Combustion flows are widely used for the mass production of nanoparticles including fullerenes. Researches concerning with the fullerene formation in combustion flows are introduced and the experimental results are briefly shown in the present report. In the fullerene formation process in the combustion flow the temperature profiles and the chemical reactions of the intermediate chemical species are essential under the reduced pressure conditions. In order to consider the non-equilibrium phenomena in combustion flows the non-equilibrium molecular dynamics method can be applicable and the simulation results for the surface aggregation phenomena of the carbonic nanopraticles are also introduced briefly.

View full abstract

Entrained-flow biomass gasification is one of the most promising technologies for utilizing biomass as energy and chemical resources because of its high gasification rate (carbon conversion rate from biomass to gas), low GHG(greenhouse gas) emission and high controllability of synthesized gas compositions. These advantages are attributable to its unique gasification reaction of solid biomass entrained in gas of upstream, one of the typical examples of multiphase flow. However, basic gasification reactions, such as behavior of biomass in gas and time-dependence of gas compositions, are not clarified enough. In this report, simple and basic phenomena are qualitatively overviewed.

View full abstract

A general view of spray combustion is given in the present paper. Spray combustion systems are widely used in industry, but the detail is still under investigation. Atomization of fuel liquid, evaporation, mixing of fuel and air, and reaction are involved in the spray combustion, and these processes take place in turbulence and interaction each other. Examples of spray combustion and their combustion categories are given. The statistics of spray which is critical for the spray combustion is discussed. Locally-homogeneous-flow model and two phase-flow model are explained to give an insight of spray combustion. A modeling based on probability density function, which is not described in detail, is potential. Recent experimental results are also described.

View full abstract

Extraction of metal ion was studied by a countercurrent centrifugal extractor, in which oil and water were flowed countercurrently through the narrow gap between a rotated inner rotor and a static outer cylinder. Oil (dodecane) was dispersed finely by increasing the rotating speed of the inner rotor and flowed up against the downflow of water. The small drops of dispersed oil were sucked down by Taylor vortices accumulated on the inner-cylinder surface. Stable belt-shaped structures of the oil phase were observed at even intervals on the surface of the inner rotor. The extraction of Zn(II) with di-2-ethylhexylphosphoric acid dissolved in dodecane was examined. The extraction of Zn was promoted by the increase of oil hold-up and the improvement of oil dispersion, which were observed by increasing the rotating speed of the inner rotor and the flow rates of oil and water. The number of theoretical stages was evaluated as about 3 stages under the conditions that the rotating speed and the flow rates of oil and water were given as 1200 rpm and 17 ml/min, respectively. The multistage extraction was achievable successfully by the proposed centrifugal extractor with Taylor-Couette flow.

View full abstract

Flow measurement of spatio-temporal velocity field in a Taylor-Couette vortex flow (TVF) with a short annulus was investigated by using Ultrasonic Doppler velocity Profiler (UVP). These methods have significant advantages over conventional methods since it can obtain the instantaneous spatio-temporal information as a function of space and time even in the opaque liquid like solid-liquid multiphase fluids. Boundary effects with a short annulus of TVF called Ekman boundary layer are greatly related to the generation of the various modes in vortex structure. Parameters as an aspect ratio, Γ(=H/d) and radius ratio, η(=R₁/R₂) are important factors for flow bifurcation to these modes. Here, d is an annular gap width, H is a height of the test section, R₁ and R₂ are radii of the inner and outer cylinders respectively.
    In the present study, mean velocity profiles of the TVF with Γ=3 and η=0.667 are measured with the UVP. Instantaneous velocity profiles with oscillation in higher Reynolds region (Re=1140) are also measured and analyzed by using the UVP and a spectrum method. The characteristics of wavy vortex flow in the normal 2 and 4 cell modes are much different from each other. Particle behavior in TVF is much complicated. The limit cycle orbit, which has previously only been confirmed numerically in the multi-phased TVF were found experimentally. In the limit cycle, solid particles are gathered in a very limited orbit line. While this phenomenon is unique and does not occur in the general flow region, it could be useful for analyzing the anti-plugging characteristics in industrial rotating filter devices or bioreactor.

View full abstract

This paper demonstrates numerical simulations of single-phase and two-phase flow through complex geometry such as the packed bed and gas diffusion layer in packed bed by using of lattice Boltzmann method. In the simulations of the packed bed, Mass and heat transfer in the packed beds are explored computationally and pressure and temperature distributions are compared with existing experimental results. In the simulation of gas diffusion layer, the water infiltrations into GDL were performed and influence of porosity, fiber diameter, orientation degree of carbon fiber, contact angle of GDL and water inlet velocity on saturation and gas diffusion performance was examined.

View full abstract

In order to clarify the heat transfer characteristics of the subcooled pool boiling and its mechanism by numerical simulations, we are aiming for the establishment of a numerical boiling and condensation model in the subcooled pool boiling. In this paper, in order to verify the numerical boiling and condensation model, the bubble shape data (volume V, height H, width W and aspect ration H/W) were obtained from the results of visualization experiments of subcooled pool boiling by using ultrahigh speed video camera with microscope system. The bubble shape data were measured by using simple image analyses from the experimental results, and then compared them with the existing analytical equations.

View full abstract

First, experiments have been conducted on separation of ferromagnetic particles from water-ferromagnetic particles dispersion flow by a magnetic field gradient. The test section, in which the magnetic field gradient is applied, is 0.05 m in height and 0.5 m in length. The experimental conditions are 0.1 m/s for inlet velocity, 0.0001 for inlet particles volume fraction and 0.0 T to 0.5 T for magnetic field (in the magnetic pole piece). The ferromagnetic particles are cobalt particles with an average diameter (at the test section inlet) of 8.4 μm. Secondly, numerical calculations have been performed in simulating the experimental test section and experimental conditions. In the calculations, increase in the particle diameter by the aggregation of magnetized particles has been considered in order to get better agreement between calculated and experimental results. It has become clear from experimental results that the larger the magnetic field becomes the smaller the particles volume fraction at the test section exit becomes and the volume fraction at the exit is nearly zero for a magnetic field of 0.5 T. It has also become clear from calculation results that the larger the magnetic field becomes the larger the particles volume fraction at the bottom of test section (meaning the particles accumulation in this region) and the smaller the volume fraction at the test section exit becomes.

View full abstract

This paper investigates flow patterns encountered in two-phase swirling flow in a vertical pipe. Flows in the pipe are observed by using a high-speed video camera and the void fractions are calculated from the video images. Flows at various gas and liquid volumetric fluxes, J_G and J_L, are tested, i.e., 0.01 ≤ J_G ≤ 8 m/s and 0.10 ≤ J_L ≤ 0.80 m/s. When J_L is higher than a certain value, no bubbles exist in a swirling flow but a gas column forms due to the centrifugal force even at low J_G. The diameter of a gas column increases with J_G at a constant J_L. A tornado-shaped gas column forms at intermediate J_G. At high J_G, a liquid film including small bubbles and intermittent liquid slugs with many bubbles are observed. These flows are classified into four flow patterns based on the observations and the characteristics of void fraction. The statistical quantities of void fraction, i.e., the mean, standard deviation, skewness and kurtosis, are also computed. The validity of the flow pattern classification based on the statistical quantities has been confirmed.

View full abstract