Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Ionic liquid pre-treatment of microalgae and extraction of biomolecules
    Desai, Rupali K. - \ 2016
    Wageningen University. Promotor(en): Michel Eppink; Rene Wijffels. - Wageningen : Wageningen University - ISBN 9789462579804 - 126
    salts - liquids - fractionation - extraction - hydrophobicity - algae - biomass production - zouten - vloeistoffen (liquids) - fractionering - extractie - hydrofobiciteit - algen - biomassa productie

    Liquid-liquid extraction (LLE) techniques are widely used in separation primarily due to ease of scale up. Conventional (LLE) systems based on organic solvents are not suitable for extraction of fragile molecules such as proteins as it would result in denaturation. On the other hand aqueous biphasic system though suitable for extraction of proteins they are restricted by limited polarity range. Ionic liquids are salts which are liquid at room temperature. Ionic liquids have gained interest in extraction over the past years due to its non-volatility and tunable property. In this thesis we explored the feasibility of using two ionic liquid based systems for extraction: 1) Ionic liquid based aqueous two phase system for extraction of microalgae proteins and 2) ionic liquid based emulsions for separation of hydrophilic (e.g. proteins) and hydrophobic (e.g. pigments) components from complex biomass such as microalgae. Additionally the influence of IL pre-treatment on microalgae cell walls and subsequent fractionation of its components (e.g. proteins, pigments, lipids) was also investigated.

    Electrically excited liquid water : lessons from floating water bridge
    Wexler, A.D. - \ 2016
    Wageningen University. Promotor(en): Cees Buisman, co-promotor(en): J. Woisetschläger; E.C. Fuchs. - Wageningen : Wageningen University - ISBN 9789462577039 - 223
    water - liquids - electric field - thermodynamics - bridges - equilibrium - disequilibrium - electrodynamics - nuclear magnetic resonance - neutron scattering - infrared spectroscopy - spectroscopy - gas chromatography - electrical conductivity - interferometry - spectral analysis - physics - water - vloeistoffen (liquids) - elektrisch veld - thermodynamica - bruggen - evenwicht - verstoord evenwicht - elektrodynamica - kernmagnetische resonantie - neutronenverstrooiing - infraroodspectroscopie - spectroscopie - gaschromatografie - elektrische geleidbaarheid - interferometrie - spectraalanalyse - fysica

    Water is essential to a healthy and secure world. Developing new technologies which can take full advantage of the unique attributes of water is important for meeting the ever increasing global demand while reducing the production footprint. Water exhibits unexpected departures in more than 70 physical and chemical properties compared to other molecular species of similar chemical composition. The principal cause for this behavior is ascribed to the large number of hydrogen bonds which form between neighboring water molecules. Hydrogen bonds are moderately strong in water and exhibit both electrostatic as well as covalent character. When examining the liquid state these interactions play a significantly role in moderating the interchange between dynamics and structure. In disordered materials such as a liquid there are three length scales of importance: 1) at the microscopic molecular level interactions dominate, 2) the macroscopic level where classical forces act upon the statistically isotropic medium, and 3) the mesoscopic level where heterogeneous interactions dominate through evolving transient structures each with unique dynamical behaviors. The mesoscale is important to most environmental and biological processes and is even more poorly understood than the liquid state in general. The aim of this thesis is to explore the extended molecular behavior of liquid water excited by strong electric field gradients.

    The floating water bridge belongs to a larger class of phenomena called electrohydrodynamic (EHD) liquid bridges. These self-suspending liquid catenaries can occur in a number of polar liquids provided the conductivity is low. They exhibit elevated temperatures and bidirectional flow patterns, as well as sub-Hz diameter oscillations. The flow behavior and dynamics of these bridges is complex but can be addressed by continuum level EHD theory. The polarizing effect of the electric field gradient accelerates the fluid tangentially along the surface resulting in a Taylor pump which supplies the bridge with liquid. The free hanging section is stable against gravity within a band of operational parameters whereby the electric field strength is sufficient confine fluid elements within the bridge. A standardized protocol for operating stable EHD bridges in multiple configurations is developed and presented. This is the primary tool used throughout the thesis and provides a macroscopic object for the experimental examination of how forces which typically only occur over a few nanometers in nature affect the organization of polar liquids, notably water. In order to examine the role that the electric field gradient plays in the observed molecular changes found in EHD bridges a simple point-plane electrode system was also employed.

    There are available a number of tools which provide complimentary information on chemical and physical processes occurring in the liquid state. A brief introduction is given on the interaction between electromagnetic waves and matter with respect to field theory and methods from atomic physics. The basis for interaction over different length scales is established. Electrochemical characterization includes the quantification and identification of the charge carrying species present, the relative proton concentration, and the complex dielectric response. The vibrational and rotational motion of molecules is measured with a combination of infrared emission spectroscopy and imaging and permits the detection of both the thermal bath and non-equilibrium molecular excited states. The local structure of the liquid matter contained in the bridge can be elucidated through the methods discussed here. X-rays provide information on the electron density whereas neutrons reveal nuclear positions. Together with isotope substitution a complete picture of the motionally averaged local structure of the liquid in the bridge can be recovered. QENS is a special case of inelastic scattering which permits the measurement of diffusion, relaxation, and other slow energy or mass transfer modes in materials using a time-of-flight spectrometer. This data compliments the NMR methods used herein specifically to probe the environment of protons in the system; and to provide clues about the strength of both intra- intermolecular coupling in the system. Very small perturbations in the optical properties of a liquid can be detected using interferometry; these ultimately reflect changes in the polarizability of the liquid which can arise from changes in physical properties. Raman scattering is an inelastic method which can probe changes to the polarizability of a liquid that reflect shifts in the local molecular environment and can be used to determine both local and non-local vibrational coupling.

    Magnetic resonance imaging was used to track the flow field present in the bridge without the use of tracer particles; revealing that the bridge has a layered structure, with distinct flow regimes lying one on top of the other. Investigation of the electrochemistry in the water bridge found that protons account for 87% of the charge transport in the bridge. Impedance spectroscopy and pH measurement corroborate the finding that a proton gradient forms across the entire system. The results from elastic neutron and X-ray scattering reveal that the static structure is unchanged within the given accuracy of the employed measurements. However, the systematic analysis of the data using a reverse Monte Carlo computer simulation revealed significant dynamical changes that are reliable above the limited instrument precision. The imposed electric field of an EHD bridge distorts the local Coulombic interactions between molecules altering the dielectric relaxation pathway so that it becomes more favorable for the absorbed energy to become trapped locally for a longer period of time. The electric field in the bridge system is not uniform. Strong field gradients are present which stimulate changes in the molecular polarizability, generating gradients of physical properties, and restricting the allowed rotational-vibrational relaxation transitions. These trends are comparable to those from ultrafast relaxation measurements where the vibrational lifetime of the OH stretch of HDO was found to be significantly shorter in the bridge than in the neat liquid. This absorbed energy, however, remained trapped in a local intermediate state longer in the bridge before being released as a thermal perturbation. The nuclear relaxation dynamics in a glycerol bridge showed similar behavior where the transverse and longitudinal magnetization lifetimes diverged from the expectation values given the systems temperature.

    From the experimental observations several features of electrically excited water appear. At the gross continuum level the operation of a floating water bridge results in the production of a charge imbalance between anolyte and catholyte. This is in part due to the enhanced proton mobility in the bridge. Protons no longer are confined to the hydrogen bond mediated Grotthuss mechanism but can travel even faster through a delocalized state. This means that charge can be pumped faster than it can be neutralized resulting in the observed electrochemical differences. The energy level of protons in the conduction channel is the difference between the ground and excited state levels observed as a non-thermal emission feature in the mid-infrared. The proton channel will be active over relatively short distances and will experience interruptions due to fluctuations in molecular position driven by local force gradients. These channels are localized and discontinuous providing the physical basis for the onset of mesoscale dynamic heterogeneity in the excited liquid. The picture begins to emerge whereby local trapping states and long-range cooperative coupling modes dynamically exchange energy. The energy exchange is far from equilibrium and supports multiple transfer mechanisms. At the mesoscale the excited state exhibits traits of a chaotic dynamical system and provides a varied energetic landscape whereby rotational-vibrational transition dipoles, nuclear spin states, and thermodynamic potentials, such as the configurational entropy, non-adiabatically – that is there is a pumping of heat in response to the induced fluctuating gradient fields. The transfer of perturbations from local to collective modes and vice versa requires that the chemical, thermal, and electromagnetic potentials present in the molecular milieu be linked to the entropy production.

    This early foray into the non-equilibrium dynamics and mesoscale organization of electrically excited liquid water opens an opportunity to develop technologies which better mimic nature. Taking biological systems as the exemplary standard by which to compare it is necessary to develop soft matter based technical systems which take advantage of the link between electric, magnetic, and thermal fields to drive chemical and physical processes with higher efficiency. Water, as well as other polar liquids, can be locally controlled so as to induce spatial variation in the chemical potential whereby one can imagine a reactor where disparate physical or chemical process can occur in close proximity without the need for rigid segregating structures. Furthermore, this level of control is dynamical such that the organization of the partitioning in the liquid can be changed in time so that the total energy requirement of the intended process is optimized. With such an approach it is conceivable that the size, complexity, and energetic costs of performing many industrial and municipal processes can be reduced. Rather than treating liquids as bulk fluids the opportunity presents itself to use the internal structure and dynamics of liquids to build fluid technologies.

    Longer Oral Exposure with Modified Sham Feeding Does Not Slow Down Gastric Emptying of Low- and High-Energy-Dense Gastric Loads in Healthy Young Men
    Wijlens, G.M. ; Erkner, A. ; Mars, M. ; Graaf, C. de - \ 2015
    The Journal of Nutrition 145 (2015)2. - ISSN 0022-3166 - p. 365 - 371.
    food-intake - appetite - stimulation - fat - responses - humans - satiation - ghrelin - liquids - volume
    Background: A long oral exposure to food and a high-energy density of food are shown to increase satiety feelings. The effect of energy density is predominantly caused by an inhibition of gastric emptying. It is hypothesized that prolonging oral exposure may have an additional effect on this inhibition of gastric emptying. However, little human data are available to support this hypothesis. Objective: The objective was to assess the effect of oral exposure duration to food on gastric emptying rate of gastric loads (GLs) low and high in energy density and on satiety feelings. Methods: Twenty-six healthy men (22 ± 3 y, 23 ± 1 kg/m2) participated in a randomized crossover trial with 4 treatments and a control. Treatments consisted of either 1- or 8-min modified sham feeding (MSF) of cake, and a GL of either 100 or 700 kcal infused in the stomach via a nasogastric tube (500 mL, 62.5 mL/min). The control consisted of no MSF and a GL of 500 mL of water. Gastric emptying rate was assessed with a 13C breath test. Breath samples and satiety feelings were collected at fixed time points until 90 min after start of the treatment. Results: Gastric emptying rate and satiety feelings were not affected by duration of MSF (P = 0.27). However, the 700-kcal GL treatments slowed gastric emptying [41% lower area under the curve (AUC)] and increased satiety feelings (22–31% higher AUC) compared with the 100-kcal GL treatments (P <0.001). No interaction between MSF duration and energy density of GL was found (P = 0.44). Conclusions: Higher gastric energy density inhibited gastric emptying and increased satiety feelings in healthy young men. However, prolonging oral exposure to food did not have an additional effect. This study provides more insight in satiety regulation. This trial was registered at as NTR3601.
    Colloids at liquid interfaces: dynamics and organization
    Ershov, D.S. - \ 2014
    Wageningen University. Promotor(en): Jasper van der Gucht, co-promotor(en): Martien Cohen Stuart. - Wageningen : Wageningen University - ISBN 9789461738943 - 127
    colloïden - oppervlaktechemie - grensvlak - oppervlakteverschijnselen - capillairen - vloeistoffen (liquids) - colloids - surface chemistry - interface - surface phenomena - capillaries - liquids

    This thesis deals with spherical microparticles trapped at liquid interfaces. It focuses on two aspects of their behavior: firstly, the effect of the curvature of a liquid interface on interparticle interactions and their organization; secondly, the mobility of particles at visco-elastic interfaces.

    In Chapter 2of this thesis we showed that it is possible to induce capillary interactions between spherical microparticles with homogeneous surface chemistry by tailoring the curvature of the liquid interface. If the interfacial curvature is anisotropic, the constraint of constant contact angle along the contact line can only be satisfied if the interface is deformed locally. These deformations create excess surface area, which changes when two particles approach each other. This leads to a change in the surface free energy, which manifests itself as a capillary interaction between the particles.

    To study the effect of curvature on the interactions between particles, we created oil-water interfaces of different shape (ellipsoid, dumbbell, torus and squares) and added spherical negatively charged particles that adsorbed at these interfaces. On all these interfaces, we observed quadrupolar capillary interactions that organized the particles into square lattices. The order of this organization increased with increasing curvature anisotropy, indicating that capillary interactions are stronger as well. By contrast, on flat interfaces or on spherical droplets with homogeneous curvature, no attractive interaction was observed and only at very high surface coverage did the particles order in a hexagonal lattice, as a result of repulsive interactions.

    In Chapter 3we studied the interface deformations around particles at curved interfaces and the resulting capillary interactions theoretically. We used the finite element method to solve the Young-Laplace equation for the shape of the interface around a particle and calculated the interaction potential between the particles numerically.

    The main finding of these calculations is that for an anisotropically curved interface, with two different local principal curvatures, the particle deforms the interface in two ways simultaneously: concave deformation along one principal direction and convex – along the other, thus creating a deformation field with quadrupolar symmetry. Two particles with such deformations interact favorably only if the overlapping deformations are similar (concave-concave, convex-convex), which occurs when they approach each other along one of the two principal directions. Since the two local principal directions are always perpendicular, particles interacting along them will tend to arrange into a square pattern.

    As a consequence of the quadrupolar deformation field, two particles approaching each other along a line forming 45 degrees with the principal axes will repel each other (which is confirmed by our observations), because in this case the deformation fields overlap with four different “petals” (2 pairs of concave-convex), and the excessive surface area doesn’t reduce upon approaching, but increases. A system of two particles oriented at an angle with respect to the principal axis is therefore subjected to a torque rotating the axis of the system so that it gets aligned with one of the two principal directions. The torque magnitude reaches its maximum when the system’s axis is at an angle of 45 degrees with respect to the principal direction and decreases to 0 when the axis is aligned with one of the principal directions.

    The family of interaction potentials we obtained allows for calculating the minimum deviatoric curvature needed to initialize capillary interactions strong enough to compete with thermal energy, so that a stable organization can be expected. The calculated value was very close to the deviatoric curvature where ordering was observed experimentally in Chapter 2.

    In Chapter 4we studied the mobility of 3 mm polystyrene particles in a monolayer of 1.5 mm core-shell microparticles deposited at flat air-water interfaces; all the particles present in the system were stabilized by negative charges.

    In this exploratory chapter we made an attempt to characterize the mechanical properties of such monolayers by analyzing the mobility of the larger tracer particles in the monolayer. With increasing particle density of the monolayer, we observed that the mean-square displacement of the tracer particles was reduced, which can be interpreted as an increase of the viscosity of the monolayer. At very high densities the motion of the particles became subdiffusive and confined, pointing at elasticity of the monolayer. We also studied correlated movements between neighboring particles in an attempt to do two-point interfacial microrheology. A comparison between the one-point and two-point methods shows clear indications of heterogeneous dynamics of the tracer particles. Our results therefore call for a further development of two-point microrheology at interfaces.

    In Chapter 5we used tracer particles to study the properties of thin cross-linked actin networks deposited at the surface of oil droplets. These networks are a model system for the intracellular actin cortex. We used the generalized Stokes-Einstein relation to extract the complex frequency-dependent shear modulus of such networks from the movement of the added tracer particles. We studied the effects of the length of actin filaments and the cross-linker concentration on the mechanical properties of these layers.

    The advantage of this system is that actin networks are freely accessible from the water phase, and therefore can be subjected to in-situ addition of cross-linkers, enzymes or other chemicals of interest. Using this, we managed to show strong stiffening after addition of myosin motor proteins and ATP, which we ascribed to contraction of the actin-myosin network.

    The Condensation of Water on Adsorbed Viruses
    Alonso Carnicero, J.M. ; Tatti, F. ; Chuvilin, A. ; Mam, K. ; Ondarcuhu, T. ; Bittner, A.M. - \ 2013
    Langmuir 29 (2013)47. - ISSN 0743-7463 - p. 14580 - 14587.
    scanning-electron-microscopy - surfaces - wet - morphologies - diffraction - droplets - dynamics - liquids
    The wetting and dewetting behavior of biological nanostructures and to a greater degree single molecules is not well-known even though their contact with water is the basis for all biology. Here, we show that environmental electron microscopy (EM) can be applied as a means of imaging the condensation of water onto viruses. We captured the formation of submicrometer water droplets and filaments on single viral particles by environmental EM and by environmental transmission EM. The condensate structures are compatible with capillary condensation between adsorbed virus particles and with known droplet shapes on patterned surfaces. Our results confirm that such droplets exist down to
    Substitutional impurity-induced vitrification in microgel crystals
    Higler, R. ; Appel, J. ; Sprakel, J.H.B. - \ 2013
    Soft Matter 9 (2013). - ISSN 1744-683X - p. 5372 - 5379.
    medium-range order - metallic glasses - liquids - spheres - scattering - colloids - packing
    We study the effect of larger substitutional impurities on the structure of soft microgel crystals. At the size ratio we employ, rsmall/rlarge = 0.67, we observe the unexpected co-crystallisation of the large impurities with the base crystal, at low fractions of impurity particles. A single impurity takes the place of 4 tetrahedrally coordinated small particles within the lattice. However, as this is accompanied by local deformations of the particles, this distortion-minimizing structure transforms into a random surrounding of the impurity particle at higher fractions of large substitutional impurities. The distortions in the lattice become longer ranged through this transformation, and ultimately result in vitrification of the sample
    The potential of electrospraying for hydrophobic film coating on foods
    Khan, M.K.I. ; Schutyser, M.A.I. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2012
    Journal of Food Engineering 108 (2012). - ISSN 0260-8774 - p. 410 - 416.
    cone-jet mode - deposition - atomization - encapsulation - liquids
    There is a continuous need for thinner edible coatings with excellent barrier properties, and this requires new application methods. Electrospraying is known to yield fine droplets of size down to 20 µm, giving the potential of very thin and even coatings. A single electrospraying nozzle was used to characterise droplet formation and investigate the formation of thin films on well-defined surfaces. The experimental droplet size was successfully described as a function of operational parameters and liquid properties using scaling relations. The influence of operating parameters as nozzle height and electrostatic potential were evaluated as well. Thin film deposition was experimentally investigated for sunflower oil electro-sprayed on a highly conductive (aluminium) and insulating target surface (Parafilm). For both aluminium foil and Parafilm the droplet deposition was found to be random. For aluminium foil, being a conductive target, this was expected as repellence between droplets on the surface and new droplets is low, due to charge leakage to the ground. For Parafilm, droplet repellence appeared so large that droplets deposited on larger empty spots or were even pushed away from the surface. To evaluate the film formation performance, Monte Carlo simulations were carried out, and it was found that the method is a useful tool to characterise droplet deposition and film formation characteristics.
    Nieuwe techniek zet zwakke zaden aan de kant
    Derkx, R. - \ 2005
    De Boomkwekerij (2005)42. - ISSN 0923-2443 - p. 12 - 14.
    zaadkeuring - zaadkwaliteit - sorteermachines - zaden - technische vooruitgang - stratificatie (zaden) - vloeistoffen (liquids) - seed certification - seed quality - sorters - seeds - technical progress - stratification - liquids
    Een nieuwe manier van uitsorteren van slechte boomzaden is 'vloeistofscheiden'. Een geslaagde vloeistofscheiding bij vijf soorten boomzaden laat zien, door te spelen met de dichtheid van vloeistoffen, dat men goede, minder goede en zwakke zaden apart in handen krijgt. De keuze voor uitzaai is dan snel gemaakt
    Spreading of partially crystallized oil droplets on an air/water interface
    Hotrum, N.E. ; Cohen Stuart, M.A. ; Vliet, T. van; Aken, G.A. van - \ 2004
    Colloids and Surfaces. A: Physicochemical and Engineering Aspects 240 (2004)1-3. - ISSN 0927-7757 - p. 83 - 92.
    beta-lactoglobulin - milk-products - whipped cream - fat - protein - emulsions - behavior - tension - liquids - foods
    The influence of crystalline fat on the amount and rate of oil spreading out of emulsion droplets onto either a clean or a protein-covered air/water interface was measured for ß-lactoglobulin stabilized emulsions prepared with either anhydrous milk fat or a blend of hydrogenated palm fat and sunflower oil. At a clean interface, liquid oil present in the emulsion droplets was observed to completely spread out of the droplets unimpeded by the presence of a fat crystal network. Further, the presence of a fat crystal network in the emulsion droplets had no effect on the rate of oil spreading out of the droplets. At a protein-covered interface, the spreading behavior of emulsion droplets containing crystalline fat was evaluated in terms of the value of the surface pressure (¿AW) at the point of spreading; ¿AW at spreading was unaffected by the presence of crystalline fat. We conclude it is unlikely that the role of crystalline fat in stabilizing aerated emulsions such as whipped cream is to reduce oil spreading at the air/water interface. However, the temperature of the system did have an effect: spontaneous spreading of emulsion droplets at clean air/water interfaces occurred for systems measured at 5 °C, but not for those measured at 22 or 37 °C. Thus, temperature may play a more important role in the whipping process than commonly thought: the entering and spreading of emulsion droplets was favored at lower temperatures because the surface pressure exerted by protein adsorbed at the air/water interface was reduced. This effect may facilitate the whipping process.
    Warmtewisselaars met gekromde buizen
    Kelder, J.D.H. ; Klerk, S. de - \ 2004
    Voedingsmiddelentechnologie 37 (2004)13. - ISSN 0042-7934 - p. 14 - 16.
    warmteuitwisseling - voedseltechnologie - uitrusting - automatisering - thermisch rendement - reologie - vloeistoffen (liquids) - stroming - heat exchange - food technology - equipment - automation - thermal efficiency - rheology - liquids - flow
    Ultra High Temperature (UHT) sterilisation is a commonly applied technique to preserve liquid food products. Stork Food & Dairy Systems has marketed coiled tubular UHT-sterilisers. For viscous and especially for gelatinising foods (e.g. custard and pudding) spiral sterilisers bring superior performance. Heat transfer greatly increases and required temperatures are attained faster, thus reducing processing time. Coiled sterilisers are therefore shorter and more compact, minimising the loss of quality factors due to the heat treatment. Finally, gelatinisation occurs rapidly and uniformly, and de reduced thermo-mechanical stresses enable a potentially lower amount of starch needed to obtain a target consistency
    Effects of capillarity and heterogeneity on flow of organic liquid in soil
    Wipfler, E.L. - \ 2003
    Wageningen University. Promotor(en): Sjoerd van der Zee. - Wageningen : Wageningen Universiteit - ISBN 9789058088468 - 147
    bodem - water - oliën - lucht - stroming - waterstroming - luchtstroming - capillaire opstijging - vloeistoffen (fluids) - vloeistoffen (liquids) - modellen - drainage - bodemverontreiniging - soil - water - oils - air - flow - water flow - air flow - capillary rise - fluids - liquids - models - drainage - soil pollution

    Contamination of groundwater by organic liquids, such as gasoline, fuel oils and chlorinated hydrocarbons, forms a serious treat to subsurface water resources. These liquids have a low miscibility with water and move as a discrete liquid phase. A small part of the liquid may dissolve in water and small concentrations can be hazardous for humans. These organic liquids that are also referred to as Non-Aqueous Phase Liquids (NAPLs), may enter the subsurface from a surface spill or a leaking underground pipe or tank. Following a release of sufficient NAPL into the subsurface, NAPL moves through the pores of the soil due to gravitational and capillary forces.

    An enhanced understanding of NAPL flow in the subsurface is needed to identify the critical processes and to determine key parameters in the context of remediation strategies at the field scale. In this thesis we study the behavior of NAPL in soil experimentally and numerically. we focus on the physical aspects of this behavior in the unsaturated part of the soil. This implies that we study the movement, interaction and (re-)distribution in a porous medium (soil) of three fluid phases: water, NAPL and air. The porous medium is water-wet, i.e. water is the wetting fluid, NAPL is the intermediate wetting fluid and air is the non-wetting fluid. This leads to typical three-phase flow behavior. We focus on two problems that are both related to NAPL redistribution into unsaturated soil after a spill: (1) non-drainable residual NAPL and (2) the effect of soil layers on the redistribution of NAPL after a spill. In addition to the introduction, the thesis contains 4 chapters which can be read as self-contained papers.

    Non-drainable residual NAPL is considered to be the NAPL that remains in the capillaries of a porous medium after (gravity) drainage and displacement by air in the presence of residual water in a water-wet soil. Although for remediation strategies it is important to consider this residual NAPL, until now it has not been incorporated into multi phase flow models. In Chapter 2 we develop a constitutive set of saturation-capillary pressure ( Pc-S ) relationships that accounts for non-drainable residual NAPL and that can be used by multi-phase flow models. These relationships are derived from a conceptual pore scale model of which the soil is represented by packed spheres. According to the model, NAPL becomes immobilized (residual) below a certain critical total liquid saturation, S tc. This critical total liquid saturation is porous medium and fluid dependent. Next, the non-drainable residual NAPL saturation increases, when the spreading coefficient of a NAPL decreases. Furthermore, a higher water saturation results in a lower non-drainable residual saturation. Although the model adequately simulated one individual experimental non-drainable residual NAPL data set, this agreement is a shallow basis for assessing whether the model assumptions are valid.

    For this purpose we developed an experiment especially designed to measure three-phase Pc-S relationships and non-drainable residual saturation including independent measurement of the water saturation and pressure. We performed four experiments. We used the fluids water, non-spreading dodecane and air, and sand as the porous medium. The measured non-drainable residual saturation was at most 0.081. From the experimental results no correlation could be observed between the water saturation and the residual NAPL saturation. This might indicate that other mechanisms are involved that are not captured by the constitutive model. In advance of the development of the experimental set up, we searched in the literature for available macroscale experimental data that could provide us with non-drainable residual saturation data that are related to porous medium properties, fluid properties and fluid saturations. After a careful selection we obtained 26 non-drainable residual NAPL data from 9 references. Measured values of non-drainable residual saturation varied between 0.001 and 023. From these data only a relationship between the spreading coefficient Cs , and the residual saturation S or , could be assessed. The value of S or decreases as Cs becomes less negative. It would require a much more comparable description of the different porous media, and a systematic data acquisition for S or as a function of macroscale properties to assess which other factor than the spreading coefficient might be hidden in the data. Changes of porous medium properties such as permeability and porosity across an interface between two soil layers might change the redistribution of NAPL. The mobility may decrease or increase across the interface, which is dependent on the permeability of the layers, the capillarity of the layers and the wetting role that is played by the NAPL with respect to water and air. The effect of these changes have been studied in Chapter 4 and 5.

    In Chapter 4 we focused on the effect of an inclined soil layer with respect to the watertable. Two experiments were performed using a sand filled transparent chamber. The first experiment consisted of Light-NAPL infiltration into a fine sand matrix containing a coarse sand layer and the second experiment consisted of LNAPL infiltration into a coarse sand matrix containing a fine sand layer. The sand was partially saturated with water. We modeled the experiments numerically. The observed LNAPL behavior can be understood by considering that LNAPL might encounter two types of barriers. On the one hand, it may accumulate and spread above a coarse sand layer, that has a low water saturation and, that acts as a capillary barrier for the LNAPL before it may infiltrate into the layer. An on the other hand, it may accumulate and spread above a water saturated fine sand layer that has a high entry pressure for the infiltrating LNAPL. Sensitivity analysis performed with the numerical model shows that the qualitative LNAPL redistribution, in case of inclined layers, is mainly subject to the capillarity contrast between sands.

    In Chapter 5 we considered Dense-NAPL infiltration into a water unsaturated porous medium that consists of two horizontal layers, of which the top layer has a lower intrinsic permeability than the bottom layer. The layer interface forms a barrier to DNAPL flow, which causes the DNAPL to spread out horizontally just above the interface. We have developed an analytical approximation to estimate the DNAPL pressure and saturation and the horizontal extension of the DNAPL plume just above the layer interface at steady state for low water saturations. The analytical approximation shows that the steady state DNAPL infiltration is determined by five dimensionless numbers: the heterogeneity factorg, the Brooks and Corey capillary pressure parameterl, the gravity number Ng , the ratio of the capillary and gravity numbers Nc/Ng , and the critical DNAPL pressure P oc, which indicates the effect of the water saturation on the flow of DNAPL. We compared its predictions with the results of a numerical three-phase flow simulator for a number of parameter combinations. For most of these combinations the analytical approximation predicts the DNAPL pressure and saturation profiles at the interface adequately, although it slightly underestimates the horizontal spreading of the plume at the interface. Using the analytical approximation, we carried out a sensitivity study with respect to the maximum horizontal extension of the plume. The extension of the plumes appears to be highly sensitive to variation of the dimensionless numbers P oc,landg. The extension increases for increasing values oflandgand for decreasing values of P oc.

    Tabaksblad in witte- en rodekool
    Everaarts, A.P. - \ 2000
    PAV-bulletin. Vollegrondsgroenteteelt / Praktijkonderzoek voor de Akkerbouw en de Vollegrondsgroenteteelt 4 (2000)3. - ISSN 1385-5298 - p. 24 - 26.
    koolsoorten - afwijkingen, planten - plantenziektekunde - symptomen - misvormingen - gewasbescherming - cultuurmethoden - brassica oleracea var. capitata - groeitempo - sapstroom - vloeistoffen (liquids) - cabbages - brassica oleracea var. capitata - plant disorders - plant pathology - symptoms - malformations - plant protection - cultural methods - growth rate - sap flow - liquids
    Onderzoek naar tabaksblad in kool toont aan dat deze groeiafwijking ontstaat tijdens de teelt. Factoren die tijdens de teelt van sluitkool het optreden van tabaksblad (inwendig rand) in belangrijke mate beinvloeden zijn de groeisnelheid en de waterhuishouding van het gewas
    Source-sink relations in transgenic tobacco with modified trehalose metabolism : a comparative labelling study with the stable isotopes 13C and 15N of wildtype and five transgenic types
    Visser, A.J.C. de; Leeuwen, P.H. van; Pot, C.S. - \ 1999
    Wageningen : AB-DLO (Note / Agricultural Research Department, Research Institute for Agrobiology and Soil Fertility 179) - 32
    plantengroeiregulatoren - genetische modificatie - nicotiana - trehalose - vloeistoffen (liquids) - sapstroom - distributie - plant growth regulators - genetic engineering - liquids - sap flow - distribution
    Fosfaat moet in dikke fractie bij mestbewerking op varkensbedrijf
    Mandersloot, F. - \ 1999
    Praktijkonderzoek varkenshouderij 13 (1999)3. - ISSN 1382-0346 - p. 12 - 14.
    varkensmest - dierlijke meststoffen - fosfor - scheiding - vloeistoffen (liquids) - mestverwerking - mestoverschotten - pig manure - animal manures - phosphorus - separation - liquids - manure treatment - manure surpluses
    Mestbewerking op bedrijfsniveau blijft financieel gezien een moeilijke zaak. Mechanische scheiding is op bedrijven met vleesvarkens vaak te duur. Bezinken van zeugenmest heeft wel perspectief voor bedrijven die grond beschikbaar hebben om de dunne fractie uit te rijden.
    Dubbele emulsies controleren afgifte of scheiding voedingscomponenten
    Horst, B.M. van der; Langelaan, H.C. - \ 1999
    Voedingsmiddelentechnologie 32 (1999)24. - ISSN 0042-7934 - p. 10 - 16.
    ingrediënten - voedselindustrie - voedseltechnologie - emulsies - dispersie - emulgeermiddelen - scheiding - segregatie - zuiveren - filtratie - technologie - verwerking - vloeistoffen (liquids) - pigmenten - modellen - ingredients - food industry - food technology - emulsions - dispersion - emulsifiers - separation - segregation - purification - filtration - technology - processing - liquids - pigments - models
    Een nieuw concept voor het scheiden van voedingscomponenten, alsmede voor toepassing in de cosmetische en farmaceutische industrie. Het onderzoek op dit gebied door ATO-DLO is gericht op het encapsuleren van (vluchtige) componenten, nieuwe emulgeringsmethoden, bereidingsaspecten, lange termijnstabiliteit, reologische eigenschappen, typen emulgatoren en gecontroleerde afgifte. Tevens werd een modelsysteem ontwikkeld voor het verwijderen van ongewenste componenten uit voedingsmiddelen
    Vochtverbruik en droogtegevoeligheid van voedergewassen : experimenteel onderzoek 1994 - 1996
    Smid, H.G. ; Grashoff, C. ; Aarts, H.F.M. - \ 1998
    Wageningen : AB-DLO (Rapport / Dienst Landbouwkundig Onderzoek, Instituut voor Agrobiologisch en Bodemvruchtbaarheidsonderzoek 91)
    voedergewassen - oogsttoename - oogstverliezen - opbrengsten - groei - gewassen - oogstschade - beschadigingen door droogte - waterbehoefte - vloeistoffen (liquids) - absorptie - emissie - omloop - bodemwatergehalte - fodder crops - yield increases - yield losses - yields - growth - crops - crop damage - drought injury - water requirements - liquids - absorption - emission - circulation - soil water content
    Levering drie Rossum-stuwen Schouwen West
    Boiten, W. - \ 1998
    Wageningen : Landbouwuniversiteit Wageningen (Rapport / Landbouwuniversiteit Wageningen, Afdeling Waterhuishouding 76) - 5
    hydrodynamica - vloeistoffen (liquids) - vloeistoffen (fluids) - stroming - kanalen - kanalen, klein - meting - snelheid - nederland - zeeland - zeeuwse eilanden - hydrodynamics - liquids - fluids - flow - canals - channels - measurement - velocity - netherlands - zeeland - zeeuwse eilanden
    Effecten van het vernevelen van vloeistoffen ter verlaging van de stofconcentratie in pluimveestallen
    Ellen, H.H. ; Drost, H. - \ 1998
    Beekbergen : Praktijkonderzoek Pluimveehouderij (PP uitgave : praktijkonderzoek pluimveehouderij 76) - 33
    pluimveehouderij - pluimveehokken - luchtverontreiniging - stof - stofbestrijding - vernevelen - spuiten - vloeistoffen (liquids) - arbeidsomstandigheden - poultry farming - poultry housing - air pollution - dust - dust control - fogging - spraying - liquids - working conditions
    Het Praktijkonderzoek Pluimveehouderij 'Het Spelderholt' (PP) en het Instituut voor Milieu-en Agritechniek (IMAG-DLO) hebben gezamenlijk onderzoek opgestart naar verlaging van de stofconcentratie in pluimveestallen. Dit heeft geresulteerd in het project 'Effecten van het vernevelen van vloeistoffen ter verlaging van de stofconcentratie in pluimveestallen'. Op basis van een literatuurstudie is binnen dit project gekozen om het terugdringen van de stofconcentratie in pluimveestallen door middel van hetvernevelen van vloeistoffen nader te bekijken.
    Mestscheiding met stro
    Kant, P. ; Blanken, K. - \ 1998
    Praktijkonderzoek Rundvee, Schapen en Paarden. Praktijkonderzoek 11 (1998)1. - ISSN 1386-8470 - p. 20 - 22.
    mest - vloeibare meststoffen - rundveedrijfmest - varkens - scheiding - vloeistoffen (liquids) - klaring - stro - mestoverschotten - mestverwerking - manures - liquid manures - cattle slurry - pigs - separation - liquids - clarification - straw - manure surpluses - manure treatment
    Mestscheiding staat regelmatig in de belangstelling. Er kunnen allerlei redenen zijn waarom het creëren van een dikke en een dunne fractie uit gewone mest interessant kan zijn, zoals mestafzet of een preciezere bemesting. Vaak zijn echter de kosten van het scheiden te hoog. Het PR heeft daarom gekeken naar de technische mogelijkheden van een eenvoudige scheidingstechniek met stro als filtermedium. Het lijkt mogelijk een groot deel van de fosfaat in de dikke fractie te concentreren, waarbij echter weleen deel van de stikstof verloren gaat.
    Modelling water and nutrient uptake of crops grown in protected cultivation
    Willigen, P. de; Heinen, M. - \ 1998
    Acta Horticulturae 456 (1998). - ISSN 0567-7572 - p. 227 - 236.
    bodem - elektrische eigenschappen - elektrische geleiding - magnetische eigenschappen - vloeistoffen (liquids) - absorptie - modellen - onderzoek - computersimulatie - simulatie - simulatiemodellen - glastuinbouw - soil - electrical properties - electrical conductance - magnetic properties - liquids - absorption - models - research - computer simulation - simulation - simulation models - greenhouse horticulture
    This paper presents results of model calculations on uptake of water and nutrients by a lettuce crop grown in a sand bed. Emphasis is on the effect of salt concentration (osmotic head) on water uptake. This effect was studied using a two-dimensional model of water and nutrient transport in and uptake from a rooting medium. The main conclusion is that under normal conditions as found in Dutch horticulture, osmotic effect on water uptake is not important, but that it depends on the distribution of salts with respect to that of the roots.
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