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Bubble removal in viscoelastic solution is an important challenge in both industry production and laboratory experiments. However, no effective physical bubble removal technique in viscoelastic solutions has been reported until now. In this study, the ultrasonic vibration effect on bubble removal in viscoelastic solution (300ppm-CTAC/300ppm-NaSal viscoelastic solution) was firstly observed. The ultrasonic vibration can successfully remove bubbles whose diameter is ranging from 200 μm to 1mm, and from 300ppm CTAC/NaSal at 28°C through assembling bubbles to be a large size bubble cluster in our experiments. The detailed bubble-assembling process were observed and analyzed. It is pointed out that the bubble-assembling process was directly associated with the intensity of ultrasonic vibration and the distance between bubbles in the solutions. However, the detail mechanism of the bubble-assembling behavior is still unclear, which is worth of further observation.

In this study, in order to clarify the heat transfer characteristics of the subcooled boiling phenomena and to discuss on their mechanism, a non-empirical boiling and condensation model for numerical simulation has been adopted. This model consists of an improved phase-change model and a consideration of a relaxation time based on the quasithermal equilibrium hypothesis. The transient three-dimensional numerical simulations based on the MARS (Multiinterface Advection and Reconstruction Solver) with the non-empirical boiling and condensation model have been conducted for an isolated boiling bubble behavior in a subcooled pool. The subcooled bubble behaviors, such as the growth process of the nucleate bubble on the heating surface, the condensation process and the extinction behaviors after departing from the heating surface were investigated, respectively. In this paper, the bubble departing behavior from the heating surface was discussed in detail. The overall numerical results showed in very good agreement with the experimental results.

The liquid-column break problem is one of the well-known validation tests for the multiphase flow computations. However, a few experimental data are available until now regarding the liquid-column break problem. In the validation process, it is necessary to consider the differences of the boundary and initial conditions between both experiment and numerical simulation. In this study, we conducted the liquid-column break experiments and measured the position of the water-front and the gravity center of the water region by using a high-speed camera and an image analyzing software. These experimental results were compared with the numerical simulation results. The water front position is usually taken as a scaling measure to evaluate the accuracy of numerical method for multiphase flows. However, when the real sizes of the liquid column changed to double without changing the aspect ratio (height/width), the non-dimensional water front positions were changed. From this fact, it is considered that the position...

At a gas‐liquid interface, there are many physics and unknown phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. Therefore, a modeling of gas‐liquid interface is one of key issues of the numerical research on multiphase flow. In this study, assuming that the interface is a thin fluid‐membrane and has a finite thickness, we develop a new gas‐liquid interfacial model based on thermodynamics (Phase Field theory) via mathematical approach. In particular, we derive the equation of free energy based on the lattice gas model. In the derivation, the effect of the electric double layer caused by a contamination at the interface is considered. Moreover, we consider the importance of the contamination from the perspective of our experiment: microbubbly flow. In general, it is believed that the microbubble is hard to coalesce with each other unlike bubbles of millimeter size. However, we found lots of microbubble coalescence in the microbubbly flow. In the experiment, we report new findings regarding the microbubble coalescence by using a high speed camera, and try to elucidate the mechanism of the microbubble coalescence. Through our experiment and interfacial modeling, we consider the possible mechanism of bubble coalescence.

In this paper, the numerical simulations based on the MARS (Multi-interface Advection and Reconstruction Solver) with a phase-change model including the bubble growth and the condensation processes are performed. As the results, it was found that the numerical results for both bubble growth and condensation rates were very slow compared with the experimental results and the existing analytical model. In order to solve this discrepancy, the original model is improved by introducing the following models based on the quasi-thermal equilibrium state: (1) the improved phase-change model including the large density change between water and vapor; (2) a relaxation time model derived by considering the unsteady heat conduction. Resulting from the numerical simulation with the present improved model, the numerical results in both bubble growth and condensation processes show in good agreement with the experimental results and the existing analytical model.