Solid oxide fuel cell: Decade of progress, future perspectives and challenges

Physical principles and state-of-the-art of modeling of the pulsating heat pipe: A review

When a wetting liquid is displaced by air in a capillary tube, a wetting film develops between the tube wall and the air that is responsible for the snap-off mechanism of the gas phase. By dissolving a dye in the wetting phase it is possible to relate a measure of the absorbance in the capillary to the thickness of liquid films. These data could be used to compare with cutting edge numerical simulations of the dynamics of snap-off for which experimental and numerical data are lacking. Drainage experiments in constricted capillary tubes were performed where a dyed wetting liquid is displaced by air for varying flow rates. We developed an optical method to measure liquid film thicknesses that range from 3 to 1000μm. The optical measures are validated by comparison with both theory and direct numerical simulations. In a constricted capillary tube we observed, both experimentally and numerically, a phenomenon of snap-off coalescence events in the vicinity of the constriction that bring new insights into our understanding and modeling of two-phase flows. In addition, the good agreement between experiments and numerical simulations gives confidence to use the numerical method for more complex geometries in the future.

/pdf/measurements-and-simulation-of-liquid-films-during-drainage-15x3vtr3z8.pdf

Measurements and simulation of liquid films during drainage displacements and snap-off in constricted capillary tubes.

Flat plate pulsating heat pipes: A review on the thermohydraulic principles, thermal performances and open issues

Solid oxide fuel cells (SOFC) are promising, environmentally friendly energy sources. Many works are devoted to the study of materials, individual aspects of SOFC operation, and the development of devices based on them. However, there is no work covering the entire spectrum of SOFC concepts and designs. In the present review, an attempt is made to collect and structure all types of SOFC that exist today. Structural features of each type of SOFC have been described, and their advantages and disadvantages have been identified. A comparison of the designs showed that among the well-studied dual-chamber SOFC with oxygen-ion conducting electrolyte, the anode-supported design is the most suitable for operation at temperatures below 800 °C. Other SOFC types that are promising for low-temperature operation are SOFC with proton-conducting electrolyte and electrolyte-free fuel cells. However, these recently developed technologies are still far from commercialization and require further research and development.

/pdf/classification-of-solid-oxide-fuel-cells-3nipuxb6.pdf

Classification of Solid Oxide Fuel Cells

Liquid film formed between confined vapor bubble and tube wall in micro-scale two phase flow plays an important role in heat exchangers and chemical reactors, since local heat and mass transfer is effectively enhanced at the thin liquid film region (Taha and Cui, 2006). However, characteristics of the liquid film in micro-scale two phase flows are not fully understood, and thus designing two-phase flow systems still remains as a difficult task. It is reported that the thickness of the liquid film is one of the most important parameters for predicting two phase flow heat transfer in micro tubes, see Thome et al., 2004; Kenning et al., 2006; Qu and Mudawar, 2004; Saitoh et al., 2007. For example, in the three zone evaporation model proposed by Thome et al. (2004), initial liquid film thickness is one of the three unknown parameters which must be given from experimental studies. Many researches have been conducted to investigate the characteristics of liquid film both experimentally and theoretically. Taylor (1961) experimentally obtained mean liquid film thickness in a slug flow by measuring the difference between bubble velocity and mean velocity. Highly viscous fluids, i.e. glycerol, syrup-water mixture and lubricating oil, were used so that wide capillary number range could be covered. It was found that the ratio of bubble velocity to mean velocity approaches an asymptotic value of 0.55. This asymptotic value was re-evaluated by Cox (1964), which was reported to be 0.60. Schwartz et al. (1986) investigated the effect of bubble length on the liquid film thickness using the same method as Taylor (1961). It was reported that longer bubbles move faster than shorter ones. Bretherton (1961) proposed an analytical theory for the bubble profile and axial pressure drop across the bubble using lubrication equations. Assuming small capillary number, it is shown that the dimensionless liquid film thickness can be scaled by an exponential function of capillary number, Ca2/3. Liquid film thickness can also be measured from the temperature change of the channel wall under the assumption that the whole liquid film on the wall evaporates and the heat is wholly consumed by the evaporation of the liquid film. Cooper (1969) measured liquid film thickness with this method and investigated the bubble growth in nucleate pool boiling. Moriyama and Inoue (1996) measured liquid film thickness during a bubble expansion in a narrow gap. It was reported that liquid film thickness is affected by the viscous boundary layer in the liquid slug when acceleration becomes large. Their experimental data was correlated in terms of capillary number, Bond number and dimensionless boundary layer thickness. Heil (2001) numerically investigated the inertial

/pdf/liquid-film-thickness-in-micro-scale-two-phase-flow-48w3785aue.pdf

Liquid Film Thickness in Micro-Scale Two-Phase Flow

The high energy density of hydrogen, in addition to its convenience for transportation and infinite resource base, make it a promising energy carrier. Solid oxide fuel cells (SOFCs), in particular®which utilize the oxidation of hydrogen at high temperatures to generate electricity®have been studied widely because of their high efficiency and relatively low cost. However, the lack of a suitable mass production method currently precludes the commercialization of SOFCs. To address this, we herein evaluate tape-casting as a means to reduce the cost of SOFC mass production. A simple de-airing technique is used to simplify the production process and an electrolytesupported SOFC is produced without employing a buffer or functional layers. The rheological properties of green tape slurries are explored to improve tape completeness and electrolyte performance. Electrolyte conductivity is measured for a fabricated half-cell; the fine structural details are analyzed via scanning electron microscopy. As a result, a unit cell with an open-circuit voltage of 1.05V and an electric power density of 0.476Wcm12 at 800 °C was fabricated. ©2020 The Ceramic Society of Japan. All rights reserved.

Fabrication of electrolyte-supported solid oxide fuel cells using a tape casting process

Dip-coating can be used to obtain a relatively uniform film thickness on a substrate and is widely used in industry. The thickness of the liquid film is a very important parameter for the desired function. In this study, a laser focus displacement meter is used to measure the liquid film thickness. The thickness of liquid film coated on the withdrawing plate increases initially and then becomes constant as time passes. The liquid film of the constant film thickness zone is in good agreement with these two existing correlations. For the transition region where the liquid film thickness increases, a comparison of the profiles of dimensionless liquid film thickness shows that as the withdrawal speed increases, the profile of dimensionless liquid film thickness becomes more convex. However, at a capillary number higher than 0.1, the profiles are consistent within a certain range. It is confirmed that the profile of dimensionless liquid film thickness can be classified into a viscous dominant region and a surface tension dominant region, similar to the tendency of liquid film thickness in the constant film thickness region.

Measurement of liquid film thickness on moving plate during dip-coating process

3D printing using polyampholyte hydrogel with reversible behavior

Liquid film thicknesses of oscillating slug flows in a capillary tube

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