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We have investigated the effect of the surfactant Sodium Dodecyl Sulfate on the bubble growth and detachment processes in a bubble column system. A modified pendant drop model was employed to determine the dynamic surface tension. The dynamic surface tension approached the static surface tension value within a few seconds. A photographic technique and a laser-based electro-optical method were used to study the bubble size variation and the generation frequency, respectively. Parameters like bubble generation frequency, size, growth rate, and contact angle were found to be a strong function of surfactant concentration. Our results show that the addition of surfactant significantly reduces the bubble lifetime at the orifice. Such a decrease in the bubble lifetime has a direct impact on the bubble growth rate and departure size. Furthermore, bubble parameters vary with surfactant concentration only up to the critical micellar concentration. [ABSTRACT FROM AUTHOR]

Surface wettability plays an essential role in bubble nucleation. This paper investigates the phase transition behaviour of argon films placed on inhomogeneous wettability substrates using molecular dynamics simulations. The location of bubble nucleation and initial nucleation time is investigated to reflect the effect of hydrophobic area fraction of inhomogeneous wettability surfaces on bubble nucleation. The results show that the bubbles appear first on the hydrophobic part of the inhomogeneous wettability surface. The relationship between hydrophobic area fraction and initial nucleation time is nonlinear. The initial nucleation time first decreases and then increases as the area of the hydrophobic region increases. In addition, the bubble nucleation process is restricted when the hydrophobic occupation is relatively large on inhomogeneous wettability surfaces. At last, the mechanism of bubble nucleation on inhomogeneous wettability surfaces is discussed in combination with the restrictive relationship between heat absorption and solid–liquid interaction energy. The amount of heat absorption does not directly determine the bubble nucleation. Bubble nucleation can arise in the location with a lower surface energy barrier once the heat absorption can overcome the solid–liquid interaction energy. [ABSTRACT FROM AUTHOR]

Butanol is mainly produced by acetone-butanol-ethanol (A-B-E) fermentation. The higher costs associated with the separation of butanol from the A-B-E mixture has prohibited the large-scale production of butanol. The direct use of the intermediate product (A-B-E mixture) could be an economical pathway if utilized for clean combustion. The present investigation deals with the puffing and micro-explosion characteristics in the combustion of a single droplet comprising butanol/Jet A-1, A-B-E/Jet A-1 blends, and A-B-E. The complete sequence of processes leading to micro-explosion, i.e., onset of nucleation, growth of vapor bubble, and subsequent breakup of droplet, for various fuel blends has been analyzed from the high-speed images. It is witnessed that puffing plays a crucial role in enhancing the micro-explosion especially in droplets with 50/50 composition. The probability of microexplosion in droplets with A-B-E blends was found to be higher than that of butanol blends. Although the rate of bubble growth was almost similar for all butanol and A-B-E blends, the final bubble diameter before the droplet breakup was found to be higher for 50/50 blends than that of 30/70 blends. The occurrence of micro-explosion shortened the droplet lifetime, and this effect appeared to be stronger for droplets with 50/50 composition. Micro-explosion led to the ejection of both larger and smaller secondary droplets; however, puffing resulted in relatively smaller secondary droplets. Bubble growth and subsequent puffing/micro-explosion were also observed in the secondary droplets, which might play an important role in enhancing the atomization and, hence, combustion. [ABSTRACT FROM AUTHOR]

Bubble formation and growth play an important role in various processes and industries, where the dispersion of gas bubbles in a liquid medium occurs frequently. In this paper, the formation, growth, and detachment of gas bubbles produced from a submerged needle in water are numerically and experimentally investigated. The effect of injected gas properties on bubble characteristics, including bubble diameter, contact angle, and the frequency of bubble formation, is evaluated. In particular, the changes in bubble characteristics during the injection process are investigated for three different gases to evaluate the effect of density and surface tension on the bubble detachment criteria. The present numerical results show an acceptable agreement with experiments under different operating conditions. The results show that the increase in surface tension, and the decrease in gas density result in larger bubble sizes before detachment occurs. Moreover, the bubble generation frequency is found to strongly depend on the contact angle and the surface tension. [ABSTRACT FROM AUTHOR]

Some of the heavy oil reservoirs show high primary recovery and high flow rate under solution gas drive. The foamy oil theory has been proposed for the anomalous behavior. There have been numerous studies of diffusion-induced growth or collapse of bubbles in a fluid. However, there are some limits about them such as the determination of initial bubbles radius. Pointed to the problem that how to determine the initial bubble radius, this article proposes a new method base on the hydrodynamic equation, and then regards the bubble as a production well with source and sink theory based on the similarity between the bubbles concentration distribution and the pressure distribution of production well. According to the model established, the bubble growth by pressure and time is predicted, that is, how the amount and size of bubbles change during solution-gas drive is presented, which provided the guidance to determine the parameters of foamy oil due to bubbles change, such as foamy oil viscosity, compressibility, permeability, and so on. This model proved to be reasonable and correct by the agreement between the bubble concentration distribution and the pressure distribution during solution-gas drive. [ABSTRACT FROM PUBLISHER]

In this study, pool boiling heat transfer performance of de-ionized water on horizontal plates sintered with copper fiber of various geometries was experimentally investigated under atmospheric pressure. Copper fiber felt with different structural parameters was proposed to provide artificial nucleate sites to improve heat transfer performance. A high-speed camera was used to photograph bubble growth processes. Pool boiling curves were obtained. Effects of fiber felt porosity and fiber diameter on the onset of nucleate boiling (ONB) and boiling heat transfer coefficient were investigated. It was revealed that copper fiber felt surfaces can reduce wall superheat at boiling incipience and exhibit significant enhancement of heat transfer compared with smooth surface. The influence of porosity on heat transfer performance for metal fiber felts was more sensitive than fiber diameter. A bubble with an average diameter of less than 0.3 mm was defined as a small-sized bubble (SSB) from visualization photograph by high-speed camera, and pool boiling heat transfer performance was highly dependent on the percentage of small-sized bubbles (PSSB) to help illustrate enhancement mechanisms between bubble size distribution and boiling heat transfer performance. Smaller mean pore diameter can be achieved through decreasing either porosity or fiber diameter, as it allowed the fiber felt to create stronger capillary force to form bigger size bubble and lower PSSB to result in improved heat transfer coefficient. [ABSTRACT FROM PUBLISHER]

Microstructures of He ion-implanted pure Ag, pure V and polycrystalline V/Ag multilayers with individual layer thickness ranging from 1 nm to 50 nm were investigated by transmission electron microscopy (TEM). The bubbles in the Ag layer were faceted and larger than the non-faceted bubbles in the V layer under the same implantation conditions for both pure metals and multilayers. The substantially higher single defects surviving the spike phase and lower mobility of trapped He in bcc than those in fcc could account for this difference. For multilayers, the bubbles nucleate at interfaces but grow preferentially in Ag layers due to high mobility of trapped He in fcc Ag. In addition, the He concentration above which bubbles can be detected in defocused TEM images increases with decreasing layer thickness, from 0 for pure Ag to 4-5 at. % for 1 nm V/1 nm Ag multilayers. In contrast, the bubble size decreases with decreasing layer thickness, from approximately 4 nm in diameter in pure Ag to 1 nm in the 1 nm V/1 nm Ag multilayers. Elongated bubbles confined in the Ag layer by the V-Ag interfaces were observed in 1 nm multilayers. These observations show that bubble nucleation and growth can be suppressed to high He concentrations in nanoscale composites with interfaces that have high He solubility. [ABSTRACT FROM AUTHOR]

Bubble nucleation and growth are the key steps in polymer foam generation processes. The mechanical properties of foamed polymer are closely related to the size of bubbles created inside the material. Thus, it is necessary to study how to improve mechanical strength by producing extremely fine bubbles inside polymer resin. We developed a theoretical framework to help produce uniformly distributed microcellular bubbles and experimentally verified the theoretical analysis results using an injection molding machine modified to make microcellular foaming products. [ABSTRACT FROM AUTHOR]

We present an internally heated autoclave, modified in order to permit in situ studies at pressure up to 0.5 GPa and temperature up to 1000 °C. It is equipped with transparent sapphire windows, allowing the observation of the whole experiment along the horizontal axis. In the experimental cell, the sample is held between two thick transparent plates of sapphire or diamond, placed in the furnace cylinder. The experimental volume is about 0.01 cm 3 . Video records are made during the whole experiment. This tool is developed mainly to study the magmatic processes, as the working pressures and temperatures are appropriate for subvolcanic magma reservoirs. However, other applications are possible, such as the study of subsolidus phase equilibria as we have used well-known phase transitions, such as the system of AgI, to calibrate the apparatus with respect to pressure and temperature. The principle of the apparatus is detailed. Applications are presented, such as studies of melt inclusions at pressure and temperature and an in situ study of magma degassing through the investigation of nucleation and growth processes of gas bubbles in a silicate melt during decompression. [ABSTRACT FROM AUTHOR]