Search results for "BUBBLE"

Porous structure of fibre networks formed by a foaming process: a comparative study of different characterization techniques

2016

Recent developments in making fibre materials using the foam-forming technology have raised a need to characterize the porous structure at low material density. In order to find an effective choice among all structure-characterization methods, both two-dimensional and three-dimensional techniques were used to explore the porous structure of foam-formed samples made with two different types of cellulose fibre. These techniques included X-ray microtomography, scanning electron microscopy, light microscopy, direct surface imaging using a CCD camera and mercury intrusion porosimetry. The mean pore radius for a varying type of fibre and for varying foam properties was described similarly by all …

A new method in investigations of bubble cluster shapes in two-phase flow

1991

Abstract In this paper a new probabilistic method is used to analyse the distribution of air bubbles in two-phase flow. So far, the method has been applied in astronomy and cosmology to investigate the distribution of galaxies. The basic idea is presented and the method applied to the photographed population of air bubbles in a liquid. The method allows the homogeneity of the flow to be evaluated qualitatively and quantitatively.

Argon bubble flow in liquid gallium in external magnetic field

2020

Annihilation Characteristics of Confined 2D Positronium

2012

The 2D Positronium (2D Ps) atom confined in the 2D cave has been considered and its properties were compared with the 3D Positronium located in the infinity square well potential. Basing on the solution of Schrödinger equation for the 2D hydrogen atom the wave function of the 2D Ps was given. It allows us to calculate, for instance the angular correlation of the annihilation radiation (ACAR) of such a system. It was shown that the ACAR is much broad than ACAR for the 3D Ps and that for the Ps in the bubble model.

Electroweak baryogenesis at high bubble wall velocities

2020

It is widely believed that electroweak baryogenesis should be suppressed in strong phase transitions with fast-moving bubble walls, but this effect has never been quantitatively studied. We rederive fluid equations describing transport of particle asymmetries near the bubble wall without making the small-wall-velocity approximation. We show that the suppression of the baryon asymmetry is a smooth function of the wall speed and that there is no special behavior when crossing the sound speed barrier. Electroweak baryogenesis can thus be efficient also with strong detonations, generically associated with models with observably large gravitational waves. We also make a systematic and critical c…

Comparison between adaptive and uniform discontinuous Galerkin simulations in dry 2D bubble experiments

2013

Accepted by the Journal of Computational Physics Adaptive mesh refinement generally aims to increase computational efficiency without compromising the accuracy of the numerical solution. However it is an open question in which regions the spatial resolution can actually be coarsened without affecting the accuracy of the result. This question is investigated for a specific example of dry atmospheric convection, namely the simulation of warm air bubbles. For this purpose a novel numerical model is developed that is tailored towards this specific application. The compressible Euler equations are solved with a Discontinuous Galerkin method. Time integration is done with an IMEXmethod and the dy…

Periodic volcanic degassing behavior: The Mount Etna example

2013

[1] In contrast to the seismic and infrasonic energy released from quiescent and erupting volcanoes, which have long been known to manifest episodes of highly periodic behavior, the spectral properties of volcanic gas flux time series remain poorly constrained, due to a previous lack of hightemporal resolution gas-sensing techniques. Here we report on SO2 flux measurements, performed on Mount Etna with a novel UV imaging technique of unprecedented sampling frequency (0.5Hz), which reveal, for the first time, a rapid periodic structure in degassing from this target. These gas flux modulations have considerable temporal variability in their characteristics and involve two period bands: 40–250…

A NOVEL TECHNIQUE FOR MEASURING LOCAL BUBBLE SIZE DISTRIBUTION

2009

A novel experimental technique for measuring the local gas hold-up and the statistical distribution of local bubble size, is proposed. The technique is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available in PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and a band-pass optical filter is placed in front of the camera optics, in order to allow only fluoresced light to reach the camera CCD. In this way bubbles intercepted by the laser sheet are clearly identified thanks to the neat shade resulting in the images. This allows excluding from subsequent analysis all bubbles visible in the images but not…

Actinides in the Source of Cosmic Rays and the Present Interstellar Medium

2003

The abundances of the actinide elements in the cosmic rays can provide critical constraints on the major sites of their acceleration. Using recent calculations of the r-process yields in core collapse supernovae, we have determined the actinide abundances averaged over various assumed time intervals for their supernova generation and their cosmic-ray acceleration. Using standard Galactic chemical evolution models, we have also determined the expected actinide abundances in the present interstellar medium. From these two components, we have calculated the U/Th and other actinide abundances expected in the supernova-active cores of superbubbles, as a function of their ages and mean metallicit…

Mass transfer and hydrodynamic characteristics of unbaffled stirred bio-reactors: Influence of impeller design

2014

Abstract Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of processes where the presence of baffles is undesirable for some reason. For instance, in the case of shear sensitive cell cultivation (e.g. human cells), unbaffled tanks have been recently found to be able to provide sufficient mass transfer through the free surface vortex. As a consequence the need for bubble formation and subsequent bursting, along with relevant cells damage, is conveniently avoided. In this work the influence of impeller geometry on mass transfer performance and power demand of an unbaffled stirred vessel operating both in sub-critical conditions (t…