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AbstractThis study reports the effects of the grid spacer with mixing vane (MV) on gas velocity for air single-phase flow and liquid film thickness for air-water two-phase annular flow in a 3 × 3 rod bundle channel. To investigate the effects of the shape of the spacers, three kinds of spacers were installed into the channel: spacer without MV (without MV), spacer with four MVs (4-MV30), and spacer with two MVs (2-MV30). The 4-MV30 and 2-MV30 had vanes that were inclined 30 deg from the vertical axis. Gas velocity was measured with a hot-wire anemometer and liquid film thickness was measured with the constant electric current method. From the gas velocity measurement, it was found that the irregularities in the velocity distribution became smaller toward downstream of the spacer. For the 2-MV30, the flow distribution was asymmetric and the flow was biased. From the liquid film thickness measurement, it was found that the liquid film thickness became thicker downstream of the spacer.

Abstract: At a gas–liquid interface, there are many unknown physical and chemical phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. It is very difficult to understand all these mechanisms in detail; therefore, modeling the gas–liquid interface is one of the key issues in interfacial phenomena of multiphase flows. In our previous study, we developed a new gas–liquid interfacial model based on thermodynamics and a mathematical approach. In that study, we derived a new equation of free energy based on the lattice gas model, including the influence of an electric double layer on the interface caused by contamination. Then, an interfacial jump condition at the gas–liquid interface treated by thermodynamics was derived on the basis of our interfacial model. In this study, we analytically discuss the interfacial interaction on the basis of the thermodynamic jump condition on the macroscopic scale. Finally, we reveal the force vector fields on the gas–liquid interface depending on an electric potential. The result implies that contamination at the interface is very important to interfacial interaction. [Copyright &y& Elsevier]

This paper reports on a new technique of measurements of microbubble position in three dimensions with high time-resolution. The technique is based on micro digital holographic particle tracking velocimetry. In this technique, an intensity profile is constructed from a holographic image of a microbubble where the profile results in showing two peaks. The distance between the two peaks appears to relate to the size of the microbubble’s diameter. The three-dimensional position of the bubble can be detected by the center of the two peaks and the center point of the bubble image focused by a digital hologram. We also theoretically obtained the intensity profile of a microbubble by considering a refraction of light on a bubble surface to a ring-shaped aperture model. The theoretically obtained distance between the two peaks is found to be in good agreement with the values obtained experimentally.

A gas-liquid interface involves complex physics along with unknown phenomena related to thermodynamics, electromagnetics, hydrodynamics, and heat and mass transfer. Each phenomenon has various characteristic time and space scales, which makes detailed understanding of the interfacial phenomena very complex. Therefore, modeling the gasliquid interface is a key issue for numerical research on multiphase flow. Currently, the continuum surface force (CSF) model is popular in modeling the gas-liquid interface in multiphase flow. However, the CSF model cannot treat the various chemical and physical phenomena at the gas-liquid interface because it is derived based only on mechanical energy balance and it assumes that the interface has no thickness. From certain experimental observations, bubble coalescence/repulsion was found to be related to a contamination at the interface.The present study developed a new gas-liquid interfacial model based on thermodynamics via a mathematical approach, assuming that the interface has a finite thickness like a thin fluid membrane. In particular, free energy, including an electrostatic potential due to the contamination at the interface, is derived based on a lattice gas model. Free energy is incorporated into the conventional Navier-Stokes equation as new terms using Chapman-Enskog expansion based on the multiscale concept. Using the Navier-Stokes equation with the free energy terms, we derived a new governing equation of fluid motion that characterizes mesoscopic scale phenomena. Finally, the new governing equation was qualitatively evaluated by simulating an interaction between two microbubbles in two dimensions while also accounting for electrostatic force.

AbstractPellet injection with a bent drift tube is considered as one of the flexible methods to have a variety of fueling locations and injection angles in fusion plasma. Since both pellet mass and velocity greatly affect the plasma properties, mass loss and velocity attenuation of the pellet in the drift tube should be evaluated properly. We focused on the impact of the pellet on the tube wall and numerically estimated the mass loss and the velocity attenuation.

The importance of cell mechanical properties is apparent in many physiological processes; measuring these properties can therefore provide insight into the behavior of cells and tissues in human disease. Here, we describe a method of evaluating cellular deformation of cells by using a cell compression microdevice. The method comprises two steps: 1) observation and evaluation of cell deformation behavior during compression using the microdevice and 2) theoretical calculation of cellular deformation. We constructed the microdevice by stacking two layers of self-adhesive polydimethylsiloxane on a glass plate. The first layer consisted of microchannels, a cell culture chamber, and a diaphragm on the chamber for applying pressure to cells; the second layer consisted of cell inlet ports and a pressure inlet port. The microdevice was made of transparent materials, which permitted in situ monitoring of cellular behavior by optical microscopy. The microdevice was designed to control the magnitude of the pressure applied to cells. We measured the cell compressive strain to evaluate the Young's modulus; the measured values ranged from 3.5 to 4.2 kPa. These results demonstrate that our microdevice is useful for measuring and calculating the mechanical properties of cells under strain. [ABSTRACT FROM AUTHOR]