, NL and the neighboring households with the same characteristics along the same street.
Homes in the Netherlands are likely to have their heat requirements fulfilled by conventional natural gas systems due to the relatively cheap cost compared to other systems (installation and investment wise) that could have a lower carbon footprint. However, innovative installations could make other more environmentally friendly systems as accessible as conventional systems.
The Netherlands as one of the European member states have the goal of reducing CO2 emissions to accomplish their Kyoto targets; however, The Netherlands was not able to meet this target by 3.24% (target of 200.4 megaton CO2eq). Besides, there is a general lack of financial incentives, making it in many cases an obvious decision to keep and use standard fossil fuel energy systems (both large and smallscale) regardless of the environmental impact they may have.
The building energy consumption sector provides a great opportunity and focus area for trying to reduce even more those emissions, and efforts have been made to introduce into the market more environmentally friendly systems. Until now, exploitation of geothermal shallow energy using a Ground Source Heat Pump (GSHP) has generally been limited to large commercial / industrial units. One reason for this is that the technology used for obtaining the geothermal energy and raising it to an appropriate temperature for the heat requirements of a typical house requires a big space for its installation which in turn proves to be a disruptive and complex process that requires the use of heavy and bulky machinery which immediately translates in a restriction for small homes.
Innovations for installations of Ground Source heat pumps are starting to appear in the market, giving the possibility and the opportunity to install those systems in smaller areas, with less disruption and lower investment costs, although some concerns may arise when considering the thermal interference between the boreholes.
This project examined the geological characteristics of the case study as determined by a Thermal Response Test (TRT) where parameters such as the thermal conductivity, the thermal resistance and the thermal diffusivity of the ground were obtained. Furthermore, the heat requirements of the test house were calculated with real data obtained during a year between 2012 and 2013 in order to determine the size of the system that would be required for each one of the houses assuming they all have the same demand throughout the year, having a peak demand for a winter day of 16 KW and an average demand of 10 KW in the winter months.
Calculations of the length required of every Borehole Heat Exchanger (BHE) and the distance between them were made for the area of each house assuming no thermal interference. The first set of results indicated that a BHE length of 268 m would be needed, and with borehole thermal interference introducing a temperature penalty calculated with an analytical model, the length required increased to 332 m, 68 m more. After this a proposed design of borehole arrangement is suggested for the test house considering the space constraints.
Calculations on the Economic and Environmental advantage from Ground Source Heat Pump (GSHP) compared to a Gas Boiler is done, taking into consideration two scenarios for the GSHP, 1) with a Seasonal Performance Factor (SPF) of 3.5 and 2) with a SPF of 3.0. Domestic gas and electricity price fluctuations over the past years were included, extrapolating this behavior for the years 2015 and 2020. Gas prices are considered to have changed 9% per year given the data from 1996 – 2013. Having extrapolated the prices, calculations are done on running costs and investment cost, to give the payback times when considering current power and gas prices for 2015 and 2020. The current situation (2013) seems the more expensive moment for having the system with a payback time of 24 years however a GSHP system in 2020 with electricity and gas prices following a 9% increase for gas prices would take just 8 years to have the investment back.
For the environmental performance the Dutch footprint of power generation is calculated for the average predicted trends of different scenarios in the future for European power generation where GSHP with a SPF of 3.5 in 2020 seems to have the best Carbon Footprint advantage of all with 59% advantage of the compared systems. Recommendations are made in order to come up with connected scenarios of Dutch power and natural gas to have a coherent and timely understanding of GSHP and other renewable systems in the Dutch heating market for the coming years.
Further recommendations are made in order to have a clear understanding on all the interrelated factors that have an impact on the efficiency, feasibility and performance of GSHP systems and how this research project could be broadened.

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15 

An LDA of the precessing vortex core in a cyclone
In a cyclone the centre of the swirling flow, denoted as the vortex core, is precessing about the geometrical centre of the cyclone. In this research project, the aim was to get more insight in the influence of this precessing vortex core (PVC) on the velocity field of the cyclone. Therefore, at several horizontal stations Laser Doppler Anemometry (LDA) measurements were carried out to determine the axial and tangential velocity components along the cyclone radius.
A trigger procedure has been developed to estimate the velocity profiles corresponding to the extreme positions of the PVC with respect to the LDAprobe. This trigger procedure makes use of the periodical component in the measured tangential LDA signal itself to estimate the trigger time intervals.
To estimate the periodical interference from the tangential velocity signal, an adaptive noise canceling configuration (ANCC) has been implemented. This algorithm is capable of tracking the quasi periodic circular movement of the PVC.
By combining the trigger procedure and the ANCC it is possible to estimate the triggered profiles of both the axial and the tangential velocity components. The resulting standard deviation of the triggered velocity does not show the expected decrease. By subtracting the estimation of the periodical component and the tangential velocity signal, the standard deviation in the centre of the cyclone was reduced by 40%.
A remarkable observation was the disappearance of the periodical interference in the LDA signal at r ≈ 0.6Rc for all measured profiles. It was assumed that the extreme velocity profiles intersect at this position. Further research is necessary to confirm this.

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16 

A computational approach to curtain coating
In curtain coating, a falling liquid film impinges on a substrate that traverses underneath. In this thesis the flow in the area of impact, the socalled impingement zone, was investigated using the commercially available code NEKTON Release 3.0. The computational method used in this code is the spectralelement method and belongs to the class of variational methods. Since the flow is bounded by free surfaces, not only velocity and pressure have to be calculated but also the nodal position. Therefore, the following strategy has been implemented in NEKTON, the free surface boundary is fixed and the flow field is solved until convergence, then the geometry is updated. These steps are repeated till convergence. The simulations in this thesis cover two areas:
* the influence of numerical parameters on the accuracy of the solution: the direct and iterative solvers in NEKTON were compared with regard to consistency, the polynomial order of the basis functions in the spectralelement method has been increased, and, finally, the grid in the heel zone has been refined.
* the influence of physical parameters, such as web speed and dynamic contact angle, on the flow field. The outcome is compared to theoretical models found in the literature.
Simulations have been complemented by experimental work covering four different areas. First, characterisation of the coating fluid; the data obtained has been used as input to the simulations. Second, both static as well as dynamic offline experiments have been done to get a feel for the process and to study the achievable coating window. Third, results obtained in the offline setup have been verified with pilot coater experiments, to judge their consistency. Finally, the design of he edge guides, needed to maintain the curtain at full width, and related edge effects have been studied more closely.

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17 

Application of electrical capacitance tomography image reconstruction algorithms to real data
Electrical capacitance tomography (ECT) has recently been developed for the insitu measurement of the crosssectional gassolid distribution in a duct carrying a nonconductive 2phase flow. The technique rehes on the detection of electrical capacitances between electrodes placed on the periphery of the duct. The data depend on the permittivity distribution inside the crosssection, which has to be reconstructed. Information on the flow regime, vector velocity, and gassohd distribution in process vessels and pipehnes can be determined from the reconstructed images.
The main bottleneck is still the poor quality ofthe image reconstruction part. In the frame ofthe ECT project at Delft University of Technology (DUT), research is done towards a new direct reconstruction algorithm, based on the least squares solution.
The investigation has two goals. The investigation ofthe influence of noise on the data and the reconstruction of the permittivity distribution from measured data using well known material distributions as test cases to determine the spatial resolution.
To investigate the influence of noise on the reconstruction, simulated noise is added to synthetic data. The reconstructions show that the more constraints are added to the least squares solution, the more robust the algorithm becomes. Noise measurements show that the noise level of real measured data has a negligible influence on the constrained least squares reconstruction.
Reconstruction of a rod (about  of the pipe diameter) near the wall of the sensor is possible. In the centre region of the pipe the quality of the reconstructed image decreases due to the underdeterminacy in the centre of the pipe.
Two rods can be reconstructed when both positioned close to the pipewall. However, they can not be seen seperately in the centre region and when they are close to one another. Bubbles (about 1/10 of the pipe diameter) are hard to reconstruct when positioned in the pipe centre. Due to their finit height 3D effects disturb the interpretation of the measurements. The bubbles, however, can be detected when looking at the raw data.

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18 

Bubble street behaviour in a highly viscous laminar bubble column
In this research project the bubble street behaviour and stabihty of a high viscous (77 =31, 47, 61, 99 mPas) laminar bubble column is studied (diameter 23 cm, height 80 cm), using gas flow rates of Qd = 23.6 and 36.7 cm^3/s. The Hquid is a solution of PVP powder in tap water. The Reynolds numbers, based on the maximum liquid velocity and the bubble street diameter, vary from 190 to 540.
The investigation has two goals. The first is to compare the Rietema k Ottengraf theory [1] concerning a circulating steady state bubble column to experimental results. The second is to make an inventory of the transition traject to a chaotic laminar ('normal') bubble column.
Laser Doppler measurements were performed on the hquid, together with visual observations. The high concentration of PVPparticles solved in the liquid causes a large standard deviation in the velocity measurements, while the mean values are unbiased.
In the circulating regime the flow has quite a smooth proflle with a very regular bubble pattern. The bubbles move via fixed patterns through the liquid. However, both the axial velocity and the hquid fiow rate increase with height. Assuming an axisymmetrical flow, the liquid fiow must have a radial component, which means that the flow cannot be one dimensional. The radial flow causes the bubbles to move to the centre of the column. The position of the zero velocity in the axial hquid profile is almost constant over the height, even though the bubble street (based on the bubble positions) narrows.
In the transition regime the fiow develops from a bubble street in the lower part of the column to a chaotic regime in the upper part. Two mechanisms control the transition. The draftingkissingtumbhng mechanism according to Fortes et al. [2] for bubble pairs is the first. The second is a mechanism that causes waving and oscillating bubble chains.

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19 

Snelheidsmetingen aan gemengde convectie in een model Chemical Vapour Deposition reactor
Experimenteel onderzoek is verricht aan laminaire gemengde convectiestroming in een model Chemical Vapour Deposition reactor. De reactor bestaat uit twee cirkelvormige parallelle horizontale platen. Tussen de onderste en bovenste plaat is een temperatuurverschil aangebracht. Dit temperatuurverschil tussen de platen resulteert in natuurlijke convectie verschijnselen. Naast natuurlijke convectie is er ook gedwongen convectie ten gevolge van een radieel uitwaartse stroming. De interactie tussen natuurlijke en gedwongen convectie resulteert in een tijdsafhankelijke stroming. Met behulp van twee 'whole field velocimetry' meettechnieken, Partiele Image Velocimetry (PIV) en Partiele Tracking Velocimetry (PTV), zijn snelheidsmetingen verricht aan deze stroming. De resultaten van deze twee meettechnieken zijn met elkaar en met Computational Fluid Dynamics (CFD) simulaties vergeleken.
Er treedt een systematische fout in PIV op ten gevolge van de snelheidsgradiënt inherent aan deze stroming. Teneinde de grootte van deze fout in PIV metingen ten gevolge van snelheidsgradiënten te bepalen worden resultaten verkregen met PIV vergeleken met resultaten die verkregen zijn met PTV. De grootte van de snelheden blijkt overeen te komen binnen een marge van 10 — 20%. Dit verschil blijkt niet aan de snelheidsgradiënt te wijten te zijn, maar aan de onnauwkeurigheid in de frequentie van de sweepende laserbundel.
Uit vergelijking met simulaties blijkt dat gemeten snelheden een systematische afwijking hebben ten opzichte van de snelheden uit de simulaties van 10 — 20%. Deze afwijking valt binnen de onnauwkeurigheid van de experimentele opzet.
Geconcludeerd kon worden dat met PIV en PTV betrouwbare metingen haalbaar zijn met een systematische fout van minder dan 10% en dat de groottes van de snelheden binnen 10  20% overeenkomen met simulaties. Omdat PIV een volledig vectorveld oplevert, in tegenstelMng tot PTV, zijn in een doorsnede van de stroming alle snelheden bekend en wordt de voorkeur aan PIV gegeven boven PTV

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20 

Voltage control in MV distribution networks with a large share of distributed renewable generation
Traditionally, voltage control in MV distribution networks has been focused on dealing with voltage drop along radially operated feeders. The actual implemented controllers use local voltage measurements and have been designed and calibrated for a passive and radial use of the MV system. The presence of distributed renewable generation (DRG) makes these assumptions no longer valid. The power generated by DRG units will increase the voltage at adjacent nodes and even cause it to be higher than the voltage at the primary substation. Consequently, the presence of DRG will affect voltage control in distribution systems and it needs to be reconsidered whether methods like local voltage control and reactive power injection can still enable the network operator to cope with the newly introduced voltage rise issues.
The aim of this study is to create a new voltage control strategy, which will not only successfully limit voltage variations, but also allow for an increased penetration of DRG. The proposed coordinated voltage control strategy deploys control of HV/MV transformers OnLoad Tap Changers in combination with active power control provided by Intelligent Nodes, that allows network reconfiguration. The Cigré MV distribution network benchmark is used as a basis for the test system, while appropriate models for the PV Power Plants, the Wind Power Plants and the Intelligent Nodes were developed. In order to draw realistic simulation results, a summer / winter seasonal variation is featured. The proposed voltage control algorithm is incrementally developed, allowing for the identification of factors hindering the controller performance and the development of a control algorithm which is more targeted towards dealing with specific issues. The commercial power system simulation software DIgSILENT PowerFactory 15.0 is used for carrying out these simulations.
The analysis of simulation results shows that the proposed voltage control strategy is capable of facilitating the transition towards active MV distribution networks, by offering considerably higher DRG penetration levels and strictly bound network voltages. The modelled controller is particularly applicable to MV distribution networks across North Europe. Among others, the limiting factors for an increased DRG penetration are identified, along with the effects that the reactive power control and the choice of voltage limits have. Finally, recommendations for future research are provided.

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