Particle In-Flight Velocity and Dispersion Measurements at Increasing Particle Feed Rates in Cold Spray

Cold spray (CS) is attracting interest of research and industry due to its rapid, solid-state particle deposition process and respective advantages over conventional deposition technologies. The acceleration of the particles is critical to the efficiency of CS, and previous investigations rarely consider the particle feed rate. However, because higher particle loadings are typically used in the process, the effect of this cannot be assumed negligible. This study therefore investigates the particle velocities in the supersonic jet of an advanced CS system at low- and high pressure levels and varying particle feed rates using particle image velocimetry. The particle dispersion and velocity evolution along the jet axis were investigated for several feedstock materials. It was found that the average particle velocity noticeably decreases with increasing particulate loading in all cases. The velocity distribution and particle dispersion were also observed to be influenced by the feed rate. Effects are driven by both mass loading and volume fraction, depending on the feedstock’s particle velocity parameter. Increased particle feed rates hence affect the magnitude and distribution of impact velocity and consequently the efficiency of CS. In particular, numerical models neglecting this interconnection are required to be further improved, based on these experimental studies.     

Differential effects of monensin and a blend of essential oils on rumen microbiota composition of transition dairy cows

In response to oral application, monensin alters the rumen microbiota, increasing ruminal propionate production and energy availability in the animal. Data from different studies indicate that the susceptibility of rumen bacteria to monensin is mainly cell-wall dependent but tracing its activity to specific microbial groups has been challenging. Several studies have shown a similar effect for essential oils but results are inconsistent. To investigate the influence of monensin and a blend of essential oils (BEO, containing thymol, guaiacol, eugenol, vanillin, salicylaldehyde, and limonene) on the rumen microbiome, rumen liquid samples were collected orally on d 56 postpartum from cows that had either received a monensin controlled-release capsule 3 wk antepartum, a diet containing a BEO from 3 wk antepartum onward, or a control diet (n = 12). The samples were analyzed for pH, volatile fatty acid, ammonia, and lipopolysaccharide concentrations and protozoal counts. A 16S rRNA gene fingerprinting analysis (PCR–single-strand conformation polymorphism) and sequencing revealed that the BEO treatment had no effect on the rumen microbiota, whereas monensin decreased bacterial diversity. Twenty-three bacterial species-level operational taxonomic units were identified for which monensin caused a significant decrease in their relative abundance, all belonging to the phyla Bacteroidetes (uncultured BS11 gut group and BS9 gut group) and Firmicutes (Lachnospiraceae, Ruminococcaceae, and Erysipelotrichaceae). Ten bacterial operational taxonomic units belonging to the phyla Actinobacteria (Coriobacteriaceae), Bacteroidetes (Prevotella), Cyanobacteria (SHA-109), and Firmicutes (Lachnospiraceae and Ruminococcaceae) increased in relative abundance due to the monensin treatment. These results confirm the hypothesis that varying effects depending on cell-wall constitution and thickness might apply for monensin sensitivity rather than a clear-cut difference between gram-negative and gram-positive bacteria. No effect of monensin on the archaea population was observed, confirming the assumption that reported inhibition of methanogenesis is most likely caused through a decrease in substrate availability, rather than by a direct effect on the methanogens. The data support the hypothesis that the observed increase in ruminal molar propionate proportions due to monensin may be caused by a decrease in abundance of non-producers and moderate producers of propionate and an increase in abundance of succinate and propionate producers.     

Technical note: Flow cytometric identification of bovine milk neutrophils and simultaneous quantification of their viability

The aim of the present study was to develop a flow cytometric procedure for the quantification of the proportion of viable, apoptotic, and necrotic polymorphonuclear neutrophilic leukocytes (PMNL) isolated from both low- and high-somatic-cell-count quarter milk samples. Milk PMNL were differentiated from other cells by indirect fluorescent labeling using a primary anti-bovine granulocyte monoclonal antibody (CH138A) and an Alexa 647-labeled secondary antibody. Polymorphonuclear neutrophilic leukocytes were identified flow cytometrically based on their cytoplasmic granularity and CH138A-positivity. Additional labeling with annexin-V-fluorescein isothiocyanate and propidium iodide was used to determine milk PMNL viability. Thirty milk samples were run in parallel to assess the repeatability of the immunoassay and 6 repeated measurements per sample were performed to assess the instrument stability. Fluorescence microscopic verification of the CH138A staining pattern showed both a high sensitivity (90.9%) and specificity (92.3%). The combination of the side-scatter properties of granulated PMNL and CH138A-Alexa 647 positivity allows the distinction of labeled PMNL from other milk cells and particles that may bind nonspecifically, and from autofluorescent particles present in milk. Quantification of the proportion of PMNL and viable, apoptotic, and necrotic subpopulations in parallel samples gave repeatable results with concordance correlation coefficients varying between 0.93 and 0.99. The average coefficient of variation for repeated measurements in identical samples ranged between 4.2 and 9.7%. In conclusion, this is the first flow cytometric method suited for the simultaneous quantification of viable, apoptotic, and necrotic bovine milk PMNL in a straightforward manner.     

Different risk thresholds in pedestrian road crossing behaviour: A comparison of French and Japanese approaches

When crossing the road, pedestrians have to make a trade-off between saving time and avoiding any risk of injuries. Here, we studied how culture influences an individual's perception of risks when crossing a street, using survival analysis. This study is the first to use this analysis to assess cognitive mechanisms and optimality of decisions underlying road crossing behaviour. We observed pedestrian behaviour in two city centres: Inuyama (Japan) and Strasbourg (France). In each city, observations were made at a safe site consisting of a crosswalk and a street light and at an unsafe site (i.e. no crosswalk or street light). At the unsafe site, we measured the time needed by a pedestrian to take a decision (T_dec). During T_dec, a pedestrian estimates whether he can (T_safe) or cannot (T_risk) cross the road. Using survival analysis, we studied the distributions of these three time variables and showed that French pedestrians took more risks than Japanese pedestrians, and that males took more risks than females, but only in Japan. More studies would considerably broaden our understanding on how culture may affect decision-making processes under risky circumstances.     

Synthesis of Au microwires by selective oxidation of Au–W thin-film composition spreads

Abstract

We report on the stress-induced growth of Au microwires out of a surrounding Au–W matrix by selective oxidation, in view of a possible application as ‘micro-Velcro’. The Au wires are extruded due to the high compressive stress in the tungsten oxide formed by oxidation of elemental W. The samples were fabricated as a thin-film materials library using combinatorial sputter deposition followed by thermal oxidation. Sizes and shapes of the Au microwires were investigated as a function of the W to Au ratio. The coherence length and stress state of the Au microwires were related to their shape and plastic deformation. Depending on the composition of the Au–W precursor, the oxidized samples showed regions with differently shaped Au microwires. The Au₄₈W₅₂ composition yielded wires with the maximum length to diameter ratio due to the high compressive stress in the tungsten oxide matrix. The values of wire length (35 μm) and diameter (2 μm) achieved at the Au₄₈W₅₂ composition are suitable for micro-Velcro applications.     

Dynamic measurements of hydrogen reaction with LaNi5−xSnx alloys

The study focuses on the reaction between hydrogen gas and LaNi_5−xSn_x alloys, where 0 ≤ x ≤ 0.5, in broad temperature and pressure ranges. It was performed by means of dynamic volumetric techniques using specific equipment developed at our laboratory. The substitution of Ni by Sn lowers the system equilibrium pressure and increases the hydrogen absorption reaction rate. Reaction pressures at room temperature range from 8 kPa (x = 0.5) to 250 kPa (x = 0). At 415 K the reaction pressure is within the range from 200 kPa to 4000 kPa for x = 0.5 and 0, respectively. The measured characteristic absorption time at 750 kPa for LaNi₅ is around 1 min, while it remains below 2.5 s for LaNi_4.5Sn_0.5. The maximum H concentration goes from 1.3 wt.% for LaNi₅ down to 0.95 wt.% for LaNi_4.5Sn_0.5. These results are useful to identify a metal system where the hydrogen interaction equilibrium properties can be tuned in a wide pressure range by choosing the chemical composition and the process temperature.     

Metal injection moulding of nickel-based superalloy CM247LC*

Metal injection moulding (MIM) is a promising new production technology for small- to medium-sized parts with high complexity for high-temperature applications like aero engines or turbochargers. This study concerns the feasibility of manufacturing parts from nickel-based superalloy CM247LC via MIM. CM247LC poses a serious challenge for MIM processing. Because of its high aluminium content, the strength potential is very high, but the sintering capability is severely restricted. Differential scanning calorimetry and dilatometry measurements as well as ThermoCalc simulations are used to optimise the sintering step of the MIM process route. Carbon, nitrogen and oxygen contents of the powder and the as-sintered specimens are measured to evaluate the pick-up of impurities during processing. The microstructure of the as-sintered specimens is characterised with respect to residual porosity, grain size, carbide content and γ′ precipitation size and morphology. Ways to further improve the microstructure and strength will be discussed.     

On the study of catalytic membrane reactor for water detritiation: Membrane characterization

Tritium waste recycling is a real economic and ecological issue. Generally under the non-valuable Q₂O form (Q = H, D or T), waste can be converted into fuel Q₂ for a fusion machine (e.g. JET, ITER) by isotope exchange reaction Q₂O + H₂ = H₂O + Q₂. Such a reaction is carried out over Ni-based catalyst bed packed in a thin wall hydrogen permselective membrane tube. This catalytic membrane reactor can achieve higher conversion ratios than conventional fixed bed reactors by selective removal of reaction product Q₂ by the membrane according to Le Chatelier's Law.This paper presents some preliminary permeation tests performed on a catalytic membrane reactor. Permeabilities of pure hydrogen and deuterium as well as those of binary mixtures of hydrogen, deuterium and nitrogen have been estimated by measuring permeation fluxes at temperatures ranging from 573 to 673 K, and pressure differences up to 1.5 bar. Pure component global fluxes were linked to permeation coefficient by means of Sieverts’ law. The thin membrane (150 μm), made of Pd–Ag alloy (23 wt.%_Ag), showed good permeability and infinite selectivity toward protium and deuterium. Lower permeability values were obtained with mixtures containing non permeable gases highlighting the existence of gas phase resistance. The sensitivity of this concentration polarization phenomenon to the composition and the flow rate of the inlet was evaluated and fitted by a two-dimensional model.     

Heat Transfer during Annular Tube Contact in a Helically Coiled Tube-in-Tube Heat Exchanger

Abstract

Helically wound tube-in-tube heat exchangers are manufactured by coiling two tubes, one placed inside the other. This method often results in the tubes not sharing the same center line, and therefore annular contact occurs in some cases. An experimental comparison was made of such tubes in a heat exchanger with annular contact, as opposed to an aligned (concentric) device without annular contact, in order to quantify the effect of annular contact in terms of heat transfer coefficients and pressure drop. By comparing the heat transfer characteristics, it was concluded that the heat transfer coefficient in the annulus was found to increase substantially. The result was an improved performance by the heat exchanger where annular contact occurs, compared to the heat exchanger with the inner tube in a concentric position.