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In this work, we propose a new fire shaping approach for manufacturing glass nozzles that heats a rotating vertical capillary at the Top of a Lateral Flame (TLF). We use image analysis to evaluate its performance focusing on the reproducibility in the nozzle size and shape, and on its symmetry. Our results show that this new approach has satisfactory diameter reproducibility, and produces highly axisymmetric nozzles (with very little nozzle neck offset or misalignment). The shape reproducibility is very good for the same heating position, and additionally, it allows to produce nozzles of different shapes by working at different positions. TLF overcomes the problems of the previous fire shaping approaches, which used a vertical flame. In comparison with pulling, which is a well-established method, TLF has a similar diameter reproducibility and produces a superior symmetry. [ABSTRACT FROM AUTHOR]

The breakup of a charged liquid column is studied numerically using Volume-OF-Fluid (VOF) for a range of timescales where electrokinetic phenomena may become significant, i.e when the time to breakup becomes comparable or shorter than the diffusion and the electroosmotic migration times of charged species. Here we propose a conservative method to deal with the diffusion of a tracer in VOF schemes when the diffusion is limited to one of the phases. The method consists in weighing the diffusivity with the value of the volume fraction computed from the analytically reconstructed interface. In this way, the interface is made impermeable to the tracer, which is conservatively kept within one of the phases. The performance of this method is first tested by comparing simple configurations with existing analytical solutions. In the cases when the diffusion, electroosmotic motion and hydrodynamic singularities compete, the results indicate that, after breakup, charges distribute between droplets differently from models assuming homogeneous and constant electrical conductivities (i.e. no electrokinetic effects). However, such departure does not alter the main hydrodynamic balances leading to well-established scaling laws of breakup. [ABSTRACT FROM AUTHOR]

• Agronomical biofortification increased Selenium (Se) in Iberian pig diets. • These Se-biofortified diets increased the antioxidant capacity of Iberian pork. • These biofortified diets increased Se in meat but not in blood plasma. • Main meat effects persisted for 2 months after biofortified diet withdrawal. • This biofortification was inexpensive, safe and had long-lasting effects. Due to its valuable high intramuscular fat content and lipid composition, Iberian pork is very prone to rancidity. Selenium (Se) supplementation delays meat post-mortem oxidation, but organic Se reaches tissues more efficiently and durably than the inorganic forms, which may even be toxic at high concentrations. Agronomical Se biofortification (incorporating Se to crops) provides organic Se, is not expensive and is effective and safe for producing animal feed and human food. This study aimed to: (1) Determine the effectiveness of Se-biofortification in triticale crops. (2) Evaluate the use of Se-biofortified triticale grain in Iberian pigs during the pre-finishing vs the pre-finishing + finishing periods to determine the permanence of Se and the effects on pork antioxidant capacity. A 4-ha triticale plot was sprayed with sodium selenate (10 g Se/ha) and a similar, control plot was not sprayed. Treated plot grain had greater Se concentration (430 ± 22 µg Se/kg) than that from the control one (<25 µg). Starting at 7 months of age (m), castrated Iberian pigs were fed with standard concentrate, containing 45 % of triticale, which was standard (Control; Ctrl , n = 10), or the Se-biofortified one (Treated groups; Trt), which were fed until they were 12 m (Se-1 ; n = 10) or until slaughter time (60 days later; Se-2 ; n = 10). Blood samples were collected at the end of the finishing period for Se content and metabolic parameters. Pre-slaughter loin and gluteal ultrasonography was performed. Carcass and prime cuts were weighed, and meat samples analyzed for Se content and meat quality (before or after 7-day maturation; d0 or d7 respectively). Meat Se content was greater in Trt vs Ctrl, and greater in Se-2 vs Se-1. Treatment did not affect body weight nor blood Se content, but it increased ultrasonographic subcutaneous fat thickness in Se-1 and triglyceride blood levels in Se-2. Compared with Ctrl, Se-1 and Se-2 had higher pH on d0 and lower L* and b* colors on d7. Cooking losses were lowest for Se-1. Loin TBARS was greatest (more oxidized pork) on d7 in Ctrl. Pork springiness and resilience at 20% compression were greatest for Se-2. These results suggest (for the first time, as far as we know) a great potential for this sustainable strategy to increase meat antioxidant capacity through agronomical Se biofortification for animal feeding and for Iberian pigs in particular, even after a 2-month period of concentrate withdrawal, which is required for montanera -finished (free-ranging, acorn-fed) animals. [ABSTRACT FROM AUTHOR]

• We describe the whipping instability in gaseous flow focusing. • Whipping instability is explained in terms of the global stability analysis. • We analyze the influence of the geometry on the whipping instability. We study both theoretically and experimentally the whipping instability in axisymmetric gaseous flow focusing realized in a converging-diverging nozzle. The lateral oscillation of both the tapering meniscus and emitted jet is explained in terms of the global linear instability of the lateral mode with the azimuthal number m = 1. A comparison with previous experiments shows good agreement. The distance between the feeding capillary and the nozzle neck hardly affects the m = 1 stability limit for the conditions considered in those experiments. We analyze the influence of the nozzle shape on the parameter conditions leading to whipping. As the nozzle convergence rate (the inverse of the length over which the diameter reduction takes place) increases, the flow becomes more stable under m = 1 perturbations. The above results are in marked contrast with those of the axisymmetric mode m = 0. For the axisymmetric mode, the minimum flow rate increases with the nozzle convergence rate, while the capillary-to-neck distance has considerable influence on the jetting-to-dripping transition. We also conduct experiments with different nozzles and capillary-to-neck distances to examine the effect of those factors on the stability of the jetting regime. The experiments allow us to distinguish between absolute whipping, in which both the tapering meniscus and the emitted jet oscillate, and convective whipping, in which the jet oscillates while the meniscus remains practically steady. Absolute whipping is observed for water and 1-cSt silicone oil focused with the nozzle with the smallest convergence rate and capillary-to-neck distance. The increase of the liquid viscosity stabilizes the liquid meniscus, producing the transition from absolute to convective whipping. In the high-viscosity case, the oscillation of the emitted jet far away from the discharge orifice is considerably affected by the shape of the nozzle in front of its neck. In fact, the increase of the convergence rate and capillary-to-neck distance eliminates the convective whipping as well. The reduction of surface tension enhances absolute whipping. We explain the appearance of the two types of whipping in terms of the flow pattern induced by the nozzle shape in front of the neck. [ABSTRACT FROM AUTHOR]

Coaxial electrospray is a well established procedure to generate coaxial micro- and nano-structures (microcapsules and coaxial fibers). In this work we show the capabilities of a high-precision numerical code using dynamic mapping, analytic Jacobian formulation and the Taylor–Melcher leaky dielectric model (LDM) to deal with real coaxial electrospray configurations. Since the number of parameters involved in the problem is large, we focus on an experimentally tested liquid pair configuration where the thickness, relative position, and end sharpness of the coaxial feeding tubes are geometrical parameters of interest. The effects of those parameters and the voltage applied at the tubes on the coaxial liquid menisci, liquid streamlines, size of jet and core, and electric current are discussed. • The influence of the outlet tube geometry on coaxial electrosprays is studied. • Accurate numerical solutions are given using Taylor–Melcher Leaky Dielectric model • Protruding, flush and recessed tube outlet setups, and edge sharpening are explored • Physical details (streamline patterns, menisci geometries, stresses) are provided [ABSTRACT FROM AUTHOR]

Flow focusing is providing new tools in Analytical Chemistry for its unique combination of simplicity, droplet size control just above the micrometer scale, and aerosol beam collimation. However, the most interesting droplet size range lies at the stability limit of the standard flow focusing operating mode. Nevertheless, that stability limit can be forced down to produce jets on the submicrometer scale by underpinning the cone-like meniscus at the tip of a hypodermic needle. Using a nebulizer design based on that concept, we show that the flow focusing steady jetting regime extends down to the limit imposed by the instability of jet itself, even for Reynolds numbers as low as 10 −2 . This stability enhancement leads to droplet sizes well below those previously obtained with flow focusing. In this work, we experimentally determine the influence on the jet's radius of the liquid flow rate and viscosity, as well as the focusing orifice. We analyze the instability mechanisms that impose the minimum values of the issued flow rate and jet's size. Finally, the jet's breakup and the size of the resulting micron-sized droplets are examined from high-speed optical imaging. [ABSTRACT FROM AUTHOR]

The production of viscoelastic capillary jets with gaseous flow focusing is studied experimentally. In this technique, the liquid is injected at a constant flow rate through a feeding capillary located in front of the discharge orifice. A gas stream coflows with the jet across the orifice driven by a constant pressure drop. The gas stream sucks and drags the liquid, reducing the jet’s diameter well below the orifice diameter. Because of the rheological nature of the liquid, this focusing phenomenon differs from the Newtonian one in several regards. For given values of the polymer concentration, the injected flow rate, and the applied pressure drop, there is an interval of the capillary-to-orifice distance for which the jetting regime is reached. Outside that interval, the jet either suffers from the pull-out instability or breaks up before reaching the discharge orifice. Significant free surface oscillations can be observed in most of the jetting realizations. This oscillatory behavior is caused by a transient die swell effect which continuously appears right at the capillary exit. Ejection interrupts because the jet bulges to such an extent that the free surface pinches. Because of the stabilizing effect of the polymeric contribution to the axial stress, micrometer filaments with lengths up to 1 cm and Weber numbers on the order of 10 − 4 can be produced in front of the discharge orifice. The shear viscous stresses exerted on the emitted jet by the gas stream beyond the discharge orifice prevent the macromolecule recoiling. The resulting extensional viscosity inhibits the break-up process, and thus very long jets are produced. [ABSTRACT FROM AUTHOR]

A novel microfluidic technique has been recently proposed to produce quasi-monodisperse collections of microbubbles with a controlled size. In this technique, a gaseous stream is injected through a T-junction into a microchannel transporting a liquid current. The gas adheres to a hydrophobic strip printed on the channel surface. When the gas and liquid flow rates are set appropriately, a gaseous rivulet flows over that strip. The rivulet breaks up downstream due to a capillary pearling instability, which leads to a quasi-monodisperse collection of microbubbles. Motivated by this application, we here analyze the stability of both gas and liquid rivulets coflowing with a current in a quadrangular microfluidic channel. The results essentially differ from those of cylindrical jets because the contact-line-anchorage condition affects fundamentally the rivulet’s instability nature. The temporal stability analysis shows that the rivulet becomes unstable not only for (unperturbed) contact angles larger than 90° (as can be expected) but also for values smaller than that angle. Interestingly enough, the maximum growth factor exhibits a non-monotonic dependence with respect to the Reynolds number (i.e., the viscosities). In fact, there are intervals of that parameter where the fluid system becomes unstable, while all the perturbations are damped outside that interval. The gaseous rivulet does not stabilize as the Reynolds number decreases, which means that it can be unstable even in the Stokes limit and for contact angles less than 90°. In addition, the stability of a flowing liquid rivulet is not determined by its contact angle exclusively (as occurs in the static case), but by the Reynolds number as well. Liquid rivulets with contact angles less than 90° can be unstable for sufficiently high Reynolds numbers. [ABSTRACT FROM AUTHOR]

• We analyze the stability of transonic flow focusing. • We determine the minimum liquid flow rate for steady jetting. • We derive a scaling law for the jet diameter. We study numerically and experimentally the stability of the transonic flow focusing used in serial femtosecond crystallography (SFX) to place complex biochemical species into the beam focus. Both the numerical and experimental results indicate that the minimum flow rate for steady jetting increases slightly with the gas stagnation pressure. There is a remarkable agreement between the stability limit predicted by the global stability analysis and that obtained experimentally. Our simulations show that the steady jetting interruption at the critical flow rate is caused by the growth of a perturbation with a constant phase shift. This result is consistent with the experimental observations, which indicate that both the meniscus tip and the emitted jet collapse almost simultaneously at the stability limit. We derive a scaling law for the jet diameter as a function of the liquid flow rate and gas density/pressure from more than one hundred simulations. The scaling law provides accurate predictions for the jet diameter within the range of values [0.549,10.9] μ m analyzed in this work. [ABSTRACT FROM AUTHOR]