Considerations on bubble fragmentation models

n this paper we describe the restrictions that the probability density function (p.d.f.) of the size of particles resulting from the rupture of a drop or bubble must satisfy. Using conservation of volume, we show that when a particle of diameter, D0, breaks into exactly two fragments of sizes D and D2 = (D30−D3)1/3 respectively, the resulting p.d.f., f(D; D0), must satisfy a symmetry relation given by D22 f(D; D0) = D2 f(D2; D0), which does not depend on the nature of the underlying fragmentation process. In general, for an arbitrary number of resulting particles, m(D0), we determine that the daughter p.d.f. should satisfy the conservation of volume condition given by m(D0) ∫0D0 (D/D0)3 f(D; D0) dD = 1. A detailed analysis of some contemporary fragmentation models shows that they may not exhibit the required conservation of volume condition if they are not adequately formulated. Furthermore, we also analyse several models proposed in the literature for the breakup frequency of drops or bubbles based on different principles, g(ϵ, D0). Although, most of the models are formulated in terms of the particle size D0 and the dissipation rate of turbulent kinetic energy, ϵ, and apparently provide different results, we show here that they are nearly identical when expressed in dimensionless form in terms of the Weber number, g*(Wet) = g(ϵ, D0) D2/30 ϵ−1/3, with Wet ~ ρ ϵ2/3 D05/3/σ, where ρ is the density of the continuous phase and σ the surface tension

Conformal mapping of ultrasonic crystals: confining ultrasound and cochlear-like wave guiding

Conformal mapping of a slab of a two-dimensional ultrasonic crystal generate a closed geometrical arrangement of ultrasonic scatterers with appealing acoustic properties. This acoustic shell is able to confine ultrasonic modes. Some of these internal resonances can be induced from an external wave source. The mapping of a linear defect produces a wave-guide that exhibits a spatial-frequency selection analogous to that characteristic of a synthetic "cochlea". Both, experimental and theoretical results are reported here.Comment: 4 pages, 4 figure

Bubble size distribution resulting from the breakup of an air cavity injected into a turbulent water jet

We investigated experimentally the shape of the final size PDF(D) resulting from the breakup of an air bubble injected into the fully developed region of a high Reynolds number turbulent water jet. It is shown that the PDF(Dcirc) of the normalized bubble size Dcirc=D/D32, where D32 is the Sauter mean diameter of the distribution, has a universal single shape independent of the value of the turbulent kinetic energy of the water jet at the bubble injection point and of the air void fraction, α. The shape of the exponential tails characterizing each PDF(D) is shown to be only a function of the initial bubble size D0 and the critical bubble size Dc, defined as Dc=(1.46σ/ρ)3/5ɛ-2/5, where ɛ is the value of the dissipation rate of turbulent kinetic energy per unit mass at the air injection point

Estudio de las propiedades mecánicas de armaduras corroídas cuando se modifica la velocidad de deformación

Estudio de la evolución de las propiedades mecánicas del acero en función de su nivel de corrosión y de la velocidad de deformación

Electrochemical study of the diffusion of cupric ion in aqueous and aqueous-glycerol solutions containing sulphuric acid

The diffusion coefficient of cupric ion in sulphuric acid solutions containing glycerol from 0 to 10 M has been determined with the aid of the rotating disk electrode. The viscosity of the solutions has also been measured. Experiments covered a temperature range from 18 to 40°C. The experimental results are in agreement with the predictions of the Einstein-Stokes theory for diffusivity and viscosity. The ratio Dη/T is (2·23 ± 0·31) × 10−10 cm2 poise/s°K and it is reasonably constant within the whole range of viscosity and temperature investigated.Le coefficient de diffusion de l'ion cuivre(II) dans des solutions d'acide sulfurique contenant du glycérol d'une concentration de 0 à 10 M a été déterminé au moyen d'une electrode à disque tournante. La viscosité des solutions a également été mesurée. Les expériences furent effectuées à une témperature entre 18 et 40°C. Les résultats se rapprochent d'une façon satisfaisante des prédictions de la théorie d'Einstein-Stokes pour la diffusivité et la viscosité. Le rapport Dη/T est (2,23 ± 0,37) × 10−10 cm2poise/sec°K et reste assez constant dans tout le champ de la viscosité et de la témperature étudiés.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Electrochemical study of the diffusion of cupric ion in aqueous and aqueous-glycerol solutions containing sulphuric acid

The diffusion coefficient of cupric ion in sulphuric acid solutions containing glycerol from 0 to 10 M has been determined with the aid of the rotating disk electrode. The viscosity of the solutions has also been measured. Experiments covered a temperature range from 18 to 40°C. The experimental results are in agreement with the predictions of the Einstein-Stokes theory for diffusivity and viscosity. The ratio Dη/T is (2·23 ± 0·31) × 10−10 cm2 poise/s°K and it is reasonably constant within the whole range of viscosity and temperature investigated.Le coefficient de diffusion de l'ion cuivre(II) dans des solutions d'acide sulfurique contenant du glycérol d'une concentration de 0 à 10 M a été déterminé au moyen d'une electrode à disque tournante. La viscosité des solutions a également été mesurée. Les expériences furent effectuées à une témperature entre 18 et 40°C. Les résultats se rapprochent d'une façon satisfaisante des prédictions de la théorie d'Einstein-Stokes pour la diffusivité et la viscosité. Le rapport Dη/T est (2,23 ± 0,37) × 10−10 cm2poise/sec°K et reste assez constant dans tout le champ de la viscosité et de la témperature étudiés.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasFacultad de Ciencias Exacta

Estudio de las propiedades mecánicas de armaduras corroídas cuando se modifica la longitud de superficie corroída

En este trabajo se estudia el efecto de la corrosión sobre el comportamiento mecánico de la armadura cuando se corroen distintas longitudes de barra. Se han ensayado a tracción 72 barras corrugadas de acero B500SD (con altas propiedades de ductilidad) que previamente se han corroído aceleradamente, localizándose la corrosión en tres longitudes de barra diferentes. Los resultados muestran que se producen variaciones significativas en la curva tensión-deformación obtenida en los ensayos de tracción, incluso con grados de corrosión por debajo del 1%. Además, al aumentar la longitud de barra corroída, tanto la resistencia a tracción como el límite elástico, disminuyen