Channel Depth Research Articles

Effects of the geometrical features of flow paths on the flow behaviour of a multi-stage labyrinth pressure reducing valve throttling components

It is important to note that an inappropriate design of the valve can generate noise and vibration, causing harmful effects on both personnel and equipment.However, the impact of geometric parameters of throttling elements on the internal flow mechanism of pressure reducing valves and their effect on pressure drop and Mach number is not yet clear. To address this gap, we employ both experimental and numerical methods to investigate the flow mechanism and its impact on pressure drop and Mach number for various geometrical parameters. With these insights, we conduct a sensitivity analysis and adopt the L9 (34) orthogonal design method to optimize the design of the throttling components. The results demonstrate that steam flow within the MSLPRV operates in a supersonic regime. However, excessively high expansion coefficients (γ) can lead to structural changes that are too drastic, posing challenges for achieving stable pressure reduction and controlling the outlet Mach number within the flow channel. Moreover, we observe that the channel shape and outer wall radius (R/DH) exhibit a weak functional relationship with the pressure drop and Mach number. To ensure a reasonable pressure distribution within the labyrinth flow channels, it is crucial to adopt a smaller internal wall radius (r/DH) and appropriate channel depth(λ/DH). Furthermore, under the same boundary conditions, increasing the number of stages (N) in the throttling components proves advantageous for achieving staged pressure reduction, thereby resulting in lower outlet Mach numbers and reduced kinetic energy within the flow channel. Finally, optimized design of labyrinth flow channels is achieved with expansion coefficients γ = 1.05, stage numbers N = 10, channel depths λ/DH=1.2, and internal wall radius r/DH=0.

Study on heat transfer enhancement of spray cooling with bionic vein channel structured surface

Inspired by the fluid transportation capabilities of leaf vein structures in nature, a novel approach is proposed to enhance spray cooling heat transfer performance through improving liquid film distribution. In this study, a leaf vein channel structure was laser etched onto a heat exchange surface and a non-contact open spray cooling test platform based on the principle of induction hea ting was established. The spray cooling heat transfer performance of the enhanced surfaces with identical leaf vein channel shapes but varying channel depths was investigated under different flow rates. The results indicate that, across all tested flow rate conditions, the spray cooling heat transfer performance of the leaf vein channel surpasses that of the smooth surface. Notably, within the two-phase region, an observed 50 % increase in heat flux density highlights significant enhancement effects provided by the leaf vein channels. Furthermore, research findings suggest that for leaf vein channel depths <0.5 mm, greater depth corresponds to improved enhanced heat transfer effects during spray cooling processes. Utilizing high-speed camera technology throughout our investigation allowed us to capture distinct liquid motion phenom ena known as “liquid columns” occurring at the center of each leaf vein channel. These liquid columns exhibit changes in shape and motion mode corresponding to variations in surface temperature.

Dielectrophoretic cell sorting with high velocity enabled by two-layer sidewall microelectrodes extending along the entire channel

Dielectrophoresis has been widely applied in microfluidic cell separation, and it enables label-free and size-independent cell sorting based on their dielectric fingerprints which is prerequisite for downstream biomedical analysis. The linear flow velocity and cross-sectional area are the two key factors proportional to the flow rate and thus directly related to the sample processing throughput. Aiming at higher flow rate, the state-of-art techniques mostly focus on the cross-sectional area, either by using wide chamber with angled electrode digits or 3D volumetric electrodes with expanded channel depth. On the other hand, the velocity is always carefully limited because cells have very squeezed time to interact with the DEP force that drives them to migrate, and the flow drag induced by high velocity potentially poses adverse effect against the DEP-driven cell migration. In this paper, we present DEP-activated cell sorting at high-velocity being 1–2 orders of magnitude higher than the existing DEP separators, which is enabled by easily-fabricated two-layer 3D sidewall electrodes extending along the entire flow channel. Such electrodes project DEP force fully decoupled from the flow drag, and acting on cells continuously, allowing sufficient time for cell migration. The two-layer design leads to cell migration across a shorter distance between the upper and lower layers, with a unique bridge adaptor evolved at the downstream for the collection of the cells vertically separated. The DEP device achieves separation of live and dead yeast cells at high velocity up to 78.3 mm/s, more than a full order of magnitude higher compared to any reported DEP platforms. This velocity corresponds to a competitive flow rate of 3.1 mL/h given the fairly small cross-sectional area, where the averaged collection rate is over 95 %. For the separation between the live and dead Hela cells, our device enables a high velocity up to 50.5 mm/s with an averaged collection rate of ∼85 %. A high throughput of 1.79 × 1 0^(5) cells/min for the live and dead Hela cell separation has been achieved with 89.7 % collection for live cells and a velocity of 30.3 mm/s.

Research on the Effects of an Electrode Drill Bit during the Rock Drilling Process by High-Voltage Electric Pulse

Summary High-voltage electric pulse rock-breaking (HVEPB) has proved to be a novel and inexpensive method of breaking rock regardless of rock composition, but the design of the electrode drill bit lacks a theoretical basis. In this paper, we first establish a plasma channel model for electric breakdown and a numerical rock-breaking model for HVEPB, which can simulate the rock electrical breakdown plasma channel and the effect of different electrode drill bits on HVEPB. Second, we analyze the effects of different electrode arrangement structures and high-voltage electrode angles on plasma channels and the effects of internal cracks and rock-breaking processes through numerical simulation. Finally, we describe HVEPB experiments conducted using electrode drill bits with different electrode arrangement structures and high-voltage electrode angles, and with the boreholes reconstructed in three dimensions to analyze the effects of different electrode arrangement structures and high-voltage electrode angles on HVEPB drilling. The results show that the effects of the electrode drill bits on HVEPB are reflected mainly in the difference between the plasma channel and shock wave. Different electrode arrangement structures and high-voltage electrode angles result in different electric fields and energy utilization efficiencies within the rock, resulting in different shock waves and differences in the depth, shapes, and penetration of the plasma channels. The simulations and experimental studies in this paper can guide and optimize the design of the discharge tool to upgrade the drilling efficiency of HVEPB.

On the contribution of the top and bottom walls in micro-pillar array columns and related high-aspect ratio chromatography systems

We report on a steady-state based, and hence highly accurate numerical modelling study of the effect of the top and bottom wall in the current generation of micro-pillar array columns. These have a mesoporous retention layer that not only covers the pillar walls but also the bottom wall. Our results show that the performance of these columns can in general not be improved by also covering the top wall with the same layer, despite the increased column symmetry this approach would offer. The reason for this is that the local species retardation caused by a retentive layer is much stronger than the pure flow arresting effect of an uncovered wall. At least, this has a crucial impact in high aspect-ratio systems such as micro-pillar array columns because these require a small inter-pillar distance to promote mass transfer together with a large channel depth to enable a sufficiently high flow rate. On the other hand, a notable improvement could be made if micro-pillar array would be produced without having a retentive layer at the bottom. At Péclet number Pe = 50 and aspect ratio AR = 5 for flow-channels, this gain amounts up to about 4.5 h-units at a zone retention factor k’’ = 2 and 1.75 h-units at k’’ = 16 (gain scales almost linearly with Pe).To verify these results, we also considered another high aspect-ratio system with a simplified geometry: the open-tubular channel with a flat-rectangular cross-section. This led to very similar observations, thus confirming the findings for the micro-pillar array.The results produced in the present study also allow us to conclude that the classic modelling paradigm adopted in chromatography, which is based on the independency and hence additivity of the hCm- and hCs-contributions, can lead to large modelling errors in chromatographic systems with a high aspect-ratio, even when their geometry is so simple as that of a straight open-tubular channel with constant cross-section. Indeed, when both zones are treated independently, the analysis misses how the vertical diffusion through the retentive layer helps suppressing the vertical gradients in the mobile zone. The diffusion through this layer occurs in a ratio of k’’Ds/Dm (Dm being the diffusion coefficient in mobile phase zone and Ds being the diffusion coefficient in stationary phase zone), such that at high retention factors this diffusion contribution even becomes the dominant one.

Conservation planning for Gangetic dolphin (Platanista gangetica) in smaller rivers of the Ganga River Basin, India

The complex and dynamic networks of river system, vital for the maintenance of biodiversity and ecosystem services, are under pressure due to human-induced water stress disrupting ecological processes. Recognition of the importance of rivers as source of life though has led to efforts towards protecting large rivers, nevertheless the conservation and management of smaller rivers remained mostly neglected, creating significant gaps in ecological restoration initiatives. In the present study, we assess the distribution and population status of Gangetic dolphin (Platanista gangetica) in the small rivers in the Ganga River Basin for integrating it into the basin wide river conservation strategy. We observed that the Gangetic dolphin inhabited most tributaries and sub-tributaries of the Ganga River, with a naïve occupancy rate of Ψ̂ = 0.68 ± 0.04 (mean ± SE) having 606 ± 142.77 (mean ± SE) individuals and accounts for 15% of the total Gangetic dolphin population in the Basin. The results of N-mixture and MaxEnt models demonstrate that channel depth, presence of meanders and water discharge were key predictors of distribution in these rivers, and the proximity to confluences were identified as a critical predictor. About 54% (620 km) of 1150 km of the surveyed river stretches exhibited suitability for dolphins in the Basin, indicated by a probability distribution score of ≥0.50. Combining this data with the available information, we delineated a total of 2850 km stretch covering entire Ganga River System suitable for Gangetic dolphins within the Basin. Notably, the 620 km of suitable stretches identified in smaller rivers represent 22% of the overall suitable stretches across the entire basin. These stretches were translated to conservation priority stretches for systematic conservation planning involving various stakeholders for improved river conservation in the Basin.

Optimization design of proton exchange membrane fuel cell cooling plate based on dual-objective function topology theory

To enhance the cooling performance of proton exchange membrane fuel cell (PEMFC), the structural design of cooling channel of PEMFC with dual-objective function model is conducted based on topology optimization. The cooling characteristics of topological and traditional cooling plates under different channel depths (dc) and coolant inlet velocities (Vin) were comparatively investigated by constructing the fuel cell convective heat transfer experimental platform. The results indicate that with the increase of channel depth, the maximum and average temperatures of both cooling plates gradually decrease, while the pressure drop increases gradually. When the channel depth changes from 1 mm to 2 mm, the maximum temperatures of topological and traditional cooling plates decrease by 2.5 °C and 3.6 °C, respectively. At dc = 1 mm, the pressure drop of topological cooling plate is 16.7 Pa, which is 22.7% lower than that of traditional cooling plate. The maximum and average temperatures of cooling plate gradually decrease as coolant inlet velocity increases. At Vin = 0.25 m/s, the average temperature of topological cooling plate has the lowest value of 43.85 °C. The optimized cooling plate has better heat transfer efficiency, especially when the coolant velocity is large. The topological cooling plate has lower temperature uniformity index (IUT) and the maximum temperature under the same pump power consumption.

The present and future contribution of ships to the underwater soundscape

Since the industrial revolution the ocean has become noisier. The global increase in shipping is one of the main contributors to this. In some regions, shipping contributed to an increase in ambient noise of several decibels, especially at low frequencies (10 to 100 Hz). Such an increase can have a substantial negative impact on fish, invertebrates, marine mammals and birds interfering with key life functions (e.g. foraging, mating, resting, etc.). Consequently, engineers are investigating ways to reduce the noise emitted by vessels when designing new ships. At the same time, since the industrial revolution (starting around 1760) greenhouse gas emissions have increased the atmospheric carbon dioxide fraction x(CO2) by more than 100 μmol mol-1. The ocean uptake of approximately one third of the emitted CO2 decreased the average global surface ocean pH from 8.21 to 8.10. This decrease is modifying sound propagation, especially sound absorption at the frequencies affected by shipping noise lower than 10 kHz, making the future ocean potentially noisier. There are also other climate change effects that may influence sound propagation. Sea surface warming might alter the depth of the deep sound speed channel, ice melting could locally decrease salinity and more frequent storms and higher wind speed alter the depth of the thermocline. In particular, modification of the sound speed profile can lead to the appearance of new ducts making specific depths noisier. In addition, ice melting and the increase in seawater temperature will open new shipping routes at the poles increasing anthropogenic noise in these regions. This review aims to discuss parameters that might change in the coming decades, focusing on the contribution of shipping, climate change and economic and technical developments to the future underwater soundscape in the ocean. Examples are given, contrasting the open ocean and the shallow seas. Apart from the changes in sound propagation, this review will also discuss the effects of water quality on ship-radiated noise with a focus on propeller cavitation noise.

Meteotsunamis in the Tamsui River estuary, Taiwan

This study presents meteotsunami evolution and statistics in the Tamsui River estuarine system from 12 years observations. In the tide-dominated estuary, a strong correlation is observed between high tidal levels and the upstream propagation of meteotsunami waves. Such long waves travel the Tamsui River at an average speed of 6 m/s, while their speed slightly decreases to 4 m/s in the upstream rivers. The propagation changes are likely due to the contraction channel and shallow depth of the upstream rivers. During the upstream propagation, low-frequency waves (an average period of 44.5 min) have the significantly low reduction of wave height compared to high-frequency waves (an average period of 21.5 min). Findings suggest that low-frequency waves are capable of propagating over longer distances within the river estuary than high-frequency waves. In terms of long-term statistical analysis in 2014–2020, meteotsunamis predominantly occur in late winter and early spring. These events are primarily triggered by cluster and frontal convective storms, which are predominant atmospheric forcings responsible for initiating meteotsunami waves. These convective storms are often associated with incoming cold surges or cold fronts crossing the Taiwan Strait, which has implications on the role of pressure and wind disturbances, as well as the resonance mechanism in meteotsunami initiation. Furthermore, the study assesses the probability of meteotsunami occurrences, revealing that an annual prediction of wave height can reach up to 0.3 m. This finding raises concerns regarding potential hazards in Taipei City, where the population exceeds 6.8 million people. Of particular concern is the vulnerability of the Keelung River, which flows through the city center. In summary, the potential hazards posed by meteotsunamis in the Tamsui River estuary underscore the importance of risk management and preparedness measures.

Laser Lithography of Monolithically‐Integrated Multi‐Level Microchannels in Silicon

Laser Lithography of Monolithically‐Integrated Multi‐Level Microchannels in Silicon

Characterization and prediction of micro channel depth of ultra-thin bipolar plates for PEMFCs

In this study, a combination of experimental and statistical methods were employed to precisely determine the micro channel depth in ultra-thin metallic bipolar plates fabricated from 316 stainless steel with a thickness of 0.1 mm. The investigation centers on the rubber pad forming process and its role in the production of these critical components for Proton Exchange Membrane Fuel Cells (PEMFCs). To advance the understanding of this manufacturing process, experimental tests were designed using a Design of Experiment (DOE) technique and subsequently developed a predictive model using Response Surface Methodology (RSM). The research reveals a direct, quantifiable relationship between the channel depth in metallic bipolar plates and the magnitude of the applied force. Also, the pivotal role of rubber thickness as a dominant factor influencing channel depth was explored. Furthermore, it is revealed that augmenting the channel depth in these plates is attainable through a reduction in rubber hardness and an increase in rubber thickness. However, the benefits diminish once the rubber layer thickness exceeds a specific threshold. Moreover, the results underscore that the primary influential factors in this process include force, hardness, thickness, as well as the interplay between force and rubber thickness. The proposed model's accuracy is reaffirmed through an average error rate of approximately 5.39%, signifying its reliability in predicting microchannel depth. This research contributes novel insights into the manufacturing of ultra-thin metallic bipolar plates for PEMFCs, shedding light on the critical parameters influencing channel depth and their interrelationships. The significance and engineering value of this work lies in its potential for enhancing the design and manufacturing of metallic bipolar plates for PEMFCs. Precise control of microchannel dimensions is crucial for enhancing PEMFC performance and efficiency. This research not only advances clean energy technology but also contributes to the broader goal of achieving sustainable energy solutions, making it a noteworthy and timely contribution to the field.

Hydrothermal analysis of archimedean spiral single and dual channel heat sink for CPU cooling

Engineering modeling and simulation represent a predominantly design tool in the modern manufacturing industry in which the actual system is reproduced using a mathematical and scientific model. This requires CPUs with higher computational capacities. However, increas-ing the computational capacities of CPU and GPU imposes challenges in the cooling process due to space limitations. CPU liquid cooling system has attracted more interest as an efficient heat dissipation tool. This work presents computational modeling of the conjugate heat and flow for the CPU liquid heat sink cooling. An Archimedean spiral channel is grooved into the cold plate of the heat sink. Single and dual channel passes are used in this work. The out-er diameter of the cold plate is 105 mm and the channel depth is 5 mm for both single and dual-channel configurations. The conjugate heat sink model was constructed to have four different domains: CPU (alumina), glue layer (ethoxy), cold plate (copper), and liquid cool-ant (water). To incorporate the effect of turbulence, the flow rate varied to cover a range of Reynolds number from 3000 up to 15000 at a constant inlet temperature of 25 °C. The used turbulence model was the Shear Stress Transport (k-ω) to better capture the viscous, high-fre-quency flow fluctuation in the near-wall region. The bottom surface of the CPU is subjected to 450 W of heat energy. The results showed that the channel configuration and Reynolds number have a decisive impact on controlling the CPU temperature. The CPU temperature decrease as Reynolds number increases, however, the pressure drop increases at an exponen-tial rate. These findings are supported by Darcy–Weisbach equation for internal flow in which the pressure drop depends on the square of the average fluid velocity and it was noticed that the pressure drop in the dual channel was three times higher than that in the single channel. The hydrothermal performance of the Archimedean spiral channel rapidly decreased with Reynolds number and the single-channel had a slightly better performance compared with the dual-channel.

Numerical Investigations of the Thermal-Hydraulic Characteristics of Microchannel Heat Sinks Inspired by Leaf Veins

A microchannel heat sink (MCHS) is a potential solution for chip and battery thermal management. The new microchannel structure is beneficial for further improving the thermal-hydraulic performance of MCHSs. Inspired by leaf veins, six new channel structures were designed, and the effects of the channel structures (three parallel structures named PAR I, II, and III and three pinnate structures named PIN I, II, and III), channel depths (0.4, 0.8, and 1.6 mm), and heat fluxes (20, 50, and 80 kW/m2) were investigated via numerical simulation. The cooling medium was water, and the heating area was 40 × 40 mm2. Both PAR II and PIN III exhibit superior overall performance, characterized by the highest Nusselt number and the lowest heating wall temperature. Moreover, PIN III demonstrates the lowest standard deviation in heating wall temperature, while PAR II exhibits the lowest friction factor. The greater the channel depth is, the larger the solid–liquid contact area is, leading to a reduced wall temperature at the interface under identical conditions of inlet Reynolds number and heating wall heat flux. Consequently, an increase in the Nusselt number corresponds to an increase in the friction factor. The maximum value and standard deviation of the heating wall temperature increase with increasing heat flux, while the Nusselt number and friction factor remain unaffected. The overheating near the two right angles of the outlet should be carefully considered for an MCHS with a single inlet–outlet configuration.

Analysis of the causes of silting of natural channels

The theory of river flow transport is the major cause in the development of the irrigation sector and largely determines the stability of the irrigation scheme. Crop water requirements vary due to climate and crop growth stages. For this reason, the flow of sediments changes during the irrigation season. In this article, in order to evaluate the carrying capacity of the canals, researches in natural field conditions were carried out in the Amu-zang canal belonging to the “Amu-Surkhan Irrigation Systems” basin administration. Flow transportability in natural channels was calculated for particles with d=0.05 mm by S.Kh.Abalyans, A.Zamarin, A.M.Arifzhanov and Engelund and Hansen methods. A histogram of the dependence of flow capacity, channel depth and average speed on the Amuzang channel was obtained, according to which it was determined that the flow capacity is 1.5-1.8 kg/m3 in the range of 0.6-0.8 m/s.

Droplet-based fluorescence anisotropy insulin immunoassay.

Over the last several decades, multiple microfluidic platforms have been used for measurement of hormone secretion from islets of Langerhans. Most have used continuous flow systems where mixing of hormones with assay reagents is governed by diffusion, leading to long mixing times, especially for biomolecules like peptides and proteins which have large diffusion coefficients. Consequently, dispersion of rapidly changing signals can occur, reducing temporal resolution. Droplet microfluidic systems can be used to capture reagents into individual reactors, limiting dispersion and improving temporal resolution. In this study, we integrated a fluorescence anisotropy (FA) immunoassay (IA) for insulin into a droplet microfluidic system. Insulin IA reagents were mixed online with insulin and captured quickly into droplets prior to passing through a 200 mm incubation channel. Double etching of the glass device was used to increase the depth of the incubation channel compared to the IA channels to maintain proper flow of reagents. The droplet system produced highly precise FA results with relative standard deviations < 2% at all insulin concentrations tested, whereas the absolute fluorescence intensity precisions ranged between 5 and 6%. A limit of detection of 3 nM for insulin was obtained, similar to those found in conventional flow systems. The advantage of the system was in the increased temporal resolution using the droplet system where a 9.8 ± 2.6 s response time was obtained, faster than previously reported continuous flow systems. The improved temporal resolution aligns with continued efforts to resolve rapid signaling events in pancreatic islet biology.

Effect of Operating Temperature and Pressure on the Limiting Current Density of PEM Electrolysis Cell Based on Theoretical Prediction Model and Experiments

Introduction The PEM electrolysis cell (PEMEC) exhibits great potential to produce hydrogen gas. However, the high cost associated with cell components, such as the iridium oxide catalyst and titanium porous transport layer, poses a challenge to the commercialization of PEMEC. So, continued research is needed to improve the cost-effectiveness of PEMEC. Operation at high current densities can minimize the electrode area and reduce capital expenses. However, high current density operation is limited by limiting current density (LCD), which causes a sharp increase in electrolysis voltage. At high current densities, the generation of oxygen gas bubbles creates additional flow restrictions to the water supply and increase overvoltage. Although previous studies have achieved relatively high current densities [1-2], the limit of operating current density and its mechanism still remain unknown.In this study, it reveals the impact of operating temperature and pressure on LCD of a lab-scale PEMEC. The experiments are conducted over a range of temperatures from 80 to 90 ℃ and pressures from 0.1 to 0.3 MPa. In conjunction with experiments, a mathematical model is developed to analyze the mechanism of LCD. The model includes mass and momentum equations for liquid water and oxygen gas through the porous transport layer. And the model also involves electrochemical equations to study overvoltages associated with mass transport. By combining experimental and theoretical analysis, this study provides valuable insights into the factors affecting LCD of PEMECs and facilitates the optimization of high-performance operation. Experimental apparatus The specifications of crucial components such as membrane (PEM), catalyst layer (CL), porous transport layer (PTL) is listed in Table.1 . Nafion NR212 is used as PEM, and the thickness is 51 μm. The catalyst is contained on CL, and its loading amount are 1.5 mg/cm2 IrO2 on anode and 0.5 mg/cm2 Pt on cathode, respectively. The anodic PTL is a Titanium mesh plated by Pt (Nikko Techno, NKT-1803-03), and the carbon paper (SGL 38BA) is used as cathodic GDL. For separators, the anode separator is fabricated from titanium, and the cathode separator is carbon. The anodic and cathodic flow pattern is designed as single-serpentine channels, and the channel depth, channel width, and rib width are 1 mm ×1 mm ×1 mm, respectively. Results and discussions Fig.1 shows the theoretical and experimental I-V curves. In Fig.1, the electrolysis voltage in both experiment and simulation raises abruptly, which is corresponding to LCD. The experimental LCD is 11.6 A/cm2 as indicated by the black circle, and the predicted LCD is 10.1 A/cm2. Although the prediction of LCD is qualitative, simulation could follow the IV characteristics obtained by experiment before LCD.Fig.2 and Fig.3 shows the effect of operating temperature and pressure on LCD. The electrolysis voltage “E” is experimentally determined, while the gas saturation at interface of PTL-CH “Sg” is obtained through simulation. As shown in Fig.2, the lower operation temperature enlarges the LCD, the experimental LCD increases 8% from 90 ℃ to 80 ℃. Theoretically, high operating temperature increases oxygen bubbles and then rises the gas saturation S g at the anode CL. So, the water supply flowing to CL is insufficient, and the electrochemical performance also decrease. Therefore, the overvoltages caused by mass transport becomes larger in higher operating temperature. As shown in Fig.3, higher operating pressure shrinks the volume of oxygen gas and enhance the water supply from CH to CL, leading to a larger LCD. Under 80 ℃, the experimental LCD rises by 17 % from 0.1 MPa to 0.3 MPa.Although the theoretical analysis reproduced the experimental results in a qualitative manner, the theoretical analysis suggests that, when electrolysis current density is quite close to the LCD, water mass transport at anode reaches a limitation, indicating that water saturation drops to zero at anodic catalyst layer. References Lee J K, et al. Cell Reports Physical Science, 2020:100147.A Zinser, et al. International Journal of Hydrogen Energy, 2019, 44(52): 28077-28087. Figure 1

An Investigation in Sub-Millimeter Channel Fabrication by the Non-Aqueous Electrolyte Jet Machining of Zr-Based Bulk Metallic Glasses.

Zr-based bulk metallic glasses (BMGs) have many unique properties. Due to their excellent performance and manufacturing process, they have become a research focus in the material science community. Electrolyte Jet Machining (EJM) is a non-contact electrochemical processing method with high surface integrity and high material removal rate (MRR). In this research, the sub-millimeter channels fabricated by EJM on Zr-based BMGs have been studied to explore the dissolution mechanisms and surface integrity under different scanning rates and voltages. The results show that, with other machining parameters holding constant, an increase in voltage leads to a substantial enhancement in both the depth and width of the channels machined on Zr-based BMGs. Notably, the influence of voltage on the depth of the channels is particularly pronounced. Additionally, an escalation in scanning rate correlates with a decrease in channel depth, with minimal variation in channel width. This study indicates that alcohol-based EJM is an effective method to fabricate sub-millimeter channels and modulate structures on Zr-based BMGs.

Design and fabrication of microfluidic devices: a cost-effective approach for high throughput production

Microdevices have been recognized as a potential platform for performing numerous biomedical analysis and diagnostic applications. However, promising and viable techniques for a cost-effective and high throughput production of microfluidic devices still remain as a challenge. This paper addresses this problem with an alternative solution for the fabrication of microfluidic devices in a simple and efficient manner. We utilized laser-assisted engraving technique to fabricate a master mold on an acrylic sheet of different thicknesses from 4 to 20mm. Low cost indigenously developed CO2 (10.6μm wavelength) laser engraving device was used for the experiments. The effect of various laser parameters such as power and speed of operation on the height of engraved structures was studied in detail. Optimal engraving results were obtained with a laser speed of 200–250mm s−1 with a spacing interval of 0.002mm at a laser power of 10–12W. Master mold of microdevice with a channel width of 100μm were produced using this technique. The replica transfer was performed by a simple imprinting method using a benchtop universal testing machine that can provide a maximum compressive load upto 1kN. The replicas were successfully generated on various thin film substrates including polymers, plastics, Whatman filter paper, teflon, vinyl sheets, copper, and aluminum sheets. The effect of load applied on the depth of the microfluidic channel was studied for the substrates such as teflon and Whatman filter paper. A load of 1kN can generate a depth of a few hundred micrometers on various substrates mentioned above. The replicas were also transferred to thermoformable PETG (polyethylene terephthalate glycol) sheets under load with an elevated temperature. The channel-imprinted PETG substrates were later sandwiched between two acrylic sheets with adhesive-coated polymer sheets and screws at the corners. Soft lithographic techniques were also performed to replicate the channel on a poly dimethyl siloxane substrate which was later bonded to a glass plate using an oxygen plasma cleaner device. Fluidic flow testing was conducted by pumping dye-mixed deionized (DI) water through the channels using a syringe pump and connecting tubes at a constant flow rate of 5ml min−1. The outcomes of this study provide an alternative solution for a simple and low-cost method for microdevice fabrication at a large scale.

Multi-objective optimization design and sensitivity analysis of proton exchange membrane electrolytic cell

Proton exchange membrane electrolytic cells (PEMECs) are considered cleaner energy-conversion devices with potential commercial applications in hydrogen production. However, the heat- and mass-transfer characteristics inside the cell remain unclear, and its performance should be optimized to achieve future commercial applications. A three-dimensional multi-physical field-coupling model is developed for the PEMEC. Subsequently, a multi-objective optimization design is used to optimize the structural and operational parameters of the cell based on a neural-network regression model. The results of the sensitivity and response-surface analyses indicate that the initial working temperature has the most significant impact on the reaction temperature, the current density is increased by up to 65.22% under the coupling effects of temperature and flow rate. The cell performance is also enhanced by the increased channel width and depth, although this is accompanied by limitations. Under the combined effects of increasing the working temperature and channel width or height, the current density can be increased by a maximum of 65.22% and 38.61%, respectively. The improvement in cell performance requires a trade-off between improved mass and heat transfer and larger pressure drop, and the optimal design achieves this trade-off. In optimal design, the current density is improved by up to 16.56%, the oxygen mass fraction of the catalytic layer is reduced by 40.90% compared with the original design, accompanied by a reasonable pressure drop and uniform temperature distribution. This study provides a novel perspective for the optimization of the PEMEC to promote its commercial application, offering a reference for further advanced optimization of cell performance and reducing trial-and-error costs. It is also expected to have practical applications in energy conservation and sustainable development.

Evaluation of WATERMARK Channel for Underwater Communication using Dual Tree Complex Wavelet Transform based Orthogonal Frequency Division Multiplexing Model

Underwater communication is one of the important research areas which involves design and development of communication systems that can demonstrate high data rate and low Bit Error Rate (BER). In this work three different modulation schemes are compared for their performances in terms of BER and Peak to Average Power Ratio (PAPR). The realistic channel model called WATERMARK is used as a benchmark to evaluate channel performances. The mathematical model is developed in MATLAB and channel environments such as Norway Oslo fjord (NOF1), Norway Continental Shelf (NCS1), Brest Commercial Harbour (BCH1), Kauai (KAU1, KAU2) are considered for modelling different underwater channels. The data symbols are modulated using Dual Tree Complex Wavelet Transform (DTCWT) Orthogonal Frequency Division Multiplexing (OFDM) model to generate multi subcarriers and are demodulated at the receiver considering underwater channel environments. The BER results are evaluated for channel depth less than 10m and 10-50m. An improvement of 2x10-2 in terms of BER is observed when compared with Fast Fourier Transform (FFT) based OFDM model.