1,161 research outputs found
Acoustic bubble removal method
A method is described for removing bubbles from a liquid bath such as a bath of molten glass to be used for optical elements. Larger bubbles are first removed by applying acoustic energy resonant to a bath dimension to drive the larger bubbles toward a pressure well where the bubbles can coalesce and then be more easily removed. Thereafter, submillimeter bubbles are removed by applying acoustic energy of frequencies resonant to the small bubbles to oscillate them and thereby stir liquid immediately about the bubbles to facilitate their breakup and absorption into the liquid
Localization of Denaturation Bubbles in Random DNA Sequences
We study the thermodynamic and dynamic behaviors of twist-induced
denaturation bubbles in a long, stretched random sequence of DNA. The small
bubbles associated with weak twist are delocalized. Above a threshold torque,
the bubbles of several tens of bases or larger become preferentially localized
to \AT-rich segments. In the localized regime, the bubbles exhibit ``aging''
and move around sub-diffusively with continuously varying dynamic exponents.
These properties are derived using results of large-deviation theory together
with scaling arguments, and are verified by Monte-Carlo simulations.Comment: TeX file with postscript figure
Small bubbles formation and contribution to the overall gas holdup in large diameter columns of very high viscosity oil
A limited number of studies are available in literature on the small bubbles which create from gas-very high viscosity oils interaction and its contribution to the gas holdup in the system. The rate of small bubble formation has an important impact on heat and mass transfer in many chemical and industrial processes. The work presented in the current paper provides unique information on the formation of bubbles of millimetre diameter in high viscosity oil. A column of 290 mm diameter and Silicon oil of 330 Pa.s viscosity, were employed besides Electrical Capacitance Tomography and a high-resolution camera to investigate the characteristics of the small bubbles. Mechanism of bubble generation, effect of gas injection time and flowrate were studied. The average void fraction, total gas-liquid height, overall Probability Density Function (PDF) profile, small bubbles volume fractions and diameter were measured. Small bubbles generate from the eruption of large bubbles, at gas injection nozzles, coalescence of large bubbles, and at liquid bridges at transition to churn flow regime. Properties and concentration of the small bubbles are controlled by the location of the bubble generation, gas flowrate, and gas injection time. Small bubbles contribute by 6.6- 30% to the total gas holdup. Bubble diameter increased from 0.68 mm to 0.75 mm and decreased from 1.1 mm to 0.75 mm at the top and the bottom sections of the column respectively after 60 minof gas injection
Viscous instabilities in flowing foams: A Cellular Potts Model approach
The Cellular Potts Model (CPM) succesfully simulates drainage and shear in
foams. Here we use the CPM to investigate instabilities due to the flow of a
single large bubble in a dry, monodisperse two-dimensional flowing foam. As in
experiments in a Hele-Shaw cell, above a threshold velocity the large bubble
moves faster than the mean flow. Our simulations reproduce analytical and
experimental predictions for the velocity threshold and the relative velocity
of the large bubble, demonstrating the utility of the CPM in foam rheology
studies.Comment: 10 pages, 3 figures. Replaced with revised version accepted for
publication in JSTA
Is CHF triggered by the vapor recoil effect?
This paper deals with the triggering mechanism of the boiling crisis, a
transition from nucleate to film boiling. We observe the boiling crisis in pool
saturated boiling experimentally at nearly critical pressure to take advantage
of the slowness of the bubble growth and of the smallness of the Critical Heat
Flux (CHF) that defines the transition point. Such experiments require the
reduced gravity conditions. Close to the CHF, the slow growth of the individual
dry spots and their subsequent fusion on the transparent heater are observed
through the latter. As discussed in the paper, these observations are
consistent with numerical results obtained with the vapor recoil model of the
boiling crisis
Gas maldistribution in a fermenter stirred with multiple turbines
The study is focused on modeling of gas maldistribution of aerated liquid systems in a
multiple impeller bioreactor. The phenomenon may or may not depend on column design. The latter
case is dependent merely on bed fluid dynamics and could be treated by using the methodology of the
residence time distribution (RTD) theory. Accordingly, a specific methodology is proposed, as follows:
the fermenter has been modelled as a reactor network involving a combination of zones representing
basic ideal flow patterns. The methodology is based on the wide-spread experimental gas tracer
technique extended by a new systemic identification approach. The approach is based on a Mellinmodification
of the Laplace transform over the relevant equations. The method allows zero-time
solutions for identification analysis. Unlike the diffusion model approximation, the technique
considered allows exact approximation of the RTD curves with circulation. The proposed transfer
function represents adequately the bioreactor gas maldistribution thus allowing fast overview of the
studied reaction and prompt feed back control on the physical situation
Hysteresis and re-entrant melting of a self-organized system of classical particles confined in a parabolic trap
A self-organized system composed of classical particles confined in a
two-dimensional parabolic trap and interacting through a potential with a
short-range attractive part and long-range repulsive part is studied as
function of temperature. The influence of the competition between the
short-range attractive part of the inter-particle potential and its long-range
repulsive part on the melting temperature is studied. Different behaviors of
the melting temperature are found depending on the screening length ()
and the strength () of the attractive part of the inter-particle potential.
A re-entrant behavior and a thermal induced phase transition is observed in a
small region of ()-space. A structural hysteresis effect is observed
as a function of temperature and physically understood as due to the presence
of a potential barrier between different configurations of the system.Comment: 8 pages, 6 figure
Influence of positional correlations on the propagation of waves in a complex medium with polydisperse resonant scatterers
We present experimental results on a model system for studying wave
propagation in a complex medium exhibiting low frequency resonances. These
experiments enable us to investigate a fundamental question that is relevant
for many materials, such as metamaterials, where low-frequency scattering
resonances strongly influence the effective medium properties. This question
concerns the effect of correlations in the positions of the scatterers on the
coupling between their resonances, and hence on wave transport through the
medium. To examine this question experimentally, we measure the effective
medium wave number of acoustic waves in a sample made of bubbles embedded in an
elastic matrix over a frequency range that includes the resonance frequency of
the bubbles. The effective medium is highly dispersive, showing peaks in the
attenuation and the phase velocity as functions of the frequency, which cannot
be accurately described using the Independent Scattering Approximation (ISA).
This discrepancy may be explained by the effects of the positional correlations
of the scatterers, which we show to be dependent on the size of the scatterers.
We propose a self-consistent approach for taking this "polydisperse
correlation" into account and show that our model better describes the
experimental results than the ISA
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