Effect Of Channel Geometry Research Articles

Spiral microchannels with concave cross-section for enhanced cancer cell inertial separation.

Inertial microfluidic technologies have proven effective for particle focusing and separation in many microchannels, typically the channels with the rectangular and trapezoidal shapes. To advance particle focusing in complex channels, we propose a spiral channel combining rectangular and concave cross-sections for high-resolution particle and cell focusing and separation. Numerical simulations were conducted to illustrate the effects of channel geometry on secondary flow distribution and particle focusing positions. The simulation shows the concave cross-section generates two asymmetrical Dean vortices skewing towards the inner and outer channel walls, resulting to stronger flow velocity magnitudes near the walls than the channel center. Consequently, larger particles focus near the inner wall, while smaller particles are trapped closer to the outer wall under the influence of the stronger velocity magnitude near the walls. A microfluidic chip with the proposed channelgeometry, along with a traditional rectangular channel, was fabricated by 3D printing and PDMS casting. Fluorescent microbeads were used to investigate inertial focusing and separation behaviors in the microfluidicchips. Experimental results show that the concave channel facilitates particle focusing or trapping much closer to the walls than the traditional rectangular channel, achieving better separation resolution. Finally, the proposed channel was applied to separate lung cancer A549 cells from human blood, achieving a cancer cell recovery rate of ~ 84.78% (enrichment ratio over 820-fold) and a blood cell rejection rate of ~ 99.88%. This innovative channel design in inertial microfluidics offers new insights for enhanced particle focusing and holds significant promise for cell manipulation with improved separation resolution.

Experimental investigation on the effect of channel geometry on performance heterogeneity in hydrogen PEM fuel cell

Straight parallel graphite-based flow fields are experimentally assessed to evaluate the effect of geometrical parameters on the performance of polymer electrolyte membrane fuel cell. A 1+1D fuel cell model is exploited to evaluate the local operating conditions occurring along various positions of the flow field channel for different load requirements. The estimated operating conditions are implemented in a zero-gradient hardware to perform a broad experimental campaign, conducting tests under controlled and uniform operating conditions. The achieved experimental results depict the impact of the flow field geometry along different positions of the flow field channel under real operating conditions, identifying the individual contributions of the geometric parameters on water transport, oxygen transport and electrical resistance. The proposed methodology provides detailed information on the local operation of a large-area bipolar plate using a small-area sample, demonstrating the effect of rib and channel geometrical parameters on real-world operation of a PEMFC.

Evaluation of wavy wall configurations for accelerated heat recovery in triplex-tube energy storage units for building heating applications

Efficient thermal energy storage (TES) is crucial for integrating intermittent renewable energy sources and managing fluctuations in energy supply and demand. Among TES methods, latent heat TES (LHTES) using phase change materials (PCMs) is highly promising due to its high energy storage density and nearly isothermal operation during phase transitions. However, the inherently low thermal conductivity of PCMs hinders heat transfer rates, negatively impacting charging and discharging performance. This study investigates novel wavy channel geometries for the PCM container in a triplex-tube LHTES unit to enhance heat transfer and improve solidification rates during the discharge process. A comprehensive computational model based on the enthalpy-porosity method is developed to simulate the PCM (paraffin wax RT35) solidification inside wavy channels with sinusoidal, zigzag, and step-function profiles. The effects of channel geometry, heat transfer fluid (HTF) velocity, and inlet temperature on solidification rate and heat recovery are systematically evaluated. Results demonstrate that the step-function geometry significantly accelerates solidification compared to straight channels, reducing discharge time by 65.1 % and increasing heat recovery rate by 147.9 %. Decreasing waviness width from 15 mm to 5 mm further reduces solidification time by 70.1 %, while increasing waviness height from 5 mm to 15 mm leads to a 74.4 % reduction. Moreover, increasing HTF flow from Re = 250 to 1000 enhances heat recovery by 92.3 %, and lowering inlet temperature from 20 °C to 10 °C improves it by 76.9 %. The findings provide valuable insights for designing efficient LHTES units with wavy channel geometries for renewable energy integration and thermal management applications.

Enhanced Rectification Performance in Bipolar Janus Graphene Oxide Channels by Lateral Electric Fields.

Improving the ionic rectification in nanochannels enables versatile applications such as biosensors, energy harvesting, and fluidic diodes. While previous work mostly focused on the effect of channel geometry and surface charge, in this work via a series of molecular dynamics simulations, we find a striking phenomenon that the ionic current rectification (ICR) ratio in Janus graphene oxide (GO) channels can be tremendously promoted by lateral electric fields. First, under a given axial electric field, an additional lateral electric field can improve the ICR ratio by several times to an order, depending on the channel symmetry. The symmetric channel has an obviously greater ICR ratio because it maintains a more pronounced ion transport disparity at opposite axial fields. The underlying mechanism for the function of the lateral electric field is that it promotes the lateral migration of ions and thus amplifies the ion-residue electrostatic interaction at opposite axial fields, enlarging the ion dynamical difference. Furthermore, for different axial electric fields, the ICR ratio can always be improved by lateral electric fields (up to two orders), suggesting that the ICR improvement is universal. Our results demonstrate that applying a lateral electric field could be a new method to improve the rectification performance of nanochannels, providing valuable guidance for the design of efficient ionic diode devices.

Effect of channel geometry on the flame acceleration and transition to detonation in acetylene-oxygen-nitrogen mixtures

The study of unsteady combustion modes and, in particular, the deflagration-to-detonation transition, is of particular importance for the aerospace industry. Knowledge of the basic mechanisms, as well as the criteria for the development of detonation, helps to control this process in the framework of its applications for novel propulsion devices and safety issues. In this paper, a series of calculations are carried out in order to distinguish the role of channel geometry (planar or circular) in the flame dynamics at all the stages of acceleration prior to the deflagration-to-detonation transition. The combustion of a stoichiometric acetylene-oxygen mixture diluted with nitrogen is considered. It is established that in channels with a circular cross-section, the flame front is stretched and the combustion process evolves up to the transition to detonation, in accordance with the experiment. At the same time, in planar channels (slits), the primary flame acceleration leads to the establishment of a quasi-stationary mode. The peculiarities of the compression and rarefaction waves evolution in the cylindrical and planar geometry are responsible for such a difference between the flame dynamics in channels of different geometry. The detonation onset takes place via the formation of a “chocked flame” structure characterized by permanent joint compression and acceleration of the combustion. As well as in experiments the deflagration-to-detonation transition occurs exactly at the flame front.

Continuous Flow Synthesis of 4‐methyl‐3‐oxo‐n‐phenyl‐pentanamide

Abstract4‐methyl‐3‐oxo‐n‐phenyl‐pentanamide, as a crucial component of atorvastatin calcium, often generates a large amount of by‐products in conventional synthesis. Here, we first developed a continuous microflow system for the continuous flow synthesis of 4‐methyl‐3‐oxo‐n‐phenyl‐pentanamide. Compared to traditional batch reactors, the reaction time was reduced by 1/12 in the microreactor. Using this device, the kinetic parameters of the reaction were determined, and a reaction kinetics model was established to investigate the effects of channel geometry and material inlet velocity on the entire reaction system. Furthermore, we studied the subsequent reactions and successfully established a fully continuous synthesis device, where the two‐step continuous flow chemical reactions were achieved at 40 minutes and a total yield of 32 %.

Liquid plug propagation in computer-controlled microfluidic airway-on-a-chip with semi-circular microchannels.

This paper introduces a two-inlet, one-outlet lung-on-a-chip device with semi-circular cross-section microchannels and computer-controlled fluidic switching that enables a broader systematic investigation of liquid plug dynamics in a manner relevant to the distal airways. A leak-proof bonding protocol for micro-milled devices facilitates channel bonding and culture of confluent primary small airway epithelial cells. Production of liquid plugs with computer-controlled inlet channel valving and just one outlet allows more stable long-term plug generation and propagation compared to previous designs. The system also captures both plug speed and length as well as pressure drop concurrently. In one demonstration, the system reproducibly generates surfactant-containing liquid plugs, a challenging process due to lower surface tension that makes the plug formation less stable. The addition of surfactant decreases the pressure required to initiate plug propagation, a potentially significant effect in diseases where surfactant in the airways is absent or dysfunctional. Next, the device recapitulates the effect of increasing fluid viscosity, a challenging analysis due to higher resistance of viscous fluids that makes plug formation and propagation more difficult particularly in airway-relevant length scales. Experimental results show that increased fluid viscosity decreases plug propagation speed for a given air flow rate. These findings are supplemented by computational modeling of viscous plug propagation that demonstrates increased plug propagation time, increased maximum wall shear stress, and greater pressure differentials in more viscous conditions of plug propagation. These results match physiology as mucus viscosity is increased in various obstructive lung diseases where it is known that respiratory mechanics can be compromised due to mucus plugging of the distal airways. Finally, experiments evaluate the effect of channel geometry on primary human small airway epithelial cell injury in this lung-on-a-chip. There is more injury in the middle of the channel relative to the edges highlighting the role of channel shape, a physiologically relevant parameter as airway cross-sectional geometry can also be non-circular. In sum, this paper describes a system that pushes the device limits with regards to the types of liquid plugs that can be stably generated for studies of distal airway fluid mechanical injury.

3D Printed Tubulointerstitium Chip as an In Vitro Testing Platform.

Chronic kidney disease (CKD) ranks as the twelfth leading cause of death worldwide with limited treatment options. The development of in vitro models replicating defined segments of the kidney functional units, the nephrons, in a physiologically relevant and reproducible manner can facilitate drug testing. The aim of this study was to produce an in vitro organ-on-a-chip platform with extrusion-based three-dimensional (3D)printing. The manufacturing of the tubular platform was produced by printing sacrificial fibers with varying diameters, providing a suitable structure for cell adhesion and proliferation. The chip platform was seeded with primary murine tubular epithelial cells and human umbilical vein endothelial cells. The effect of channel geometry, its reproducibility, coatings for cell adhesion, and specific cell markers were investigated. The developed chip presents single and dual channels, mimicking segments of a renal tubule and the capillary network, together with an extracellular matrix gel analogue placed in the middle of the two channels, envisioning the renal tubulointerstitium in vitro. The 3D printed platform enables perfusable circular cross-section channels with fully automated, rapid, and reproducible manufacturing processes at low costs. This kidney tubulointerstitium on-a-chip provides the first step toward the production of more complex in vitro models for drug testing.

Evaluating river morphology change with a geomorphic form variation approach

AbstractGeomorphic river design strives for natural resilience by encouraging geomorphic form complexity and morphological processes linked to greater habitat diversity. Increasing availability of high‐resolution topographic data and spatial feature mapping methods provide advantages for morphological analysis and river restoration planning. We propose and evaluate an approach to quantifying topographic variability of geomorphic form and pixel‐level surface roughness resulting from channel planform geometry differences using spatially continuous variety computation applied to component metrics including flow direction, aspect and planform curvature. We define this as the geomorphic form variation (GFV) approach and found it scalable, repeatable and a multi‐stage analytical metric for quantifying physical aspects of river‐bed topographic variability. GFV may complement process‐based morphological feature mapping applications, hydraulic assessment indices and spatial habitat heterogeneity metrics commonly used for ecological quality evaluation and river restoration. The GFV was tested on controlled synthetic channels derived from River Builder software and quasi‐controlled sinuous planform flume experiment channels. Component variety metrics respond independently to specific geometric surface changes and are sensitive to multi‐scaled morphology change, including coarser‐grained sediment distributions of pixel‐level surface roughness. GFV showed systematic patterns of change related to the effects of channel geometry, vertical bed feature (pool‐bar) frequency and amplitude, and bar size, shape and orientation. Hotspot analysis found that bar margins were major components of topographic complexity, whereas grain‐scale variety class maps further supported the multi‐stage analytical capability and scalability of the GFV approach. The GFV can provide an overall variety value that may support river restoration decision‐making and planning, particularly when geomorphic complexity enhancement is a design objective. Analysing metric variety values with statistically significant hotspot cluster maps and complementary process‐based software and mapping applications allows variety correspondence to systematic feature changes to be assessed, providing an analytical approach for river morphology change comparison, channel design and geomorphic process restoration.

Flow study of Dean’s instability in high aspect ratio microchannels

Dean’s flow and Dean’s instability have always been important concepts in the inertial microfluidics. Curved channels are widely used for applications like mixing and sorting but are limited to Dean’s flow only. This work first reports the Dean’s instability flow in high aspect ratio channels on the deka-microns level for De>162. A new channel geometry (the tortuous channel), which creates a rolled-up velocity profile, is presented and studied experimentally and numerically along with other three typical channel geometries at Dean’s flow condition and Dean’s instability condition. The tortuous channel generates a higher De environment at the same Re compared to the other channels and allows easier Dean’s instability creation. We further demonstrate the use of multiple vortexes for mixing. The mixing efficiency is considered among different channel patterns and the tortuous channel outperforms the others. This work offers more understanding of the creation of Dean’s instability at high aspect ratio channels and the effect of channel geometry on it. Ultimately, it demonstrates the potential for applications like mixing and cell sorting.

Experimental investigation on the effects of the geometry of microchannels based heat sinks on the flow boiling of HFE-7100

In this paper, nine Microchannel Heat sinks (MCHs) all with channel lengths of 20 mm and heights of 1 mm but with different aspect ratios 1.33; 2 and 4, wall thicknesses 0.25–0.75 were tested in single and two-phase flows using the HFE-7100 as the working fluid. Three different scenarios were established, changing only the inlet temperature of the fluid: ambient (18–25 °C), intermediate (38–42 °C) and near saturation (55–58 °C). In all experiments the flow at the inlet was in the laminar region with Reynolds (Re) number values ranging from 50 to 130. A thermographic camera was placed below the microchannel heat sink, to observe the cooling process during the flows. Thus, the main objective of this study is to evaluate the effects of channel geometry on both the overall heat transfer coefficient and the pressure losses. The results demonstrate that, for both single and two-phase flow, narrower channels exhibit better thermal performance but higher-pressure losses than wider channels. When maintaining channel width constant and varying thicknesses, channels with wider walls presented higher overall heat transfer coefficients and lower pressure losses.

Numerical Investigation of the Effects of Channel Geometry on Heat Transfer in a Mini Channel with Narrowing and Expanding Geometry

Bu çalışmada yüksek sıcaklıklara ulaşan yüzeylerin soğutulması için kullanılan mini kanallı bir ısı alıcısının soğutma performansı incelenmiştir. Bu mini kanalın kanal uzunluğu boyunca kesit alanı değiştirilerek, düz kanal, daralan-genişleyen kanal ve genişleyen-daralan kanal olmak üzere üç ana kanal geometrisi belirlenmiştir. Ayrıca bu ana model geometrilerinde genişleme ve daralma açıları değiştirilerek farklı bölme sayısına sahip alt geometrik modeller oluşturulmuştur. Reynolds sayısı 500-2000 aralığında, bölme adeti de 3-12 aralığında değiştirilerek analizler yapılmıştır. Yapılan analizler sonucunda, tüm model geometrilerinde akışın Reynolds sayısının artması ile ısı transferinin arttığı gözlemlenmiştir. Bölme sayısının artışı ile hem daralan-genişleyen hem de genişleyen-daralan kanal tiplerinde Nusselt sayısının artış gösterdiği, dolayısıyla kanalın sahip olduğu bölme sayısının artırılması ısı transferini olumlu yönde etkilediği gözlemlenmiştir. Daralan-genişleyen kesite sahip kanal tipinde diğer kanal tiplerine oranla daha yüksek Nusselt sayıları elde edilmiştir. Daralan-genişleyen kesite sahip modelin sonuçları düz kanal tipi ile kıyaslandığında, Nusselt sayısının ve termal performans faktörünün sırasıyla yaklaşık %50 ve %100 kadar artış gösterdiği görülmüştür. Dolayısıyla incelenen parametre aralığında daralan-genişleyen kesite sahip mini kanal geometrisinin soğutma performansının incelenen diğer kanal geometrilere oranla daha yüksek olduğu söylenebilir.

Multiple-open-tubular column enabling transverse diffusion. Part 3: Simulation of solute dispersion along a real three dimensional-printed column with quadratic channels

Multiple-open-tubular columns enabling transverse diffusion (MOTTD) consist of straight and parallel flow-through channels separated by a mesoporous stationary phase. In Part 1, a stochastic model of band broadening along MOTTD columns accounting for longitudinal diffusion, trans-channel velocity bias, and mass transfer resistance in the stationary phase was derived to demonstrate the intrinsic advantage of MOTTD columns over classical particulate columns. In Part 2, the model was refined for the critical contribution of the channel-to-channel polydispersity and applied to address the best trade-off between analysis speed and performance. In this Part 3, a MOTTD column with a square array of quadratic channels is fabricated by 3D-printing (combining polymer stereolithography with photolithography using photomasks) to deliver unprecedently small apparent channel diameters of 117.6 ± 5.0 μm. The colors in the microscopy photographs of the actual 3D-printed channels are binarized to delimitate the mobile phase volume from the stationary phase volume. The same numerical simulations as those in Part 2 are then performed for two MOTTD columns (external porosity ϵe=31.7%, same apparent channel diameter 117.6 μm): one containing 16 virtual perfect quadratic channels and the other 16 real 3D-printed channels. The reduced velocities (or Peclet numbers) are varied over a wide range from 0.2 to 5000 and the zone retention factors were fixed at k1=1.04, 5, and 25.The results demonstrate that smoothing the edges of the targeted quadratic channels by the 3D-printed technique is advantageous in terms of solute dispersion. It outperforms the negative effect of the channel-to-channel polydispersity which is mitigated by transverse diffusion of the analyte in the stationary phase. For Peclet numbers larger than 50, the HETP of the 3D-printed MOTTD column is found 7%, 15%, and 16% smaller than that of the MOTTD column consisting of a square array of perfect quadratic channels. This confirms the known effect of channel geometry on solute dispersion in microfluidic systems. Flow channels in fabricated MOTTD columns are preferred to be circular so that the distribution of transverse diffusion lengths across the open channels remains as tight as possible. Finally, the general theory of nonuniform columns of Giddings reveals that the polydispersity of the cross-sectional area (RSD 8.4%) along a single 3D-printed channel has no negative impact on solute dispersion in MOTTD columns. Overall, MOTTD columns could become a serious alternative technology to conventional particulate columns. This implies a novel fabrication process that delivers circular channel diameters smaller than 10 μm, cross-sectional area polydispersity no larger than 25%, external porosities in a range from 15% (high speed separations) to 75% (high performance separations), and conventional mesoporous silica as the stationary phase. It adresses new synthesis routes based on either organic fibers or tubular micelle templating agents in suspension with silica gel solutions.

Effect of channel width on droplet generation inside T-junction microchannel

In a T-junction microchannel, channel geometry plays a major role that affects the physics behind droplet generation. The effect of channel width on droplet size and frequency in a T-junction microchannel is investigated in the present study. The current work is an extension of our previous work, where a model was developed to predict the size of the droplets generated in a T-junction microchannel when both the continuous and dispersed phase channels have equal widths. In the present work, we extended the model to account for the varying width ratio between the dispersed and continuous phase channels. We performed in-house experiments by varying the channel width and viscosity ratios between the fluids to study the size of the droplets generated and to validate the proposed scaling law. We further investigated the effect of channel geometry on the frequency of droplet generation in the T-junction microchannels. The experimental results show that the droplet length increases with an increase in the width of the continuous phase channel. On the other hand, the droplet production frequency decreases with an increase in the width of the continuous phase channel. With variations in the width of the dispersed phase channel, similar behavior in droplet sizes and the frequency of droplet production is observed. The analysis of this study provides new insight into the effect of channel width on the droplet length and frequency. Overall, this research intends to provide a thorough understanding of the design of microchannels based on the geometry and manipulation of droplets with varying widths.

Rarefied gas flow into vacuum through linearly diverging and converging channels

Using the direct simulation Monte Carlo direct method, rarefied gas flow into a vacuum through linearly diverging and сonverging сhannels has been studied. The problem has been solved in the complete geometrical setup, namely with including certain pre- and post-channel regions in the geometry under consideration. In a wide range of gas rarefaction, a mass flow rate through the channel, the gas flow diodicity, and flow field both inside the channel and in the regions upstream and downstream have been computed. Computation results are compared to corresponding data for the channel with a constant cross-section. A strong effect of channel geometry and gas rarefaction has been stated. In particular, in the dependence of the mass flow rate on the gas rarefaction, a so-called Knudsen minimum has been revealed; while in the flow field, one-dimensional distribution of gas density in the channel has been found.

The effect of channel geometry and check dam location on sediment transport discharge in the Kuranji River

Rivers as infrastructure carry water from upstream to downstream to meet the water needs of communities along the river and as drainage. Therefore, it is necessary to maintain the stability of the river from erosion and sedimentation. Changes in river geometry are mostly caused by the high intensity of rainfall in the upstream section. This causes the geometry to change easily, many bends are found, river embankments collapse, and the slope and flow of the river change suddenly. As a result, water will wash away sediment from upstream to downstream with high sediment discharge. However, the sediment rate/discharge can be reduced by building a check dam, but it needs the right location so that the construction of the check dam is effective and the river flow is stable. Research using HEC-RAS has been carried out at the location of the middle section of the Kuranji River, where simulating three check dam locations shows that the reduction in sediment discharge is very effective, but other places are still the same as without the check dam. Therefore, it is recommended to build check dam series and groundsills at narrowing locations and strengthen river banks at Sta. 16 to Sta. 32.

Syngas production from chemical-looping steam methane reforming: The effect of channel geometry on BaCoO3/CeO2 monolithic oxygen carriers

Chemical-looping steam methane reforming (CL-SMR) is a promising technology to achieve the co-production of syngas and hydrogen. The performance of oxygen carriers in the partial oxidation of methane stage is crucial for the composition of syngas products. In this study, the performance of BaCoO3/CeO2 monolithic oxygen carrier for syngas production was investigated. The result of characterizations suggested that the oxygen carriers maintain the ideal crystal structures, the macroporous layer of BaCoO3/CeO2 adhered to monolith achieved a good energy supply and a high gas-solid contact area. To determine the reaction heat of partial oxidation of methane, the standard enthalpy of formation of BaCoO3 was measured by DSC, the obtained value was −957.794 kJ/mol. Based on the experimental result, a kinetic model of partial oxidation of methane was established, the obtained value of A and Ea were 75.902 and 74.772 kJ/mol, respectively. The effect of geometry on reaction performance was investigated by numerical simulation. It suggested increasing number of channel faces could improve the uniformity of reaction, the uniform reaction along the channel was beneficial to control the extent of reaction. Monolithic oxygen carriers need a proper geometry design to find a compromise between the heat storage for temperature control and reaction surface area.

The effects of coastal marsh geometry and surge scales on water level attenuation

Coastal wetlands are an effective natural and nature-based feature to mitigate coastal flood hazards. While the sheltering and attenuation offered by wetlands are recognized, the protection level varies based on wetland and storm characteristics. Here we focus on the effects of the spatial scales of the coastal wetlands (i.e., channel geometry, marsh elevation-gradient) and the temporal scales of storm forcing (i.e., storm surge amplitude and duration) on peak water level attenuation. The study was conducted by performing hydrodynamic simulations on an idealized marsh geometry. One hundred seventy-one hydrodynamic simulations were conducted by varying wetland features under variable hydrodynamic forcing. Increased tidal channel area enhances water flow across marshes by reducing the capacity of vegetated platforms to resist propagation of a storm surge. The level of surge attenuation and channel area shows a non-linear relationship. Storm scales also affect surge attenuation for a given channel geometry. Higher amplitudes and lower surge durations provide greater attenuation of peak water levels. The level of attenuation and surge scales also show a non-linear correlation. A multivariate scaling relationship was developed that successfully integrates the combined effects of channel geometry and surge scales on water level attenuation by salt marsh. This research provides guidance to engineers and coastal managers on salt marsh's flood hazard reduction benefits.

Surface dense discharge from rectangular and trapezoidal channels

In this paper, the effect of channel geometry on the characteristics of surface dense jets was experimentally investigated. Their geometric properties for various densimetric Froude numbers were studied for rectangular and trapezoidal channels. A simple innovative image processing technique was implemented to study flow trajectory, jet width, plunge point location, impact point, and location of ultimate discharge mixing zone. For small Froude numbers, Frd≤20, it was observed that the channel geometry was an important parameter influencing the dense flow behavior. The plunge point and impact point for the trapezoidal section were 1.37 and 1.53 times more than the rectangular section, linearly proportional to densimetric Froude number. Longer trajectory in trapezoidal channels leads to better dilution at the impact point. The comparisons showed when the objective was to achieve higher mixing, the trapezoidal section was preferable. However, in terms of the ultimate mixing location, both sections were the same. The closer the shape of the channel to the best hydraulic section (semi-circle section), the geometrical parameters and mixing characteristics would be more appropriate. The non-dimensional equations were determined based on dimensional analysis and regression with R2 > 0.9 in the rectangular section and R2 > 0.8 in the trapezoidal section, which are beneficial to design and optimization of marine outfalls on large scales.

Using Membranes with Internal Microchannels to Prevent Drying-out during CO2 Electrolysis

Scaling up CO2 electrolysis is a vital aspect in the transition to manufacturing sustainable fuels and chemical compounds, satisfying the demand for chemicals and demand for storing renewable electricity. Depending on the employed catalyst, different products can be produced, such as carbon monoxide and ethylene, by applying a voltage on a CO2 and H2O fed electrolyzer. CO is a desirable product according to techno-economic analysis, because it can be produced selectively using a silver catalyst and is a precursor for hydrocarbons in the Fischer–Tropsch process. In a state-of-the-art CO2 electrolyzer, two electrodes are directly pressed against an ion-exchange membrane – this is called a zero-gap configuration. Therefore, the membrane is a crucial component for the system, since it has the role of providing a conductive medium between the electrodes.One of the challenges in CO2 electrolysis is that water is consumed in the reaction. At high current density, this may cause the membrane's surface near the cathode to dry out, lowering efficiency or perhaps stopping the process entirely, since there is no longer a conductive medium. As a result, water management is critical for this process.In this work, we approach the drying-out challenge by studying the novel concept of a membrane with internal microchannels. These channels allow the circulation of water or an electrolyte inside the membrane, which reduces the water diffusion path and affects the membrane’s conductivity.The effects of channel geometry, location, and concentrations of electrolyte inside on water content, conductivity and overall performance are studied in a 2D COMSOL model. In addition, the effect of internal concentration of electrolyte on the membrane’s resistance, on the process performance and the K+ cross-over to cathode side were investigated experimentally.Our modeling results prove that the presence of the channels can keep the membrane hydrated. The highest current densities are observed when the channel is closest to the cathode, and with smaller pores. Smaller pores are advantageous due to the trade-off between enhanced membrane conductivity and the lower conductivity of the liquid itself. If water is circulated in a large channel, it increases the membrane’s ionomer conductivity due to hydration but the overall conductivity is decreased since water is not highly conductive. Nonetheless, the results also show that a higher concentration of electrolyte inside the microchannels can significantly increase the total conductivity of the membrane, and therefore the energy efficiency of the process. These effects are most significant at higher current densities.In the experimental results, we’ve observed similar effects in terms of membrane conductivity and current density of the process – the higher the electrolyte concentration the higher the current density. Furthermore, a low concentration decreases the amount of potassium which crosses over to the cathode side, inhibiting salt deposition.We’ve concluded that a small channel, up to 90 µm wide, close to the pore with an electrolyte with a concentration of up to 10 mM could be very beneficial for the water management and energy efficiency of the process. This helps to keep the membrane hydrated at higher current densities, improves the conductivity of the membrane, and it doesn’t have significant impacts on the salt deposition. Figure 1