Dynamics of the free surface of stratified two-phase flows in channels with rectangular cross-sections

Stratified two-phase flows were investigated at different test facilities with horizontal test sections in order to provide an experimental database for the development and validation of computational fluid dynamics (CFD) codes. These channels were designed with rectangular cross-sections to enable optimal observation conditions for the application of optical measurement techniques. Consequently, the local flow structure was visualised with a high-speed video camera, delivering data with high-resolution in space and time as needed for CFD code validation. Generic investigations were performed at atmospheric pressure and room temperature in two air/water channels made of acrylic glass. Divers preliminary experiments were conducted with various measuring systems in a test section mounted between two separators. The second test facility, the Horizontal Air/Water Channel (HAWAC), is dedicated to co-current flow investigations. The hydraulic jump as the quasi-stationary discontinuous transition between super- and subcritical flow was studied in this closed channel. Moreover, the instable wave growth leading to slug flow was investigated from the test section inlet. For quantitative analysis of the optical measurements, an algorithm was developed to recognise the stratified interface in the camera frames, allowing statistical treatments for comparison with CFD calculation results. The third test apparatus was installed in the pressure chamber of the TOPFLOW test facility in order to be operated at reactor typical conditions under pressure equilibrium with the vessel atmosphere. The test section representing a flat model of the hot leg of the German Konvoi pressurised water reactor (PWR) scaled at 1:3 is equipped with large glass side walls in the region of the elbow and of the steam generator inlet chamber to allow visual observations. The experiments were conducted with air and water at room temperature and maximum pressures of 3 bar as well as with steam and water at boundary conditions of up to 50 bar and 264°C. Four types of experiments were performed, including generic test cases as well as transient validation cases of typical nuclear reactor safety issues. As an example, the co-current flow experiments simulate the two-phase natural circulation in the primary circuit of a PWR. The probability distribution of the water level measured in the reactor pressure vessel simulator was used to characterise the flow in the hot leg. Moreover, the flooding behaviour in this conduit was investigated with dedicated counter-current flow limitation experiments. A comparison of the flooding characteristics with similar experimental data and correlations available in the literature shows that the channel height is the characteristic length to be used in the Wallis parameter for channels with rectangular cross-sections. Furthermore, for the analysis of steam/water experiments, condensation effects had to be taken into account. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a PWR over a large range of pressure and temperature conditions. Not least, different examples of comparison between experiment and simulation demonstrate the possibilities offered by the data to support the development and validation of CFD codes. Besides the comparison of qualitative aspects, it is shown exemplarily how to treat the CFD results in order to enable quantitative comparisons with the experiments

The classification of chronic daily headache in French children and adolescents: A comparison between the second edition of the International Classification of Headache Disorders and Silberstein-Lipton criteria

Few data are available on the applicability of both the criteria proposed by Silberstein and Lipton (S-L) and the International Classification of Headache Disorders-II (ICHD-II) in the classification of children and adolescents with chronic daily headache (CDH). The International Headache Society recently added revised criteria (ICHD-IIR) for chronic migraine to its Appendix. We retrospectively reviewed all charts of 34 children and adolescents (<17 years) with primary CDH presenting to the outpatient clinic of the Universitary Department of Neuropediatrics of Lille between February 2004 and February 2006 and tried to classify their CDH according to both S-L criteria and the recently published ICHD-IIR. Thirty-two children (94%) and 33 children (97%) could respectively be successfully classified into one subtype of CDH according to the S-L classification and the ICHD-IIR. Transformed migraine was the most common diagnosis (61.8%), followed by new daily-persistent headache (20.6%) when the S-L criteria were used. Twenty-three children and adolescents (67.6%) could be classified under one of the migraine categories according to the ICHD-IIR classification. We think that both S-L and ICHD-II classifications, when used with detailed headache histories and diaries, are adequate to classify chronic daily headache in children and adolescents

Experimental investigation and CFD simulation of slug flow in horizontal channels

For the investigation of stratified two-phase flow, two horizontal channels with rectangular cross-section were built at Forschungszentrum Dresden-Rossendorf (FZD). The channels allow the investigation of air/water co-current flows, especially the slug behaviour, at atmospheric pressure and room temperature. The test-sections are made of acrylic glass, so that optical techniques, like high-speed video observation or particle image velocimetry (PIV), can be applied for measurements. The rectangular cross-section was chosen to provide better observation possibilities. Moreover, dynamic pressure measurements were performed and synchronised with the high-speed camera system. CFD post-test simulations of stratified flows were performed using the code ANSYS CFX. The Euler-Euler two fluid model with the free surface option was applied on grids of minimum 4∙105 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying horizontal two-phase flow. Furthermore, CFD pre-test calculations were done to show the possibility of slug flow generation in a real geometry and at relevant parameters for nuclear reactor safety. The simulation was performed on a flat model representing the hot-leg of the German Konvoi-reactor, with water and saturated steam at 50 bar and 263.9°C. The results of the CFD-calculation show wave generation in the horizontal part of the hot-leg which grow to slugs in the region of the bend

Global currencies for tomorrow: a European perspective

This report examines how the international monetary system (IMS) might evolve and the implications of different scenarios for the euro area over the next fifteen years.After the collapse of the Bretton Woods system forty years ago, the IMS gradually developed into its present state, a hybrid mix of exchange-rate flexibility, capital mobility and monetary independence. The US dollar retains a dominant, but not exclusive, role and the IMS governance system blends regional and multilateral surveillance. It combines IMF-based and ad-hoc liquidity provision. Although it has proved resilient during the crisis, partly thanks to ad-hoc arrangements, the IMS has serious flaws, which are likely to be magnified by the rapid transformation of the global economy and the increasing economic power of emerging economies.

Experimentelle Untersuchung von geschichteten Luft/Wasser Strömungen in einem horizontalen Kanal

Für die Untersuchung von Luft/Wasser-Strömungen wurde ein horizontaler Acrylglas-Kanal mit rechteckigem Querschnitt gebaut. Der Kanal ermöglicht Gleich- und Gegenstrom-Versuche bei Atmosphärendruck, insbesondere die Untersuchung der Schwallströmung. Es wurden optische Messungen mit einer Hochgeschwindigkeits-Kamera durchgeführt, die durch synchronisierte dynamische Druckmessungen ergänzt wurden. Für die Analyse der Bilder wurde eine Methode zur Erfassung der Phasengrenze entwickelt und diese anhand möglicher Anwendungen getestet. Die Druckmessungen zeigten, dass der Druck bei Schwallströmungen um einige Kilopascal ansteigt und wieder abfällt, sobald der Schwall aus dem Kanal austritt. Zudem wurden Geschwindigkeiten in der flüssigen Phase mittels nicht invasiver Verfahren gemessen. Das durchschnittliche Geschwindigkeits-Profil am Kanaleintritt wurde mit Ultraschall-Köpfen bestimmt. Die Ermittlung des Geschwindigkeitsfeldes in einem Schwall erfolgte mit PIV (Particle Image Velocimetry)

Comparison between tagged MRI and standard cine MRI for evaluation of left ventricular ejection fraction

Global left ventricular function is a prognostic indicator and is used to evaluate therapeutical interventions in patients with heart failure. Regional left ventricular function can be determined with tagged MRI. Assessment of global left ventricular function using the tagging data may have additional clinical value without incurring extra scanning time, which is currently a limiting factor in cardiac imaging. Direct determination of end-diastolic volume is not possible with conventional tagged MRI. However, end-systolic volume can be directly measured because myocardium-blood contrast improves through a tagged image series. We investigated the potential of tagged MRI using frequency-domain analysis software to retrospectively track end-diastolic contour from end-systolic contour and subsequently calculate the ejection fraction. Tagged MRI was compared with the standard bright-blood cine MRI in healthy volunteers (n=20) and patients with previous myocardial infarction (n=8). Left ventricular ejection fraction derived from tagged MRI is linearly correlated to left ventricular ejection fraction obtained by standard cardiac cine MRI (y=1.0x+1.31, r>0.98, p=0.014). In addition, the inter-observer and intra-observer coefficient of variation for left ventricular ejection fraction measurements was low (CVintra=0.4%, CVinter=1.3%). With tagged MRI, only end-systolic volume needs to be manually determined, and accurate estimation of left ventricular ejection fraction is obtained because end-diastolic and end-systolic volumes are determined using identical anatomical points. Our data indicate that tagged MRI can be used to quantitatively assess both regional and global left ventricular function. Therefore, tagged MRI may be a valuable clinical tool for determining the prognosis and evaluating the effect of therapeutical intervention using a single imaging session in patients with left ventricular dysfunctio

Nanometric 3D Printing of Functional Materials by Atomic Layer Deposition

Atomic layer deposition (ALD) is a chemical vapour deposition (CVD) method that allows the layer-by-layer growth of functional materials by exposing a surface to different precursors in an alternative fashion. Thus, thanks to gas-solid reactions that are substrate-limited and self-terminating, precise control over thickness below the nanometer level can be achieved. While ALD was originally developed to deposit uniform coatings over large areas and on high-aspect-ratio features, in recent years the possibility to perform ALD in a selective fashion has gained much attention, in what is known as area-selective deposition (ASD). ASD is indeed a novel 3D printing approach allowing the deposition of functional materials (for example metals to oxides, nitrides or sulfides) with nanometric resolution in Z. The chapter will present an introduction to ALD, which will be followed by the description of the different approaches currently being developed for the ASD of functional materials (including initial approaches such as surface pre-patterning or activation, and newer concepts based on spatial CVD/ALD). The chapter will also include a brief overview of recent works involving the use of ALD to tune the properties of 3D printed parts

Treatment of primary headache in children: a multicenter hospital-based study in France

The aim of this 6-month, prospective, multicenter study of 398 children and adolescents with primary headaches was to collect data on headache treatment in neuropediatric departments. Treatments were compared before and after consultation. Prior to consultation, the acute treatments that had been prescribed most frequently were paracetamol (82.2% of children) and non-steroidal anti-inflammatory drugs treatment (53.5%); 10.3% had received a prophylactic treatment. No differences in either acute or prophylactic treatment with respect to headache diagnosis were observed. After the neuropediatric consultation, paracetamol was replaced by a non-steroidal anti-inflammatory drug in about three-quarters of cases and by triptan in about one-quarter of cases. The number of children prescribed a prophylactic treatment nearly doubled, whereas there was a 5-fold and 23-fold increase in psychotherapy and relaxation training, respectively, between pre-referral and referral. We conclude that specific treatments were underused for primary headache

The prevalence of triggers in paediatric migraine: a questionnaire study in 102 children and adolescents

The prevalence and characterization of migraine triggers have not been rigorously studied in children and adolescents. Using a questionnaire, we retrospectively studied the prevalence of 15 predefined trigger factors in a clinic-based population. In 102 children and adolescents fulfilling the Second Edition of The International Headache Classification criteria for paediatric migraine, at least one migraine trigger was reported by the patient and/or was the parents’ interpretation in 100% of patients. The mean number of migraine triggers reported per subject was 7. Mean time elapsed between exposure to a trigger factor and attack onset was comprised between 0 and 3 h in 88 patients (86%). The most common individual trigger was stress (75.5% of patients), followed by lack of sleep (69.6%), warm climate (68.6%) and video games (64.7%). Stress was also the most frequently reported migraine trigger always associated with attacks (24.5%). In conclusion, trigger factors were frequently reported by children and adolescents with migraine and stress was the most frequent

Lexical stress and phonetic processing in word learning in 20- to 24-month-old English-learning children

PubMed ID: 2147719