Liquid Channel Research Articles

Fabrication and Evaluation of Catalyst Layers in Polymer Electrolyte Fuel Cells: A Comparison of Decal and Inkjet Printing Techniques

In polymer electrolyte fuel cells (PEFCs), an enhancement of oxygen transport with excess water removal in membrane electrode assemblies can lead to better cell performance especially in high current density operation. Controlling porous structure in the catalyst layers is of great concern, satisfying these demands as well as achieving less precious catalyst loading and reduction of overpotential that are necessitated for automobile application of PEFCs. Depositing and engineering the catalyst layers have been gathering much attention intensively in these two decades [1-2]. Porous electrodes in PEFCs are generally fabricated by either coating or spraying the electrode slurry on substrate materials. Mixing, coating and drying processes of the slurry inherently affect the structural formation of the porous electrode and thus cell performance [3].In this study, we focused our attention on the inkjet printing technique as a versatile method to control catalyst layer structure. Catalyst layers (CL) with micro-grooves, which potentially provide liquid water channels in the electrodes, were fabricated by adjusting an electrode slurry injectable from a single capillary nozzle in a printing device (Fig.1). Catalyst layers made by a decal transfer technique were also prepared for comparison. The catalyst layers prepared by each method were controlled to gain the same amount of contents, i.e. platinum, ionomer and carbon, within 5% variation.Porous structure and cell polarization of each catalyst layer were examined. A two-stage ion-beam method using ion milling and focused ion beam (FIB) [4] was applied to analyze the spatial distribution of both ionomer and pore in the catalyst layers as shown in Fig.1. In this technique, a relatively wide cross-section of the CL was firstly formed by a broad ion beam and then, the ionomer impregnated in the CL was removed selectively by a focused ion beam. It was revealed that the electrode thickness was affected by fabrication methods, presumably due to mixing and coating processes. Cell performance shows its variation, depending on fabrication methods and this suggests an optimized electrode structure for further cell performance improvements. Acknowledgements This work was supported by JSPS KAKENHI Grant Number 18H01383.

Liquidity-Driven Cross-Market Linkages between Securitized REITs and Stock Markets

This study examines the cross-market linkages between public real estate investment trusts (REITs) and the stock market based on multiple return and liquidity channels. We measure cross-market linkages using the multivariate generalized autoregressive conditional heteroskedasticity model (GARCH-BEKK model) with daily U.S. data from 1998 to 2015 at both market and sector level. The results suggest that U.S. REITs and the Dow Jones Industrial Index are weakly linked in returns but strongly linked in liquidities. The two additional cross-characteristic linkages, REIT return and stock market liquidity, as well as REIT liquidity and stock market return, are found to be highly significant. Our findings show that liquidity plays a critical role in determining the linkages between REITs and the stock market. The paper translates these linkages into effective hedging strategies at both the market and sectoral levels.

Scale Effects in Nanoscale Heat Transfer for Fourier's Law in a Dissimilar Molecular Interface.

The dependence of the heat transfer of a nanoscopic liquid channel residing at the solid–liquid interface is traditionally ascribed to the temperature jump, interfacial thermal resistance, wettability, and heat flux. Other contributions stemming from the channel width dependence such as the boundary position are typically ignored. Here, we conducted nonequilibrium molecular dynamics simulations to better understand the relation between channel width and boundary positions located at the solid–liquid interface. The system under investigation is a simple liquid confined between the solid from nanochannels of different sizes (3.27–7.35 nm). In this investigation, the existence of the correlation between the boundary position and the channel width is observed, which follows an exponential function. The thermal conductivity of the boundary positions is compared with the experimental value and Green–Kubo prediction to verify the actual boundary position. Atomistic simulation reveals that the solid–liquid boundary position, which matches the experimental value of thermal conductivity, varies with the channel width because of the intermolecular force and the phonon mismatch of the solid and the liquid.

Characterization of mesoscale inhomogeneity in nonwovens and its relevance in the filtration of fine mists

Structural properties in nonwoven materials, such as porosity and layer thickness, are typically spatially distributed on a micro- and mesoscale. The mesoscale inhomogeneity is visually perceived, inter alia, as the cloudiness of the nonwoven fabric or as inclusions in the bulk material. Differential box counting, which is a fractal based image analysis method, was used to assess the inhomogeneity of several wet laid nonwoven glass fiber filter media. It has been shown that the subjectively perceived extent of media inhomogeneity strongly correlates with the lacunarity of the analyzed image.The analyzed media were then tested in different configurations for their operating behavior in the filtration of oil mist. The inhomogeneity of a medium significantly affected the formation of liquid channels in the medium, more specifically the inhomogeneity of the media layer on the filter upstream side. As most droplets are deposited on the filter upstream side, liquid likely accumulates in regions of finer pore structure in the foremost media layer. Distinct oil channels that transport the coalesced liquid to the filter rear side subsequently form behind these regions. Homogeneous media that lack such regions show a depth-filter like increase of Δp before the formation of channels, i.e. the Δp curve shows an increasing gradient with filter loading, which then changes into a linear increase of Δp. When filtering at low velocities, the liquid distribution inside the media drastically changed from distinct channels to a conically tapering form towards the filter rear for a homogeneous medium and a system of many interconnected channels in an inhomogeneous medium.

Hydrate Plugging and Flow Remediation during CO2 Injection in Sediments

Successful geological sequestration of carbon depends strongly on reservoir seal integrity and storage capacity, including CO2 injection efficiency. Formation of solid hydrates in the near-wellbore area during CO2 injection can cause permeability impairment and, eventually, injectivity loss. In this study, flow remediation in hydrate-plugged sandstone was assessed as function of hydrate morphology and saturation. CO2 and CH4 hydrates formed consistently at elevated pressures and low temperatures, reflecting gas-invaded zones containing residual brine near the injection well. Flow remediation by methanol injection benefited from miscibility with water; the methanol solution contacted and dissociated CO2 hydrates via liquid water channels. Injection of N2 gas did not result in flow remediation of non-porous CO2 and CH4 hydrates, likely due to insufficient gas permeability. In contrast, N2 as a thermodynamic inhibitor dissociated porous CH4 hydrates at lower hydrate saturations (<0.48 frac.). Core-scale thermal stimulation proved to be the most efficient remediation method for near-zero permeability conditions. However, once thermal stimulation ended and pure CO2 injection recommenced at hydrate-forming conditions, secondary hydrate formation occurred aggressively due to the memory effect. Field-specific remediation methods must be included in the well design to avoid key operational challenges during carbon injection and storage.

What’s wrong with Pittsburgh? Delegated investors and liquidity concentration

What makes an asset institutional quality? This paper proposes that one reason is the existing concentration of delegated investors in a market through a liquidity channel. Consistent with this intuition, it documents differences in investor composition across US cities and shows that delegated investors concentrate their investments in cities with higher turnover. It then estimates a search model showing how heterogeneity in liquidity preferences makes some markets more liquid, even when assets have identical cash flows. The paper provides evidence for clientele equilibria arising in frictional asset markets and suggests that a liquidity channel may explain divergent paths in city development.

Modifications and Improvements to the Collector Metal Method Using an mhd Pump for Recovering Platinum from Used Car Catalysts

Today recovery of platinum from used auto catalysts has become a necessity due to great demand for this catalytic metal. There are many methods of recovering platinum from used catalysts on the market, one of them is the original collector metal method using the magneto-hydrodynamic (mhd) pump. This method is based on the continuous flow of the collector metal (lead) in the channel of the device, which can be obtained by using the mhd pump at the device operating temperature of 673 K. Proper selection of process parameters such as power frequency (25–100 Hz), inductor current density (20 A, 40 A, 60 A), gaps between the inductor and the liquid metal channel (2,4,8), flow velocity, secondary voltage (19 V, 40 V, 60 V) ensures proper efficiency of the device. Some parameters were selected on the basis of numerical simulations, others were experimentally verified—the tests were carried out for different washing out times (600 s to 3600 s), and different secondary voltage and inductor supply frequency (25 Hz to 45 Hz). Platinum washing out efficiency of up to 98% was obtained with a relatively short washing out time and low values of secondary voltage and inductor frequency. To improve the efficiency of the process, the thermal efficiency of the device was increased by 8% by insulating the cover of the device. Further modifications to the process include changing the collector metal—preliminary studies show that the addition of lithium increases the extraction of platinum from thin catalytic layers as a result of reduced surface tension of the extraction liquid. The preliminary results of the PbLi alloy spread on platinum coated surface seem to be very promising.

Semi-solid compression of nano/micro-particle reinforced Al-Cu composites: An in situ synchrotron tomographic study

Four-dimensional fast synchrotron X-ray tomography has been used to investigate the semi-solid deformation of nano- and micro-particle reinforced aluminum-copper composites (Al-10 wt% Cu alloy with ~1.0 wt% Al2O3 nano and ~1.0 wt% Al2O3 micro particles). Quantitative image analysis of the semi-solid deformation behavior of three alloys (base, nano- and micro-particle reinforced) revealed the influence of the particulate size on both microstructural formation and dominant deformation mechanisms. The results showed that initial void closure and incubation period were present in the particle-free and nano-particle reinforced Al-Cu composite during semi-solid compression, while the micro-particle reinforced alloy only showed continual void growth and coalescence into cracks. The results suggest that the nano-particle reinforced composite has the best hot-tearing resistance amongst the three alloys. Improved hot-tear performance with nano-particulate reinforcement was attributed to the small liquid channel thickness, fine grain size which alters the distribution/morphology of the liquid channels, more viscous inter-dendritic liquid, and fewer initial voids.

Trapping of swimming microalgae in foam.

Massive foam formation in aquatic environments is a seasonal event that has a significant impact on the stability of marine ecosystems. Liquid foams are known to filter passive solid particles, with large particles remaining trapped by confinement in the network of liquid channels and small particles being freely advected by the gravity-driven flow. By contrast, the potential role of a similar retention effect on biologically active particles such as phytoplankton cells is still relatively unknown. To assess if phytoplankton cells are passively advected through a foam, the model unicellular motile alga Chlamydomonas reinhardtii (CR) was incorporated in a bio-compatible foam, and the number of cells escaping the foam at the bottom was measured in time. Comparing the escape dynamics of living and dead CR cells, we found that dead cells are totally advected by the liquid flow towards the bottom of the foam, as expected since the diameter of CR remains smaller than the typical foam channel diameter. By contrast, living motile CR cells escape the foam at a significantly lower rate: after 2 hours, up to 60% of the injected cells may remain blocked in the foam, while 95% of the initial liquid volume in the foam has been drained out of the foam. Microscopic observation of the swimming CR cells in a chamber mimicking the cross-section of foam internal channels revealed that swimming CR cells accumulate near channels corners. A theoretical analysis based on the probability density measurements in the micro chambers has shown that this trapping at the microscopic scale contributes to explain the macroscopic retention of the microswimmers in the foam. At the crossroads of distinct fields including marine ecology of planktonic organisms, fluid dynamics of active particles in a confined environment and the physics of foam, this work represents a significant step in the fundamental understanding of the ecological consequences of aquatic foams in water bodies.

A Zero-Power Ubiquitous Wireless Liquid-Level Sensor Based on Microfluidic-Integrated Microstrip Antenna

Harmonic transponder sensors, receiving radio-frequency (RF) signal and converting it to a modulated second harmonic, have been demonstrated to be effective for signal interrogation in environments with strong clutters. Here, we propose a compact dual-resonance microstrip antenna consisting of an elliptical patch loaded with shorting pins. Such an antenna utilizes the TM e 110 resonant mode to intercept the perpendicularly-polarized fundamental tone (2.86 GHz) and uses the TM o 110 resonant mode to retransmits the parallelly-polarized second harmonic (5.72 GHz). Moreover, we have developed a harmonic-based wireless liquid sensor comprising the proposed antenna and a micromachined liquid channel. Our measurement results show that even in the noisy environment, the second harmonic strength can precisely indicate the dielectric property of liquid filled in the microfluidic tank (e.g., acetone-water mixtures with various concentrations). However, a similar setup without frequency and polarization modulations (i.e., linear and passive backscatter tag) fails to provide a sensitive and quantitative measurement of liquid property. The proposed low-profile dual-resonance antenna with sensing capability will pave the way for the development of harmonic sensors and nonlinear radio-frequency identification (RFID) tags.

Experimental measurement of fluid flow in high-speed GMAW assisted by transverse magnetic field

Abstract The visual measurement system was established to investigate the fluid flow during high-speed gas metal arc welding. The two-dimensional fluid flow velocity on weld pool surface was measured using the tracer particles. The characteristic parameters of the backward liquid metal flow were extracted, then the speed of the liquid metal flow was compared with different welding speeds. The results showed that the high-speed backward liquid metal flow and the pinching & earlier solidification of the backward liquid metal flow channel caused the humping bead formation. A transverse magnetic field was used to control the fluid flow behavior to prevent the humping bead. Due to the introduction of transverse magnetic field, the thickness of liquid metal layer underneath the arc was increased. The longitudinal velocity of the liquid metal flow was decreased while the transverse velocity was increased so the humping bead can be suppressed.

Catalytic wet air oxidation of phenol: Review of the reaction mechanism, kinetics, and CFD modeling

Advanced oxidation processes, specifically catalytic wet air oxidation (CWAO), are considered as useful and robust methods for the treatment of refractory organic compounds such as phenol in wastewater. This paper reviews reaction mechanisms, kinetics and computational fluid dynamics (CFD) modeling of CWAO of phenol. Different reaction mechanisms have been proposed by various researchers to account for possible intermediates during phenol oxidation. These mechanisms can be either direct or indirect; with the indirect path resulting in the formation of intermediates, while with the direct mechanism, no intermediates are formed, the reaction proceeds straight to carbon dioxide and water. Acetic acid is considered as the most stable intermediate of phenol oxidation. Power law and Langmuir–Hinshelwood models were used to account for the adsorption/desorption of the reactants on the surface of the catalyst. The reviewed studies show that phenol conversion increases with increased temperature, pressure, gas velocity and decreases with increasing liquid space velocity. The formation of hot spots next to the walls of the reactor leads to safety issues and may cause catalyst deactivation and reactor thermal run away. This prompted a review of liquid mal-distribution and the formation of hot spots inside the reactor using the CFD modeling technique. In most cases, liquid channeling was observed, resulting in the formation of hot spots and catalyst deactivation.

Pattern Engineering of Living Bacterial Colonies Using Meniscus-Driven Fluidic Channels.

Creating adaptive, sustainable, and dynamic biomaterials is a forthcoming mission of synthetic biology. Engineering spatially organized bacterial communities has a potential to develop such bio-metamaterials. However, generating living patterns with precision, robustness, and a low technical barrier remains as a challenge. Here we present an easily implementable technique for patterning live bacterial populations using a controlled meniscus-driven fluidics system, named as MeniFluidics. We demonstrate multiscale patterning of biofilm colonies and swarms with submillimeter resolution. Utilizing the faster bacterial spreading in liquid channels, MeniFluidics allows controlled bacterial colonies both in space and time to organize fluorescently labeled Bacillus subtilis strains into a converged pattern and to form dynamic vortex patterns in confined bacterial swarms. The robustness, accuracy, and low technical barrier of MeniFluidics offer a tool for advancing and inventing new living materials that can be combined with genetically engineered systems, and adding to fundamental research into ecological, evolutional, and physical interactions between microbes.

Burring Process and Fracture Criterion of Large Diameter Steel Pipe

This paper describes finite element method analysis (FEM analysis), results of burring processing of large diameter steel pipe and fracture criterion in burring process of large diameter steel pipe. In this study, the pipe is the 150A SGP pipe with a diameter of 165.2 mm and a wall thickness of 5 mm. The pipe is used for a plant as a flow channel of gas and liquid. A burring process of pipe is generally for forming the branch. The burring process is achieved by drawing of die from prepared hole. And the branch pipe is welded to the formed pipe. This process has some problem. One is the forming limit of pipe, and the other is needed to machining the end surface to be welded. Therefore, in this study, the forming limit of SGP pipe was estimated by FEM analysis of burring process. The parameters used for criteria for forming limit are the maximum shear stress and the equivalent strain. As a result of comparing the analysis result and the experimental result, the forming limit of the 150A SGP pipe was estimated that the maximum shear stress is 350 MPa and the equivalent strain is around 0.8.

Soft actuators using liquid crystal elastomers with encapsulated liquid metal joule heaters

We present a soft actuator composed of fluidic channels of liquid metal alloy embedded in a liquid crystal elastomer (LCE). The LM channels function as stretchable Joule heating elements that deliver heat to the LCE to induce a shape memory phase transition. Because the heater is fluidic, it can deform with the surrounding LCE as the actuator extends and contracts during actuation. In addition to contractile actuation, the LCE can be programmed to perform in-plane or out-of-plane flexural actuation, which exhibit deformations predictable using a simple finite element analysis model. By combining a liquid metal heater with a shape memory polymer, we achieve a soft actuator that does not require an external heat source and can instead be directly activated with electrical current. Finally, we show that the liquid metal channels can also function as a sensor during the actuation cycle, allowing for closed-loop control of the soft actuator.

Full-scale finite element analysis of deformation and contact of a wire-wrapped fuel bundle subject to realistic thermal and irradiation conditions

The fuel bundle in a fast breeder reactor (FBR) is wrapped with wires for guiding the flow of liquid metal. Under operation condition with irradiation and high temperature, the wrapped bundle undergoes complex contact so that the flow channel of liquid will be affected. There are mainly four factors involved: radiation swelling, thermal expansion, radiation creep and thermal creep. In the present study, a full-scale finite element model (FEM) is established to consider the effect of these factors on the complex contact during operation. The established model can capture the contact separation, spacer wire’s dispersion, oval distortion and bowing details of fuel pins. The results show that the local contact dispersion caused by the wire slip can alleviate the severe transverse bending deformation of the bundle. What is more important, we find out that the dispersion of contact points in the peripheral direction of the bundle is another key factor for alleviating the severe deformation of the bundle during operation, this new mechanism – peripheral dispersion of contact – has not been achieved in previous studies.

Roughness effects of gas diffusion layers on droplet dynamics in PEMFC flow channels

Water management remains one of the major challenges in optimising the performance of PEMFCs, in which liquid accumulation and removal in gas diffusion layers (GDLs) and flow channels should be addressed. Here, effects of GDL surface roughness on the water droplet removal inside a PEMFC flow channel have been investigated using the Volume of Fluid method. Rough surfaces are generated according to realistic GDL properties by incorporating RMS roughness and roughness wavelength as the main characteristic parameters. Droplet dynamics including emergence, growth, detachment, and removal in flow channels with various airflow rates are simulated on rough substrates. The influences of airflow rate on droplet dynamics are also discussed by comparing the detachment time and droplet morphology. The liquid removal efficiency subject to different surface roughness parameters is evaluated by droplet detachment time and elongation, and regimes of detachment modes are identified based on the droplet breakup location and detachment ratio. The results suggest that rough surfaces with higher RMS roughness can facilitate the removal of liquid inside flow channel. Whilst surface roughness wavelength is found less significant to the liquid removal efficiency. The results here provide qualitative assessments on identifying the key surface characteristics controlling droplet motion in PEMFC channels.

Improvement of the subcooled boiling model for thermal–hydraulic system codes

In thermal–hydraulic system codes, such as MARS and RELAP5/MOD3, the Savannah River Laboratory (SRL) model has been used as a subcooled boiling model for recent two decades. However, it has been known that the SRL model cannot properly capture the effects of liquid velocity and channel diameter on the development of axial void profile. The authors suggested the modifications of the SRL model in the previous studies, focusing on the net vapor generation model and the wall vapor generation model, and validated the modified model using 103 subcooled boiling experiments, of which pressures were limited up to 69 bar.In this work, the previous subcooled boiling model has been further improved for its extension to high-pressure conditions up to ∼ 150 bar using additional 42 sets of high-pressure experiments. The new model has been validated against a wide range of experiments. It was shown that the new model predicts axial void fractions better than the SRL model and the previous model for the whole pressure range and that it can completely replace the SRL model without any limitation.

Liquid flow and control without solid walls

When miniaturizing fluidic circuitry, the solid walls of the fluid channels become increasingly important1 because they limit the flow rates achievable for a given pressure drop, and they are prone to fouling2. Approaches for reducing the wall interactions include hydrophobic coatings3, liquid-infused porous surfaces4-6, nanoparticle surfactant jamming7, changes to surface electronic structure8, electrowetting9,10, surface tension pinning11,12 and use of atomically flat channels13. A better solution may be to avoid the solid walls altogether. Droplet microfluidics and sheath flow achieve this but require continuous flow of the central liquid and the surrounding liquid1,14. Here we demonstrate an approach in which aqueous liquid channels are surrounded by an immiscible magnetic liquid, both of which are stabilized by a quadrupolar magnetic field. This creates self-healing, non-clogging, anti-fouling and near-frictionless liquid-in-liquid fluidic channels. Manipulation of the field provides flow control, such as valving, splitting, merging and pumping. The latter is achieved by moving permanent magnets that have no physical contact with the liquid channel. We show that this magnetostaltic pumping method can be used to transport whole human blood with very little damage due to shear forces. Haemolysis (rupture of blood cells) is reduced by an order of magnitude compared with traditional peristaltic pumping, in which blood is mechanically squeezed through a plastic tube. Our liquid-in-liquid approach provides new ways to transport delicate liquids, particularly when scaling channels down to the micrometre scale, with no need for high pressures, and could also be used for microfluidic circuitry.

Reversible Surface Wettability by Silanization

AbstractThe chemistry and wettability of oxygen containing surfaces can be conveniently modified by silanization with various organosilanes which form SiO bonds on the surface. This work shows that a superhydrophobic nanoporous polymer coating can be reverted to its previous hydrophilic state by removing the fluoroalkyl silane with fluoride anions using tetrabutyl ammonium fluoride. This leads to a completely reversible process of silanization and desilanization which can be performed in less than 2 min for each step as proven by droplet shape analysis and secondary ion mass spectrometry. Additionally, the desilanization solution can be applied spatially by an automated liquid dispenser or manually by a brush, leading to patterns with different wettability, such as droplet microarrays or liquid channels.