Air Entrainment by Two-Dimensional Plunging Jets : the Impingement Region and the Very-Near Flow Field

In the developing flow region of a plunging jet, the very-near field (i.e. (x-x1)/d1 < 5) is strongly affected by the entrapment process at the impingement. New quantitative results show that, although the distributions of void fraction and mean velocity have smooth shapes, the flow is highly fluctuating and unstable. At a given location in the mixing layer, the probability distribution function of the mean velocity exhibits two distinctive peaks : the jet impact velocity and the induction trumpet velocity. The water velocity fluctuates between the two characteristic values

Developing Air-Water Shear Layers Of Two-Dimensional Water Jets Discharging Into Air

The paper presents new experiments performed in the developing flow region of two-dimensional water jets discharging into air. The results indicate that the distributions of void fraction follow closely an analytical solution of the diffusion equation, and that the transfer of momentum between the water jet and the surrounding air is negligible for x/do < 20. An analogy with self-aerated open channel flows is further developed. The distributions of air bubble frequency have the same shape for both flow situations suggesting some similarity in the air-water flow structure

European views on the UK’s renegotiation: Czech Republic, Hungary, Sweden, and Lithuania

The success or failure of David Cameron’s planned renegotiation of the UK’s EU membership will depend to a large extent on how the other 27 EU member states respond to his proposals. But how do countries across the EU view the UK’s renegotiation? Building on a report published in 2014 by the German Council on Foreign Relations, EUROPP is running a series of overviews of the renegotiation from each of the EU’s member states. Compiled by the LSE’s Tim Oliver and written by authors based at universities and research institutions, the overviews will set out what discussion – if any – there has been about the renegotiation and the wider views within each country on the renegotiation and a potential Brexit. This post is the sixth in the series and gives views from the Czech Republic, Hungary, Sweden, and Lithuania. Czech Republic: A desire to accommodate British demands, but without treaty changes Hungary: A natural supporter for Cameron, but with caveats Sweden: Both risks and opportunities in EU renegotiation Lithuania: Britain is threatening the EU’s fundamental principle

A thermodynamic database for simulation of CMAS and TBC interactions

A thermodynamic database has been developed for calculating thermochemical interaction of thermal barrier coatings, namely 7YSZ (yttria partially stabilized zirconia), with CaO-MgO-Al2O3-SiO2 (CMAS) deposits. CaO-MgO-Al2O3-SiO2-Y2O3-ZrO2 is thus the core system for understanding and modeling of processes occurring between CMAS and TBC. A good thermodynamic description of all phases in the system is essential in modeling related to materials design and process optimization. An efficient technique used to obtain a self-consistent thermodynamic database is called the CALPHAD method [1], where the Gibbs energy of each phase is described with a mathematical model. The Gibbs energy of the total system is then minimized with respect to temperature and composition in order to predict the most stable phases under equilibrium conditions. In this work Y2O3-ZrO2 was incorporated into an existing description [2] of the CaO-MgO-Al2O3-SiO2 system. Many pseudo-binaries and ternaries are assessed within the CaO-MgO-Al2O3-SiO2-Y2O3-ZrO2 system. Two examples on calculated phase diagrams are shown below. The compound energy formalism [3] is used to model solid oxide solutions such as spinels, monoxide, corundum, zirconia, yttria etc. The ionic two-sublattice liquid model [4,5] is used to model molten slags

Air-Water Bubbly Flow in Free-Shear Layers

Air-water bubbly flows are encountered in many engineering applications ranging from chemical engineering to mechanical engineering applications (e.g. WOOD 1991, CHANSON 1995). In some cases, free-surface aeration is maximised (e.g. for re-oxygenation). In others, it must be minimised or prevented (e.g. with fire-fighting equipment and Pelton turbine jets). In some flow situations, flow aeration is not controlled (e.g. along a spillway). In each case, however, the knowledge of the air bubble/turbulence interactions is very important to predict accurately the air-water flow properties, hence to optimise the system performances and to insure a safe operation. One type of air-water shear flows is the developing flow region of a plunging jet. In chemical engineering, plunging jets are used to stir chemicals as well as to increase gas-liquid transfer. In sewage and water treatment plants, aeration cascades combine the effects of flow aeration and high turbulence level, enhancing the mass transfer of volatile gases (e.g. oxygen, nitrogen, volatile organic compounds). Despite the wide range of applications few studies investigated air bubble entrainment in the developing shear layer of plunging jets, at the exception of BONETTO and LAHEY (1993), CUMMINGS (1995) and the first author (CHANSON 1995). In the present paper, new experiments performed with a vertical two-dimensional plunging jet are described. The study is focused on the air-water flow properties in the developing shear layer. Distributions of air concentration and mean velocity are presented. The results are compared with an analytical solution of the air bubble diffusion equation. Distributions of bubble chord length are also shown

Experimental Investigations of Air Bubble Entrainment in Developing Shear Layers

Air-water bubbly flows are encountered in numerous engineering applications. One type of air-water shear flows is the developing flow region of a plunging jet. The mechanisms of air entrainment by plunging liquid jets are discussed in the light of new experimental evidence. Measurements were performed in hydraulic jumps (i.e. horizontal supported plunging jet flow) and in vertical supported plunging jets. Further measurements were recorded in free-falling jets, upstream of the impingement point (of plunging jet) to characterise the effects of inflow conditions on plunging jet entrainment. Distributions of air concentration and mean air-water velocity, and bubble chord length distributions measured in the developing shear layer are presented. The results indicate that the distributions of void fraction follow closely analytical solutions of the diffusion equation, as developed by CHANSON (1995a,1997a). The air-water shear layers exhibit the same shape of velocity distributions as monophase flows. But the location of the air-water shear layer differs from monophase flow results, because of the interactions between the entrained air bubbles and the turbulence. The rate of expansion of the shear layer is also affected by the air bubble dispersion. Altogether the momentum shear layer and the air bubble diffusion layer do not coincide. Chord length data show a wide range of air bubble sizes and overall the experimental results suggest strong interactions between the entrained air bubbles and the momentum transfer mechanisms. A comparative analysis of several types of air-water shear flows (plunging jet, hydraulic jump, free-falling jet, open channel flow) suggests some analogy between the different types of shear flows. It is thought that the similarities might derive from the predominance of the air bubble diffusion process in each case. Note that the present study extends the work presented by CHANSON (1995a), CUMMINGS (1996) and CHANSON and BRATTBERG (1996). The new experimental study presents a systematic investigation of the air diffusion process and momentum transfer mechanisms in turbulent shear flows with inflow velocities ranging from 2 to 8 m/s

Experimental Investigations of Free-Surface Aeration in the Developing Flow of Two-Dimensional Water Jets

Turbulent water jets discharging into the atmosphere are often characterised by a substantial amount of free-surface aeration. The effects can be detrimental or beneficial. In any case, the knowledge of the air entrainment mechanisms is essential for an optimum design. New experimental data are presented in the developing flow region of two-dimensional water jets discharging into air. The results indicate that the air diffusion takes place rapidly downstream of the nozzle and it is nearly independent of the momentum transfer process. Further the distribution of air bubble frequency may be related to the air content distribution by a parabolic relationshi

On nitrogen fixation in a coastal area of the northern Baltic

Nitrogen (C2H4)-fixation in planktic heterocystous blue-green algae was measured in the Askö area throughout the summer 1976. -Temporal variations in total number of heterocysts, heterocyst frequency, heterocyst activity, acetylene reduction and primary production are discussed. - The amount of nitrogen fixed is estimated to 0.6 gN/m2 x year

China, Europe, and the Pandemic Recession: Beijing’s Investments and Transatlantic Security

Given the depth and breadth of the pandemic-induced recession in Europe, private companies in need of capital and governments looking to shed state-owned enterprises may be tempted to sell shares, assets, or outright ownership to investors with liquidity to spare. Of greatest concern is the role that China might play in Europe, building Beijing’s soft power, weakening allied geopolitical solidarity, and potentially reprising the role it played in the 2010s, when its investments in Europe expanded dramatically. More specifically, there is concern over China’s investments in infrastructure and sensitive technologies relevant to American and allied military operations and capabilities. Whether Europe is prepared and able to parry Beijing’s economic statecraft is somewhat unclear, given varied attitudes toward China and the patchwork of investment screening mechanisms across the continent. Regardless, the outcomes will have significant implications for US security and for the Defense Department specifically. In support of US European Command (EUCOM) and the Department of Homeland Security (DHS), the U.S. Army War College’s Strategic Studies Institute (SSI) assembled an interdisciplinary team to examine these issues and offer actionable policy recommendations for military leaders and decisionmakers on both sides of the Atlantic. Study sponsors (nonfunding): United States European Command, United States Department of Homeland Securityhttps://press.armywarcollege.edu/monographs/1945/thumbnail.jp

Design side by side

The starting point for most of what is written here is people with disabilities. Situations of great difficulty need to be highly prioritized, for their own sake and also because that which first appears to be “special” sooner or later comes to benefit s