Staff Publications

Staff Publications

  • external user (warningwarning)
  • Log in as
  • language uk
  • About

    '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.

    We have a manual that explains all the features 

Current refinement(s):

Records 1 - 15 / 15

  • help
  • print

    Print search results

  • export

    Export search results

  • alert
    We will mail you new results for this query: keywords==powders
Check title to add to marked list
Preparation of functional lupine protein fractions by dry separation
Pelgrom, P.J.M. ; Berghout, J.A.M. ; Goot, A.J. van der; Boom, R.M. ; Schutyser, M.A.I. - \ 2014
Food Science and Technology = Lebensmittel-Wissenschaft und Technologie 59 (2014)2 part 1. - ISSN 0023-6438 - p. 680 - 688.
air classification - isoelectric precipitation - carbohydrate-composition - oncorhynchus-mykiss - rainbow-trout - fish-meal - digestibility - angustifolius - ultrafiltration - powders
Lupine protein concentrate is a promising ingredient that can be obtained by a combination of milling and air classification, generally called dry fractionation. This is a more sustainable route than conventional wet extraction and delivers a protein concentrate with native functional properties. Critical is the detachment of the protein bodies from other seed components during milling. Ideally, the protein bodies are released during milling, whereas the other components remain in larger particles (D0.5 > 40 µm) to facilitate effective air classification. Coarse milling (down to 100 µm) followed by air classification gave concentrates with protein contents between 54 and 59 g protein/100 g dry solids and yields up to 13%. The application of flowability aids (fused silica particles) during air classification doubled the yield of the protein-rich fraction. The air classified protein concentrate could provide a 2.3 times extended half-life of the foam compared to an intensively heated protein concentrate. In addition, the viscosity of the native concentrate was lower, while after (in vitro) digestion the amount of proteins smaller than 3 kDa was higher in native and mildly heated concentrates compared to intensively heated concentrate. These results suggest promising development of liquid-like formulations from air classified lupine protein concentrates.
Colorimetry and photoacoustic spectroscopy as suitable tools for direct determination of cocoa powder in confectionary products
Doka, O. ; Pragai, E. ; Bicanic, D.D. ; Kulcsar, R. - \ 2013
European Food Research and Technology 236 (2013)6. - ISSN 1438-2377 - p. 963 - 968.
phenolic content - theobroma-cacao - powders - antioxidant - quantification - polyphenols - mixtures - capacity - samples - beans
Laser photoacoustic spectroscopy (PAS) and colorimetry have been used to rapidly and accurately determine the content of fat-free cocoa solids in dark chocolates. Both techniques are inexpensive and require only a one-time calibration step versus a method capable of absolute concentration measurement (for example HPLC). Once the response of PAS and/or colorimetry has been obtained, the content of fat-free cocoa solids in dark chocolates can be determined directly (i.e. without any sample preparation including the process of extraction) from the calibration curves and the experimentally measured microphone signal (in PAS studies) and colorimetric indices L* and ¿E* (in colorimetric investigations). Both colorimetric indices and PA signals correlate positively with the content of fat-free cocoa solids. The correlation is highly linear over a wide concentration range (25–50 %).
Concentrated whey protein particle dispersions: Heat stability and rheological properties
Saglam, D. ; Venema, P. ; Vries, R.J. de; Shi, J. ; Linden, E. van der - \ 2013
Food Hydrocolloids 30 (2013)1. - ISSN 0268-005X - p. 100 - 109.
colloidal dispersions - functional-properties - thermal-stability - microparticles - beverage - delivery - powders - size
In this work heat stability and rheological properties of concentrated whey protein particle dispersions in different dispersing media are studied. Whey protein particles (protein content ~20% w/v) having an average size of a few microns were formed using a combination of two-step emulsification and heat-induced gelation. Particles were dispersed (volume fraction of particles ~ 0.35) in solutions of Na-caseinate, whey protein isolate or gum arabic at different concentrations. The microstructure, particle size distribution and flow behaviour of the dispersions were analyzed before and after heating at 90oC for 30 min. All dispersions were liquid-like and no significant change in the microstructure was observed after heat treatment. Viscosity measurements showed that both the type and the concentration of the stabilizer influenced the viscosity changes after heat treatment. When 1% (w/w) gum arabic was used as stabilizer no change in the viscosity was observed after heat treatment. However, when Na-caseinate or whey protein isolate was used, viscosity increased in low-shear regime and shear-thickening was observed in high shear regime. Heat treatment did not significantly alter the zeta potential of the particles, whereas the size of the particles increased after heating due to swelling. The results show that swelling of the particles plays a significant role in the heat stability and rheological properties of these dispersions.
Reducing the stiffness of concentrated whey protein isolate (WPI) gels by using WPI microparticles
Purwanti, N. ; Moerkens, A. ; Goot, A.J. van der; Boom, R.M. - \ 2012
Food Hydrocolloids 26 (2012)1. - ISSN 0268-005X - p. 240 - 248.
rheological properties - water-absorption - powders - aggregation - composites - starch - shear - flow
Concentrated protein gels were prepared using native whey protein isolate (WPI) and WPI based microparticles. WPI microparticles were produced by making gel pieces from a concentrated WPI suspension (40% w/w), which were dried and milled. The protein within the microparticles was denatured and the protein concentration after drying was similar to the native WPI powder. WPI microparticles had irregular shape with an average size of about 70 mm. They absorbed water when dispersed in water, but the dispersion did not gel upon heating. Replacing part of the native WPI powder with WPI microparticles in the protein gel resulted in lower gel stiffness compared with a gel with the same overall protein concentration but without microparticles. However, microparticles also strengthened the continuous phase because they take up water from this phase. This might increase gel stiffness more than would be expected from an inert particle/filler. There was also good bonding between the microparticles and the WPI continuous phase in the gel, which contributed to gel stiffness.
Effect of low dosages of powdered activated carbon on membrane bioreactor performance
Remy, M.J.J. ; Temmink, H. ; Rulkens, W.H. - \ 2012
Water Science and Technology 65 (2012)5. - ISSN 0273-1223 - p. 954 - 961.
afvalwaterbehandeling - bioreactoren - membranen - actieve kool - poeders - dosering - vervuiling door afzetting - filtreerbaarheid - energiegehalte - waste water treatment - bioreactors - membranes - activated carbon - powders - dosage - fouling - filterability - energy content - polymeric substances eps - sludge - removal - water - mbrs - dewaterability
Previous research has demonstrated that powdered activated carbon (PAC), when applied at very low dosages and long SRTs, reduces membrane fouling in membrane bioreactors (MBRs). This effect was related to the formation of stronger sludge flocs, which are less sensitive to shear. In this contribution the long-term effect of PAC addition was studied by running two parallel MBRs on sewage. To one of these, PAC was dosed and a lower fouling tendency of the sludge was verified, with a 70% longer sustainable filtration time. Low PAC dosages showed additional advantages with regard to oxygen transfer and dewaterability, which may provide savings on operational costs.
Snelle screening poeders met micro-sproeidroger
Fox, M.B. ; Perdana, J.A. ; Bereschenko, L.A. ; Schutyser, M.A.I. - \ 2011
Bulk 19 (2011)6. - ISSN 1380-569X - p. 18 - 19.
sproeidrogers - droogmethoden - voedseltechnologie - productieprocessen - poeders - druppels - spray driers - drying methods - food technology - production processes - powders - droplets
Poederfabrikanten willen de optimale droogcondities van een nieuw product snel en automatisch kunnen bepalen, met een minimum aan grondstoffen. Om aan deze wens tegemoet te komen, hebben NIZO food research en Wageningen Universiteit, een 'high throughput screening' - faciliteit voor poeders ontwikkeld; de micro-sproeidroger.
Energiezuinige productie van plantaardige ingrediënten middels elektrostatisch scheiden
Hamoen, J.R. ; Voordouw, T. ; Willemsen, J.H.A. ; Togtema, K.A. - \ 2009
Wageningen : Agrotechnology and Food Sciences Group (Rapport / Agrotechnology and Food Sciences Group (AFSG) 1003) - ISBN 9789085853442 - 32
poeders - elektrostatische lading - elektrostatische scheiding - meel - variabele lading - powders - electrostatic charging - electrostatic separation - meal - variable charge
Dit rapport beschrijft het onderzoek naar de haalbaarheid van het scheiden van droge poeders op basis van de elektrostatische oplaadbaarheid. Te denken valt aan het fractioneren van melen die niet met behulp van malen en windziften kunnen worden opgewerkt. Voor het onderzoek is gebruik gemaakt van kennis van aanverwante technologieën, zoals het opladen van agro-poeders voor coatingdoeleinden en meetapparatuur voor het karakteriseren van verfpoeders
Synthesis, characterization, and bioavailability in rats of ferric phosphate nanoparticles
Rohner, F. ; Ernst, F.O. ; Arnold, M. ; Hilbe, M. ; Biebinger, R. ; Ehrensperger, F. ; Pratsinis, S.E. ; Langhans, W. ; Hurrell, R.F. ; Zimmermann, M.B. - \ 2007
The Journal of Nutrition 137 (2007)3. - ISSN 0022-3166 - p. 614 - 619.
flame spray-pyrolysis - particle-size - iron bioavailability - delivery-system - pyrophosphate - nanotechnology - fortification - absorption - toxicity - powders
Particle size is a determinant of iron (Fe) absorption from poorly soluble Fe compounds. Decreasing the particle size of metallic Fe and ferric pyrophosphate added to foods increases Fe absorption. The aim of this study was to develop and characterize nanoparticles of FePO4 and determine their bioavailability and potential toxicity in rats. Amorphous FePO4 nanopowders with spherical structure were synthesized by flame spray pyrolysis (FSP). The nanopowders were characterized and compared with commercially available FePO4 and FeSO4, including measurements of specific surface area (SSA), structure by transmission electron microscopy, in vitro solubility at pH 1 and 2, and relative bioavailability value (RBV) to FeSO4 in rats using the hemoglobin repletion method. In the latter, the potential toxicity after Fe repletion was assessed by histological examination and measurement of thiobarbituric acid reactive substances (TBARS). The commercial FePO4 and the 2 FePO4 produced by FSP (mean particle sizes, 30.5 and 10.7 nm) had the following characteristics: SSA: 32.6, 68.6, 194.7 m2/g; in vitro solubility after 30 min at pH 1: 73, 79, and 85% of FeSO4; and RBV: 61, 70, and 96%, respectively. In the histological examinations and TBARS analysis, there were no indications of toxicity. In conclusion, nanoparticles of FePO4 have a solubility and RBV not significantly different from FeSO4. Reducing poorly soluble Fe compounds to nanoscale may increase their value for human nutrition.
Air dispersion of starch-protein mixtures : a predictive tool for air classification performance
Dijkink, B.H. ; Speranza, L. ; Paltsidis, D. ; Vereijken, J.M. - \ 2007
Powder Technology 172 (2007)2. - ISSN 0032-5910 - p. 113 - 119.
relative-humidity - pranlukast hydrate - particle adhesion - dry - lactose - force - peas - removal - powders
Milling and air classification is a well-known procedure to obtain protein and starch enriched fractions from cereals and grain legumes. Adhesion of small protein particles to larger starch granules adversely affects the separation efficiency during air classification. To gain insight into this phenomenon the dispersion of bimodal mixtures of starch granules and fine protein particles in an air stream was studied. Using a method to correct for the number of small starch particles in the protein fraction, the dispersability of protein/starch mixtures was determined. The type of protein and, particularly, of starch may affect dispersability. The effect of starch type is not only caused by differences in granule size; likely other properties such as roughness are also involved. Increasing protein content enhances dispersability but does not seem to have an effect on the adhesion between starch and protein particles itself. An increase in adhesion by relative humidity of 90% results in a decreased dispersability. The dispersability of the mixtures was related to their performance upon air classification. Both the separation efficiency and tau were strongly related to dispersability (R2 = 0.86 and 0.88 respectively). Hence, the dispersability, which can easily be measured, is a powerful tool to predict the air classification performance for separation of starch and protein.
Verbetering EU analysemethode voor fosfolipiden in melkpoeders
Baltussen, M.A.H. - \ 2006
Wageningen : RIKILT (Rapport / RIKILT 2005.012) - 20
fosfolipiden - melkpoeder - poeders - voedselanalyse - kennis - phospholipids - dried milk - powders - food analysis - knowledge
In dit rapport staan de resultaten van het onderzoek naar een verbeterde methode voor de analyse van fosfolipiden in magere melkpoed er (MMP), karnemelkpoeder (KMP) en volle melkpoeder (VMP) volgens de methode beschreven in bijlage XX van verordening (EG) nr. 213/2001.
Determination of sunset yellow in multi-vitamin tablets by photoacoustic spectroscopy and a comparison with alternative methods
Doka, O. ; Bicanic, D.D. ; Ajtony, Z. ; Koehorst, R.B.M. - \ 2005
Food Additives and Contaminants 22 (2005)6. - ISSN 0265-203X - p. 503 - 507.
spectrophotometric determination - capillary-electrophoresis - food colorants - least-squares - allura-red - identification - chromatography - tartrazine - mixtures - powders
Photoacoustic (PA) spectroscopy in the visible wavelength region was shown to be suitable for a direct (no preparatory steps involved) quantification of sunset yellow (E110) colour in effervescent multi-vitamin tablets. Measurements on powdered tablets containing E110 were performed at 480?nm at which wavelength this synthetic colour shows appreciable absorbance. The PA data obtained were compared to the results acquired by diffuse reflectance spectroscopy and conventional spectrophotometry. Intrinsic simplicity, ease of sampling and rapid response were the most important advantages of the PA technique. In terms of sensitivity the performance of the three methods were comparable
Photoacoustic study of airborne and model aerosols
Alebic-Juretic, A. ; Zetsch, C. ; Doka, O. ; Bicanic, D.D. - \ 2003
Review of Scientific Instruments 74 (2003)1. - ISSN 0034-6748 - p. 503 - 505.
ozone destruction - silica-gel - fly-ash - surface - particles - powders - alumina
Airborne particulates of either natural or anthropogenic origin constitute a significant portion of atmospheric pollution. Environmental xenobiotics, among which are polynuclear aromatic hydrocarbons (PAHs) and pesticides, often adsorb to aerosols and as such are transported through the atmosphere with the physicochemical properties of the aerosols determining the lifetime of these organic compounds. As an example, the resistance of some PAHs against the photolysis is explained by the effect of the aerosol's "inner filter" that reduces the intensity of incident light reaching the mineral particles. On the other hand, some constituents of the aerosols can act as catalytic and/or stoichiometric reagents in atmospheric reactions on the solid surfaces. In the study described here the photoacoustic (PA) spectroscopy in the UV-Vis was used to investigate natural and model aerosols. The PA spectra obtained from coal and wood ashes and of Saharan sand, all three representatives of airborne aerosols, provide the evidence for the existence of the "inner filter." Furthermore, valuable information about the different nature of the interaction between the model aerosols and adsorbed organics (e.g., PAH-pyranthrene and silica, alumina, and MgO) has been obtained. Finally, the outcome of the study conducted with powdered mixtures of chalk and black carbon suggests that the PA method is a candidate method for determination of carbon content in stack ashes
Het gebruik van de Diffuse-Reflektie-Infrarood-Techniek (DRIFT) in het gebied (4000 - 500 cm-1)
Weseman, J.M. ; Ruig, W.G. de - \ 1985
Wageningen : RIKILT (Rapport / RIKILT 85.120) - 16
infraroodspectroscopie - korrels - oppervlakten - verbetering - innovaties - modernisering - vaste stoffen - poeders - moleculaire fysica - infrared spectroscopy - granules - surfaces - improvement - innovations - modernization - solids - powders - molecular physics
Met behulp van sulfadimidine-na en nortestosteron als testcomponenten is nagegaan wat mogelijk is met DRIFT en welke gevoeligheid kan worden bereikt. Twee DRIFT units (Harrick en Barnes) zijn onderzocht op gevoeligheid en bruikbaarheid.
Een niet-stationaire naaldmethode (warmtegeleiding, warmtecapaciteit, contactweerstand)
Haneghem, I.A. van - \ 1981
Landbouwhogeschool Wageningen. Promotor(en): J. Schenk, co-promotor(en): P.J. Bruijn. - Wageningen : van Haneghem - 187
thermodynamica - warmte - warmteoverdracht - thermische geleiding - transmissie - bodemtemperatuur - thermische bodemeigenschappen - fysica - meting - methodologie - korrels - oppervlakten - poeders - moleculaire fysica - thermodynamics - heat - heat transfer - thermal conductivity - transmission - soil temperature - soil thermal properties - physics - measurement - methodology - granules - surfaces - powders - molecular physics
Precise numerical data on the thermal properties of granular materials are significant not only for fundamental research but also for a variety of applications in agriculture, science and technology. In agricultural research, the thermal conductivity and the heat capacity of the soil are relevant quantities in calculation of the heat balance at the soil surface. Thermal properties and differences in them wider various conditions can provide useful information too on the freezing process and structure of frozen soil.

To investigate these thermal properties of granular materials, the research reported in this thesis dealt with the development of a proper measuring device for thermal conductivity and heat capacity of these substances. The well known non-stationary needle-method was re-examined to improve theoretical treatment, construction of the measuring probe (the needle) and instrumentation. The study also provided a better physical understanding of contact resistance between the needle surface and the surrounding medium. The research achieved simultaneous measurement of thermal conductivity (λ), volumetric heat capacity (ρc) and contact resistance (Γ). Soil contains a variable amount of water. During measurement, migration of water might seriously disturb results. Thermal conductivity and heat capacity are defined for steady state, where possible heat effects resulting from migration of water (heat transfer by fluid flow or by transport of latent heat) are absent. To meet this complication, the total measuring time must be very short (maximum 300 s) and the final temperature rise very small (maximum 0,5°C). With these precautions, any transport of moisture was sufficiently suppressed to make the resulting effect on the steady-state thermal parameters negligible.

We distinguished the approach where volumetric heat capacity (pc) was pre viously known , and the approach where this quantity was previously unknown. In most laboratory measurements, the first approach applies with reasonable accuracy. In many outdoor measurements (especially in agricultural research), pc is previously unknown. The experiments dealt with well defined model materials, i.e. dilute agar gels, dry and wet glass beads and dry and wet silver sand. Agar gels were chosen because their thermal conductivity and volumetric heat capacity were almost equal to those of pure water. Moreover the contact resistance between the needle surface and the agar gel can be assumed to he zero.
An outline of the experimental set-up and of the measuring sensor are given in 3.2. The needle-shaped sensor consisted of a double-fold constantan heating wire and the heat junction of a manganin-constantan thermocouple which were carefully fitted into a stainless-steel envelope. To fix the position of the heating wire and the thermocouple in the cylindrical envelope and to prevent electrical contact, the remaining space was filled with silicon rubber. The diameter of the needle was 1 mm and its length 210 mm. As reference element the cold junction of the thermocouple was fitted into another stainless-steel cylinder, completely equal to the sensor needle (but without the heating wire). The measuring sensor and the reference element were fitted into the axes of the measuring cylinder and the reference cylinder, respectively. The dimensions of these cylinders were equal (both of length 240 mm and of diameter 120 mm). The two cylinders were filled with the material to be examined and were placed in a constant-temperature liquid bath. The electrical current for heating was provided by a direct-current source. During the measuring time of several minutes, the temperature in the needle was recorded once per second. Through a very sensitive amplifier, the data were recorded on paper tape by a data logger. The conditions that the measuring time must be of the order of 300 s and that the total temperature increase may not exceed 0,5°C, implies that the temperature rate near the end of the measuring time will be less than 0,001°Cs -1 . The measuring device must meet very high requirements to detect such small temperature increases . Chapter 6 describes the total set-up of the measuring device in detail and the equipment used to prepare a well defined dry or wetted granular structure.

Chapter 2 reviews literature on the non-stationary wire method, the non- stationary needle method and the various types of needle sensors. The simple line-source analysis (reproduced in 2.3) is still often used for theoretical description of the temperature-time curve in the measuring needle and in the surrounding medium. However this system of analysis is not sufficiently accurate to allow simultaneous measurement of thermal conductivity λand volumetric heat capacity ρc, and it is even impossible to measure contact resistance Γin this way. More accurate results may he obtained from the theoretical approach of Blackwell (1954), Jaeger (1956) and de Vries & Peck (1958a), who started from a cylindrical model of the measuring needle (2.4), which accounted for the different thermal properties of needle and surroundings. Size of the needle and its components, and contact resistance are also introduced in that model. The approach of the three groups of workers is very similar mathematically. There were differences in the composition and the thermal properties of the cylinder and in the position of the heating wire and of the temperature sensor.

Chapter 3 develops an adapted model for the measuring needle, based on that of Jaeger and called the modified Jaeger model. It fitted well into the aims of our study and was developed in two steps. First, we introduced some simplifying
assumptions on the measuring needle. The double-fold heating wire was replaced in our model by a cylindrical core; around that core the silicon rubber was placed as a coaxial cylinder enveloped in turn by the outer steel cylinder. The hot junction of the thermocouple was assumed to be infinitely small and its position P was given by the effective radial distance R to the axis of the system. Second, we identified our measuring needle with the solid, perfectly conducting cylinder of the original Jaeger model and so defined the modified Jaeger model (3.4). Introduction of the radial distance R facilitated estimation of the real contact
resistance Γbetween the needle surface and the surroundings. The internal resistance Wℓ,i between P and the wall of the needle could then be subtracted from the measured total heat resistance Γℓ,o reliable value for Wℓ,i was obtained with agar gels, for which real contact resistance Γwas zero (chapter 7).

In chapter 4 numerical mathematical analysis of the observed temperature-time curve is described. A time correction t 0 had to be introduced for definite determination of λ, ρc and Γ. This quantity t 0 primarily depended on the resulting measurements. Different methods of calculating t 0 are discussed in 4.4. One proved best in giving much more precise and reliable results than the others. Thermal conductivity λand contact resistance Γwere then evaluated for "ρc known" (4.5). In 4.6 the method for "ρc unknown" was developed and allowed for simultaneous estimation of λ, ρc and Γ. This simultaneous estimation was approached by repeating the procedure of "ρc known" for different values of ρc and for different time intervals. The correct value of ρc was that for which λ(or Γ) was independent of the chosen time interval.

To verify the modified Jaeger model, the quantities λand Γestimated with this model, needed to be checked. The first check was on the effective distance R as calculated from the results of the agar gel measurements. The second was on the quantities λ, Γand ρc as measured for glass beads and silver sand. The means of checking was called the four-regions model (chapter 5). Characteristic for the model was the operation with the Laplacian transforms of the measuring results, seen as the solutions of the Laplacian-transformed differential equations of heat conduction. In the four-regions model, the thermal properties and the size of the needle were better expressed than in the modified Jaeger model. Another advantage of the four-regions model was the way in which the temperature curve was used.
The modified Jaeger model does not use the first part of the temperature-time curve, whereas the four-regions model uses the complete curve (from t = 0). So the two models are more or less independent of each other. In the four-regions model too, the effective distance R can be calculated from test measurements with the agar gels. With this value of R we can derive an equation for λ, ρc and Γ, characteristic for each needle. This equation allows testing of the quantities λand Γfrom the modified Jaeger model and (ρc) s of the bulk test material for their mutual consistency.
In chapter 7 test measurements with the agar gels are discussed. The values of λwere compared with those of Powell et al. (1966), who measured the thermal conductivity of pure water. The differences were less than 1%. The differences in the values for λ, measured with several needles were not more than 1% either, and the reproducibility of the measurements was within 0,5%. In conclusion, the values of λprobably accurate to within 1%. The test measurements can also be used to calculate the internal heat resistance Wℓ,i and the effective distance R. For each element Wℓ,i and R are characteristic and were measurable to an accuracy of 3 and 0,3%, respectively. For each element, the average relative difference between the value of R from the four-regions model (7.4) and that from the modified Jaeger model (7.3) proved to be less than 0,5%, a remarkably low value that justified continuation of work on the modified Jaeger model. As a result of the slight in fluence of pc on λ(7.5) a rough estimate of ρc was sufficient to calculate an accurate value of λ.

Chapter 8 finally, describes measurements with the glass beads and the silver sand. For thermal conductivity λ, the results corresponded to those for agar gels (so far as comparable). For contact resistance Γ, average reproducibility was about 5% and accuracy was within an average of 10-20%. The influence of diameter of the grains of a dry granular material on the value of Γwas distinct and systematic: Γincreased almost rectilinearly with diameter. The relation of Γto packing density, moisture content and temperature was less clear. Measurements with glass beads saturated with water showed that (within the accuracy) Γwas zero. The simultaneous estimation of λand ρc for these materials resulted in a value for pc accurate to within an average of 5-10%. The four-regions model used the "measured" λand Γto obtain a volumetric heat capacity (ρc) 4 . The difference between (ρc) 4 and the original value (ρc) s averaged not more than 3%. This result provides confirmation of the usefulness of the modified Jaeger model. Deviations were found when the diameter of the grains was of the same magnitude as the diameter of the needle and when the measured system was unsaturated moist glass beads. Simultaneous estimation of λ, ρc and Γaveraged over a group of measurements gave a ρc accurate to within 10-20%. In general, such accuracy is more than adequate for accurate estimation of λand Γ.

Herschikking van stortgoederen door tanden van grondbewerkingswerktuigen
Kouwenhoven, J.K. - \ 1979
Landbouwhogeschool Wageningen. Promotor(en): H. Kuipers. - Wageningen : Veenman - 17
bewerking als stortgoed - verandering - componenten - cultivators - uitrusting - bewerking - eggen - omhullen - bolletjes - poeders - zaaibedbereiding - bodemstructuur - grondbewerking - gereedschappen - transport - machines - bulk handling - change - components - cultivators - equipment - handling - harrows - pelleting - pellets - powders - seedbed preparation - soil structure - tillage - tools - transport - machines
4. 1. INTRODUCTION

During tillage operations, soil aggregates and other bulk solids such as seeds, fertilizers, stones, tubers (left by the potato harvester) and roots, are often displaced from one layer to another by a sorting process causing the larger particles to be displaced into higher layers and smaller particles into lower layers. This process is influenced by particle properties and handling factors, and is counteracted by mixing.

The influence of particle properties and handling factors on mixing and sorting was studied in the laboratory both qualitatively and quantitatively.

4.2. METHODS

Most of the experiments were done in a model soil bin filled with glass spheres and worked with normal and model tines. Localization of the processes and flow of the particles around the (model) tines were determined by filming and measuring the displacement of coloured markers, whereas mixing and sorting intensity and the sorting degree were determined by sieving or by counting the markers from different layers after working the bulk solid with normal harrow tines.

Tines were used in three positions: Forward facing, straight and backward facing; travelling speeds were: 0.01, 0.10, 0.45 and 0.80 m/s. Four fractions of bulk solid were used, monosized and polysized. The influence of particle properties on angularity and fractional solids content were determined. Dilatancy and relief were measured by means of a micro-reliefmeter; positions were determined using a position indicator.

4.3. RESULTS

4.3.1. Rearrangement of soil aggregates by tines (I)

With respect to seedbed and seedbed preparation, experiments were started using dry soil aggregates as the bulk solid, that was accompanied by interparticle percolation. Sorting was characterized by sorting degree and sorting intensity and mixing by mixing intensity. It became apparent that mixing mainly occurs behind the tine and is influenced by the type and inclination of the tine and by tine travelling speed. The direct connection between particle size and mixing intensity was probably caused in front of the tine. Wider and more backward facing tines increased mixing intensity. Sorting mainly occurred in front of the tine. The greater the amount of material moved and the greater the difference in size of the particles involved, the higher was the sorting intensity.

The final effect of the rearrangement of bulk solids by tines as a result of sorting and mixing actions could only be understood if the various processes were studied separately.

4.3.2. Rearrangement of glass spheres by tines (II; IV)

Because of the necessity for high demands on uniformity of the bulk solid used, especially on the narrow limits of particle size (at mixing), dry soil aggregates were replaced by glass spheres. The sizes of glass spheres were chosen so that interparticle percolation did not occur, allowing the possibility of studying the flow of particles around the tine.

The experiments revealed that mixing occurs by a strong downward displacement of a small number of spheres behind the tine and by a small sideways and upward displacement of a large number of spheres alongside of the tine. Mixing intensity increases with a decreasing travelling speed, more backward facing inclination of the tines and larger particle diameters.

Both backward facing tine inclination and low travelling speeds had a similar effect on the mixing intensity. Differences in mixing intensity of monosized bulk solids mainly originated from differences in dispersion in front of the tine; dispersion was stronger with increasing particle size.

Even without interparticle percolation, sorting mainly occurred in front of the tine, strongest with low travelling speeds and backward facing tines. Sorting intensity decreased with an increase in travelling speed and a more backward facing inclination of the tines.

In the equilibrium state, the bulk solid was found to be sorted to a higher degree after working with a high travelling speed and forward facing tines. A high sorting degree was characterized by small vertical displacements at a pass of the tine, by a strong stratification and so by a relatively pronounced dilatancy.

When interparticle percolation was absent, sorting intensity was determined by the smallest fraction. Forward facing tines were accompanied by a relatively high sorting intensity and a high sorting degree.

4.3.3. Particle properties and handling factors (III; V)

Particle properties like size, shape, surface roughness and apparent particle density and handling factors such as size ratios, moisture content and travelling speed, influenced bed properties and sorting results: relatively large, oblong, rough and light particles were displaced into higher layers and vice versa. The proces is accelerated, when the bulk solid is dry and worked at a low travelling speed.

For glass spheres, the diameter was the predominating particle property determining the results of the experiments. With an increasing sphere diameter, bed properties such as fractional solids content and angularity increased. In order to obtain reproducible beds for mixing experiments, the depth of the inserted layers was related to the diameter of the spheres involved. Tapping increased fractional solids content by an average of about 6 per cent.

Bed properties can only be determined significantly if determination methods are standardized. For standardized methodology large containers with sufficiently roughened bottoms and very smooth walls, low speeds and tapping to improve reproducibility, are advised. The 2-dimensional angle of repose, α d2 , is the one that can be determined easily and objectively. The angles of repose increased and so flowability decreased, with an increasing particle size, surface roughness and apparent particle density. The fractional solids content of a cultivated layer is inversely related to the size ratio of the particles (and to the sorting degree).

4.3.4. Rearrangement of bulk solids in the field(V)

Particle properties are more varied in the field than in the model experiments; handling factors such as moisture content and travelling speed are higher.

Throwing and sorting by interparticle percolation normally occur in the field. Throwing offers the possibility of killing weed seedlings by covering them with soil and of incorporating granulated chemicals and broadcasted seeds superficially._

Sorting in the field is of paramount importance: fine soil aggregates, seeds and granulated chemicals are placed into or near the seed placement zone, clods and stones are transported upward with respect to erosion control and rhizomes are brought to the surface as a measure of mechanical weed control. When draught animals are used, sorting is predominant; when tractors are applicated, throwing becomes more important as the travelling speed increases.

Sorting intensity in the field is highest for forward facing and wide or widened tines and tine-like tools, when moisture content is low, with a great variation of flowability of the particles involved and with low ( < 1 m/s) travelling speeds.

The effects of tined tillage tools in the field could largely be explained from model experiments using dry soil aggregates and glass spheres.

Check title to add to marked list

Show 20 50 100 records per page

 
Please log in to use this service. Login as Wageningen University & Research user or guest user in upper right hand corner of this page.