Hydrodynamic study of fine metallic powders in an original spouted bed contactor in view of chemical vapor deposition treatments

An original gas–solid contactor was developed so as to treat by chemical vapor deposition, fine (mean diameter 23 μm) and dense (bulk density 7700 kg/m3) NiCoCrAlYTa powders with large size distribution. In order to avoid the presence of a distributor in the reactive zone, a spouted bed configuration was selected, consisting in a glass cylindrical column associated through a 60° cone to an inlet tube, connected at its bottom to a grid so as to support the powders at rest. A hydrodynamic study was conducted at ambient temperature and pressure, combining pressure drop measurements and visual observations as a function of gas velocity and of the ratio H/D of the height of the bed at rest over the bed diameter. Using conventional alumina particles belonging to Geldart's group B, it was shown that this equipment is able to ensure conventional spouted bed behavior, especially for H/D ratio equal to 1. From numerous experiments conducted with the fine metallic powders of interest, it was shown that (i) conventional pressure drop curves for spouted beds are obtained for H/D ratios between 1 and 1.8, (ii) due to the large grain size distribution of particles, minimum spouted bed velocities occur in a range rather than at precise values. Visual observations reveal the presence of the spout and fountain at the minimum spouted bed velocity and for H/D equal to 1

Adsorption of Xe atoms on metal surfaces: New insights from first-principles calculations

The adsorption of rare gases on metal surfaces serve as the paradigm of weak adsorption where it is typically assumed that the adsorbate occupies maximally coordinated hollow sites. Density-functional theory calculations using the full-potential linearized augmented plane wave method for Xe adatoms on Mg(0001), Al(111), Ti(0001), Cu(111), Pd(111), and Pt(111), show, however, that Xe prefers low-coordination on-top sites in all cases. We identify the importance of polarization and a site-dependent Pauli repulsion in actuating the site preference and the principle nature of the rare-gas atom--metal surface interaction.Comment: 5 pages including 4 figure files. Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm

Complex dynamics in simple systems with seasonal parameter oscillations

We study systems with periodically oscillating parameters that can give way to complex periodic or non periodic orbits. Performing the long time limit, we can define ergodic averages such as Lyapunov exponents, where a negative maximal Lyapunov exponent corresponds to a stable periodic orbit. By this, extremely complicated periodic orbits composed of contracting and expanding phases appear in a natural way. Employing the technique of $\epsilon$-uncertain points, we find that values of the control parameters supporting such periodic motion are densely embedded in a set of values for which the motion is chaotic. When a tiny amount of noise is coupled to the system, dynamics with positive and with negative non-trivial Lyapunov exponents are indistinguishable. We discuss two physical systems, an oscillatory flow inside a duct and a dripping faucet with variable water supply, where such a mechanism seems to be responsible for a complicated alternation of laminar and turbulent phases.Comment: New version with major change

Evaluation of a Experimental Chlorine Dioxide (Base/Activator) Teat Dip on Teat End / Teat Skin Condition and Health

A teat conditioning trial was run for a period of 60 days at the Iowa State University dairy farm under winter conditions, starting Nov 22, 2008 and ending Jan 21, 2009. Objective of this study was to evaluate the teat conditioning properties of an experimental chlorine dioxide teat dip formula (containing sorbitol as the emollient agent) against a currently marketed chlorine dioxide product using a split udder design. Left teats were dipped in the control product (4XLA) and right teats were dipped in the experimental product (372-75-2). Generally, teat condition score was measured every three days for the duration of the study, totaling 18 teat scoring events. Results showed no statistical difference between the two products in both teat skin condition scores. However, statistical differences in teat condition were only observed when time in trial was analyzed and which were associated with climatic changes. On daily average, temperatures below 32o F were observed 90% of the trial period time. The average teat skin condition at the start of the trial was 1.15 for both products and ended at 1.08 (4XLA) and 1.07 (372-75-5). On 10 out of 17 occasions, teat skin score remained relatively unchanged. On 6 other occasions it worsened, reaching a maximum of 1.49 (P\u3c0.01), and in 1 occasion it improved, reaching a low of 1.04 (P\u3c0.01). The teat end condition was 2.23 (4XLA) and 2.14 (372-75-2) at the start of the trial, and ended at 2.88 (4XLA) and 2.74 (372-75-2). In general it was observed that teat end condition remained relatively stable during the first 40 days, and then it worsened until the trial ended (P\u3c0.01). It is concluded that both 4XLA and 372-75-2 had a similar teat conditioning efficacy during the 60d trial period under winter conditions in the USA. There were, however, significant changes in teat condition scores across times and dates, with similar trends across groups and products, signifying that other factors besides teat dips influence teat condition. Changes in teat condition were associated with temperature changes and often worsened (increased scores) with cold temperatures

Evaluation of 2 Sodium Chlorite (Base/Activator) Pre- Post Milking Teat Dips on Teat End / Teat Skin Condition and Health

Objective of this study was to evaluate 2 sodium chlorite pre-post teat dips on overall teat end and teat skin condition and health using a split udder design. Both dips showed excellent teat skin and end condition, a low % of rough teats, and no differences were seen between dips

Evaluation of Teat Protection Persistency of an Experimental Novel Dry Cow Teat Dip System

Mastitis research has shown 40-50% of intramammary infections (IMI) are contracted during the dry or non-lactating period with the greatest percentages of these occurring during the first and last two weeks of the dry period. The ability to develop and apply external persistent barrier teat dip products (that can persist for these 1 week periods could decrease IMI, thus improving animal health and performance, and product quality and safety. Specific aim of this study was to evaluate the persistency of teat protection of a novel experimental dry cow teat dip system (2 products dipped sequentially to form a persistent barrier; Zurex Pharma, Inc.). The compounds were easy to apply and formed a nice polymerized film. However, only 1/24 teats had dip films on @ 12 hrs post dipping with most films cracking, peeling, or completely removed by that time