Side Walls Of Channel Research Articles

Effect of microstructure on corrosion behaviour of Al-Cu-Li alloys

The corrosion behaviour and its relationship with microstructure, especially the distribution of precipitates at grain boundaries and within grains, of two Al-Cu-Li alloys with different Cu/Li ratio were investigated using accelerated immersion testing, advanced microscopy characterization and quasi-in-situ corrosion observation. The Al-2.23Cu-0.96Li alloy with low Cu/Li ratio exhibited excellent intergranular corrosion resistance and its corrosion modes unusually remained consistent intragranular corrosion regardless of the ageing stage. The corrosion behaviour of the counterpart Al-4.03Cu-0.91Li alloy with high Cu/Li ratio was found to follow the general evolution regulation, from intergranular corrosion to intragranular corrosion with the ageing time. Microstructure characterizations demonstrated that the coarsening and discontinuous distribution of grain-boundary precipitates played the key role in lowering the intergranular corrosion susceptibility of the two Al-Cu-Li alloys. Further quasi-in-situ corrosion observation of the Al-2.23Cu-0.96Li alloy showed that the dealloying process of the grain-boundary precipitates led to the dissolution of the precipitate-free zone, which meant that the broadening of the precipitate-free zone along the grain boundary could reduce the intergranular corrosion resistance of the alloy. Besides, the thin T 1 precipitates that were uniformly distributed within the grains did not suffer preferential dissolution, but they still affected the intragranular corrosion propagation at the nanoscale. Specifically, the corroded T 1 precipitates could become {111} Al -oriented sidewalls of the intragranular corrosion channel. • The Al-2.23Cu-0.96Li alloy kept low IGC susceptibility regardless of the ageing stage. • Intragranular T 1 precipitates do not preferentially dissolve due to dealloying. • Nanoscale corrosion behaviour was investigated through quasi-in-situ TEM experiment.

Experimental Investigation of Nanofluid Turbulent Flow Over Microscale Backward-Facing Step

Experimental research was presented in this paper to illustrate the heat transmission and flow characteristics of nanofluid on a microscale backward-facing step channel. Except for the downstream wall, which was applied with uniform heat flow, the channel side walls were deemed adiabatic. Water was used as the base fluid and mixed with 30 nm diameter CuO nanoparticles with a volume fraction in the range of 0-0.04. The experiment was conducted at a Reynolds number range of 5,000–10,000. The results showed that the Nusselt number increases as the volume fraction increases. However, the increase in the nanoparticle volume fraction leads to an increment in the friction factor. Furthermore, the results indicated that increasing the Reynolds number lead to the volume fraction decreasing. It was found that there is an improvement of heat transfer by applying the CuO/water nanofluid with a 0.03 volume fraction of CuO nanoparticles with a significant performance evaluation criterion (PEC>1).

Fabrication and Performance of Lobster Eye X-Ray Micro Pore Optics with the Ultra-high Aspect Ratio

Since the idea of bionic Lobster eye micropore optics was put forward, the possibility of focusing hard X-rays by this new lightweight X-ray optics has been proposed. Limited by the technological conditions of the aspect ratio (≥500), low surface roughness (≤1 nm) and the difficulty of applying metal coatings inside such narrow square channels, the high quality of these new optics have not been realized. This work demonstrates the test results for an Ultra-high aspect ratio (500:1) of iridium-coated with microchannel plate technology and atomic layer deposition technology. The sidewalls of the square channel are smoothed with a special acid-base treatment and the Root-Mean-Square of the inner wall was 0.52 ± 0.1 nm in 3 μm × 3 μm scale roughness, such that they work well as X-ray mirrors. The thickness of the metal iridium film layer was 19 nm. At the working voltage of 2 kV, the current was 0.1 mA and the angular resolution of the slumped chip in horizontal and vertical directions was 3.′9 and 4.′2, respectively. The simulation results were in good agreement with the X-ray test results.

Alternating-current nonlinear electrokinetics in microfluidic insulator-decorated bipolar electrochemistry

We proposed herein a unique method of insulator-decorated bipolar electrochemistry (IDBE), for realizing large-scale separation of bioparticles in microchannels driven by AC dielectrophoresis (DEP). In IDBE, a pair of planar driving electrodes is placed at the bottom of channel sidewalls, between which an array of the rectangular floating electrode (FE) strips without external Ohmic contact are evenly spaced along transversal direction, and a series of insulating dielectric blocks are periodically deposited above all the inter-electrode gaps and in full contact with the channel bottom surface. By creating local field maximum and minimum at multiple sites, IDBE extends well the actuating range of DEP force field from the immediate vicinity of electrode tips in traditional bipolar electrochemistry to current fluid bulk. Considering DEP force plays the dominant role around 1 MHz, we utilize Lagrange particle tracing algorithm to calculate motion trajectories of incoming samples for testing the feasibility of microchip in continuous separation of live and dead yeast cells. By applying suitable voltage parameters, highly efficient DEP sorting is theoretically achievable under a moderate inlet flow rate, where most of the viable yeasts are trapped by positive-DEP to sharp dielectric edges, while all the incoming nonviable yeasts are repelled by negative-DEP to the top surface of both FE and insulating block to form multiple thin beams co-flowing into the channel outlet. The microfluidic device exploiting insulators on bipolar FE effectively expands the actuating range of nonlinear electrodynamics and provides invaluable guidelines for developing flexible electrokinetic frameworks in modern microfluidic systems.

Experimental study and numerical analysis of radiative losses of single-channel solar chimney

Solar chimneys provide natural ventilation for buildings, reducing the energy consumption of mechanical systems. Therefore, analyzing energy losses through solar chimney components and inlet/outlet of air channel is critical to develop a suitable design for this passive ventilation system. In this study, the performance and energy losses analysis of a single-channel solar chimney (SC-SOCH) is described; a parametric study under laboratory conditions was conducted regarding the air gap (0.10, 0.15, and 0.20 m) and heat flux of absorber plate (100, 200, 300, 400, and 500 Wm−2). The energy losses were analyzed with temperature sensors, heat flow transducers, and a net radiation transfer model. The parametric study results showed that between 10% and 15% of the total energy supplied to the absorber plate was dissipated to the laboratory environment through the glass cover. Furthermore, combining the different thermal insulation layers on the backside of the absorber plate and sidewalls of the air channel permitted only energy losses below 8% of the total energy supplied. The highest energy losses occurred due to radiative exchange; the radiative losses through the inlet and outlet of the air channel were between 9.38% and 25.78% of the total energy supplied. However, the radiative energy loss rate decreased as airflow increased; the volumetric flow rate was from 34.11 to 94.92 m3h−1, which was enough to satisfy the requirements of total ventilation rate for spaces of 9, 18, and 36 m2 according to ASHRAE 62.2–2019. Therefore, solar chimney designs must be optimized to minimize energy losses and increase airflow for natural ventilation.

Quantifying the impact load of rapid dry granular flows exerted on rigid slit structures using centrifuge experiments and DEM simulation

Granular flows are typical hazard in mountainous terrains. Slit structure has been shown to be a successful mitigating strategy. However, the interaction mechanism between granular flows and slit structure has not been completely elucidated, and the impact load and impact pressure distribution pattern of granular flow on slit structures also has not been fully discussed. Therefore, a novel centrifuge flume experiment and DEM simulation were designed. The centrifugal acceleration field and Coriolis field accounting for the Coriolis effect were also implemented in the DEM model. Results reveal that, the grain size almost has no effect on normal impact forces when the granular flows act as continuous characteristic, and the initial volume and impact force do not show a simple linear relationship. Furthermore, the impact pressure profiles indicate a trapezoidal distribution with a peak impact pressure at the bottom and a decline from the bottom to the top. In addition, the impact forces also showed a decreasing trend from the slit to the flume channel sidewall, making the inner part vulnerable. This study might contribute to the study of flow-slit structure interaction and provide scientific support for slit structure engineering design.

(Digital Presentation) Effect of Compression Pressure on Water Removal and Power Generation Performance of PEFC with Modified Electrode/Channel Structure

Water flooding in cathode electrodes of polymer electrolyte fuel cells (PEFCs) is a critical issue that must be solved for achieving high efficiency and high power density operations. To alleviate this problem, it is necessary to design the optimum electrode/channel structure for actively removing liquid water from the porous media to the flow channel. In the previous studies, Okuhata et al. [1] revealed that the introduction of penetration holes to gas diffusion electrodes (GDEs) effectively promotes the water discharge and improves the limiting current density. Nishida et al. [2] investigated the effect of channel hydrophilization on the water behavior in the cathode of an operating cell using the cross-sectional visualization technique. It was found that the hydrophilization of cathode channels encourages the water suction from the gas diffusion layer (GDL) to the channel and enhances the oxygen diffusibility to the catalyst layer (CL). Our research group has proposed a novel hybrid electrode/channel structure combining the electrode perforation and channel hydrophilization and has investigated its effect on the improvements of water drainage and cell performance. In this study, we directly visualized the liquid water distribution in the cathode GDL of a customized PEFC with the hybrid electrode/channel structure using X-ray imaging and evaluated the transient response of cell voltage under the constant-current operations. Furthermore, the influence of compression pressure on the water behavior in the perforated GDL and the performance characteristics of the customized cell was also examined.For the X-ray investigation, we fabricated a specialized miniature fuel cell with the effective electrode area of 2.88 cm2. The membrane electrode assembly (MEA) was sandwiched between two carbon separators with a single-serpentine flow field (number of channels: 7, channel width: 1.0 mm, depth: 1.0 mm, total length: 88.5 mm). Fig. 1 shows a schematic cross-sectional view on the cathode side of the experimental cell. Since the cathode GDL is irradiated with X-ray beam in the in-plane direction, the through-plane distributions of water can be observed in the GDL under the 4th channel and under the land between the 3rd and 4th channel. To promote the water discharge from the fine porous media, a penetration groove (width: 300 μm, length: 11 mm) was installed into the GDL, MPL and CL and positioned along the right sidewall of the 4th channel. The channel walls on the cathode side were coated with the silica-based hydrophilic solvent. The contact angle of water on the hydrophilized channel is 9.8o. In the hybrid electrode/channel structure, liquid water accumulated in the CL and MPL is firstly discharged into the large groove in the in-plane direction. Subsequently, water droplets gathered in the groove are grown up and attached to the hydrophilized channel walls. The droplets are spread out on the hydrophilic sidewalls and the liquid films are moved upward. Fig. 2 presents the distributions of water saturation in the perforated GDL of the customized cell assembled under two different compression pressures of 0.5 and 1.0 MPa. The current density was increased stepwise from 0.14 to 1.02 A/cm2 for 8 min under the room temperature and non-humidification condition. All images were captured at t=8 min after starting the operation. Dry hydrogen (stoichiometry: 1.5@2.0A/cm2) and oxygen (stoichiometry: 3.0@2.0A/cm2) were supplied to the anode and cathode in the counter-flow arrangement. It was found that the introduction of the hybrid structure effectively decreases the water saturation around the groove due to the in-plane water discharge. The reduction of saturation under the land is much less than under the channel because the strong mechanical compression crushes the pore structure under the land regions and suppresses the water transport. In addition, the low-saturation region of 28% or less around the groove is enlarged with a decrease in compression pressure. The low compression pressure maintains the relatively large porosities in diffusion media and facilitates the water removal.

To the Theory of Grain Motion in an Uneven Air Flow in a Vertical Pneumatic Separation Channel with an Annular Cross Section

The possibilities of the action of uneven air flows on the grain material in the separating channels are still not used enough. The reason for this is the insufficient knowledge of the processes of interaction of the components of the grain material with an uneven air flow. The purpose of the research is to increase the efficiency of grain material separation according to aerodynamic properties by purposefully changing the diagram of air velocities in the channel sections using the actions of lateral and aerodynamic forces. The separation efficiency of grain material components was determined by trajectory analysis. The different geometry of the pneumatic separation channel was studied. The study of the distribution of air velocity and air pressure vectors in a vertical annular channel was carried out using the FlowVision software. It has been established that a change in the air velocity diagram can be implemented both by changing the geometric parameters of the channel and by additional distributed air supply through the perforation in the side walls of the pneumatic channel. Based on the analysis of the velocity field, an improved scheme of a pneumatic gravitational separator is proposed for separating grain material into three fractions according to aerodynamic characteristics.

New insights into sperm rheotaxis, agglutination and bundle formation in Sharkasi chickens based on an in vitro study

Fertility in birds is dependent on their ability to store adequate populations of viable sperm for extended durations in sperm storage tubules (SSTs). The exact mechanisms by which sperm enter, reside, and egress from the SSTs are still controversial. Sharkasi chicken sperm showed a high tendency to agglutinate, forming motile thread-like bundles comprising many cells. Since it is difficult to observe sperm motility and behavior inside the opaque oviduct, we employed a microfluidic device with a microchannel cross-section resembling close to that of sperm glands allowing for the study of sperm agglutination and motility behavior. This study discusses how sperm bundles are formed, how they move, and what role they may have in extending sperm residency inside the SSTs. We investigated sperm velocity and rheotaxis behavior when a fluid flow was generated inside a microfluidic channel by hydrostatic pressure (flow velocity = 33 µm/s). Spermatozoa tended to swim against the flow (positive rheotaxis) and sperm bundles had significantly lower velocity compared to lonesome sperm. Sperm bundles were observed to swim in a spiral-like motion and to grow in length and thickness as more lonesome sperm are recruited. Sperm bundles were observed approaching and adhering to the sidewalls of the microfluidic channels to avoid being swept with fluid flow velocity > 33 µm/s. Scanning and transmission electron microscopy revealed that sperm bundles were supported by a copious dense substance. The findings show the distinct motility of Sharkasi chicken sperm, as well as sperm's capacity to agglutinate and form motile bundles, which provides a better understanding of long-term sperm storage in the SSTs.

Shallow mixing interfaces between parallel streams of unequal densities

As opposed to the case of shallow mixing layers forming between parallel streams of unequal velocities and equal densities, the spatial development of the mixing interface (MI) between two parallel streams of unequal velocities and sufficiently large density contrast is controlled by the formation of a spatially developing, lock-exchange-like flow in transverse planes. Buoyancy effects are driven by the presence of a vertical density interface near the splitter plate. Eddy-resolving numerical simulations conducted in a wide and very long channel are used to investigate the mean flow structure and the effects of the lock-exchange-like flow and the associated coherent structures on mixing and the capacity of the flow to entrain sediment from the channel bed. When the two streams have unequal densities, quasi-two-dimensional Kelvin–Helmholtz (KH) vortices still form near the MI origin, but their coherence is lost over a much shorter distance compared with the case with no density contrast, and their cores are severely stretched in the transverse direction. A main cell of recirculating (cross-) flow forms in the mean flow, in between the fronts of the near-bed intrusion of heavier fluid and the free-surface intrusion of lighter fluid. The instantaneous flow fields contain streamwise-oriented vortical cells along the interface separating the regions containing heavier and lighter fluids. These vortical cells play an important role in enhancing mixing, similar to the KH billows forming in a classical lock-exchange flow. The regions of highest turbulence amplification are situated next to the boundaries of the main recirculating cell. Once the oscillating fronts of the intrusions get sufficiently close to the channel sidewalls, streamwise cells of secondary flow form near the channel boundaries. For cases with a strong density contrast, the free-surface mixing pattern is not a good indicator of mixing between the two streams. For the same flow velocities in the incoming channels, the two streams mix faster with increasing density difference between the two streams. This is because, as opposed to the KH vortices, coherent structures induced by the formation of the lock-exchange-like flow maintain their coherence and capacity to induce mixing at very large distances from the splitter plate. Meanwhile, the redistribution of the streamwise momentum leading to uniform, fully developed flow over the whole cross-section is delayed by buoyancy effects. Away from the splitter plate, the region with the highest sediment entrainment potential is situated next to the edge of the main recirculation cell on the high-speed side of the channel. For the same flow velocities in the incoming channels, the sediment entrainment capacity of the flow is much larger in the simulations conducted with density contrast between the incoming streams and peaks for the case when the faster stream contains the denser fluid.

Efficient nanoparticle focusing utilizing cascade AC electroosmotic flow.

This study presents on‐chip continuous accumulation and concentration of nanoscale samples using a cascade alternating current electroosmosis (cACEO) flow. ACEO can generate flow motion caused by ion movement due to interactions between the AC electric field and the induced charge layer on the electrode surface, with the potential to accumulate particles, especially in low‐conductive liquid. However, the intrinsic particle diffusive motion, which is sensitive to particle size, is an essential element influencing accumulation efficiency. In this study, an electrode combining chevron and double‐gap geometry embedded in a microfluidic channel was developed to perform efficient three‐dimensional (3D) nanoparticle focusing using ACEO. The chevron electrode pattern was introduced upstream of the focusing zone to overcome particle accumulation in scattering zones near the channel sidewall. To demonstrate the efficiency of the proposed device for particle accumulation, three nanoparticle types were used: latex, metal, and biomaterial. Continuous 3D concentration of 50‐nm polystyrene particles was confirmed. The concentration factor, determined based on image processing, became quite high when 50‐nm gold nanoparticles were used. Moreover, nanoparticles with a 20‐nm diameter were accumulated using cACEO. Finally, we used the concentrator chip to accumulate 50‐nm liposome particles, confirming that the device could also successfully concentrate biomaterials.

Diffusioosmosis-driven dispersion of colloids: a Taylor dispersion analysis with experimental validation

Diffusiophoresis refers to the movement of colloidal particles in the presence of a concentration gradient of a solute and enables directed motion of colloidal particles in geometries that are inaccessible, such as dead-end pores, without imposing an external field. Previous experimental reports on dead-end pore geometries show that, even in the absence of mean flow, colloidal particles moving through diffusiophoresis exhibit significant dispersion. Existing models of diffusiophoresis are not able to predict the dispersion and thus the comparison between the experiments and the models is largely qualitative. To address these quantitative differences between the experiments and models, we derive an effective one-dimensional equation, similar to a Taylor dispersion analysis, that accounts for the dispersion created by diffusioosmotic flow from the channel sidewalls. We derive the effective dispersion coefficient and validate our results by comparing them with direct numerical simulations. We also compare our model with experiments and obtain quantitative agreement for a wide range of colloidal particle sizes. Our analysis reveals two important conclusions. First, in the absence of mean flow, dispersion is driven by the flow created by diffusioosmotic wall slip such that spreading can be reduced by decreasing the channel wall diffusioosmotic mobility. Second, the model can explain the spreading of colloids in a dead-end pore for a wide range of particle sizes. We note that, while the analysis presented here focuses on a dead-end pore geometry with no mean flow, our theoretical framework is general and can be adapted to other geometries and other background flows.

Heat transfer enhancement for microchannel heat sink by strengthening fluids mixing with backward right-angled trapezoidal grooves in channel sidewalls

To strengthen the fluids mixing in channels for enhancing heat transfer, a new design of microchannel heat sink with periodic gradual-expansion and sudden-constriction cross-sections was proposed by arranging backward right-angled trapezoidal grooves in channel sidewalls. The flow and heat transfer characteristics in the new design was numerically investigated and compared with those in two comparative microchannels, which have the same channel volume and the same or almost the same convective heat transfer area as the new design. The pressure and viscous resistances of channel walls were innovatively analyzed for explaining why grooves can maintain a lower pressure drop for microchannels. The results indicate that the new microchannel shows a significant improvement of heat transfer enhancement and overall performance although its pressure resistance and viscous resistance are much higher than those of other ones. The pressure drop and Nusselt number of the new microchannel are 1.02–1.45 and 1.31–2.14 times higher than those of the smooth straight microchannel, respectively. After an optimum process of the forward angle (θ) of grooves, the relative Nusselt number of the new microchannel can be achieved up to 2.23 at θ = 15°and Re = 737 while the overall heat transfer factor can be achieved up to 1.89 at θ = 18°and Re = 442.

Performance Enhancement of Double-Layer Microchannel Heat Sink by Employing Dimples and Protrusions on Channel Sidewalls

High-temperature gradient causes thermal stress and is indirectly responsible for other demerits in nonstacked microchannels. High-temperature gradient is overcome by employing double layers in the heat sink. Utilization of dimple and protrusion in such double-layered sink to enhance overall performance is done in the present numerical study. Before placement of dimples and protrusions on sidewalls of the sink, optimum width and depth of channel have been assessed. Microsinks with the protruded-dimpled bottom layer and microsinks with protruded-dimpled layers are investigated. The parameters such as maximum bottom wall temperature difference (ΔTb), Nusselt number ratio (Nu/Nuo), and thermal performance factor (η) have been evaluated. The impact of aligned and staggered arrangements of dimple and protrusion is also compared. Deionized water as a coolant for the range of Reynolds number of 89–924 is examined. It has been realized that aligned models offer higher heat transfer coefficient, maximum Nu, and minimum ΔTb, but in terms of overall performance, staggered sinks are superior. The heat sink with both layers protruded and dimpled, showing Nu/Nuo and η of 1.36 and 1.32, respectively, is observed as one of the optimum sinks which offers an excellent lowest ΔTb of 1.48 K.

A model of the positive column of longitudinal glow discharge in planar channel with additional gas injection through the side walls

A model of positive glow discharge column in longitudinal flowing glow discharge with an additional distributed gas injection through the side walls of flat channel is proposed. The main flow is pumped through mesh electrodes located at the beginning and end of the discharge chamber. The solution of an integro-differential system of equations is obtained, expressions for the distribution of the electric field strength, the degree of gas ionization, and the gas temperature in the discharge region are given.

Effect of an end-clearance width on the gap cavitation structure: Experiments on a wall-bounded axis-equipped hydrofoil

The paper deals with an experimental study of tip-clearance cavitation inception and development and its vortical structure coupled with dynamics of the main attached cavity on the suction side of a two-dimensional symmetric hydrofoil equipped with a rotation axis. The gap is formed by the end face of the model and a transparent sidewall of the test channel. The experiments were performed for attack angles of 3° and 9° and 0.4-, 0.8-, 1.75- and 3.75-mm gaps (or 1.8%–17% relative thickness) under various flow conditions on the cavitation number. In order to observe the tip-clearance cavitation occurrence, high-speed imaging was applied. The leakage flow velocity was measured inside the clearance by a modified Particle Tracking Velocimetry technique. It is shown that the mean velocity field of the leaking flow is split into eight distinctive zones where the flow direction and velocity magnitude substantially differ. Positions and extents of these zones are practically independent of the primary flow regime but are affected by the attack angle. Local velocity values of the leakage flow are unexpectedly found to be about 20% higher in the region of a gap cavity than the mean bulk velocity of the incoming flow. Cavitating cores of various vortices manifest themselves in the recorded images, showing that the vortex structure of the leakage flow associated with the tip-clearance cavitation is very complicated and the hydrofoil axis makes it even more complex by inducing new vortices and cavities. For the gaps considered, an increase of its size causes the tip-clearance cavitation to be initiated at higher cavitation numbers, i.e., this is favorable for its occurrence, while the development of the main cavity is hindered. In unsteady flow regimes, dynamics of the primary cavity on the hydrofoil suction side significantly influences the leakage flow direction and the tip-clearance cavitation evolution. Periods of oscillation cycles of the main and gap cavities coincide but the maximum size of the gap cavity is reached with a phase lag relative to the main one. At the small incidence angle, thicker gaps and unsteady flow conditions, extremely transient pressure waves are registered in the clearance, with their velocities ranging from 41 to 81 m/s.

CFD modelling of the flow of ice slurry in a vertical slit channel

In this article, the Euler-Euler method was applied to CFD modelling of adiabatic ice slurry flow, for different flow directions in a vertical slit channel. The mean relative accuracy of determining pressure drops compared to experimental studies was 5.6%. Calculations showed that the relative slip velocity and the effect of flow direction on slip velocity increase with decreasing carrier fluid concentration, decreasing mean flow velocity, and decreasing mean solid particles volume fraction. The mean particle slip velocity does not exceed 4%, and local slip velocity values can be 58% of the mean suspended solids flow velocity. For heterogeneous flow, the highest slip velocities occur at a distance of 15% of the channel width from the channel sidewalls. The shape of the solid particles distribution profile is determined by the mean flow velocity and the mean solid particles volume fraction. Excluding the area at a distance of 8% of the channel width from the sidewall where local maximum (for low velocities) and minimum (for higher velocities) values may occur, the profile is stabilised in the central part of the channel. In this study, the boundary curves between heterogeneous and homogeneous flow were determined for ice slurry flow in a vertical slit channel.

Particle image velocimetry evaluation of flow-altering countermeasures for local scour around a submerged circular cylinder

The effect of scour countermeasures on the mechanism of local scour around a cylinder requires clarification in order to develop design methodology for use in practice. Previous investigations on countermeasure performance, though useful, have not provided adequate measurements to support this understanding. In the present investigation, particle image velocimetry (PIV) measurements were acquired at several streamwise-vertical planes in the flow field surrounding a submerged circular cylinder with a vertical splitter plate and with a rectangular collar (a horizontal base plate). Analysis of the distribution of mean streamwise velocity and Reynolds shear stress as well as the scour formation indicated that the splitter plate disrupted shear layer interaction in the wake region, reducing the width of scour downstream of the cylinder by 3%. The collar eliminated scour upstream of the cylinder entirely by providing protection at the sides of the cylinder where the shear stress exceeds the critical bed shear stress, and the streamwise velocity distribution in the region between the cylinder and the channel sidewall indicated that installation of a rectangular collar causes flow separation at a point further upstream on the cylinder surface.

An experimental study on gas and liquid two-phase flow in orientated-type flow channels of proton exchange membrane fuel cells by using a side-view method

Proton exchange membrane fuel cells are widely utilized in the areas of aerospace, military and vehicles. Enhancing the reactant transportation and improving water, heat management can effectively increase the electrochemical reaction rate and power output. Orientated-type flow channels have been proved to be effective on improving mass transporting and enhancing performance. In this study, a flow field plate with transparent observation window, whose channel side wall is designed as transparent side-plates, is fabricated to achieve the side-view observation on liquid movement behaviors inside fuel cells. The visualization results of reactant gas and liquid water generation and flowing behaviors in channel regions are observed through the side direction for the first time. Experimental results infer that: orientated-type flow channels having baffles affect droplet generation, moving and shape in gas flow channels, and higher current densities result in more liquid water generation. The baffle downstream region having sudden expanded region slows down droplet moving, and baffle upstream sides accelerates droplet moving. Moreover, the generated heat of electrochemical reaction cannot satisfy maintaining a higher cell working temperature requirement, and an extra heating procedure is required.

Experimental Investigation of Flood Management by an Instantaneous Levee Breach

Laboratory experiments were conducted to investigate the reduction of flood depth in a channel due to an engineered levee breach. Different combinations of inflow hydrographs, breach openings, and floodplain storage areas were considered. Inflow hydrographs with various peak discharges, hydrograph shapes, and flood durations were generated by a computer-controlled valve. A breach was created instantaneously on the channel sidewall as the flood wave approached the breach location. Regression analyses were conducted to express the reduction of flood depth as a function of the breach width, channel width, distance of the selected location from the breach centerline, hydrograph characteristics, and the area of the floodplain basin. The results show that the engineered levee breach provided an effective reduction of flood depth both upstream and downstream of the breach—more so upstream of the breach—by modifying the flood wave. The breach width and floodplain area are found to play a significant role in depth reduction.