Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. The difference in the refractive indices makes the visualization in the vicinity of the boundary of the multiple phases almost impossible. In this study, the refractive index of the aqueous phase has been equalized to that of the oil phase by adjusting the concentration of aqueous solution. Presently, the simultaneous visualization and the PIV measurement have been carried out about the both phases of the liquid-liquid two-phase flow. The measurement has been carried out for the flow field around and inside of two falling droplets interacting each other while they travel.

Liquid water behaviors in the porous gas diffusion layer used for PEMFCs were investigated by high-resolution soft X-ray radiography. We observed water evaporation process from the soaked carbon paper GDL and showed the gradual disappearance of liquid water with spatial inhomogeneity. The visualization of liquid water revealed that thin water film was retained in the GDL. This was also observed in the operating fuel cell. Our soft X-ray observation suggests that this thin water film formed in the carbon paper GDL possibly caused increase in the toutuosity of the GDL, resulting in deterioration of cell performance due to less mass transport in fuel cells.

A compact micro pulsating heat pipe was developed and tested to investigate thermal performance. Micro Flat Plate Pulsating Heat Pipe (FP-PHP) was fabricated using DRIE MEMS technique. A total of 10 parallel interconnected rectangular channels forming a meandering closed loop are engraved on the silicon wafer with a thickness of 1 mm. The top of the silicon wafer was covered by a transparent glass plate (#7740PyrexTM) with a thickness of 0.5 mm to allow visualization of the internal thermo-hydrodynamic behavior in the PHP. The overall FP-PHP has length of 50 mm, width of 15.5 mm, and thickness of 1.5 mm, respectively. The width and height of the engraved rectangular channel is 1 mm and 0.6 mm and the hydraulic diameter is 0.75 mm. The ethanol is used for working fluid. The results show that the FP-PHP without working fluid has thermal resistance of 17 °C/W and the FP-PHP with working fluid of filling ratio of 50% has thermal resistance of 4 °C/W. In other words, the FP-PHP has effective thermal conductivity of 650 W/mK which is about 1.6 times as much as of that of the Copper ( k eff = 400 W/mK). Therefore the developed FP-PHP can be used as compact high performance electronic cooling system.

We describe micro-scale mass transport plays a key role for R&D of the two realistic countermeasures of global warming, hydrogen fuel-cell energy system and CO 2 capture and sequestration (CCS). Understanding of the phenomena based on in-situ measurements leads to the implementation and practical use of these systems. Water inside the fuel cells plays a key role for both cell performance and durability. We have been developing magnetic resonance imaging (MRI) and also soft X ray techniques as in-situ visualization methods for water transport in operational fuel cells. MRI visualization of water content in membrane achieved high spatial resolution, 5 μm, to obtain fundamental insights on water transport process in membrane of 50 μm thickness. Soft X ray has been firstly introduced to measure water transport phenomenon in gas diffusion layer. On the other hand, we clarified CO 2 distribution and its behavior by micro-focus X-ray CT and LBM simulation for CCS.

A comprehensive analysis of heat distribution and thermal mixing in steady laminar natural convective flow in discretely heated square cavities has been carried out via Bejan’s heatlines. Heatlines are analogous to streamlines and heat energy flow may be visualized by heatlines similar to streamlines which display fluid flow. The trajectories of heatlines indicate direction and magnitude of heat flow and zones of high heat transfer. The heatline approach is implemented to study heat flow in the following three different square cavities which are filled with water ( Pr = 7): (1) uniformly heated bottom wall (2) distributed heating with heat sources present on central portions of the walls and (3) multiple heat sources on the walls of the cavity. Top wall is maintained adiabatic in all the cases. Galerkin finite element method with penalty parameter has been used to solve non-linear coupled partial differential equations for flow and temperature fields over a range of Rayleigh numbers ( Ra = 10 3 –10 5 ). The Galerkin method is further employed to solve the Poisson equation for streamfunctions and heatfunctions. Finite discontinuity exists at the junction of hot and cold walls leading to mathematical singularity. Solution of heatfunction for such type of situation demands implementation of non-homogeneous Dirichlet conditions. Heatlines illustrate that in uniformly heated bottom wall case, the heat from the bottom wall is not adequately distributed to the lower portion of side walls which leads to low temperature in those regions (case 1). In order to improve the heat distribution, the uniform heat sources is divided into three parts and are applied along the central regimes of the walls (case 2). It is observed that, heat distribution and thermal mixing in the cavity is significantly enhanced. However, the lower corner portions are still retained cold. In case 3, multiple heat sources are placed along the walls of the cavity along with heat sources at lower corner regions of the cavity. Heatlines indicate that, the temperature at the core is reduced compared to case 2, but uniform heat distribution results in uniformity of temperature across large area of cavity.

For studying the designs and running operations of an extractor which uses Taylor-Couette vortex flow, we focused on a metal extraction system as one of the extraction models of heat generating nuclides and observed the flow patterns of dispersed phase by dyeing the phase in the extractor, and we investigated the effects of hydrophobic coating applied to the inner cylinder surface on the flow characteristics. Moreover, for the quantitative measurement and analysis of the flow field, we evaluated the applicability of Ultrasonic Velocity Profiler (UVP) to flow field measurement. Thorough these visualization methods of dispersed phase in a centrifugal extractor using Taylor-Couette vortex flow, we examined the relation between flow field and extraction characteristics of the extractor.

Water management is very important in the development of the PEFC with high performance and high reliability. We found that the moisturizing effect in the straight-type channel is marked as compared with the serpentine-type channels, and the draining performance in the serpentine-type channel is better than that in the straight-type channel. Then, we have developed the movable rib which can change the position of the rib manually. Experimental study shows that the movable rib can control water behavior and can improve the cell performance.