This paper describes experimental research on two-phase flow of supercritical carbon dioxide (CO2) and water in porous media under sequestration conditions. We used a magnetic resonance imaging technique to directly visualize the distribution of supercritical CO2 injected into porous media containing water. In-situ water saturation distributions in a Berea sandstone core and a packed bed of glass beads were successfully visualized at conditions that simulate those at 700 - 1000-m depths in an aquifer. By applying a coreflood interpretation method to our saturation data, we could describe the local Darcy phase velocities and capillary dispersion rate as a function of saturation. Next, the effect of buoyancy on the displacement process and gravity-dominated pure counter-current flow is discussed by comparing the data obtained at two conditions that model the aquifers at depths of 700 m and 1000 m. We found that buoyancy largely controls the pure counter-current flow in permeable porous media for conditions at 700 and 1000-m depths.
We investigate the spectral reflectivity of photonic crystals assembled with silica spheres. The propagation of electromagnetic wave can be controlled by periodic structures known as photonic crystals. Therefore photonic crystals are anticipated for advanced control of thermal radiation beyond solid state properties. The close-packed photonic crystals well-defined thickness are rapidly made on a Si wafer by using self-assembly of colloidal silica spheres. We measure spectral reflectivities of the samples with an FT-IR (Fourier Transform - Infrared Spectroscopy). The spectral reflectivity is enhanced at specific wavelength designed with numerical analysis. The peak of spectral reflectivity shifts to shorter wavelength with increasing incident angle. The angular dependency of the spectral reflectivity can be roughly calculated by the modified Bragg's equation taking into account Snell's law of refraction. We show that the reflectivity in infrared range is well enhanced by using large photonic crystals assembled with silica micro-spheres.
High-frequency pulse heating of heaters in microactuators utilizing the rapid expansion of boiling bubbles causes a gradual increase in the temperature of the heater and the substrate material in the immediate vicinity of the heater, resulting in a loss of reproducibility of the boiling phenomena. In the present report, the maximum frequency at which the steady increase in heater temperature can be maintained within the allowable limit for the succession of pulse heating is obtained by numerical simulations based on the heat conduction from the heater to the adjacent materials in the system having an electrical insulation layer between the heater element and the silicon substrate. Calculations are carried out using a model in an axisymmetrical system for two different heating conditions, that is, transient heating by a single pulse and steady heating by the time-averaged power during repetition of pulses, instead of the direct calculation of the entire repetition process. The effects of heater size and pulse width on the allowable repetition frequency are examined over wide ranges of these parameters. The influence of the insulation layer on allowable repetition frequency is investigated by comparing the calculation results with those of the case of without the insulation layer. Approximate correlations for the allowable repetition frequency are also derived based on an analytical examination.
The laminar burning velocity of pre-mixed hydrogen-air mixtures was measured in a fan stirred combustion bomb. Unstretched laminar burning velocities and Markstein lengths were obtained at 0.10MPa for equivalence ratios of 0.4, 0.6, 0.8 and 1.0 using high speed flame imaging. The difficulties which arose whilst obtaining similar measurements at 0.25MPa and 0.50MPa are outlined. The turbulent burning velocity was measured at equivalence ratios of 0.4 and 0.8 from explosions carried out at 0.10MPa with turbulence intensities of 0.8 and 1.6m/s. Higher turbulent burning velocity ratios were observed for mixtures which yielded lower Markstein lengths in the laminar combustion experiments.