Microscopic Imaging Spray Diagnostics under High Temperature Conditions: Application to Urea–Water Sprays

The quantitative investigation of droplet laden turbulent flows at high temperature conditions is of great importance for numerous applications. In this study, an experiment was set up for investigation of evaporating urea-water sprays, which are relevant for the effective reduction of nitrogen oxide emissions of diesel engines using Selective Catalytic Reduction. A shadowgraphy setup is pushed to its limits in order to detect droplet diameters as small as 4µm and droplet velocities up to 250m/s. In addition, the operating conditions of the gaseous flow of up to 873K and 0.6MPa are an additional challenge. Due to the high temperature environment, image quality is prone to be compromised by schlieren effects and astigmatism phenomena. A water-cooled window and an astigmatism correction device are installed in order to correct these problems. The results to be presented include characteristics of the turbulent gas flow as well as detailed spray characteristics at different positions downstream of the atomizer. It is demonstrated that the velocity of the gas can be approximated by the velocity of the smallest detectable droplets with sufficient accuracy. Furthermore, the statistical analysis of velocity fluctuations provides data for predicting the turbulent dispersion of the droplets

The Impact of Vegetation on Archaeological Sites in the Low Arctic in Light of Climate Change

Vegetation is changing across the Arctic in response to increasing temperatures, which may influence archaeological sites in the region. At the moment, very little is known about how different plant species influence archaeological remains. In this study we visited 14 archaeological sites stretching across a climatic gradient from the outer coast to the inner fjords in the Nuuk Fjord area of West Greenland to assess the impact of vegetation growth on archaeological preservation. Examination of the physical disturbance of archaeological layers and materials by roots from different plant species showed that horsetail (Equisetum arvense) was particularly destructive because of its deep penetrating rhizomes and ubiquity across the study area. Willow (Salix glauca) also caused physical disturbance due to a dense root network, but its roots were mainly found in the upper 30 cm of the soil. Focus was also given to the impact from vegetation on the visibility of sites, where growth of willow was found be the main problem, especially in the inner fjords. Historic descriptions and aerial photographs from the sites show that shrub growth was already widespread in the region by the 1930s, but photos of some of the sites investigated show that the willow shrubs are significantly taller today, which has decreased the visibility of site features. The impact from horsetail and willow on archaeological sites may be mitigated using geotextiles and grazing by livestock, but both methods require further studies before being implemented in the study area.À la grandeur de l’Arctique, la végétation change en réaction aux températures à la hausse, ce qui peut exercer une influence sur les sites archéologiques de la région. En ce moment, on en sait peu sur la manière dont les différentes espèces végétales influencent les restes archéologiques. Dans le cadre de cette étude, nous avons visité 14 sites archéologiques répartis sur un gradient climatique allant de la zone côtière extérieure aux fjords intérieurs de la région du fjord de Nuuk, dans l’ouest du Groenland, afin d’évaluer l’incidence de la croissance de la végétation sur la préservation archéologique. L’examen de la perturbation physique des couches et du matériel archéologiques au moyen des racines de différentes espèces végétales a permis de constater que la prêle (Equisetum arvense) jouait un rôle particulièrement destructeur en raison de ses rhizomes profonds et omniprésents dans toute la zone étudiée. Le saule (Salix glauca) entraîne aussi des perturbations physiques en raison de son réseau de racines denses, bien que ses racines se trouvent principalement dans la couche supérieure de sol de 30 cm. Nous avons aussi accordé de l’importance à l’incidence de la végétation sur la visibilité des sites, ce qui a permis de conclure que la croissance du saule constituait le problème principal, surtout dans la zone intérieure des fjords. Les descriptions historiques et les photographies aériennes des sites montrent que la croissance d’arbustes était déjà répandue dans la région dans les années 1930, bien que certaines photos des sites étudiés permettent de comprendre que les saules arbustifs sont beaucoup plus grands aujourd’hui, ce qui diminue la visibilité des caractéristiques des sites. L’incidence de la prêle et du saule sur les sites archéologiques pourrait être atténuée par l’utilisation de géotextiles et le broutage du bétail. Il y a toutefois lieu de se pencher de plus près sur ces deux méthodes avant de les adopter dans la zone étudiée

Modeling the Formation of Urea-Water Sprays from an Air-Assisted Nozzle

Ammonia preparation from urea-water solutions is a key feature to ensure an effective reduction of nitrogen oxides in selective catalytic reduction (SCR) systems. Thereby, air-assisted nozzles provide fine sprays, which enhance ammonia homogenization. In the present study, a methodology was developed to model the spray formation by means of computational fluid dynamics (CFD) for this type of atomizer. Experimental validation data was generated in an optically accessible hot gas test bench using a shadowgraphy setup providing droplet velocities and size distributions at designated positions inside the duct. An adaption of the turbulence model was performed in order to correct the dispersion of the turbulent gas jet. The spray modeling in the near nozzle region is based on an experimentally determined droplet spectrum in combination with the WAVE breakup model. This methodology was applied due to the fact that the emerging two-phase flow will immediately disintegrate into a fine spray downstream the nozzle exit, which is also known from cavitating diesel nozzles. The suitability of this approach was validated against the radial velocity and droplet size distributions at the first measurement position downstream the nozzle. In addition, the simulation results serve as a basis for the investigation of turbulent dispersion phenomena and evaporation inside the spray

Dynamic modeling of uteroplacental blood flow in IUGR indicates vortices and elevated pressure in the intervillous space - a pilot study

Ischemic placental disease is a concept that links intrauterine growth retardation (IUGR) and preeclampsia (PE) back to insufficient remodeling of uterine spiral arteries. The rheological consequences of insufficient remodeling of uterine spiral arteries were hypothesized to mediate the considerably later manifestation of obstetric disease. However, the micro-rheology in the intervillous space (IVS) cannot be examined clinically and rheological animal models of the human IVS do not exist. Thus, an in silico approach was implemented to provide in vivo inaccessible data. The morphology of a spiral artery and the inflow region of the IVS were three-dimensionally reconstructed to provide a morphological stage for the simulations. Advanced high-end supercomputing resources were used to provide blood flow simulations at high spatial resolution. Our simulations revealed turbulent blood flow (high-velocity jets and vortices) combined with elevated blood pressure in the IVS and increased wall shear stress at the villous surface in conjunction with insufficient spiral artery remodeling only. Post-hoc histological analysis of uterine veins showed evidence of increased trophoblast shedding in an IUGR placenta. Our data support that rheological alteration in the IVS is a relevant mechanism linking ischemic placental disease to altered structural integrity and function of the placenta

Development of a ³He magnetometer for a neutron electric dipole moment experiment

We have developed a highly sensitive 3He magnetometer for the accurate measurement of the magnetic field in an experiment searching for an electric dipole moment of the neutron. By measuring the Larmor frequency of nuclear spin polarized 3He atoms a sensitivity on the femto-Tesla scale can be achieved. A 3He/Cs-test facility was established at the Institute of Physics of the Johannes Gutenberg University in Mainz to investigate the readout of 3He free induction decay with a lamp-pumped Cs magnetometer. For this we designed and built an ultra-compact and transportable polarizer unit which polarizes 3He gas up to 55% by metastability exchange optical pumping. The polarized 3He was successfully transfered from the polarizer into a glass cell mounted in a magnetic shield and the 3He free induction decay was detected by a lamp-pumped Cs magnetometer.PACS numbers07.55.Ge Magnetometers for magnetic field measurements; 13.40 Electric and magnetic moments; 14.20 Protons and neutrons

Повторный гидравлический разрыв пласта в горизонтальных скважинах с нецементируемым хвостовиком

Myocardial perfusion imaging with 99mTc-tetrofosmin is based on the assumption of a linear correlation between myocardial blood flow (MBF) and tracer uptake. However, it is known that 99mTc-tetrofosmin uptake is directly related to energy-depen-dent transport processes, such as Na/H ion channel activity, as well as cellular and mitochondrial membrane potentials. Therefore, cellular alterations that affect these energy-depen-dent transport processes ought to influence 99mTc-tetrofosmin uptake independently of blood flow. Because metabolism (18F-FDG)–perfusion (99mTc-tetrofosmin) mismatch myocardium (MPMM) reflects impaired but viable myocardium showing cel-lular alterations, MPMM was chosen to quantify the blood flow– independent effect of cellular alterations on 99mTc-tetrofosmin uptake. Therefore, we compared microsphere-equivalent MBF (MBF_micr; 15O-water PET) and 99mTc-tetrofosmin uptake i