401 research outputs found
Comparison of spray quality for two different flow configurations: Central liquid jet versus annular liquid sheet
The research work of the present study is focused on the detailed comparison of two external mixing twin fluid nozzle concepts: (i) a central liquid jet with annular gas stream, (ii) an annular liquid sheet with central gas jet. Both nozzle types are applied in high pressure entrained flow gasifiers (EFG), where atomization is characterized by low Gas-to-liquid ratio (GLR) and high fuel viscosity. In order to compare spray formation as well as atomization efficiency in terms of Sauter mean diameter, a nozzle with equal orifice area of the gas and liquid exit is investigated. The nozzle enables equal atomization conditions concerning GLR, liquid mass flow, velocity of liquid and gas, as well as momentum flow ratio for both nozzle configurations. 4 Newtonian liquids: water and three glycerol/water mixtures with viscosity of 1mPas, 50mPas, 100mPas and 200mPas are used for the experiments in both nozzle configurations at various GLR. For spray analysis, a high speed camera, a shadowgraphy system as well as a phase-doppler analyzer are applied. The use of three different measuring techniques allows for characterization of primary breakup as well as local drop size distribution. With the high speed camera the breakup regime morphology is detected and classified for both operating configurations. Radial measurements of the local Sauter mean diameter are conducted with the phase-doppler analyzer. Furthermore, the spray angle is detected and the integral Sauter mean diameters for all operating conditions is compared for both nozzle configurations to evaluate atomization efficiency
Towards system pressure scaling of gas assisted coaxial burner nozzles – An empirical model
The present study investigates the influence of system pressure, gas velocity, and annular gas gap width on the resulting droplet size. Three external-mixing twin-fluid atomizers are operated at a constant liquid mass flow. The nozzle geometry is kept similar, except that the annular gas gap width is changed. At every system pressure level (1 – 21 bar), three different gas velocities were investigated by changing the gas mass flow. High-speed camera images are used for observation of primary breakup and discussed with regard to local measurements of droplet size performed by a phase Doppler anemometer. The gas momentum flux as well as the gas momentum flow were applied to describe the atomization process under varying operating conditions. Finally, an empirical model is derived, enabling the system pressure scaling of external-mixing twin-fluid atomizers for the range of gas momentum flow under investigation
Experimental investigation on the influence of system pressure on resulting spray quality and jet breakup applying pressure adapted twin-fluid nozzles
Effect of gas jet angle on primary breakup and droplet size applying coaxial gas-assisted atomizers
This study investigates the influence of gas jet angle on primary jet breakup and the resulting droplet size distribution for coaxial gas-assisted atomizers. In industrial applications, the gas jet of these atomizers are typically angled towards the liquid jet, whereas in most spray investigations in literature, parallel flow configurations are used. To enable a detailed analysis of the influence of the gas jet angle, three atomizers with angles of 0°, 15° and 30° were examined. Other geometric parameters, such as liquid jet diameter, gas gap width and wall thickness were kept constant. For each atomizer, two gas velocities at constant liquid mass flow were investigated i.e., two gas-to-liquid ratios (GLRs). An additional set of experiments was performed at increased system pressure using three atomizers with identical gas jet angles, but with an adapted gas orifice area in order to keep gas velocity, GLR and momentum flow ratio constant for all pressure levels. Water and a glycerol/water-mixture were applied in order to investigate the influence of liquid viscosity. The primary breakup process was monitored by a high-speed camera, whereas the resulting droplet size was detected using a phase-Doppler anemometer. For all system pressures and liquid viscosities under investigation, a distinct influence of gas jet angle on primary breakup as well as on resulting droplet size distribution was observed for low gas velocity
Effect of Solid Particles on Droplet Size Applying the Time-Shift Method for Spray Investigation
Detektion und Quantifizierung von Koronarkalk mittels Elektronenstrahl-Tomographie und konventioneller Computertomographie
Als Goldstandard der nicht-invasiven Erfassung der Verkalkungen der Herzkranzgefäße gilt bisher die Elektronenstrahl-Computertomographie. Wie die vorliegende Arbeit aufzeigt, ist die konventionelle Computertomographie mit EKG-Triggerung in der Lage die Ergebnisse der Elektronenstrahl-Computertomographie bei der Detektion und Quantifizierung atherosklerotischer Veränderungen der Herzkranzgefäße mit hoher Genauigkeit zu reproduzieren und damit auch mit den flächendeckend vorhandenen und ubiquitär einsetzbaren konventionellen Subsekundenscannern durchgeführt werden kann.
Die konventionelle Koronarangiographie stellt den Goldstandard bei der Evaluation des Lumens der Herzkranzgefäße dar. Sie stellt jedoch eine invasive, mit seltenen Komplikationsrisiken behaftete Untersuchung dar, die gerade bei Patienten mit atypischem Brustschmerz, bzw. asymptomatischen Patienten mit einem niedrigen bis intermediären Risikoprofil einer genauen Abwägung bedarf. Das Ausmaß der verkalkten atherosklerotischen Wandveränderungen kann mit der konventionellen Katheterangiographie, einer Luminographie nur ungenügend erfasst werden. Möglichkeiten der Quantifizierung des Verkalkungsgrades fehlen vollständig.
Da die Sensitivität zur Erfassung der koronaren Kalzifikationen mit dem konventionellen CT dem EBCT ebenbürtig ist, ist zu erwarten, dass in klinischen Studien auch mittels der konventionellen Computertomographie eine Ausschlussdiagnostik zur atherosklerotischen koronaren Herzkrankheit möglich sein dürfte. Weiterhin erlaubt die exakte Reproduzierbarkeit der Untersuchungsergebnisse die Verlaufskontrolle der Herzkranzgefäßverkalkungen bei einer Therapie bekannter Risikofaktoren bzw. Modifizierung der Lebensweise.
Da effektive Therapiekonzepte für die Behandlung und Verzögerung der Progression der koronaren Herzerkrankung zur Verfügung stehen, ist und wird die frühzeitige Erfassung der Atherosklerose der Herzkranzgefäße von zunehmender Bedeutung sein.
Daten der Framingham Studie belegen, dass nahezu 50% der Individuen, die an einem plötzlichen Herztod versterben zuvor keine kardiale Symptomatik in ihrer Krankengeschichte aufweisen. Eine erst kürzlich veröffentlichte Studie demonstriert, dass das Vorhandensein von Koronarverkalkungen deutlich mit dem Auftreten akuter koronarer Ereignisse bei initial asymptomatischen Patienten assoziiert ist. Zusätzlich scheint die Wertigkeit von Verkalkungen der Herzkranzgefäße stärker mit dem Auftreten kardialer Ereignisse assoziiert zu sein, als die bekannten konventionellen Risikofaktoren (Nikotinabusus, Bluthochdruck, Hypercholesterinämie, usw. ...). Der Grad der Verkalkung korreliert mit der Wahrscheinlichkeit für den Patienten zukünftig ein kardiales Ereignis zu erleiden.
Umso bedeutender ist daher eine zuverlässige Abschätzung eines zukünftigen Risikos für ein akutes koronares Ereignis für eine effektive und präventive Medizin. Wie die vorliegende Arbeit demonstriert, ist die konventionelle Computertomographie mit EKG-Triggerung in der Lage die Ergebnisse der Elektronenstrahl-Computertomographie bei der Detektion und Quantifizierung atherosklerotischer Veränderungen der Herzkranzgefäße mit hoher Genauigkeit zu reproduzieren und stellt daher eine Alternative der als Goldstandard angesehenen EBCT dar
Einfluss des Reaktordrucks auf die Spraygüte außenmischender Zweistoffdüsen
The present work is focused on the detailed investigation of the influence of ambient pressure on spray quality using external mixing twin fluid atomizers. Radial SMD-Profiles were measured using a Phase Doppler Anemometer (PDA). Additionally, primary jet breakup was investigated using a high speed camera
Disorder control in crystalline GeSb2Te4 and its impact on characteristic length scales
Crystalline GeSb2Te4 (GST) is remarkable material, as it allows to
continuously tune the electrical resistance by orders of magnitude without
involving a phase transition or stoichiometric changes, just by altering the
short-range order. While well-ordered specimen are metallic, increasing amounts
of disorder can eventually lead to an insulating state with vanishing
conductivity in the 0K limit, but a similar number of charge carriers. These
observations make disordered GST one of the most promising candidates for the
realization of a true Anderson insulator. While so far the low-temperature
properties have mostly been studied in films of small grain size, here a
sputter-deposition process is employed that enables preparation of a large
variety of these GST states including metallic and truly insulating ones. By
growing films of GST on mica substrates, biaxially textured samples with huge
grain sizes are obtained. A series of these samples is employed for transport
measurements, as their electron mean free path can be altered by a factor of
20. Yet, the mean free path always remains more than an order of magnitude
smaller than the lateral grain size. This proves unequivocally that grain
boundaries play a negligible role for electron scattering, while intragrain
scattering, presumably by disordered vacancies, dominates. Most importantly,
these findings underline that the Anderson insulating state as well as the
system's evolution towards metallic conductivity are indeed intrinsic
properties of the material
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