Increase In Bubble Volume Research Articles

Monodispersed Bubble Generation Using Hydrophobic Orifices: The Extended Tate's Law.

The use of submerged orifices for bubble generation is ubiquitous in industries with wettability known to influence the bubble departure diameter. In this study, we investigated bubble generation and departure from the orifices (0.3-2 mm) drilled on hydrophobic perfluoroalkoxy (PFA) tubes in water. By varying the gas inflow rate (33 to 200 mL/min), we found that the Sauter mean diameter closely matched those generated by hydrophilic quartz orifices. However, monodispersed bubbles were formed on the PFA tube compared to those on quartz with much wider size distributions. By examining the dynamic bubbling process, we confirmed its agreement with Tate's law, which was originally developed for quasi-steady conditions and emphasizes a balance between capillary and buoyancy forces. However, it should be noted that dynamic conditions lead to an increase in bubble volume compared to the quasi-steady condition despite following the same principle, which is explained by the continuous gas inflow when the bubble departs from the orifice at a necking stage. The above understandings enable generation of monodispersed bubbles under dynamic conditions, benefiting industries requiring precise control on bubble size, such as the bubble assisted wet etching and cleaning processes in semiconductor fabrication.

Hydrodynamics of Gas–Liquid Slug Flows in a Long In-Plane Spiral Shaped Milli-Reactor

An experimental investigation of gas–liquid Taylor flows in a millimetric in-plane spiral shaped reactor with various tube curvature ratios (52 < λ < 166) is reported. Thanks to the compactness of the reactor and the use of an ad hoc imaging system and processing, the axial evolution of bubble lengths and velocities could be recorded and extracted along the whole reactor length (~3 m). The experimental results showed a significant linear increase of bubble length and velocity with axial position. Very long, stable Taylor bubbles (LB/dit up to 40) and liquid slugs were generated, in particular due to the poor wettability of the surface and the important role it played in bubble formation. At identical inertial force (i.e., identical Reynolds number), a higher centrifugal force (i.e., lower tube curvature ratio) likely led to shorter Taylor bubble lengths while only slightly affecting the liquid slug lengths. The axial pressure drop could be estimated from the axial increase in bubble volume, and compared with the measured pressure drop and that predicted by the correlations from literatures. By considering both the friction and capillary pressure drops, it was observed that the predicted two-phase pressure drop was slightly dependent on the centrifugal force and that the capillary pressure drop, determined from the unit cell number, capillary number and static contact angle, was dominant.

Pattern of bubble evolution in liquids under repetitive pulsed power

Pulsed electric fields (PEFs) are employed in a newly developed food sterilization technology via repetitive electric pulses. The evolution of bubbles and the consequent electrical breakdown of the liquid treatment chamber are the main technical hurdles for industrial applications of this technology. The evolution pattern of the bubbles and the effect of pulse parameters on the bubbles under repetitive pulses are studied. Repetitive bipolar rectangular pulses (6–10 kV, 20–80 μs in duration, with a 50–200 Hz repetition rate) are applied to a gap (1 cm) containing sodium chloride solution (with a conductivity of 30 μS/cm). A high-precision bubble monitoring system is developed to recognize and count microbubbles with diameters greater than 50 μm. The pattern of the bubble evolution can be divided into 4 stages: the initial stage, developing stage, converging stage and discharging stage. The saturated time, number, area and average diameter of the bubbles are introduced as feature parameters to better characterize the bubble evolution, and the relevant time-varying curves for different pulse parameters are obtained based on experimental images. The experimental results show that a stronger electric field, a longer pulse duration and a higher repetition rate speed up the evolution of the bubbles. The growth of the bubbles depends more on the effect of continuous long pulses, and the electric field might be a deciding factor concerning the initiation of microbubbles, while the increase in bubble volume is mainly a result of the thermal effect of current.

Experimental observations of bubbling regimes at in-line multi-orifice bubblers

Bubble formation and bubbling regimes are well-characterized for the cases of single-orifice bubblers and industrial perforated plates. However, bubbling regimes from bubblers with multiple in-line orifices remain poorly described. Here, we investigate the dynamics of bubble formation at both single-orifice and multi-orifice bubblers, with one, three, five and nine in-line orifices in an 80-cm-long bubbler. We use high-speed videography and image processing to identify the effects of bubbler volume, and the number, spacing, and diameter of orifices, on bubbling regimes, bubble period, and bubble formation time. We identify five main bubbling regimes based on synchronization among orifices, and discuss the parameters affecting the bubbling dynamics. Decreasing bubbler volume leads to a decrease in bubble volume and bubble period, and enhances synchronization. Increasing orifice diameter leads to an increase in bubble volume and enhances synchronization. Spacing between orifices doesn't play an important role in determining the bubbling regime. Based on the experimental observations, we develop new bubbling regime maps constructed using the dimensionless Capacitance number and Weber number.

Flow around individual Taylor bubbles rising in a vertical column with water: Effect of gas expansion

This paper presents an experimental study to evaluate the effect of bubble expansion on the dynamics of an isolated Taylor bubble rising in a vertical column of water by inspection of the liquid flow around the bubble front. An increase in bubble volume results from gas decompression due to hydrostatic pressure drop as the bubble ascends through the liquid. Two reduced pressures (33.3 and 20.0kN/m2) and atmospheric pressure were maintained at the free liquid surface to provide a wide range of expansion rates.PIV coupled with a Shadowgraphy Technique was used to simultaneously obtain the flow field ahead the bubble and a well-defined gas–liquid interface.A very good correlation was found between predicted bubble volume expansion rates considering ideal gas behavior and the upward net volumetric liquid flow rate obtained by integration of the velocity profiles. Above the bubble nose, the liquid velocity at the centerline decreases rapidly from the value of the Taylor bubble velocity at the tip of the bubble. For distances greater than 0.5D, the liquid flow is undisturbed, with a significant axial velocity component for high bubble volume expansion rates due to the displacement of the liquid promoted by gas expansion. The Reynolds number calculated for the liquid flow was less than 2100 for all conditions used. While this suggests a laminar flow regime in the liquid, coefficient C from Nicklin’s equation obtained from data was equal to 1.4. The shapes of the velocity profiles obtained at the undisturbed liquid flow show that for high expansion rates they resemble the power-law velocity profile for turbulent flow. The bubble volume expansion rate modifies continuously during the Taylor bubble rise and a well-defined liquid velocity profile is never attained.

Influence of venous reservoir level on microbubbles in cardiopulmonary bypass

Patients undergoing open-heart surgery may, post-operatively, suffer from neurological disorders due to microbubbles created during extracorporeal circulation. Venous air is not completely removed in open hard-shell venous reservoirs. We, therefore, investigated the relationship between venous reservoir blood level and the amount of microbubbles in different commercially available reservoirs for comparison and determination of safe level. An in vitro flow loop with a heart-lung machine was used to compare three different reservoirs (Maquet, Sorin and Medtronic) at different levels. Microbubbles were measured after the reservoir and after the arterial filter with a GAMPT BCC200 detector. Microbubble count and volume were significantly higher with decreasing reservoir level (p = 0.014), but not as much as earlier studies have shown. Reducing the level from 1000 ml to 250 ml resulted in a 12.4% increase in bubble volume after the reservoir and 40.2% after the arterial filter. There was an almost linear trend towards more bubble volume with decreasing reservoir level (R2 = 0.98-0.83). There was a significant difference in microbubbles between the 3 tested reservoirs, up to 32.6%, p < 0.001 measured after the reservoir. Bubble volume from the Sorin reservoir was markedly lower after the arterial filter than from the Medtronic and Maquet reservoirs (up to 60 times p < 0.001). A lower reservoir level results in a moderate rise in microbubbles passing the reservoir. The minimum levels recommended by the manufacturers are safe. There was a significant difference in bubbles between the different reservoirs, especially after the arterial filter.

Observed bubble dynamics in oxygen or heliox breathing and altitude decompression sickness

altitude decompression sickness (DCS) is a common risk in aviation and has been extensively studied over the past two decades ([2][1], [3][2], [9][3]). Attempts have been made to find a correlation between ultrasonic bubble detection and symptoms of altitude DCS ([1][4], [8][5]). Models

Effect of nitrous oxide on gas bubble volume in the anterior chamber.

Nitrous oxide is often used as anesthesia during ophthalmic surgery that requires intraocular injection of sulfur hexafluoride gas or air. Ventilation with N2O is known to increase intraocular pressure in the presence of intraocular bubbles, but little is known about the effect of N2O on intraocular bubble volume. Accordingly, we have compared the effect of N2O:O2 ventilation (66% N2O, balance O2) with that of air ventilation and oxygen ventilation on intraocular bubbles of SF6 or air. Aspiration of anterior chamber gas after 180 minutes of N2O:O2 ventilation in cats showed an increase in bubble volume of more than threefold when the original intraocular bubble was SF6 and an increase of more than twofold when the original intraocular bubble was air. In contrast, during air ventilation, intraocular SF6 bubble volume increased by 50%, and intraocular air bubble volume increased by only 7.5%. During O2 ventilation, intraocular SF6 bubble volume increased by 35%, and intraocular air bubble volume decreased by 13%. Our results indicate that N2O is contraindicated when gas is injected into the closed eye.

Precipitation and trapping of hydrogen in copper

Abstract Copper samples containing dissolved hydrogen up to a few hundred atomic p.p.m. have been prepared by quenching from equilibrium at higher temperatures. Measurements of the annealing of the residual resistivity up to 150°C show that the hydrogen precipitates around room temperature and the precipitation is controlled by diffusion of the hydrogen. Microscope investigations confirm this result and show that the hydrogen precipitates as bubbles which form preferentially at grain boundaries and dislocations. The number of bubbles formed was typically 109 cm−3. Consideration of bubble growth leads to the conclusion that the increase in bubble volume during growth is due to plastic deformation of the lattice near the bubble and that the precipitation is a diffusion limited process, conclusions which are confirmed by the experimental evidence. A model for the trapping of the dissolved hydrogen at impurities is also discussed. It is shown that by quenching quickly to low enough temperatures the hydrogen is quenched as in a homogeneous solute phase.