Porosity Configuration Research Articles

Predicting pressure buildup behind perforated plates under blast wave impact: A simplified approach

This study experimentally investigates the interaction of an incident blast wave with a perforated multiple plate array and the subsequent pressure buildup on an end wall. Experiments are conducted in a square tunnel using arrays composed of plates with varying porosities and perforation diameters positioned at different distances from the end wall. High-speed shadowgraphy and pressure measurements quantify the influence of these parameters on transmitted wave attenuation and pressure buildup on the end wall. Results demonstrate that wave attenuation and pressure buildup rates are significantly influenced by plate porosity, array length, and stand-off distance, whereas the perforation diameter has a negligible effect. A theoretical model is employed to predict the measured end wall pressure history. The model accurately predicts overall pressure history, including peak pressure and decay, for various porosities, plate numbers, and stand-off distances. Deviations between model predictions and experimental data are analyzed. Additionally, the pressure measurements reveal a power-law relationship between the transmitted wave attenuation rate and the porosity index. Notably, arrays with lower porosity, consisting of fewer plates, can effectively attenuate the transmitted wave compared to higher porosity configurations with more plates. By attenuating the peak pressure on the target wall/end wall and extending the pressure buildup time, the perforated plate arrays provide a promising approach to enhance blast protection.

A novel preparation of porous Li2TiO3 pebbles with a distinctive structure

Optimization of the pore structure stands out as an effective approach for bolstering the tritium release performance of lithium-based tritium breeding ceramics, particularly when employing a high open porosity configuration. In this study, Li2TiO3 fibers were synthesized via the hydrothermal method, with the assistance of TiO2-B nanowires acting as templates. Subsequently, porous Li2TiO3 pebbles with varying microstructures were fabricated through a combination of the wet method and a sintering process. Sintering process plays a crucial role in determining the microscopic morphology. An increase in temperature resulted in a suppression of the growth of fibrous grains and the transformation of fibrous grains into quasi-spherical grains. Moreover, a two-step sintering process was proposed as a means of improving the crush load (15.9 N vs. 22.0 N) of Li2TiO3 pebbles while simultaneously preserving their high porosity (24.91%). The Li2TiO3 pebbles, produced by the two-step sintering process, exhibited a distinctive micromorphology characterized by interconnected particles forming short rod-shaped microstructures. This distinctive micromorphology contributes to the maintenance of a high degree of open porosity (10.52%).

Independent Configuration and Reprogramming of Porous Characters in Macroporous Hydrogel Enabled by the Orthogonal Dynamic Network.

Macroporous hydrogels have attracted much attention in both industry and academia, where the morphological characteristics of pores are essential. Despite significant improvements on regulating porous structures, the independent configuration and reprogramming of porosity and pore size still remain challenging owing to the lack of a chemical design to decouple the mechanism for adjusting each characteristic. Here, we report a strategy to adaptively control porous features relying on an orthogonal dynamic network. Disulfide bonds are employed to relax polymer chains during freezing via UV irradiation, thus, generating pores in hydrogels. On such a basis, the porosity is continuously switched from 0 to 75% by controlling network relaxation ratios. Subsequently, the pore size is further reversibly manipulated through the association or dissociation of dynamic metallic coordination. As a result, the porosity and pore size achieved independent configurations. Meanwhile, the dynamic nature of the network makes it possible to reprogram the porous character of a prepared hydrogel. Beyond these, the photopatterning of pores represents the capability to regulate the third feature. Our strategy provides an effective way to arbitrarily manipulate porous morphologies, which can inspire the design of future functional porous materials.

Computational biomechanical analysis of Ti-6Al-4V porous bone plates for lower limb fractures

The current study investigates the biomechanical performance of porous bone plates augmented with three different cellular lattice structures, e.g., body-centered cube (BCC), simple cube (SC), and the superposition of simple and body-centered cube (SC-BCC) structures. The SC-BCC cellular structures, exhibiting improved torsional, compression, and bending stiffness, were strategically integrated into the bone plates. Configurations ranging from one to three rows, with porosity ranging from 30% to 90%. Increasing the number of rows and porosity maximized the interfragmentary movement at the fracture site. Specifically, SC-BCC configurations with one, two and three rows at 90% porosity demonstrated callus volume improvements of 31.33%, 42%, and 43.2%, respectively, compared with the lowest callus volume observed with SC-BCC at one row and 30% porosity. Regardless of the improved volume, callus stiffness was highest at 30% and 90% porosity levels across all cases, indicating more mature tissue formation in calluses and better physiological load support. High stresses located at 90% porosity, followed by 50% porosity, discouraged their mechanical performance. Therefore, employing 30% porosity configurations with appropriate vertical rows for desired movement is recommended for optimal biomechanical performance. However, 90% porosity may be suitable in scenarios involving minimal forces and restricted patient movement.

Field synergy analysis on thermal-hydraulic behavior of phase change slurry in porous microchannel heat sink with graded porosity configuration

In this study, a novel design of porous microchannel heat sink (MCHS) with graded porosity configuration is proposed in the hope of attaining lower flow and thermal resistances than constant porosity (CP) configuration. The efficacy of new scheme is validated by utilizing a three-dimensional solid-fluid conjugate model based on the finite volume method, which considers the flow and heat transfer of microencapsulated phase change material slurry (MPCMS) inside the porous fins. It is reported that the thermal performance of porous MCHS with constant and graded porosity configurations is significantly better than that of non-porous MCHS. The feasibility of new design is verified by comparing the hydrothermal behavior of multiple graded porosity MCHSs and CP configuration for different fin designs (involving the number of graded equidistant fins N, graded length ratio R, and fin-to-pitch width ratio β) and operating conditions (including Reynolds number Re, mass fraction cm, and inlet velocity uin). The comprehensive performance improvement mechanism of MPCMS in graded porosity microchannels is discussed through the analysis of flow and thermal details, field synergy angle (θ) and field synergy number (Fc), and the overall performance of new design is evaluated by performance evaluation factor (PEF). Results indicate that the six types of porous MCHS with stepwise varying porosity exhibit lower thermal resistance than CP mode, and better thermal behavior and larger PEF can be obtained at N = 2 and β = 0.7. Smaller and larger R should be chosen for stepwise increasing porosity (SIP) and stepwise decreasing porosity (SDP) modes, respectively, to achieve higher heat transfer enhancement while avoiding greater friction losses. The Fc value of porous MCHS with various porosity configurations is about two orders of magnitude less than 1 and shows a monotonically reducing trend with Re, and the synergistic effect deteriorates at high Re. Compared to the CP mode, a low-θ “drift” toward the low porosity region of porous fin occurs within the graded porosity MCHS, which decreases and increases in the downstream and upstream directions of the “drift”, respectively. Among the novel MCHS designs, the z-directional SIP mode acquires the best overall performance due to the excellent synergy between the velocity and temperature fields, and its PEF consistently exceeds 1.13 and reaches up to 1.33. Generally speaking, the fin porosity of graded porosity MCHS near the channel cavity, channel top, and channel inlet should be greater for superior comprehensive performance.

Biomass derived evaporator with highly interconnected structure for eliminating salt accumulation in high-salinity brine

Solar-driven evaporator is regarded as an energy-saving and eco-friendly desalination technology. However, available unfriendly synthetic materials and salt crystallization problems limit the evaporator's performance and development, especially in high-salinity condition. Hence, inspired by the highly interconnected microchannels, a carbonized white gourd (CWG) derived self-desalting evaporator was developed to evaporate and desalinate seawater. To evaluate the efficacy of the porous features, the effect of different porosity configurations on water evaporation and anti-salt abilities of CWG was discussed. High and stable evaporation rates of 1.76 and 1.44 kg·m−2·h−1 were reached for 3.5 wt% and 20 wt% NaCl solutions, respectively, which were attributed to the highly efficient water transport and self-desalting capabilities, and it further increased to 2.19 kg·m−2·h−1 by adding an extra convective air (2 m/s) located at the evaporation interface. Moderate airflow effectively enhanced the evaporation efficiency and delayed re-crystallization of salt, promoting a long-term stable desalination process. Conversely, excessive convective flow (4 m/s) may directly impair evaporative stability and salt resistance. This research is expected to provide a new insight into the design of high performance, low cost, eco-friendly and salt-resistant evaporator applied to solar desalination.

Computational fluid dynamic analysis of an adsorption-based cogeneration osmotic heat engines with stepwise porosity distribution

Adsorption-based osmotic heat engines offer an alternative way for converting ultra-low temperature waste heat into electricity. Here, considering the heat and mass transfer characteristics in the adsorbent bed, a computational fluid dynamic model is developed to describe the adsorption-based osmotic heat engine for power and refrigeration cogeneration. Impacts of the porosity distribution, adsorption time, switching time, fin number and working solution-adsorbent pairs on system performance are comprehensively analyzed under different porosity distribution configurations. Results reveal that Configuration I leads to higher coefficient of performance (COP), exergy efficiency. However, Configuration II renders higher electrical efficiency. Compared with the uniform porosity configuration, COP and exergy efficiency are respectively elevated by 1.96% and 1.19% under the stepwise porosity configuration of 0.3–0.5. The electrical efficiency is increased by 15.5% with porosity configuration of 0.7–0.2. LiCl and AQSOA-Z02 under the stepwise porosity configuration of 0.7–0.2 can lead to the highest exergy efficiency of 7.76%.

Ultra-sensitive H2O2 sensing with 3-D porous Au/CuO/Pt hybrid framework

A 3-D porous Au/CuO/Pt hybrid platform is proposed to overcome the drawbacks of non-enzymatic H2O2 sensing. The Au/CuO/Pt hybrid sensor exhibits an extraordinary catalytic performance towards H2O2 reduction with an ultra-high sensitivity of 25,836 µA mM−1 cm−2 and a limit of detection of 1.8 nM (S/N = 3). It demonstrates an excellent anti-interference ability for NaCl, fructose, ascorbic acid, citric acid, dopamine, and glucose. The hybrid Au/CuO/Pt sensor exhibits outstanding stability for a wide range of molarity applications as well as a stable current for a long period of 30 h. These rank the proposed Au/CuO/Pt framework as one of the best-performing non-enzymatic H2O2 sensors. The rapid redox reaction is the synergistic result of superior catalytic response, large electrochemical-active surface area, high conductivity, and improved electron transfer pathways offered by the unique configuration of high porosity and metallic nano-micro-NP decoration.

Integrated core-shell structured smart textiles for active NO2 concentration and pressure monitoring

Energy crisis and atmospheric contamination urgently warrants the low-energy consumption and scalable hazardous gas detection for environmental government. However, most of existing gas sensors are restricted by tremendous power supply and burdensome maintenance as well as bulky volume. Herein, a core-shell structured smart textile (CST) was constructed via coaxial electrospinning to synchronously and sympatrically couple the piezoelectric transduction of polyvinylidene fluoride/lead zirconate titanate (PVDF/PZT) core layer and chemoresistor-sensing of polyaniline/polyvinyl pyrrolidone (PANI/PVP) shell layer in a single fiber, enabling autonomous and simultaneous monitoring of pressure and concentration of NO2 gas. The three basic gas sensing attributes of receptor function, transducer function and utility factor of the sensing body can be concurrently modulated/optimized by tuning the composition and mesoscopic configuration of porosity and sensing-transducing component ratio. A high sensitivity of 0.32 ppm−1, low detection limit (∼100 ppb) and good selectivity was achieved toward NO2 detection. Furthermore, the as-prepared CST demonstrates great capability in simultaneous gas pressure (57 mV/KPa) and concentration detection. By combining theoretical modeling and numerical simulation, a sensing mechanism was established to well unravel/predict the gas sensing behaviors. This work opens a new paradigm for constructing active multifunctional environmental sensors and multimodal smart textiles.

Mapping of quench front propagation in a heated cylindrical particle bed – MONET tests

In case of a severe accident in nuclear reactor, a debris bed may be formed from the fragmentation of the molten core at different stages of the accident. Debris bed coolability is an important issue, as it will determine the accident progression, its termination, and mitigation. One of the major concerns of debris bed coolability investigations is to understand and evaluate the effect of water re-flooding. Many experiments have been conducted to study the two-phase flow and heat transfer in porous medium configuration. However, the understanding of debris bed quenching with multi-dimensional characteristics are limited. Here, a test facility MCCI-mitigatiON through passive cooling Effect Test (MONET) apparatus is established to conduct the porous debris bed re-flooding investigation. The objective is to understand the mechanism of heat transfer and quench front movement inside the cylindrical heated debris bed during quenching by cooling water supplied from the bottom of the bed. Specifically, the effect of Homogeneous bed (with different external boundary conditions) and radially stratified bed (with different internal porosity configurations) conditions of the cylindrical debris bed on the quench front movement has been investigated. The particulate debris bed is formed with two different types of particles (SS 304, alumina) and sizes (2–3.5 mm). The effect on the quench front movement inside the particle bed has been reported by using temperature measurements together with direct visualizations. Present findings suggest non-uniform quench front propagation pattern even for the homogeneous bed conditions. While the tests with the stratified bed indicate a clear influence of low porosity region on the quench front and vapor movement.

Numerical investigation on transpiration cooling performance with different porosities and mainstream pressure gradients

Improving transpiration cooling performance is a challenge to meet the requirements for the cooling performance and thermal stress restrict. In the current study, numerical simulations are carried out to investigate the transpiration cooling performance with different porosity configurations and mainstream pressure gradients. Eight porosity configurations, three mainstream pressure gradients, and three injection ratios are considered. Cooling effectiveness distributions and cooling effectiveness uniformities are evaluated. Velocity distributions and coolant allocations are also studied to reveal the cooling mechanism. Results show that all the transpiration cooling cases gain higher cooling effectiveness than the film cooling cases, and the maximum enhancement reaches up to 100%. However, the transpiration cooling cases have non-uniformity distributions of cooling effectiveness due to the uneven coolant allocations caused by the superposition effects. For uniform porosity configuration cases, the cooling effectiveness increases monotonically with the increasing porosity due to the enhanced external coolant coverage, whereas the uniformity of cooling effectiveness decreases due to the more uneven coolant allocation distribution along the mainstream direction, especially for the configurations with large porosity. In addition, when streamwise pressure gradients exist in the mainstream, only the TC-3 case with a small uniform porosity and the TC-8 case with a streamwise decreasing porosity perform better robustness. Among them, the TC-8 case gains obvious advantages in engineering applications due to the highest cooling effectiveness and the smallest non-uniformity, which is caused by the better coolant coverage and more uniform coolant allocation.

Design and evaluation of variable porosity charring composite for thermal protection system of reentry vehicles

Charring composites can provide the most efficient thermal protection shield for the thermal protection system (TPS), which is essential for hypersonic reentry vehicles. It is of great importance to clarify the implication of different porosity configurations of charring composite on the bondline temperature. In the present study, a one-dimensional transient thermal model considering the pyrolysis without the surface recession is built and validated. Based on this model, the thermal protection performance of various porosity distribution design schemes is analyzed when keeping the total pore volume unchanged. The present results show that the scheme with the linear increasing porosity from the bondline to the heated surface can decrease the bondline temperature by 7.8 K and 15.8 K compared with the homogeneous scheme and the linear decreasing scheme, respectively. Further, a scheme with parabolic increasing distribution of porosity are evaluated. It is found that it can reduce the bondline temperature by an additional 2.9 K.

Thermal performance of double-layer porous-microchannel with phase change slurry

Combining porous media paved on sidewall and microencapsulated phase change material (MPCM) suspension as coolant is presented in double-layered microchannel heat sink (MCHS), in which more surface area of porous copper matrix with high thermal conductivity as well as greater temperature difference between the heating wall and working fluid during phase transition of MPCM will enhance heat transfer. The Forchheimer-Brinkman-Darcy model together with energy equation in local thermal equilibrium are employed to deal with fluid flow and heat transfer in porous ribs, and the equivalent heat capacity method is used to describe the phase change process of microcapsules under laminar flow. The influences of coolants, heat sink designs (including the thickness, height, porosity and pore size of porous medium as well as channel number) and working conditions (involving inlet velocity, heat flux and suspension concentration) on thermal and hydraulic characteristics are numerically investigated. The performance evaluation factor (PEF) is introduced to evaluate the comprehensive thermal–hydraulic performance of double-layered MCHS, and the effective performance evaluation factor (PEFeff) is used to compare the overall performance of porous-wall MCHS between conventional arrangements, different channel aspect ratio and channel height ratio configurations. The thickness and height of porous media paved on sidewall should be adjusted reasonably, especially for the arrangement of non-equal porous media, to obtain better overall performance. Different from the variable porosity configuration, the double-layered MCHS cannot rely on losing part of flow performance to obtain better thermal performance in smaller pore size mode, so a larger pore size can be selected to obtain better thermal–hydraulic performance according to actual working conditions. The PEF at larger flow velocity decreases due to higher pressure drop exceeding the benefit of more convection on heat transfer enhancement, in which case the phase change effect in porous-wall mode with MPCM suspension as coolant is suppressed and higher viscosity amplifies the effect of frictional resistance, resulting in a greater drop ratio of PEF than water. The greater PEF in porous-wall MCHS with suspension concentration increasing from 3% to 20% arises than that in non-porous mode, due to the larger surface area of copper matrix with high thermal conductivity and more MPCM particles available for phase transition. The larger aspect ratio configuration can achieve greater PEFeff rise and better overall performance by optimizing fluid velocity in the current mode due to greater thermal resistance drop and less pressure drop rise at lower flow rates, but the variable height ratio structure makes the comprehensive performance of porous-wall MCHS inferior to conventional arrangement due to larger pressure drop rise outweighing the benefits of heat transfer enhancement at the same total volume flux.

Worst-Case Latency Analysis for AVB Traffic Under Overlapping-Based Time-Triggered Windows in Time-Sensitive Networks

Deterministic and low end-to-end latency communication is an urgent demand for many safety-critical applications such as autonomous vehicles and automated industries. The time-sensitive network (TSN) is introduced as Ethernet-based amendments in IEEE 802.1 TSN standards to support time-triggered (TT) traffic in these applications. In the presence of TT flows, TSN is designed to integrate Audio/Video Bridging (AVB) and Best Effort (BE) traffic types. Although AVB traffic has a lower priority than TT, it still requires low and deterministic latency performance, which may not be guaranteed under strict predefined TT scheduling constraints. For this reason, a window-overlapping scheduling algorithm is recently proposed in different works as analytical forms for TT latency under overlapping-windows based. But worst-case AVB latency evaluation under overlapped TT windows is also essential for critical optimizations and tradeoffs. In this paper, a worst-case end-to-end delay ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WCD</i> ) for AVB traffic under overlapping-based TT windows (AVB-OBTTW) algorithm is proposed. Separate analytical models are derived using the network calculus (NC) approach for AVB-OBTTW with both non-preemption and preemption mechanisms. Using an actual vehicular use case, the proposed models are evaluated with back-to-back and porosity configurations under light and heavy loading scenarios. For specific AVB credit bounds, a clear <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WCD</i> reduction has been achieved by increasing the overlapping ratio ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OR</i> ), especially under back-to-back configuration. Preemption and non-preemption modes are compared under different loading conditions, resulting in lower <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WCD</i> s using preemption mode than non-preemption, especially with porosity style. Compared to the latest related works, AVB-OBTTW reduces <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">WCD</i> bounds and increases unscheduled bandwidth, leading to the highest enhancements with the maximum allowable <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OR</i> .

On the effect of porosity and functional grading of 3D printable triply periodic minimal surface (TPMS) based architected lattices embedded with a phase change material

Triply Periodic Minimal Surface (TPMS) topologies have recently gain widespread attention due to their promising performance in several areas like structural strength enhancement, heat transfer augmentation, scaffold and tissue engineering, etc. to name a few. Evolution in 3D printing technology has realized the manufacturing of these complex topologies in an extremely simplistic and straightforward manner. Recent research progress has shown that upon impregnations with phase change material (PCM), lattices based on TPMS topologies exhibited better heat transfer performance than the conventional metal foam in Latent Heat Thermal Energy Storage (LHTES) systems. However, the effect of lattice's porosity and functional grading is not understood and requires further investigation. In order to bridge this gap. This numerical study aims at studying the effect of porosity and functional grading of TPMS-PCM lattices on heat transfer performance. Three TPMS structures namely Primitive, Gyroid and IWP are considered in this study. The porosity study analyzes the heat transfer performance of TPMS structures at three distinct levels of porosity i.e., 60%, 75% and 90% with the 75% porosity case being the benchmark. Furthermore, to study the effect of functional grading, 75% uniform porosity configuration of each TPMS configuration was compared with 75% overall porosity configurations having first a positive and then a negative functional gradient in the porosity. It was found that both porosity and functional grading have a significant effect on both conductive and convective heat transfer enhancement. A reduction in porosity significantly reduces the PCM melting time owing to enhancement in the heat transfer. On the other hand, a positive gradient in the porosity outperforms both uniform porosity and negative porosity gradient cases. Moreover, in both porosity and functional grading studies, the extent of heat transfer enhancement is topology-dependent i.e., each TPMS structure exhibits a different extent of heat transfer enhancement that can be traced back to its topology. This study may therefore serve as a guideline for design and selection of a suitable TPMS candidate according to the applied boundary conditions/problem constraints of the respective LHTES system.

Fabrication and resonance simulation of 3D-printed biocomposite mesoporous implants with different periodic cellular topologies

In order to achieve more efficient additive materials having precise desired porosities with excellent performance, advanced manufacturing techniques can be put to use. In the present study, 3D printing technology is employed to fabricate mesoporous bioceramic-based bony scaffolds made of various periodic cellular topologies including cubic, cylindrical and hexagonal porosity configurations. The samples are composed of polylactic acid-hydroxyapatite (PLA-HA) mesoporous bioceramic-based nanocomposites. Via the respective experiments, the mechanical properties of the fabricated bony scaffolds are extracted corresponding to each porosity configuration with different pore sizes. Moreover, by using the scanning electron microscopy (SEM), X-ray diffraction (XRD) and the permeability characteristics of the fabricated bio-composite samples after soaking in the simulated body fluid (SBF) are captured. Thereafter, based on the experimentally obtained mechanical properties, the multiple time-scales method is utilized to develop an analytical solution for the nonlinear secondary resonance of PLA-HA mesoporous beam-type implants under subharmonic and superharmonic excitations. The frequency-response and amplitude response associated with the both types of hard excitations are depicted corresponding to different periodic cellular topologies and pore sizes. It is observed that among various periodic cellular topologies, the gap between two branches of the subharmonic frequency-response associated with the cubic and hexagonal ones is maximum and minimum, respectively. In the case of superharmonic excitation, it is found that through reduction of the pore size, the peak of frequency-response and its associated value of the detuning parameter decrease.

Implications of non-uniform porosity distribution in gas diffusion layer on the performance of a high temperature PEM fuel cell

The present study discusses a detailed investigation on the implications of non-uniform porosity distribution in the gas diffusion layer (GDL) on the performance of proton exchange membrane fuel cell (PEMFC). A three-dimensional, single-phase, isothermal model of high-temperature PEMFC is employed to study the effect of non-uniform porosity distribution in GDL. The different porosity configurations with stepwise, sinusoidal, and logarithmic variation in porosity along the streamwise direction of GDL are considered. The numerical experiments are performed, keeping average porosity as constant in the GDL. The electrochemical characteristics such as the oxygen molar concentration, power density, current density, total power dissipation density, average diffusion coefficient, vorticity magnitude, and overpotential are studied for a range of porosity distributions. Furthermore, the variations of oxygen concentration, average diffusion coefficient, and vorticity magnitude are also discussed to showcase the influence of non-uniform porosity distribution. Our study reveals that the PEM fuel cell performance is the best when the porosity of the GDL decreases logarithmically in the streamwise direction. On the contrary, the performance deteriorates when the GDL porosity decreases sinusoidally. Also, it has been observed that the effects of non-uniform porosity distribution are more pronounced, especially at higher current densities. The outcomes of present investigation have potential utility in GDL fabrication and membrane assembly's sintering process for manufacturing high valued PEMFC products.

Numerical investigation of multi-layered porosity in the gas diffusion layer on the performance of a PEM fuel cell

A mathematical model is developed to investigate the influence of porosity configurations in the gas diffusion layer (GDL) of the cathode on the electrochemical performance characteristics of a 3-D high-temperature proton exchange membrane (PEM) fuel cell. Four different non-uniform porosity configurations are defined through step functions and analyzed with uniform porosity case. The results are presented in terms of the cell performance characteristics viz. Current density, power density, vorticity magnitude, oxygen molar concentration, overpotential, and total power dissipation density. Our study reveals that oxygen molar concentration, current density, power density are found to be maximum when the stepwise porosity in GDL decreases in the streamwise direction. However, these parameters observed to be the least when the stepwise porosity in GDL increases along the streamwise direction. Additionally, the highest total power dissipation density is observed when the porosity in GDL varies across cross-stream wise direction among other configurations considered. However, it is found to be the least when porosity varies in a streamwise direction. The overpotential becomes the least when stepwise porosity decreases in the streamwise direction although the same is found to be maximum when the porosity in GDL increases along the streamwise direction. The performance is found to be optimal when porosity is maximum at cathode gas channel inlet and GDL-cathode gas channel interface.

On the Implication of Porosity Configuration on Lithium-Ion Cell Performance: A Numerical Study

AbstractThe present study numerically investigates the implication of different porosity configurations, viz., uniform, algebraic, trigonometric, logarithmic, and stepwise constant porosities at the negative electrode on performance characteristics of Lithium-ion cell. We assess the merit of nonuniform porosity over uniform one in terms of cell performance characteristics, viz., specific energy, capacity, electrolyte salt concentration, local volumetric current density, power dissipation density, and solid lithium concentration. Our results reveal that specific energy and capacity are found to be maximum when the porosity increases logarithmically in the direction from the negative electrode–current collector to negative electrode–separator interface. Also, it is found that the variation of power dissipation density and electrolyte salt concentration characteristics are dictated by the interplay of the porosity and the length of the negative electrode. Furthermore, the effect of charging rates (quick charge, fast charge, and ultrafast charge) on cell performance is carried out. It is seen that the increment in C-rates strongly influences the cell performance. It is found that the average capacity increases by 44% at the higher C-rate, i.e., 5C when the porosity increases logarithmically. On the contrary, sinusoidal variation in porosity yields in the worst cell performance. The findings of the present study bear utility toward designing an efficient battery system that can operate for a higher number of cycles with minimal power dissipation density and can fit into the ultrafast charging technique.

Aero-Driven Bleed-Air Applied to Roll Control

Aero-driven bleed-air (ADB) is a flow control technology that offers a unique alternative to novel aircraft concepts that are not conducive to traditional flapped control surfaces. The primary source of mechanical energy for ADB control is derived from the motion of the vehicle. Inherent pressure differences across aerodynamic surfaces are communicated by means of internal channels, with the intent of affecting the local crossflow. Effected across a large area, ADB can significantly alter the global aerodynamic forces and moments. This investigation explores the performance of large-area-distributed ADB as a roll control mechanism on a low-speed, fixed-wing air vehicle. A series of wind tunnel experiments is presented, aimed at characterizing the effects that various porosity configurations have on the lift and drag of a Clark-Y airfoil section. ADB was found to be capable of reducing the sectional lift coefficient across a broad domain of angles of attack () by as much as relative to the baseline airfoil. A mathematical model for estimating the steady-state roll rate of a wing with ADB is developed. Several pore opening schedules are considered, with an emphasis on finding a nearly linear relationship between bleed level and steady-state roll rate. The selected schedule is implemented on a flight test vehicle equipped with ADB roll control effectors. Roll rates of up to were achieved in flight, and flight test data were found to validate the steady-state roll rate model. The aircraft was piloted from takeoff through landing using ADB for roll control.