15 research outputs found
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Numerische Berechnung von Partikel- und Luftströmung in einem Dächerschachttrockner
Dächerschachttrockner werden weltweit in der Landwirtschaft zur Trocknung verschiedenster
Getreidearten sowie Mais und Reis eingesetzt. Im Vergleich zu anderen Trocknungsverfahren
weist das Trocknen in Dächerschachttrocknern noch ein deutliches Potenzial zur Steigerung der
Energieeffizienz auf. Der vergleichsweise hohe Primärenergieverbrauch wird überwiegend durch
ungleichmäßige Trocknung hervorgerufen, die sich weniger auf Ursachen wie eine mangelhafte
Trocknerregelung als auf ein ungünstiges Trocknerdesign und unzureichende Isolierung zurückführen
lässt. Zur Optimierung der verarbeitenden Prozesse in agrartechnischen Anlagen werden
immer häufiger numerische Methoden angewendet. Ein hohes Potenzial zur Effizienzsteigerung
von Dächerschachttrocknern bietet die Optimierung der Trocknergeometrie. Im Folgenden werden
die Methoden der Computational Fluid Dynamics (CFD) und der Diskreten-Elemente-Methode
(DEM) verwendet, um den aktuellen Stand der Technik numerisch zu untersuchen.Mixed flow dryers (MFD) are widely used in agriculture for the
drying of various crops including maize and rice. As compared
to other drying methods in the industrial drying, mixed flow
dryers still have considerable potential for improving energy
efficiency. The comparatively high primary energy consumption
is mainly caused by uneven drying, which, in turn, is
caused less by poor dryer control rather than by unfavorable
dryer design. In order to optimize the processes in agricultural
engineering, such as the mixed flow dryer, numerical
methods are being increasingly used. Optimization of the
dryer geometry provides a high potential to further increase
the efficiency of MFD. In the following, the methods of Computational
Fluid Dynamics (CFD) and the Discrete Element
Method (DEM) are used to investigate the state of the art
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Untersuchung der Trocknungsluftströmung an einer neu entwickelten Geometrie für Dächerschachttrockner
Der Dächerschachttrockner wurde in den letzten Jahren hinsichtlich der Trocknungseffizienz,
Regelungstechnik und Leistungssteigerung vielfach analysiert. Dennoch besteht erheblicher
Optimierungsbedarf bezüglich Energieeffizienz und Gleichmäßigkeit der Trocknung. Zur Analyse
des spezifischen Energieverbrauchs und der Homogenität des Trocknungsprozesses
wurden thermodynamische Prozesszustände anhand der konventionellen Trocknergeometrie
numerisch und experimentell analysiert. Aus den gewonnenen Ergebnissen wurde eine neue
Trocknergeometrie entwickelt, mit der eine deutliche Effizienzsteigerung erreicht werden soll.
Wie die strömungsmechanische Analyse des ersten Designentwurfs ergab, ist weiterer Entwicklungsbedarf
bis zur Praxisüberführung erforderlich. Während im Kernflussbereich in der
Trocknermitte gleichmäßige Strömungsbedingungen nachgewiesen werden konnten, ist die
Konstruktion in den wandnahen Bereichen zu optimieren.The mixed-flow dryer has been a matter of investigation many times regarding drying efficiency,
dryer control, and performance enhancement over the past years. However, there is still
considerable demand for optimization in terms of energy efficiency and homogeneity of drying.
In order to analyze the specific energy consumption and the homogeneity of the drying
process, different thermodynamic process conditions have been investigated for the conventional
MFD design using numerical and experimental methods. Based on the results obtained,
a novel dryer design has been developed. With this, a considerable increase of efficiency is
expected. As the fluid dynamic analysis of the first design draft revealed, further development
is required until scaling-up and transfer into practice will be possible. While homogeneous
airflow conditions could be demonstrated in the core flow region in the center of the dryer,
the configuration must be optimized in the near wall regions
Investigation of the drying airflow at a newly developed dryer geometry for mixed flow grain dryers
The mixed-flow dryer has been a matter of investigation many times regarding drying efficiency, dryer control, and performance enhancement over the past years. However, there is still considerable demand for optimization in terms of energy efficiency and homogeneity of drying. In order to analyze the specific energy consumption and the homogeneity of the drying process, different thermodynamic process conditions have been investigated for the conventional MFD design using numerical and experimental methods. Based on the results obtained, a novel dryer design has been developed. With this, a considerable increase of efficiency is expected. As the fluid dynamic analysis of the first design draft revealed, further development is required until scaling-up and transfer into practice will be possible. While homogeneous airflow conditions could be demonstrated in the core flow region in the center of the dryer, the configuration must be optimized in the near wall regions
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Experimente zum Partikelfluss an einer neu entwickelten Geometrie für Dächerschachttrockner
Um große Mengen an Körnerfrüchten über einen längeren Zeitraum lagerfähig zu machen,
werden weltweit zunehmend Dächerschachttrockner (DST) eingesetzt. Trocknereinbauten, die
ungünstig konstruiert oder angeordnet sind, können eine breite Verweilzeitverteilung des zu
trocknenden Gutes verursachen. Dadurch kommt es lokal zu unterschiedlichen Trocknungsbedingungen,
die zu einer inhomogenen Trocknung und damit zu einem erhöhten spezifischen
Energieverbrauch, zu wirtschaftlichen Verlusten und zu Qualitätseinbußen führen. Mit dem Ziel
der Sicherung der Produktqualität und der Steigerung der Energieeffizienz wurde daher eine
neuartige Apparategeometrie entwickelt. Um das traditionelle Design mit der neu entwickelten
Geometrie hinsichtlich der Partikeldurchströmung vergleichen zu können, wurden Durchflussversuche
am Modellgut Weizen mit eingefärbten Körnern als Tracerpartikel im Technikumsmaßstab
durchgeführt.To preserve large mass flows of grain for long term storage, mixed-flow dryers (MFD) are increasingly
used worldwide. Design elements which are unfavorably constructed or arranged can
cause broad residence time distributions. Hence, locally different drying conditions occur followed
by inhomogeneous drying. As a result, the specific energy consumption increases accompanied
by economic and quality losses. With the objective of saving product quality and increasing
energy efficiency a new dryer geometry was developed. To compare and evaluate the new
design with the traditional geometry regarding solids transport, a series of semi-technical particle
flow experiments were performed using wheat as bed material and colored tracer particles
Experimente zum Partikelfluss an einer neu entwickelten Geometrie für Dächerschachttrockner
To preserve large mass flows of grain for long term storage, mixed-flow dryers (MFD) are increasingly used worldwide. Design elements which are unfavorably constructed or arranged can cause broad residence time distributions. Hence, locally different drying conditions occur followed by inhomogeneous drying. As a result, the specific energy consumption increases accompanied by economic and quality losses. With the objective of saving product quality and increasing energy efficiency a new dryer geometry was developed. To compare and evaluate the new design with the traditional geometry regarding solids transport, a series of semi-technical particle flow experiments were performed using wheat as bed material and colored tracer particles
Telomere length varies with sex, hatching rank and year of birth in the Little Owl, <i>Athene noctua</i>
International audienceTelomeres are non-coding DNA sequences located at the end of linear chromosomes, protecting genome integrity. In numerous taxa, telomeres shorten with age and telomere length (TL) is positively correlated with longevity. Moreover, TL is also affected by environmental stressors and/or resource-demanding situations particularly during early-life. Thus, TL has been used as a physiological marker of individual quality and also as an indicator of population trend in conservation physiology. In this study, we investigated the effects of hatching rank, year of birth (2014 to 2017), sex and nest environment on TL of 137 Little Owls nestlings (Athene noctua). Little Owls' populations in Europe showed a marked declined in the end of the 20th century. Nowadays, in the studied Alsatian population, the population is increasing. In this study, our results indicated that telomeres are longer in females and, independently of sex, in nestlings with the highest body condition. There was also a negative effect of hatching rank but only for last-hatched nestlings in large clutches of 5 nestlings. We did not find any effect of the environmental covariates on nestlings' TL. Finally, we found that nestlings' TL were shorter the last year of the study, while nestlings' body condition stayed unchanged over the same period. This result is intriguing given the local positive population dynamics and is further discussed in the context of physiological conservation. Future studies should investigate the link between reduced TL and survival prospects in this species
Process optimization of mixed flow dryers for drying agricultural crops
Dächerschachttrockner kommen meist dann zum Einsatz, wenn große Mengen an Getreide, Mais und Sojabohnen haltbar gemacht werden müssen. Obwohl der Prozess der konvektiven Trocknung bereits umfangreich untersucht wurde und Stand der Technik bei der thermischen Getreidekonservierung ist, bestehen noch immer Wissenslücken in der Beschreibung des Gesamtprozesses und vor allem ein großes Optimierungspotenzial in der konstruktiven Gestaltung der zur Trocknung verwendeten Apparate. Durch verfahrenstechnische Analyse und Entwicklung des Trocknungsapparates können erhebliche Fortschritte in der Prozess- und Produktqualität bei der Getreidetrocknung erzielt werden. Dazu ist es notwendig, das Wissen über den Dächerschachttrockner durch Untersuchung der Teilprozesse der Partikelbewegung, Luftströmung sowie der Wärme- und Stoffübertragung zu erweitern. Basierend auf experimentellen und numerischen Untersuchungen dieser Prozesse mittels diskreter Partikelmodellierung und numerischer Strömungssimulation wurden verschiedene, innovative Trocknerkonfigurationen entwickelt. Diese führen zu einer Homogenisierung der Trocknungsbedingungen, zu einer besseren Ausnutzung des Trocknungspotenzials der Luft und damit zu höheren Trocknungseffizienz
Measuring Device for Air Speed in Macroporous Media and Its Application Inside Apple Storage Bins
In cold storage facilities of fruit and vegetables, airflow is necessary for heat removal. The design of storage facilities influences the air speed in the surrounding of the product. Therefore, knowledge about airflow next to the product is important to plan the layout of cold stores adapted to the requirements of the products. A new sensing device (ASL, Air speed logger) is developed for omnidirectional measurement of air speed between fruit or vegetables inside storage bins or in bulk. It consists of four interconnected plastic spheres with 80 mm diameter each, adapted to the size of apple fruit. In the free space between the spheres, silicon diodes are fixed for the airflow measurement based on a calorimetric principle. Battery and data logger are mounted inside the spheres. The device is calibrated in a wind tunnel in a measuring range of 0–1.3 m/s. Air speed measurements in fruit bulks on laboratory scale and in an industrial fruit store show air speeds in gaps between fruit with high stability at different airflow levels. Several devices can be placed between stored products for determination of the air speed distribution inside bulks or bin stacks in a storage room