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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    Hoog isolerende en lichtdoorlatende schermconfiguraties
    Zwart, H.F. de; Stanghellini, C. ; Knaap, L.P.M. van der - \ 2010
    Wageningen : Wageningen UR Glastuinbouw / TNO (Nota / Wageningen UR Glastuinbouw ) - 38
    schermen - thermische schermen - energie - tomaten - kassen - convectie - warmteoverdracht - kastechniek - duurzame energie - energiebesparing - glastuinbouw - blinds - thermal screens - energy - tomatoes - greenhouses - convection - heat transfer - greenhouse technology - sustainable energy - energy saving - greenhouse horticulture
    Hoogisolerende schermsystemen bestaan uit meerdere lagen waarvan tenminste een laag van gealuminiseerd materiaal is gemaakt om de reflectie van de warmtestraling te maximaliseren. Dit is de hoofdconclusie die op grond van de analyse van de fysische processen rond convectieve- en stralingswarmteoverdracht bij schermen een rol spelen. Convectieve warmte-overdracht is de energie-overdracht die plaatsvindt middels de verplaatsing van lucht van de ene naar de andere temperatuur. Stralingsoverdracht is energie-overdracht tussen materie op grond van de emissie-coefficient van die materialen. Stralingsoverdracht is niet gekoppeld aan luchtbeweging en vindt plaats tussen alle oppervlakken in de kas. Het rapport bespreekt deze processen.
    Growth of Cronobacter spp. under Dynamic Temperature Conditions Occurring during Cooling of Reconstituted Powdered Infant Formula
    Kandhai, M.C. ; Breeuwer, P. ; Gorris, L.G.M. ; Zwietering, M.H. ; Reij, M.W. - \ 2009
    Journal of Food Protection 72 (2009)12. - ISSN 0362-028X - p. 2489 - 2498.
    enterobacter-sakazakii - domestic refrigerators - neonatal meningitis - milk - performance - convection - foods - time
    Reconstituted infant formulae are excellent growth media for Cronobacter spp. (formerly Enterobacter sakazakii) and other microorganisms that may be present in such products. Immediate consumption or rapid cooling and storage at a low temperature are therefore recommended as control measures to prevent microbial growth. Placing a container filled with reconstituted liquid formula in the refrigerator, however, does not mean that the temperature of the liquid is directly the same as the set-point of the refrigerator. This study describes the temperature profiles and methods to predict lag time and possible growth of Cronobacter spp. during the cooling process in three types of containers. The overall heat transfer coefficients (a) were determined and were shown to have a very large variability in both household refrigerators and an air-ventilated refrigerator equipped with a fan. A mathematical model was built to predict the growth of Cronobacter spp. under dynamic temperature conditions using three models for the lag time. The various estimations for the lag time had a remarkably strong impact on the predicted growth. The assumption of a constant k-value (k = lag time × specific growth rate = ¿ × µ = 2.88) fitted the experimental data best. Predictions taking into account the large variability in heat transfer showed that proliferation of Cronobacter spp. during cooling may be prevented by limiting the volume to be cooled to portion size only, or by reconstituting at temperatures of 25°C or lower. The model may also be used to predict growth in other situations where dynamic temperature conditions exist.
    Sturing gewastemperatuur aan herziening toe
    Stanghellini, C. ; Heuvelink, E. - \ 2008
    Groenten en Fruit. Algemeen 2008 (2008)34. - ISSN 0925-9694 - p. 18 - 19.
    kassen - gesloten systemen - teelt onder bescherming - klimaatregeling - kasgewassen - huidmondjes - luchttemperatuur - zonnestraling - convectie - vaporisatie - glastuinbouw - greenhouses - closed systems - protected cultivation - air conditioning - greenhouse crops - stomata - air temperature - solar radiation - convection - vaporization - greenhouse horticulture
    De temperatuur van een gewas hangt af van veel factoren. Een plant ontvangt niet alleen energie, maar geeft die ook af, tot er evenwicht ontstaat. Dat proces wordt gestuurd via de huidmondjes, maar ook een teler heeft mogelijkheden om de gewastemperatuur te sturen
    Estimation and prediction of convection-diffusion-reaction systems from point measurement
    Vries, D. - \ 2008
    Wageningen University. Promotor(en): Gerrit van Straten, co-promotor(en): Karel Keesman; H.J. Zwart. - [S.l. : S.n. - ISBN 9789085048572 - 170
    systemen - systeemanalyse - stroming - convectie - diffusie - gasbewaring - gecontroleerde omgeving - desinfectie - ultraviolette straling - wiskundige modellen - operating systems - modelleren - systems - systems analysis - flow - convection - diffusion - controlled atmosphere storage - controlled atmospheres - disinfection - ultraviolet radiation - mathematical models - operating systems - modeling
    Different procedures with respect to estimation and prediction of systems characterized by convection, diffusion and reactions on the basis of point measurement data, have been studied. Two applications of these convection-diffusion-reaction (CDR) systems have been used as a case study of the proposed estimation and prediction methods. One is a climate room for bulk storage of agricultural produce (Case A) and the other is a UV disinfection process used in water treatment, food industry and greenhouse cultivation (Case B).
    An essential step in the implementation of estimation and prediction for these types of systems is model reduction. The proposed procedures not only differ by the nature of the estimation and prediction method, but also with respect to early or late model reduction. In the context of this thesis, early model reduction encompasses approximation of the infinite-dimensional system to finite-dimensional form before estimation and prediction is worked out, whereas in late model reduction, the approximation step is applied after synthesis of an infinite-dimensional estimator (observer) or predictor.
    The first contribution of this thesis is an identification approach with output-error (OE) modelling techniques that links important physical parameters in a reduced order model to the OE parameters. This technique is illustrated by Case A, using real experimental data. Local parametric sensitivity analysis shows how physical parameters affect the dominant time constant in an identified, first order output-error model.
    The second contribution is a realization approach from a discrete-time linear finite-dimensional system affine in parameters to linear regressive form. The resulting linear regression form allows the formulation of a convex parameter estimation and prediction problem. Such an approach is attractive for reduced order, discretized CDR models with specific boundary conditions. For such models, it turns out that the response and regressor functions can be formulated explicitly as functions of the number of compartments, sensor and actuator location. Once available, they can further be used for a priori identifiability checks, parameter and input sensitivity analysis. Results are illustrated by two diffusion examples with different boundary conditions.
    Finally, the last contributions are a static and a dynamic boundary observer for CDR systems. Detectability and observability results aid in the design of a static gain boundary observer of an infinite-dimensional system where only boundary measurements are available. The dynamic observer is synthesized by formulating an H∞-filtering problem in a linear fractional transformation framework in order to cope with disturbances on the input and output of the system. Both observer synthesis approaches are illustrated by a CDR model of Case B.
    Spatial model reduction for transport phenomena in environmental and agricultural engineering
    Dirkse, M.H. - \ 2008
    Wageningen University. Promotor(en): Gerard Bot, co-promotor(en): Wilko van Loon; Hans Stigter. - [S.l.] : S.n. - ISBN 9789085048633 - 143
    transportprocessen - warmteoverdracht - massaoverdracht - simulatiemodellen - convectie - tweedimensionale stroming - warmtewisselaars - ruimtelijke verdeling - ruimtelijke variatie - systemen - systeemanalyse - elektrodialyse - computationele vloeistofdynamica - modelleren - procesbewaking - transport processes - heat transfer - mass transfer - simulation models - convection - two dimensional flow - heat exchangers - spatial distribution - spatial variation - systems - systems analysis - electrodialysis - computational fluid dynamics - modeling - process control
    Tijdens het ontwerpen van landbouwkundige en industriële installaties is het belangrijk om het energieverbruik van tevoren in te schatten. Simpele berekeningen volstaan om het energieverbruik globaal te schatten, maar vaak kan het energieverbruik significant worden verminderd door de vorm van het systeem slim te kiezen. De invloed van deze verbeteringen kan niet met simpele berekeningen worden voorspeld. Deze promotie gaat over een nieuwe methode om de invloed van de geometrie te analyseren. De methode is gebaseerd op toepassing van complexe functietheorie op stromingsproblemen; de zognaamde potentiaaltheorie. Als voorbeelden worden een warmtewisselaar en een omgekeerde elektrodialyse installatie onderzocht. Als de methode verder wordt uitontwikkeld, dan kan dit in de toekomst leiden tot besparingen van tijd en geld tijdens de ontwerpfase van technische installaties.
    Understanding heat transfer in 2D channel flows including recirculation
    Dirkse, M.H. ; Loon, W.K.P. van; Stigter, J.D. ; Bot, G.P.A. - \ 2007
    International Journal of Thermal Sciences 46 (2007)7. - ISSN 1290-0729 - p. 682 - 691.
    comprehensive approach - cfd simulations - verification - validation - convection
    Inviscid, irrotational two-dimensional flows can be modelled using the Schwarz¿Christoffel integral. Although bounded flows including boundary layer separation and recirculation are not irrotational, a model is presented that uses the Schwarz¿Christoffel integral to model these flows. The model separates the flow domain in the main flow area, where irrotational flow is assumed, and recirculation areas, which are modelled as monopolar vortices. The model has unknown parameters, which are geometric characteristics of the velocity field. The method is demonstrated on a channel with alternating baffles. Many variations of this system were modelled using CFD modelling, and the flow was a typical combination of main flow and recirculation. The CFD results were used as reference to calibrate the parameters of the Schwarz¿Christoffel model. Many parameters appeared to be constant, and calibrating only three variable parameters yielded about 22% error for most velocity fields. After this, heat transfer was added to the CFD models, and the heat flux was analysed using the three variable parameters representing the velocity field. This way, a new model is found for the heat flux from a wall bounding a vortex, which has an error of 7%. Finally, we have calibrated the parameters using a limited number of given velocity vectors, demonstrating that the parameters can be calibrated against a real set of measurements.
    Turbulent dispersion in the Atmospheric Convective Boundary Layer
    Dosio, A. - \ 2005
    Wageningen University. Promotor(en): Bert Holtslag; P.J.H. Builtjes, co-promotor(en): Jordi Vila-Guerau de Arellano. - [S.l.] : s.n. - ISBN 9789085041719 - 173
    atmosfeer - turbulentie - convectie - chemische samenstelling - ruimtelijke verdeling - grenslaag - atmosphere - turbulence - convection - chemical composition - spatial distribution - boundary layer - cum laude
    cum laude graduation (with distinction)
    Buoyancy-driven flow in a peat moss layer as a mechanism for solute transport
    Rappoldt, C. ; Pieters, G.J.J.M. ; Adema, E.B. ; Baaijens, G.J. ; Grootjans, A.P. ; Duijn, C.J. van - \ 2003
    Proceedings of the National Academy of Sciences of the United States of America 100 (2003)25. - ISSN 0027-8424 - p. 14937 - 14942.
    horizontal porous layer - boundary-conditions - large peatlands - sphagnum - stability - carbon - modulation - convection - growth - bog
    Transport of nutrients, CO2, methane, and oxygen plays an important ecological role at the surface of wetland ecosystems. A possibly important transport mechanism in a water-saturated peat moss layer (usually Sphagnum cuspidatum) is nocturnal buoyancy flow, the downward flow of relatively cold surface water, and the upward flow of warm water induced by nocturnal cooling. Mathematical stability analysis showed that buoyancy flow occurs in a cooling porous layer if the system¿s Rayleigh number (Ra) exceeds 25. For a temperature difference of 10 K between day and night, a typical Ra value for a peat moss layer is 80, which leads to quickly developing buoyancy cells. Numerical simulation demonstrated that fluid flow leads to a considerable mixing of water. Temperature measurements in a cylindrical peat sample of 50-cm height and 35-cm diameter were in agreement with the theoretical results. The nocturnal flow and the associated mixing of the water represent a mechanism for solute transport in water-saturated parts of peat land and in other types of terrestrializing vegetation. This mechanism may be particularly important in continental wetlands, where Ra values in summer are often much larger than the threshold for fluid flow. The upper part of a living mire consists of a sponge-like layer of predominantly moss species, the acrotelm (1), with a porosity above 95%. The green and brownish plants near the surface (Fig. 1) intercept light and fix CO2. Further down, the older plants turn yellow and start to decay. Aerobic decay in the acrotelm takes place relatively rapidly and makes nutrients available for recycling. Below the acrotelm, a denser layer, the catotelm, is present, where the hydraulic conductivity is much lower than in the acrotelm (2), and where the decay rate is several orders of magnitude smaller due to the anoxic conditions (3). It is the peat formation (4, 5) in the slowly growing catotelm that represents a sink of atmospheric CO2 (5, 6). The production of organic matter at the surface largely depends on the recycling of nutrients originating from decomposing plant material. Because decomposition and photosynthesis take place at different depths, the transport of oxygen, carbon compounds, and nutrients forms an important element in the functioning of the mire ecosystem. This transport takes place both inside (7) and outside the plants by diffusion and fluid flow. In this paper, we investigate a mechanism for fluid flow in a water-saturated peat moss layer, which does not depend on capillarity or an external hydraulic pressure. During the night, the surface cools, leading to relatively cold water on top of warm water, and if the temperature drop is sufficiently large, the cold water sinks and the warm water rises. This type of flow is called buoyancy flow, and it implies convective transport of the heat and solutes carried with the water. Buoyancy flow often occurs as ``cells¿¿ consisting of adjacent regions with upward and downward flow. We studied the phenomenon in a peat moss layer by means of a mathematical model, numerical simulation, and laboratory measurements.
    Shallow cumulus convection = Ondiepe cumulus convectie
    Neggers, R. - \ 2002
    Wageningen University. Promotor(en): A.A.M. Holtslag; A.P. Siebesma. - S.l. : S.n. - ISBN 9789058087744 - 202
    wolken - convectie - atmosfeer - turbulentie - simulatiemodellen - grenslaag - clouds - convection - atmosphere - turbulence - simulation models - boundary layer

    Clouds play an important role in the earth's climate. Firstly, they are important in the radiative energy budget of the global atmosphere. Clouds absorb and reflect ultraviolet solar radiation, and emit infrared radiation depending on their temperature. Secondly, an important part of the vertical transport of heat, moisture and momentum in the atmosphere is associated with the relatively strong vertical motions inside certain types of clouds, also called convective clouds. These clouds often produce intense precipitation, and play an important role in the global water cycle. In the tropics near the equator, these clouds act as the engine for whole large-scale atmospheric circulations.

    This thesis is concerned with clouds in the lowest few kilometers of the atmosphere surrounding the earth. This sphere is also known as the atmospheric or planetary boundary layer (PBL), defined as the part of the atmosphere directly influenced by the proximity of the surface of the earth. In this layer the exchange takes place of heat and moisture between the earth and the atmosphere. Basically the boundary layer is formed and maintained by vertical motions of air, known as turbulence . The turbulence is driven by heating of air close to the surface, and by the drag on the horizontal winds by the roughness of the earth's surface. The resulting turbulent eddies mix heat, moisture and momentum throughout the boundary layer. As rising air cools adiabatically, some eddies can get cooled so much in certain situations that water droplets form inside them, forming cumuliform clouds. This type of clouds is the main subject of this thesis. More specifically, the research is focused on shallow cumulus clouds, also known as fair-weather cumulus.

    Because of their important role in the earth's radiative budget and in the vertical transport of air, it is essential for weather and climate prediction modelling to know where, when and to what extent cumuliform clouds occur. Since a few decades ago numerical models for the general circulation are used to make weather and climate predictions. Despite the rapid developments in supercomputing, the typical spatial and temporal resolutions used in state of the art models are still as large as 30 to 50km. These grid-spacings are still much too large to realistically resolve shallow cumulus clouds, as their dimensions are in the order of a few kilometers at maximum. Nevertheless, their strength lies in their numbers, as these clouds typically occur in whole populations covering large areas of the globe. In order to represent the impact of these clouds on the general atmospheric circulation which is to be resolved by the models, it is necessary to implement simplified formulas which mimic the presence of shallow cumulus clouds. This technique is known as parameterization. These formulations typically are dependent on a few relevant meteorological parameters. Due to the complexity of this problem much effort has already been put in the scientific research on cumulus convection.

    In parameterizations for cumulus it is custom to separate the modeling of turbulent transport in the cloud layer and in the dry air below the clouds. This often leads to unwanted interactions of the modeling of these mechanisms in the lower atmosphere. The purpose of the research project behind this thesis was twofold: firstly to comprehend and model the exchange of air between the subcloud layer and the cumulus clouds, and secondly to quantify and model the mixing of this ventilated air over the cloud layer. Associated with this approach is a study of the typical turbulent and geometrical variability of cumulus cloud populations. The research is performed using observations of natural cumulus clouds by aircraft, surface-based meteorological instrumentation, remote sensing devices on satellites and cloud radar. To supplement these datasets which are often scarce and incomplete on important points, use is also made of high-resolution numerical models for atmospheric flow, also known as large-eddy simulation . These models simulate a domain of ten by ten by five kilometers, including whole populations of cumulus clouds. These simulated fields are used as a virtual laboratory to study cumulus convection.

    Large-eddy simulation results on shallow cumulus convection are directly evaluated against detailed cloud observations in Chapter 3, using aircraft-measurements of the Small Cumulus Microphysics Study (SCMS) as well as high-resolution Landsat images. The results show that given the correct initial and boundary conditions the LES concept is capable of realistically predicting the bulk thermodynamic properties of temperature, moisture and liquid water content of the cumulus cloud ensemble as observed in SCMS. Furthermore the vertical component of the in-cloud turbulent kinetic energy and the cloud size distribution in LES were in agreement with the observations. Several hypotheses which make use of conditionally sampled fields were tested on the SCMS data. The magnitudes and the decrease with height of the bulk entrainmen t rate following from the SCMS data confirm the typical values first suggested by Siebesma and Cuijpers (1995) using LES results on the Barbados Oceanic and Meteorological Experiment (BOMEX). An alternative formulation of the lateral entrainment rate as a function of the liquid water content and the mean lapse rate agrees well with the original form based on the conserved variables. Applying the simplified equation for the cloud vertica l velocity by Simpson and Wiggert (1969) to the aircraft-measurements results in a reasonably closed budget. These results support the credibility of cloud statistics as produced by LES in general, and encourage its use as a tool for testing hypotheses and developing parameterizations of shallow cumulus cloud processes.

    The geometrical variability of shallow cumulus cloud populations is assessed in Chapter 4 by means of calculating cloud size densities. We find a power-law scaling at the small cloud sizes and the presence of a scale break. The corresponding functional parameters have values which are typical for observed populations. The scale-break size appears to be the relevant length-scale to non-dimensionalize the cloud size, as this causes a data-collapse of the cloud size densities over several different cumulus cases. These findings suggest that a universal functional form exists for the cloud size density of shallow cumulus. A better understanding of the scale-break size is essential for for a complete definition this function. The scale-break co-determines the cloud size density, and defines the intermediate dominating size in the mass flux and cloud fraction decompositions. Its intermediate position between the largest clouds and the grid-spacing in LES implies that the clouds which do matter are resolved well by LES.

    In Chapter 5 the (thermo)dynamic variability of shallow cumulus is visualized by means of conserved variable diagrams, showing the joint pdfs of the conserved thermodynamic variables and (vertical) momentum. This approach inspired the formulation of a multi parcel model, meant to at least partially reproduce the joint pdfs. A new conceptual model for the lateral mixing of such an updraft-parcel is presented, based on an adjustment time-scale for the dilution of the excess of the conserved properties of this updraft parcel over its environment. A statistical analysis of many LES clouds showed that this adjustment time-scale is constant in all clouds, which implies a lateral mixing rate which is inversely proportional to the vertical velocity. This dynamical feedback between thermodynamics and vertical momentum is shown to be capable of reproducing the cloud population-average characteristics as well as the increase of the in-cloud variances with height.

    Chapter 6 deals with the cloud-subcloud coupling, which manifests itself in many aspects of shallow cumulus topped boundary layers, not in the last place in the turbulent variability. The parameterization of the transport properties of the simplified top-hat pdf is expressed in the mass flux model, of which the closure at cloud base represents this cloud-subcloud interaction. Three closure methods for shallow cumulus are critically examined for the difficult case of a diurnal cycle of shallow cumulus over land. First the various closures are diagnostically evaluated in a large-eddy simulation of a diurnal cycle. Subsequently they are implemented in an offline 1D model to study their impact on the development of the modelled cloudy boundary layer. Significant moistening occurs in the subcloud mixed layer in the first hours after cloud onset in LES, which makes the boundary-layer equilibrium closure Tiedtke (1989) substantially overestimate the mass flux at cloud base. As a result the boundary layer deepens unrealistically rapid at that stage in the single column model. The adjustment closure on the convective available potential energy (CAPE) of Fritsch and Chappell (1980) fails at the early and final stages of the diurnal cycle, when the cloud base transport is controlled by subcloud layer properties. The subcloud convective velocity scale closure of Grant (2001) is promising, as it reproduces the timing of both the maximum and the final decrease of the cloud base mass flux in LES. Apparently this closure catches the coupling between the two layers at cloud base. As a consequence the development of the thermodynamic structure of the boundary layer in the 1D model strongly resembles that in LES.

    The validation of global weather and climate models with observations in general shows that in many situations the characteristics of clouds are not represented well. Especially concerning low convective clouds it has become clear that existing parameterizations for important meteorological parameters such as cloud cover and occurrence of different type of clouds do not always give realistic results. Misrepresentations of these parameters can lead to serious deviations in the modelled circulation and climatology. It is clear that further research and development is required in this field of meteorology. The results as presented in this thesis have contributed to this in several ways. The thermodynamic variability and population statistics of cumulus cloud fields has been further charted and quantified. The interaction between shallow cumulus cloud layers and subcloud layers has been analyzed and the performance of several well-known conceptual models for this interaction has been compared. The dynamics of mixing between cumulus clouds and their environment has been studied and captured in a coneptual model. Finally, it has been shown that the cloud populations as produced by LES models have realistic cloud size statistics and thermodynamic properties.

    Daily cycle of Skewness and Kurtosis charateristics within and just above a crop canopy
    Jacobs, A.F.G. ; Wiel, B.J.H. van de; Holtslag, A.A.M. - \ 2001
    Agricultural and Forest Meteorology 110 (2001)2. - ISSN 0168-1923 - p. 71 - 84.
    plant canopy - turbulence - layer - forest - convection
    A measurement program is carried out within as well as above a maize crop canopy. Statistical characteristics are analyzed for the velocity components as well as for temperature for a clear weather day as well as a cloudy day. During daytime it appears that the above and within-canopy characteristics are dominated by sweeps, which means a positive u-skewness and a negative w-skewness. During daytime the within-canopy w-kurtosis is extremely high due to strong turbulence events of sweeps as well as ejections. During night-time, hot plumes released from the soil surface dominate the extremes, which results in a positive w-skewness, above as well as within the canopy. The temperature skewness is mostly positive within as well as above the canopy. After mid-day on the clear day with low wind conditions, however, the within-canopy skewness for temperature is negative nearly throughout the whole canopy due to sweeps from a relatively high and cool level.
    Simulation of water flow and bromide transport in a water repellent sandy soil using a one-dimensional convection-dispersion model
    Bosch, H. van den; Ritsema, C.J. ; Boesten, J.J.T.I. ; Dekker, L.W. ; Hamminga, W. - \ 1999
    Journal of Hydrology 215 (1999)1-4. - ISSN 0022-1694 - p. 172 - 187.
    wiskundige modellen - waterstroming - bromide - zandgronden - convectie - dispersie - waterafstotende gronden - simulatiemodellen - transportprocessen - bodemwater - infiltratie - hydratatie - mathematical models - water flow - bromide - sandy soils - convection - dispersion - water repellent soils - simulation models - transport processes - soil water - infiltration - hydration
    Water repellent soils are known to inhibit water infiltration, ultimately forcing water to flow via preferential paths through the vadose zone. To study water flow and transport in a water repellent sandy soil, a bromide tracer experiment was carried out, which started in the fall, after winter wheat had been sown. Field average soil water content and bromide profiles were determined seven times during a 474d period. A one-dimensional convection-dispersion model was used to simulate observed flow and transport. It was found that water content and bromide profiles could be successfully simulated. The main reason was that despite water repellency no distinct preferential flow occurred within this particular experimental field. Only wavy wetting fronts were observed. This was due to a uniform vegetation cover and a relatively thick A-horizon (30cm), which contrasts with known water repellent sandy soils with thin (10cm) top layers in which typical fingered flow patterns had previously been found.
    Natural convection heating of liquids, with reference to sterilization of canned food
    Hiddink, J. - \ 1975
    Landbouwhogeschool Wageningen. Promotor(en): J. Schenk, co-promotor(en): S. Bruin. - Wageningen : Centre for Agricultural Publishing and Documentation Pudoc - ISBN 9789022005743 - 128
    ingeblikte producten - inblikken - convectie - voedselbewaring - voedingsmiddelen - plantaardige producten - steriliseren - thermodynamica - canned products - canning - convection - food preservation - foods - plant products - sterilizing - thermodynamics

    In a model system the physical transport phenomena that occur during the sterilization of a canned liquid food were investigated. Flow phenomena and heat transfer were studied experimentally as well as theoretically. Experiments on flow patterns and temperature profiles revealed a boundary layer flow at the vertical sidewall, a stratified core in the upper part of the container and a perfectly mixed, unstratified region in the lower part of the container. A dimensionless correlation for the overall heat transfer coefficient from steam to liquid was determined.

    From the observed flow patterns and temperature profiles a simplified mathematical model was developed, with which temperature stratification in the liquid during heating could be simulated. The applicability of the simplified model for lethality calculations was briefly examined.

    Some attention was also paid to the effect of solid particles on heating characteristics of the container contents.

    Literature on the research of convection heating of liquids in closed containers was reviewed, as well as literature about the influence of temperature stratification on natural convection boundary layer flow.

    Warmteoverdracht en verdamping door vrije convectie langs een verticale cylinder
    Bottemanne, F.A. - \ 1970
    Wageningen : Veenman (Mededelingen / Landbouwhogeschool Wageningen 70-11) - 91
    kookpunt - toestandsverandering - convectie - dauwpunt - diffusie - gassen - warmte - warmteuitwisseling - warmtewisselaars - warmteoverdracht - warmtebehandeling - mechanica - thermodynamica - transmissie - boiling point - change of state - convection - dewpoint - diffusion - gases - heat - heat exchange - heat exchangers - heat transfer - heat treatment - mechanics - thermodynamics - transmission
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