Synergistic effects of initial volume and physical properties on instability and bubble formation in acoustically levitated droplets

PART I An understanding of the possible influence of supersaturated liquids upon the production and refining of petroleum is of industrial interest. Only limited information is available as to the influence of environment upon the duration of supersaturation for pure hydrocarbons and their mixtures. A number of measurements were made of the influence of strain upon the behavior of four mixtures of methane and n-decane at temperatures ranging from 70 [degrees] to 390[degrees] F. The mixtures exhibited equilibrium bubble-point pressures between 54 and 1048 pounds per square inch. The local strain was introduced by raising the temperature of a portion of the system above that of the remainder. The formation of bubbles in such systems appears to be randomly distributed in time and its rate is nearly directly proportional to the volume of the phase. The results indicate markedly greater tendency for the persistence of supersaturation than obtained in a pure hydrocarbon but the probability of formation of a bubble under a given condition of strain decreased with an increase in mole fraction methane. PART II An understanding of the influence of volume and surface effects upon the duration of supersaturation in hydrocarbon liquids is necessary to describe the behavior of liquids in a strained state. A very limited amount of information is available on the influence of surface and volume upon supersaturation in pure hydrocarbons. Preliminary information in this field was obtained using a mixture of methane and n-decane containing 0.2290 mole fraction methane at 220[degrees] F. The mixture exhibited an equilibrium bubble-point pressure at 220[degrees] F. of 949 pounds per square inch. These measurements were made in equipment in which the strain was introduced by raising the temperature of a portion of the system above that of the remainder. The volume and surface area of the liquid phase under strain were varied by the introduction of silica crystals. The degree of supersaturation which may be realized in such systems was found to be nearly directly proportional to the volume of the phase. The data were insufficient in number to establish the effect of surface area on bubble formation.

Hydrodynamic cavitation (HC) is a phenomenon that occurs when a liquid flows at a high velocity through a constricted space or over a sharp edge, causing the pressure to drop to vapor pressure and the formation of bubbles within the liquid. These bubbles then collapse violently, producing high pressures, shock waves and temperatures (hot spots) that can lead to chemical reactions. In summary, HC is the formation and collapse of bubbles or cavities within a liquid due to high velocity flow, which can produce intense physical and chemical effects. In hydraulic machinery it is connected with many negative effects such as erosion, pressure pulsations, vibrations and noise. However HC also has important applications in water treatment, where it can be used to disinfect water by disrupting the cell walls of microorganisms (cyanobacteria, bacteria). Several devices utilizing using HC or HC in combination with hydrogen peroxide or ozone will be presented. Nevertheless efficiency of HC only is limited. New principle of exploiting HC based on synergistic effect with cold plasma ignited within the vaporous region was recently invented by present authors’ team. This device features production of significant concentration of hydrogen peroxide, strong electric field and UV irradiation. Combined action of these phenomena leads to very strong disinfection effects that not only disinfect water from biological contamination but also degrades chemical pollution (residuals of pharmaceuticals, estrogenes, pesticides and other organic molecules).

The bubble formation at a submerged orifice in the process of aluminum foams produced by gas injection method is investigated. The experimental results show that the increase of the gas flow rate and the orifice diameter can lead to increasing of the bubble size. The large orifice can make the frequency of bubble formation decrease by slowing down the increase of the gas chamber pressure when the gas flow rate increases. The effect of the gas chamber volume on the bubble size can be ignored in the experiment when it expands from 1 to 125 cm3. A theoretical model of bubble formation, expansion, and detachment under constant flow conditions is established to predict the bubble size. The theoretical predictions for air-aluminum melt systems are consistent with the experimental results.

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.

Bubble formation on a sieve plate with multiple holes is a very complicated process. At low to intermediate gas flow rates, not all holes are actively bubbling all the time. Furthermore, the interval between bubbling events may be highly variable These phenomena are types of bubble formation transitions, and they involve both active hole location and event interruption. In this investigation, nonlinear analysis was applied to the experimental time series data obtained from light scattering, which was sensitive to active hole location. The correlation dimensions and the largest Lyapunov exponent were estimated from the delay coordinates. These findings, along with the result of the surrogate data testing suggest that active hole location transitions can be regarded as low dimensional, deterministic chaos. Effects of gas chamber volume below the sieve plate and elevated viscosity of the liquid phase upon both the transition frequency and the chaotic invariants were studied, it was found that either increased gas chamber volume or elevated liquid viscosity may lead to less frequent active hole location transitions.

Bubble formation from a free-standing tube in microgravity

Experimental study of air bubble formation from orifice plates submerged in water pools has been carried out. Air is forced through the orifice by supplying it to a chamber connected to the orifice plate. The chamber volume plays an important role in determining the bubble growth time as well as bubble size and shape at departure. The effect of chamber volume is generally correlated in term of a dimensionless parameter, capacitance number (Nc), which is proportional to the chamber volume and is inversely proportional to the square of the orifice diameter. To better understand and characterize this effect, an experimental study is performed using ten orifice plates of diameter ranging from 0.61 mm to 2.261 mm with six different chamber volumes between 12 cc and 59 cc with the corresponding capacitance numbers varying from 0.2 to 19. The shape and size of the bubble are captured using high speed videography. The orifice plate material is acrylic glass which has an equilibrium contact angle of 38° with pure water. It was observed that the value of critical capacitance number or Nc above which the bubble evolution is affected by the gas chamber volume, is around 0.85. The bubbles are more spherical in shape, and the growth time is significantly smaller. Also, at high capacitance number (Nc > 7), the air flow in the bubble is so high that the bubble departs with a sharp apex and has a large volume. Above Nc > 10, the chamber effects plateau and further increase in gas chamber volume does not alter bubble size and shape at departure.

Atomistic modeling shows that Cu–Nb and Cu–V interfaces contain high excess atomic volume due to constitutional vacancy concentrations of ∼5 at. % and ∼0.8 at. %., respectively. This finding is supported by experiments demonstrating that an approximately fivefold higher He concentration is required to observe He bubbles via through-focus transmission electron microscopy at Cu–Nb interfaces than in Cu–V interfaces. Interfaces with structures tailored to minimize precipitation and growth of He bubbles may be used to design damage-resistant composites for fusion reactors.

Gas was injected into a bath vertically upward through a nozzle, an orifice, or a lance nozzle. The frequency of bubble formation at the exit of these injection devices was determined by counting the number of bubbles per second from visual images recorded using a high-speed video camera. The measurements were carried out under the condition that the effect of the gas chamber volume on the bubble formation was negligible. An empirical correlation of the bubble frequency was proposed as a function of gas flow rate, inner diameter of the nozzles and orifices, and the physical properties of gas and liquid. This correlation could estimate measured values of the frequency of bubble formation even for a high gas flow rate within a scatter of ±30% regardless of the injection devices.

Modeling of bubble formation at a submerged orifice in a gas-fluidized bed

Jetting is a ubiquitous phenomenon that has significant applications in industries, which is often generated by the rupture of bubbles in the liquid phase. Here, we investigate the jetting dynamics of an acoustically levitated droplet during the drop-to-bubble transition by using high-speed imaging. Our results show that jetting occurs during bubble formation rather than during rupture. Both viscosity and surface tension are found to significantly influence the jetting process. Specifically, as viscosity increases, both the upward and downward jetting velocities decrease, while an increase in surface tension results in higher jetting velocities in both directions. Furthermore, finite element simulations of the ultrasonic field reveal that the downward-moving liquid experiences a stronger acoustic radiation force compared to the upward-moving liquid. During the movement of the jet, the downward jetting experiences a stronger suppression force than the upward jetting. This distinct force distribution results in a higher upward jetting velocity than downward jetting velocity. This study offers new insights into the interaction between an acoustic field and jetting dynamics, thereby providing a novel method for generating jets without cavitation.

Two bubbles in conjunct condition are often encountered in high‐viscosity liquids, but have received very little attention in the literature. The conjunct bubbles rise together with unchanged shapes and constant velocities, showing some unique properties compared to single bubbles. The current research built on the previous work of Cai et al.,[1] and extended the bubble size ratio (κ) to the range 1.0–1.2. The formation and motion characteristics of conjunct bubbles made by direct collision of two in‐line bubbles were investigated, including the effects of bubble volume, bubble size ratio, and liquid viscosity. Models for the conjunct bubbles and the single bubbles were provided for predicting the projected area diameters and the rising velocities respectively, and the predicted values closely agreed with the measurements in glycerol‐water solutions with Morton numbers in the range of 1.690–661.8. The dynamic forces on the conjunct bubbles were analyzed, and a succinct algorithm was proposed for calculating the drag forces on the conjunct bubbles and the interaction force between the two bubbles.

Baker, Warner, and Jenkins found that levitated droplets of Fe-0.8 pet C alloys exploded when decarburized at 1660°C, whereas during the present investigation, the drops remained intact during decarburization at temperatures above 1850°C. Therefore, the object of this work was to determine whether heterogeneous nucleation of CO bubbles at an iron-iron oxide interface could occur at 1900°K but could not occur at 2200°K. An equation was developed to calculate the nucleation rate of CO bubbles at an iron-iron oxide interface in iron at 1900°K containing 0.8 pct C and in iron at 2200°K containing 0.1 pct C. The results of the calculation showed that an iron-iron oxide interface could not serve as a site for CO bubble nucleation. Therefore, a new mechanism is postulated in which cavities swept into the levitated droplet from the surface serve as nuclei for CO bubble formation instead of nuclei formed at the iron-iron oxide interface.

The synergistic effect between imidazole reagents and kinetic hydrate inhibitors

Effects of helium on critical hydrogen concentration for bubble formation in molybdenum