Results 1 - 10 of 17
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[en] Tomography has been investigated to observe bubble behaviors in two-phase flows. A bubbly flow and an annular flow have been reconstructed by tomography methods such as an Algebraic Reconstruction Technique (ART) and a Multiplicative Algebraic Reconstruction Technique (MART). Computer synthesized phantom fields have been used to calculate asymmetric density distributions for limited cases of 3, 5 and 7 projection angles. As a result of comparison of two tomography methods, the MART method has shown a significant improvement in the reconstruction accuracy for analysis of the two-phase flows
[en] Bubble behaviors in two-phase flows have been analyzed by tomography methods such as an algebraic reconstruction technique (ART) and a multiplicative algebraic reconstruction technique (MART). Initially, a bubbly flow and an annular flow have been investigated by cross-sectional view using computer synthesized phantoms. Two tomography methods have been compared to obtain more accurate results of the two-phase flows. Then, reconstruction of three-dimensional density distributions of phantoms with two and three bubbles have been accomplished by the MART method which provided the better results for the two-dimensional reconstructions accurately to analyze the bubble behaviors in the two-phase flow
[en] Bubble behaviors in a circular tube have been analyzed numerically and experimentally by a three-dimensional tomography method, Initially, a multiplicative algebraic reconstruction technique (MART) which showed better results for previous studies of numerical simulations has been performed to confirm the accuracy of the three-dimensional reconstruction for the two-phase flow using a computer-synthesized phantom, Then, bubble behaviors have been investigated experimentally by the three-dimensional MART method using real projected data captured simultaneously by a laser and three CCD cameras for three angles of view, Also, the transient reconstructions have been attempted to analyze the real-time oxygen-bubble movements in water by the interval of 1/30 second
[en] In this study, we designed a reed valve pump using a piezoelectric device (PZT) as a power source and analyzed its performance. Numerical analysis and preliminary design were carried out in order to construct a pump chamber, and a valve port design was used so as to take advantage of the characteristics of a reed valve. The performance of the manufactured pump was investigated with glycerin solution, a working fluid. As expected, the flow rate of the pump increased with operating frequency as long as sufficient pressure relaxation could be given. From the measured results of the time resolved pressure, the maximum and minimum pressures were determined by the pressure relaxation. The investigation about the duty ratio of the square wave operation probed that the 50 % duty provided the maximum performance, and the duty ratio could be reduced at a high operating frequency without a performance reduction.
[en] Transient and asymmetric density distributions of butane flow have been investigated from laser image signals by developed three-dimensional digital speckle tomography. Moved signals of speckles have been captured by multiple CCD images in three angles of view simultaneously because the flows were asymmetric and transient. The signals of speckle movements between no flow and downward butane flow from a circular half opening have been calculated by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays fur density gradients. The three-dimensional density fields have been reconstructed from the fringe shift signal which is integrated from the deflection angle by a real-time multiplicative algebraic reconstruction technique (MART)
[en] In this study, mean streamline and Computational fluid dynamics (CFD) analyses were performed to investigate the performance of a small centrifugal steam compressor using a latent heat recovery technology. The results from both analysis methods showed good agreement. The compression ratio and efficiency of steam were found to be related with those of air by comparing the compression performances of both gases. Thus, the compression performance of steam could be predicted by the compression performance of air using the developed dimensionless parameters
[en] The characteristics of the supercritical fluids should be precisely investigated for the next generation nuclear power reactor, i.e., Super-critical water Cooled Reactor (SCR). There are few experiments for visual observation especially in forced convection, because of the difficulty of the experiment. In this study, the upward forced convection of supercritical carbon dioxide is visualized. Shadow-graph technique and Shrielen interferometry have been applied for measurement of density disturbances around pseudo-critical temperature. Large thermal plume are observed in high heat flux conditions. (author)
[en] The electrohydrodynamic (EHD) inkjet method is a printing technology using electricity. This technique allows for the printing of EML (Emission layer) materials, usually used for OLED devices, on a substrate. In this study, ejection experiments were performed with various solvents to verify which of them is properly ejected in the EHD method. The solvents employed were dielectric liquids with low viscosity and it was confirmed that among them two solvents, 1,2-Dichlorobenzene (DCB) and 1,2-Dichloroethane (DCE), produced the pulsating cone-Jet mode and stable cone-jet mode well. In addition, experiments were conducted to find out how the voltage and applied flux influence the ejection mode, in order to apply the result to the ejection control. It was found that the selected solvent was easily ejected and printed, due to the free surface charge and charge density determined by the dielectric constant. Finally, a patterning experiment was performed to verify proper printing.
[en] Electrolysis has been applied to many industrial fields because of the simple configuration and various usages. The bubble on the surface of electrodes is one of the most important factors that reduce the transport of electrons in the channel. In this study, the nucleation process of bubbles on electrodes against the time and the characteristics of bubble motion right after departure from the electrode were analyzed according to the Reynolds number of convective electrolytes. To verify the influence of the flow convection, the bubble behavior such as size and motion was analyzed by image processing. For an efficient configuration, the length of the electrode could be designed using empirical equations about the thickness of the bubble layer. Graphic abstract: .
[en] We propose a novel micro/nano-scale nozzle structure, featuring an interfacial line between the hydrophilic and the hydrophobic surfaces for a jetting system, such as an inkjet head or electrospray devices. This research will investigate the impact of the interfacial line on flow instability and momentum augmentation as the liquid meniscus moves across the line. The research methods used in this paper, in respect to micro-and nano-scale channels, are computational fluid dynamics (CFD) and non-equilibrium molecular dynamics (MD), respectively. With the growing interest in micro/ nano electromechanical systems (MEMS/NEMS), many studies have been conducted to develop an advanced micro/ nanofluidic system. However, until now, there have been few in-depth studies on passive flow control in micro and nano nozzles using the hydrophilic and hydrophobic surface characteristics. In this research, the sequential arrangement of hydrophilic and hydrophobic surfaces in the nozzle is presented along with an investigation into how flow instability and momentum augmentation are going to be applied to an efficient micro/nano jetting system. When a liquid meniscus arrives at the interfacial line between hydrophilic and hydrophobic surfaces, the meniscus shape changes from concave to convex and the fluid motion near the wall stops until the concave shape is fully converted. Because the momentum should be conserved, the lost momentum near the wall transfers to the center region, and therefore the liquid at the center region is accelerated as it crosses the line. If we use this nozzle structure and the augmentation of the momentum near the center, a tiny droplet can be easily generated