Generation of Steady Liquid Microthreads and Micron-Sized Monodisperse Sprays in Gas Streams

A new class of microscopic jet flows is here reported: for a certain range of physical parameters and geometrical configurations, a perfectly steady microscopic liquid thread can be formed by a laminar accelerating gas stream, eventually giving rise to a nearly monodisperse fine spray. Some interesting characteristics for many applications of this robust and versatile flow and related atomization technique are highlighted. Concentric multicomponent liquid threads can also be produced. A theoretical model is presented that shows agreement with experiments.Spanish Comisión Interministerial de Ciencia y Tecnología PB93-1181Spanish Comisión Interministerial de Ciencia y Tecnología PB96-134

Universal structures of normal and pathological heart rate variability

The circulatory system of living organisms is an autonomous mechanical system softly tuned with the respiratory system, and both developed by evolution as a response to the complex oxygen demand patterns associated with motion. Circulatory health is rooted in adaptability, which entails an inherent variability. Here, we show that a generalized N-dimensional normalized graph representing heart rate variability reveals two universal arrhythmic patterns as specific signatures of health one reflects cardiac adaptability, and the other the cardiac-respiratory rate tuning. In addition, we identify at least three universal arrhythmic profiles whose presences raise in proportional detriment of the two healthy ones in pathological conditions (myocardial infarction; heart failure; and recovery from sudden death). The presence of the identified universal arrhythmic structures together with the position of the centre of mass of the heart rate variability graph provide a unique quantitative assessment of the healthpathology gradient

Risk stratifiers for arrhythmic and non-arrhythmic mortality after acute myocardial infarction

Open Access. Publicado online: 2-Jul-2018The effective discrimination between patients at risk of Arrhythmic Mortality (AM) and Non-Arrhythmic Mortality (NAM) constitutes one of the important unmet clinical needs. Successful risk assessment based on Electrocardiography (ECG) records is greatly improved by the combination of different indices reflecting not only the pathological substrate but also the autonomic regulation of cardiac electrophysiology. This study assesses the cardiac risk stratification capacity of two new Heart Rate Variability (HRV) parameters, Breath Concurrence 6 (BC6) -sinusoidal RR variability of 6 heart beats per breath cycle- and Primary Ectopia (PE) -presence of early ventricular contractions of any etiology- together with the Deceleration Capacity (DC). While BC6 characterizes the response to physiological and pathophysiological stimuli, PE qualifies autonomic cardiac electrophysiology. The analysis of the European Myocardial Infarct Amiodarone Trial (EMIAT) database indicates that BC6 is related with the risk of Arrhythmic Mortality (AM) and PE with the risk of Non-Arrhythmic Mortality. BC6 is the only single parameter that significantly discriminates between AM and NAM. While the combination of BC6 and DC contributes to the identification of AM risk, PE together with DC improves the prediction of NAM in patients with severe ischemic heart disease

The dynamics and mixing of small spherical particles in a plane, free shear layer

The equation of motion of small rigid spheres settling under gravity in a two-dimensional inviscid flow given by the Stuart solution of the Euler equations is analyzed as a fourdimensional dynamical system. It is shown that depending on the values of the Stokes, Grashof, and a scaled Reynolds number, particles may either sediment or remain permanently suspended in the flow. When suspension occurs, the particle trajectories are shown to be attracted by a single period, quasiperiodic, or chaotic orbits. A consequence of the existence of a strange attractor (chaotic orbit) is that heavy particles can reach a stage ofjhdization by which they remain indefinitely suspended in a layer of finite height located above the center of the Stuart vortices.Secretaria de Estado de Universidades e Investigación de España FPU-2868794

Flow Blurring-Enabled Production of Polymer Filaments from Poly(ethylene oxide) Solutions

Flow blurring (FB) atomizers are relatively simple yet robust devices used for the generation of sprays from solutions of a wide range of viscosities. In this work, we have demonstrated that FB devices may also be applied for massive production of liquid filaments from polymeric solutions. They can later be transformed into solid filaments and fibers, leading to the production of so-called fiber mats. The liquid precursors consisted of poly(ethylene oxide) (PEO) solutions of varying molecular weights (105 [100k] to 4 × 106 g/mol [4M]) and concentrations. The FB device was operated in the gas pressure range of 3−6 bar. Except for solutions of PEO 100k, all solutions exhibited a shear thinning behavior. For massive filament production, a threshold polymer concentration (ct) was identified for each molecular weight. Below such concentration, the atomization resulted in droplets (the classical FB functioning mode). Such a threshold value decreased as the PEO molecular weight increased, and it coincides with the polymer coil overlap concentration, c*. The viscoelastic nature of the solutions was also observed to increase with the molecular weight. A 3.2 dependency of the zero-shear rate viscosity on a so-called Bueche parameter was found for filament production, whereas a nearly linear dependency was found for droplet production. In general, the mean diameter of the filaments decreased as they traveled downstream from the atomization point. Furthermore, at a given distance from the atomizer outlet and gas pressure, the mean filament diameter slightly shifted toward larger sizes with increasing PEO molecular weight. The tendency agrees well with the calculated filaments’ Deborah number, which increases with PEO molecular weight. The approach presented herein describes a highthroughput and efficient method for the massive production of viscous filaments. These may be transformed into fibers by an on-line drying step.Ministerio de Economía y Competitividad DPI2016-78887-C3-1-

Formation of bubbles and droplets in microfluidic systems

This mini-review reports the recent advances in the hydrodynamic techniques for formation of bubbles of gas in liquid in microfluidic systems. Systems comprising ducts that have widths of the order of 100 micrometers produce suspensions of bubbles with narrow size distributions. Certain of these systems have the ability to tune the volume fraction of the gaseous phase – over the whole range from zero to one. The rate of flow of the liquids through the devices determines the mechanism of formation of the bubbles – from break-up controlled by the rate of flow of the liquid (at low capillary numbers, and in the presence of strong confinement by the walls of the microchannels), to dynamics dominated by inertial effects (at high Weber numbers). The region of transition between these two regimes exhibits nonlinear behaviours, with period doubling cascades and irregular bubbling as prominent examples. Microfluidic systems provide new and uniquely controlled methods for generation of bubbles, and offer potential applications in micro-flow chemical processing, synthesis of materials, and fluidic optics.The U.S. Department of Energy DE-FG02- 00ER45852Foundation for Polish ScienceMinisterio de Educación y Ciencia de España DPI2002-04305-C02-02

On the physics of transient ejection from bubble bursting

Using a dynamical scaling analysis of the flow variables and their evolution due to bubble bursting, here we predict the size and speed of ejected droplets for the whole range of experimental Ohnesorge and Bond numbers where ejection occurs. The transient ejection, which requires the backfire of a vortex ring inside the liquid to preserve physical symmetry, shows a delicate balance between inertia, surface tension and viscous forces around a critical Ohnesorge number, akin to an apparent singularity. Like in other natural phenomena, this balance makes the process extremely sensitive to initial conditions. Our model generalizes or displaces other recently proposed ones, impacting on, for instance, the statistical description of sea spray.Ministerio de Economía, Industria y Competitividad DPI2016-78887Ministerio de Economía, Industria y Competitividad PID2019-108278RBJunta de Andalucía P18-FR-362

Monosized dripping mode of axisymmetric flow focusing

We identify and analyze the perfectly regular dripping mode of flow focusing. This mode occurs within narrow intervals of injected flow rates and applied pressure drops and leads to homogeneous-size droplets with diameters similar to or smaller than that of the discharge orifice. The balance between the local acceleration of the fluid particle and the applied pressure drop yields the scaling law for the droplet diameter. This scaling law is validated experimentally with excellent accord.Ministerio de Economía, Industria y Competitividad DPI2013-46485Gobierno de Extremadura GR1004

Flow blurring atomization of Poly(ethylene oxide) solutions below the coil overlap concentration

Atomization of polymer solutions has important technological implications across many fields. Here, we investigated the atomization dynamics of diluted, polymer solutions using Flow Blurring (FB) technology. Aqueous solutions of poly(ethylene oxide) [PEO] of viscosity-averaged molecular weight in the range 100000 g/mol – 4000000 g/mol and varying concentrations were sprayed with a FB atomizer having an orifice diameter (D) of 700μm and a liquid feed-tube-to-orifice separation (H) of 100μm. The solutions belong to the dilute regime, where polymer coil overlap does not occur, that is φ= [Formula presented] <φcrit (Modesto-López, Pérez-Arjona, & Gañán-Calvo, 2019). Shear viscosity measurements indicated that the solutions had viscosities of the order of that of the solvent and exhibited a Newtonian-like behavior. However, during the atomization, and due to the relatively high shear stress induced in the atomizer, the solutions exhibit extensional rheology, which most likely arises from the stretching of the polymer chains in-flight. Although initially the atomization resulted in formation of filaments, these broke up into droplets at relatively short distances from the atomizer discharge orifice as elucidated by images from ultra-high speed videos. The phenomenon is in contrast with that observed in FB-based atomization of semi-diluted polymer solutions with concentrations larger than the polymer coil overlap concentration, c∗. FB atomization of the diluted solutions resulted in a decrease in droplet size with increasing the gas-to-liquid mass ratio (GLR). The approach herein aims at understanding the droplet formation dynamics of viscoelastic, polymer solutions with FB, for applications in large-scale synthesis of materialsMinisterio de Economía, Industria y Competitividad DPI2016-78887-C3-1-