Application of the double optic probe technique to distorted tumbling bubbles in aqueous or organic liquid

The optic probe technique is widely used to investigate bubble reactors. To derive values of bubble local velocities and bubble local sizes, a specific signal treatment is usually applied under severe assumptions for bubble path and shape. However, in most industrial reactors, bubble motion is chaotic and no common shape can be assumed. In this work, the reliability of the signal treatment associated with the optic probe technique is examined for distorted and tumbling bubbles. A double-tip optic probe is settled in a glass tank and the rise of bubbles is filmed simultaneously. Several trains of bubbles are studied, interactions between bubbles being gradually increased. Referring to image analysis, several ways to derive mean bubble velocities from optic probe data have been compared. Crenels from front tipand rear tipra w signals are associated and individual bubble velocities are derived. Nevertheless, complete velocity distributions are difficult to obtain, as they depend on the choice of the time within which the bubble is searched on the second tip. Using a simpler approach it is shown that the most probable velocity, calculated through the raw signals inter-correlation, is a correct estimation of the average bubble velocity. Concerning bubble size, bubble chord distributions show too high values due to bubble distortion and deviation. A simplified estimation of bubble mean Sauter diameter, using the most reliable measurements only (i.e., local gas hold-up, local mean bubbling frequency, and most probable bubble velocity), was tested for highly distorted bubbles; this method was validated both in water and cyclohexane

Constraining Quasar and IGM Properties Through Bubble Detection in Redshifted 21-cm Maps

The infrared detection of a z>7 quasar has opened up a new window to directly probe the IGM during the epoch of reionization. In this paper we theoretically consider the possibility of detecting the ionized bubble around a z=8 quasar using targeted redshifted 21-cm observations with the GMRT. The apparent shape and size of the ionized bubble, as seen by a distant observer, depends on the parameters \dot{N}_{phs}/C, x_HI/C and \tau_Q where \dot{N}_{phs}, \tau_Q, x_HI and C are respectively the photon emission rate, age of the quasar, the neutral fraction and clumping factor of the IGM.Here we have analytically estimated the shape and size of a quasar's ionized bubble assuming an uniform IGM and ignoring other ionizing sources besides the quasar, and used this as a template for matched filter bubble search with the GMRT visibility data. We have assumed that \dot{N}_{phs} is known from the infrared spectrum and C from theoretical considerations, which gives us two free parameters x_HI and \tau_Q for bubble. Considering 1,000 hr of observation, we find that there is a reasonably large region of parameter space where a 3\sigma detection is possible. We also find that it will be possible to place lower limits on x_HI and \tau_Q with this observation. Deeper follow up observations can place upper limits on \tau_Q and x_HI. Value of C affect the estimation of x_HI but the estimation of \tau_Q remains unaffected.We have used a semi-numerical technique to simulate the apparent shape and size of quasar ionized bubbles considering the presence of other ionizing sources and inhomogeneities in the IGM. The presence of other sources increase the size of the quasar bubble, leading to underestimation of x_HI. Clustering of other ionizing sources around the quasar can produce severe distortions in bubble's shape. However, this does not severely affect parameter estimation in the bubbles that are large.Comment: 18 pages, 16 figures, 3 tables. Minor change in text. Accepted for publication in MNRA

On the reliability of an optical fibre probe in bubble column under industrial relevant operating conditions

When bubble columns are operated under industrial relevant conditions (high gas and liquid flow rates, large bubbles and vortices,. . .), local data, and especially bubble size values, are difficult to obtain. However, such data are essential for the comprehension of two-phase flow phenomena in order to design or to improve industrial installations. When high gas flow rates and organic liquids are used, intrusive optic probes are considered. This work investigates different ways to derive reliable local information on gas phase from double optic probe raw data. As far as possible, these results have been compared with global data, easier to measure in such conditions. Local gas hold-up, eG, and bubble frequency, fB, are easily obtained, but bubble velocity and bubble diameter determination is not obvious. For a better reliability, the final treatment that is proposed for velocity and size estimation is based on mean values only: the bubble velocity is considered as the most probable velocity ~v issued from raw signals inter-correlation function and the mean Sauter diameter is calculated through dSM ¼ 3~veG 2f B

First Observational Tests of Eternal Inflation: Analysis Methods and WMAP 7-Year Results

In the picture of eternal inflation, our observable universe resides inside a single bubble nucleated from an inflating false vacuum. Many of the theories giving rise to eternal inflation predict that we have causal access to collisions with other bubble universes, providing an opportunity to confront these theories with observation. We present the results from the first observational search for the effects of bubble collisions, using cosmic microwave background data from the WMAP satellite. Our search targets a generic set of properties associated with a bubble collision spacetime, which we describe in detail. We use a modular algorithm that is designed to avoid a posteriori selection effects, automatically picking out the most promising signals, performing a search for causal boundaries, and conducting a full Bayesian parameter estimation and model selection analysis. We outline each component of this algorithm, describing its response to simulated CMB skies with and without bubble collisions. Comparing the results for simulated bubble collisions to the results from an analysis of the WMAP 7-year data, we rule out bubble collisions over a range of parameter space. Our model selection results based on WMAP 7-year data do not warrant augmenting LCDM with bubble collisions. Data from the Planck satellite can be used to more definitively test the bubble collision hypothesis.Comment: Companion to arXiv:1012.1995. 41 pages, 23 figures. v2: replaced with version accepted by PRD. Significant extensions to the Bayesian pipeline to do the full-sky non-Gaussian source detection problem (previously restricted to patches). Note that this has changed the normalization of evidence values reported previously, as full-sky priors are now employed, but the conclusions remain unchange

A simple model of ultrasound propagation in a cavitating liquid. Part I: Theory, nonlinear attenuation and traveling wave generation

The bubbles involved in sonochemistry and other applications of cavitation oscillate inertially. A correct estimation of the wave attenuation in such bubbly media requires a realistic estimation of the power dissipated by the oscillation of each bubble, by thermal diffusion in the gas and viscous friction in the liquid. Both quantities and calculated numerically for a single inertial bubble driven at 20 kHz, and are found to be several orders of magnitude larger than the linear prediction. Viscous dissipation is found to be the predominant cause of energy loss for bubbles small enough. Then, the classical nonlinear Caflish equations describing the propagation of acoustic waves in a bubbly liquid are recast and simplified conveniently. The main harmonic part of the sound field is found to fulfill a nonlinear Helmholtz equation, where the imaginary part of the squared wave number is directly correlated with the energy lost by a single bubble. For low acoustic driving, linear theory is recovered, but for larger drivings, namely above the Blake threshold, the attenuation coefficient is found to be more than 3 orders of magnitude larger then the linear prediction. A huge attenuation of the wave is thus expected in regions where inertial bubbles are present, which is confirmed by numerical simulations of the nonlinear Helmholtz equation in a 1D standing wave configuration. The expected strong attenuation is not only observed but furthermore, the examination of the phase between the pressure field and its gradient clearly demonstrates that a traveling wave appears in the medium

State-dependent diffusion coefficients and free energies for nucleation processes from Bayesian trajectory analysis.

The rate of nucleation processes such as the freezing of a supercooled liquid or the condensation of supersaturated vapour is mainly determined by the height of the nucleation barrier and the diffusion coefficient for the motion across it. Here, we use a Bayesian inference algorithm for Markovian dynamics to extract simultaneously the free energy profile and the diffusion coefficient in the nucleation barrier region from short molecular dynamics trajectories. The specific example we study is the nucleation of vapour bubbles in liquid water under strongly negative pressures, for which we use the volume of the largest bubble as a reaction coordinate. Particular attention is paid to the effects of discretisation, the implementation of appropriate boundary conditions and the optimal selection of parameters. We find that the diffusivity is a linear function of the bubble volume over wide ranges of volumes and pressures, and is mainly determined by the viscosity of the liquid, as expected from the Rayleigh-Plesset theory for macroscopic bubble dynamics. The method is generally applicable to nucleation processes and yields important quantities for the estimation of nucleation rates in classical nucleation theory

Real-time diagnostics of gas/water assisted injection moulding using integrated ultrasonic sensors

YesAn ultrasound sensor system has been applied to the mould of both the water and gas assisted injection moulding processes. The mould has a cavity wall mounted pressure sensor and instrumentation to monitor the injection moulding machine. Two ultrasound sensors are used to monitor the arrival of the fluid (gas or water) bubble tip through the detection of reflected ultrasound energy from the fluid polymer boundary and the fluid bubble tip velocity through the polymer melt is estimated. The polymer contact with the cavity wall is observed through the reflected ultrasound energy from that boundary. A theoretically based estimation of the residual wall thickness is made using the ultrasound reflection from the fluid (gas or water) polymer boundary whilst the samples are still inside the mould and a good correlation with a physical measurement is observed