Fumio Kiyono

A Pore-Scale Numerical Simulation Method for Estimating the Permeability of Sand Sediment

A numerical method system to estimate the permeability of sand sediments, at a microscopic scale, was developed. Initially, 3D geometrical representations of the sand grains are reconstructed from a series of 2D X-ray CT scans of real sand grains. 2D cross-sectional slices of the grain outlines are combined together to produce 3D objects via spherical harmonics series expansions. Then, the reconstructed sand grains are packed randomly inside a cubic, microscopic, domain by a combination of a growth method and a simulated annealing method to achieve a predefined porosity. Finally, a single-phase water flow within the domain was simulated numerically, using the lattice Boltzmann method. The calculated permeability of these systems compares well with the values provided by conventional theoretical models. One of the contributions of this study is to show that it is possible to predict the permeability of sand sediments of variable porosities, using sand grains from CT images with changing size distributions and orientations.

Development of a New Method of Liquid CO2 Injection Into the Seawaters for the Ocean Sequestration

A new type of injection method of liquid CO2 into the seawaters via a Kenics-type static mixer for the ocean sequestration of CO2 has been developed. Flows of liquid CO2 and water will form a two-phase flow in a pipeline, and introduced to a static mixer, where the two-phase flow is mixed by the agitation effects of the mixing elements equipped in the mixer, and converted into various flow patterns. The following flow patterns were observed depending on the flow velocities; dispersed flow of liquid CO2 drops, flow of CO2 hydrate agglomerates, and flow of CO2 hydrate particles. The results indicate that several options for CO2 injection concerning the form of CO2 , size distribution of liquid CO2 drops, could be realized by using the present method. The choice of such options is essential to control the fate of the disposed CO2 and the consequent environmental impact. In this study, application of the present method to the disposal of liquid CO2 at the intermediate depths (500 ∼ 1500 m) is assumed. The formation of the liquid CO2 drops by the static mixer was studied experimentally, and the effect of the static mixer on the size distribution of the liquid CO2 drops was investigated. The mean size of the liquid CO2 drops were significantly reduced by using the static mixer, compared with the case without the mixer for a given flow velocity, and a sharper distribution of the drop size was obtained. Based on the experimental results, the ascending-dissolving fate of the liquid CO2 drops disposed of in the ocean at the intermediate depth was numerically simulated. The shaper distribution and smaller mean diameter of the liquid CO2 drops produced by the static mixer would results in the reduction of both the traveling distances and its dispersion of the disposed CO2 drops.Copyright

Development of a Formation Process of CO2 Hydrate Particles for Ocean Disposal of CO2

Publisher Summary Several ocean disposal scenarios of anthropogenic CO2 have been proposed to date. Among them, disposal process in the form of CO2 hydrate would be most favorable form the viewpoint of environmental impact caused by CO2. CO2 hydrate is a clathrate compound where a CO2 molecule is included in a cage-like structure formed by the hydrogen-bonded water molecules. In the disposal process, CO2 emitted from a concentrated source of CO2—such as thermal power plant—would be collected from the flue gas and converted into CO2 hydrate particles in a hydrate formation unit. Then CO2 hydrate crystal would be released to the ocean. Two-phase mixture of water and liquid CO2 will be supplied to the reactor and fluidized under a proper flow conditions. Small particles of CO2 hydrate will be supplied to the reactor as seed particles, and CO2 hydrate particles will be fluidized with the mixture of water and CO2. During the fluidization process, CO2 would be transferred from liquid CO2 phase to the hydrate phase via dissolution in the water phase, and the hydrate particles would grow. The hydrate particles of which the size is large enough for the ocean disposal would be removed from the reactor and disposed of in the ocean. The proper size of the disposed hydrate particles would be determined by considering the behavior of the hydrate particles in the ocean: descending rate and dissolution rate, which affect the environmental impact by the CO2 released form the disposed hydrate particles.

Separation Process of Hydrofluorocarbons (HFCs) by Clathrate Hydrate Formation

Publisher Summary Clathrate hydrate is an inclusion compound where a guest molecule is included in a cage-like structure formed by hydrogen-bonded water molecules. The hydrate formation conditions depend on the properties of the guest molecules such as size, hydrophilicity, and the intermolecular forces, and consequently, can vary under a wide range of pressure and temperature. A new gas separation process of HFCs (hydrofluorocarbons) from nitrogen by the formation of clathrate hydrates in the pores of a porous glass membrane was proposed. A gaseous mixture of an HFC and nitrogen was introduced to one side of the porous glass membrane (feed side), and pure water was introduced to the opposite side (permeate side). The temperature and pressure on the feed side was maintained such that only HFC hydrate was stable, while that of the permeate side was maintained outside of the hydrate formation region. Under such conditions, a thin hydrate film was formed at the interface of the gas mixture and water in the pores. The HFC was enriched in the hydrate phase because of the large difference in the hydrate formation tendency between the HFC and nitrogen, and the HFC-enriched gas permeated through the hydrate film to the permeate side. Thus, a continuous separation process could be achieved.

Dynamic Properties of the Pressure Exerted on the Material Surface by Water Jet Impingements

It is interesting to know dynamic properties of the water jet pressure acting on the surface of a cutting object in order to clarify the cutting mechanism. This pressure includes wide range of frequency components that vary from the pulsation of a plunger pump to the water hammer pressure caused by impingements of droplets. In such case the transducers’ characteristics affect the detected wave seriously, and source wave of the pressure differs from detected wave. To eliminate the transducers characteristics and obtain the original wave form, special techniques, so called the deconvolution method or the source wave analysis method, are necessary. This paper presents the method to obtain the source wave of impingement pressure of water jets and demonstrates how it works correctly. Pressures acting on the material surface were measured directly by making water jets to impinge upon the pressure sensor. After experiments, detected wave data were processed by the deconvolution method. In addition, relationship between characteristics of the impingement pressure of water jet and flow structure of water jet is examined by flash photography using pulsed laser light. As a result, it becomes clear that dynamic property of the impingement pressure is closely related to the flow structure of water jet.Copyright

Analyses of the Performances of the Oscillating Jet Nozzle driven by Piezo-electric Transducers.

An oscillating jet nozzle has been developed to improve the efficiency of water jet cutting. In this nozzle, several piezo-electric transducers attached to a vibration plate give high-frequency oscillation to inner high-pressure water. These transducers were driven by the electric circuit composed of a function generator, an amplifier and a matching box.Firstly, to evaluate the performances of this nozzle, the characteristics of electro-mechanical transformation and mechanical-acoustic transformation were analyzed. Equations which could estimate the vibration velocity, sound pressure and cutting speed were derived by simplified model of this nozzle.Secondly, photographic studies of oscillating jets and cutting experiments were done. These results were compared with analytic results qualitatively. Main results were as follows.1) In case that oscillation frequency was constant, wave length became longer according to the increase of the water jet velocity.2) Increase of the water jet velocity reduced the wave amplitude of oscillating jet under the constant electrical power.3) Mass loss increased with growing the electrical power which supplied to piezo-electic transducers, but there was a saturation point in electrical power-mass loss curve.4) In this study, by using oscillating jet the increment of mass loss was recognized from stand-off distance of 30 to 180.