Heat Transfer Processes for Hydrogen and Methane in Cooling Channels of Regeneratively Cooled Thrust Chambers of Cryogenic Rocket Engines

Die enormen Temperaturen und Wärmeströme in einer Raketenbrennkammer machen eine aktive Kühlung der Brennkammerstruktur unabdingbar. Die Regenerativkühlung, bei der der Treibstoff vor der Verbrennung durch die Struktur geleitet wird, ist eine sehr effiziente und weitverbreitete Methode der Kühlung. Kühlkanäle mit einem hohen Aspektverhältnis (Höhe zu Breite Verhältnis) können zu einer besseren Kühlung bei gleichzeitig geringerem Druckverlust führen. Die thermische Schichtung, die bei dieser Art von Kühlkanälen auftreten kann, wirkt dem positiven Effekt entgegen und limitiert das Aspektverhältnis. In der vorliegenden Arbeit werden experimentelle Untersuchungen zur regenerativen Kühlung mit Wasserstoff und Methan bei für Raketenbrennkammern repräsentativen Bedingungen vorgestellt und ausgewertet. Das verwendete Brennkammersegment ist in Umfangsrichtung in vier Quadranten unterteilt, wobei in jeden Quadrant Kühlkanäle mit einem anderen Aspektverhältnis eingebracht worden sind. Für die Auswertung der experimentellen Daten wurde eine inverse Methode verwendet, die es ermöglicht, anhand der gemessenen Strukturtemperaturen den lokalen Wärmestrom und Wärmeübergangskoeffizienten zu bestimmen. Die thermische Schichtung aufgrund von mangelnder Durchmischung in Kühlkanälen mit hohem Aspektverhältnis tritt sowohl bei Wasserstoff als auch bei Methan auf. Für Wasserstoff ist die Ausprägung allerdings deutlich größer. Der Einfluss auf die Heißgaswandtemperatur ist allerdings für beide Kühlmedien vergleichsweise gering. Bei Methan kann es aufgrund der Nähe zum kritischen Punkt zur Trennung einer heißen gasartigen Schicht an der Wand und der kalten flüssigartigen Kernströmung kommen. Dieser heat transfer deterioration (HTD) genannte Effekt führt zu einem lokalen Abfall des Wärmeübergangs und einem drastischen Anstieg der Heißgaswandtemperatur. Die wesentlichen Einflussfaktoren auf diesen Effekt sind der Druck bzw. die Nähe zum kritischen Punkt, das Verhältnis von Wärmestromdichte und Massenstrom pro Fläche qw/G sowie das Aspektverhältnis. Basierend auf den Experimenten wurden numerische Simulationen durchgeführt, die die Ergebnisse stützen und erweitern. Die Auswertung dieser Simulationen zeigt eine weitestgehend gute Übereinstimmung mit den experimentellen Ergebnissen. In der Nähe des kritischen Punktes und insbesondere wenn es zu HTD kommt, zeigen die Simulationen eine systematische Abweichung und ein deutliches Überschätzen der Heißgaswandtemperatur

Reducing Hydrogen Boil-Off Losses during Fuelling by Pre-Cooling Cryogenic Tank

Boil-off losses occur when gaseous hydrogen has to be released from a cryogenic tank due to liquid hydrogen evaporating. These are a substantial drawback for all areas in which liquid hydrogen is discussed as a potential fuel to limit the climate impact. Especially boil-off losses during fuelling are one of the most significant source of losses along the liquid hydrogen pathway. To analyse and minimize such losses, simulations of the filling process are performed with the simulation tool EcoSimPro. The simulations are validated with an analytical solution. The results show that boil-off losses can be significantly reduced by pre-cooling the cryogenic tank with liquid nitrogen. This method is most effective for relatively small tanks that could be used e.g., in small air crafts or air taxis

Generating spectral dental panoramic images from single energy computed tomography volumes

Purpose: To implement a framework generating synthetic spectral panoramic images from single energy CT volumes. Using the framework output to compare the synthetic images against experimental spectral panoramic images for cross-verification. Methods: A simulation framework for generating synthetic spectral panoramic images from CT volumes is described. A cone beam CT scan of an anthropomorphic head phantom is used as input. An experimental spectral panoramic image of the same phantom is acquired. Results: The output of the framework of an anthropomorphic head phantom is compared against an experimental spectral panoramic image of the same phantom. The synthetic and experimental spectral panoramic images resemble each other considerably, especially the bone features. In the soft tissue images, there are some deviations, which are a result of the differences between the experimental and synthetic processing pipelines. Conclusions: It is demonstrated that generating synthetic spectral panoramic images from single energy CT volumes is possible. The synthetic images have many similarities with the experimental results, increasing the confidence in the correctness of the information contained within experimental spectral panoramic images and indicating that the synthetic images could be useful in further research

Cryogenic Liquid Hydrogen (LH2) system for Refueling an Airplane, and Use for other Mobile or Stationary Applications

Liquid hydrogen (LH2) is used for energy supply for various stationary and mobile applications. Current political and economic developments show the need of storable, decentralized produced, green energy to ensure supply of fuel, heat and power for an adequate price. Hydrogen can be part of the solution for those global problems. Especially LH2 is promising as fuel for mobile applications. It is advantageous because of the high energy density, and therefore is used for space applications since decades. Currently, there are many activities, to transfer the LH2 technology to other applications, e.g. aerospace and trucks

Modulation of aggression in male mice: influence of group size and cage size

Aggression in group-housed male mice is known to be influenced by both cage size and group size. However, the interdependency of these two parameters has not been studied yet. In this study, the level of aggression in groups of three, five, or eight male BALB/c mice housed in cages with a floor size of either 80 or 125 cm2/animal was estimated weekly after cage cleaning for a period of 14 weeks. Furthermore, urine corticosterone levels, food and water intake, body weight, and number of wounds were measured weekly. At the end of the experiment, tyrosine hydroxylase (TH) activity, testosterone levels, and weight of spleen, thymus, testes, and seminal vesicles were determined. Results indicate a moderate increase of intermale aggression in larger cages when compared to the smaller cages. Aggression in groups of eight animals was considerably higher than in groups of three animals. The increase of agonistic behavior was observed both in dominant and subordinate animals. Physiological parameters indicate differences in stress levels between dominant and subordinate animals. It is concluded that aggressive behavior in group-housed male BALB/c mice is best prevented by housing the animals in small groups of three to five animals, while decreasing floor size per animal may be used as a temporary solution to decrease high levels of aggression in an existing social group.

Read-out electronics for digital silicon photomultiplier modules

A new kind of a PET-Scanner (PET = positron emission tomography) for plant research is developed asa joint project of the Forschungszentrum Jülich and Philips Digital Photon Counting (PDPC). Thisscanner will utilize digital silicon photomultiplier (dSiPM) for plant phenotyping for the very first time.The goal of this work is to get a further knowledge of the operation of digital silicon photomultiplier.On this account a test-facility for this new photo detectors has been installed at the central instituteof engineering, electronics and analytics (ZEA-2 electronic systems) to determine the usage of thissensors, having regard to use them as scintillation detectors in a PET-Scanner later on.This work has its focus on the development of a fast read-out electronic for the used photo sensorsDPC3200-22-44. As there will be high data rates a fast USB 3.0 interface has been used. All thenecessary processing and data handling has been implemented in a state of the art FPGA

Considerations for determining optimal mouse caging density

At the 2006 National Meeting of the American Association of Laboratory Animal Science, a panel discussed the question of what constitutes optimal or acceptable housing density for mice. Though there is a consensus that present guidelines are somewhat arbitrarily defined, scientific research has not yet been able to provide clear recommendations for amending them. Speakers explored the many factors that influence decisions on mouse housing, including regulatory requirements, scientific data and their interpretation, financial considerations and ethical concerns. The panel largely agreed that animal well-being should be the measure of interest in evaluating housing density and that well-being includes not only physical health, but also animals\u27 behavior, productivity and preference

Indirect Genetic Effects and Housing Conditions in Relation to Aggressive Behaviour in Pigs

Indirect Genetic Effects (IGEs), also known as associative effects, are the heritable effects that an individual has on the phenotype of its social partners. Selection for IGEs has been proposed as a method to reduce harmful behaviours, in particular aggression, in livestock and aquaculture. The mechanisms behind IGEs, however, have rarely been studied. The objective was therefore to assess aggression in pigs which were divergently selected for IGEs on growth (IGEg). In a one generation selection experiment, we studied 480 offspring of pigs (Sus scrofa) that were selected for relatively high or low IGEg and housed in homogeneous IGEg groups in either barren or enriched environments. Skin lesion scores, a proxy measure of aggression, and aggressive behaviours were recorded. The two distinct IGEg groups did not differ in number of skin lesions, or in amount of reciprocal fighting, both under stable social conditions and in confrontation with unfamiliar pigs in a 24 h regrouping test. Pigs selected for a positive effect on the growth of their group members, however, performed less non-reciprocal biting and showed considerably less aggression at reunion with familiar group members after they had been separated during a 24 h regrouping test. The enriched environment was associated with more skin lesions but less non-reciprocal biting under stable social conditions. Changes in aggression between pigs selected for IGEg were not influenced by G×E interactions with regard to the level of environmental enrichment. It is likely that selection on IGEg targets a behavioural strategy, rather than a single behavioural trait such as aggressiveness

Behavioural ecology of the caracal in the Kgalagadi Transfrontier Park, and its impact on adjacent small stock units

Please read the abstract in the section 00front of this documentDissertation (MSc (Wildlife Management))--University of Pretoria, 2007.Centre for Wildlife Managementunrestricte