Porous Layer Thickness Research Articles

MHD Convection with Joule Heating and Internal Heat Generation in a Two‐Layer Discretely Heated Chamber Partly Filled with Porous Medium

The present research presents an innovative approach by integrating magnetohydrodynamic (MHD) flow with resistive heating, integrating a partly permeable layer and interior heat production to scrutinize natural convective flow within a square domain. It also examines both straight and wavy interfaces between the porous and fluid domains. Engaging the Galerkin finite element‐based weighted residual approach, numerical solutions are obtained by unraveling the two‐dimensional Navier–Stokes and thermal energy equations for pure fluid and fluid‐saturated porous domains. The parametric variations include Rayleigh numbers (Ra), porous layer thickness (H), corrugation frequency (f), corrugation amplitude (A), Hartmann number (Ha), and the heat production coefficient (∆). This study assesses the thermal effectiveness of a discrete thermal source, considering variations in porous layer thickness, corrugation frequency and amplitude, magnetic force intensity, and heat production impacts. The discoveries are demonstrated resolvably through the Nusselt number along the warmed edge, thermal performance criterion, and a qualitative portrayal of flow and thermal fields. After extensive analysis, it becomes apparent that reduced thickness of the porous layer, corrugation frequency, and amplitude enhance thermal performance. However, diminished porous layer thickness and corrugation frequency contribute to higher thermal performance criterion (TPC), whereas decreased corrugation amplitude results in a lower TPC. Specifically, the lowest values of H, A, and f result in 11.5%, 0.6%, and 0.1% higher thermal performance, respectively, compared to their highest values. Furthermore, a straight fluid‐saturated porous to the pure fluid domain interface, as opposed to a wavy interface at the highest H, A, and f values, offers a 0.7% improvement in thermal performance.

Free Convection Heat Transfer in Composite Enclosures with Porous and Nanofluid Layers

This work conducts a numerical investigation of convection heat transfer within two composite enclosures. These enclosures consist of porous and nanofluidic layers, where the porous layers are saturated with the same nanofluid. The first enclosure has two porous layers of different sizes and permeabilities, while the second is separated by a single porous layer. As the porous layer thickness approaches zero, both enclosures transition to clear nanofluid enclosures. The study uses the Navier–Stokes equations to govern fluid flow in the nanofluid domain and the Brinkman–Forchheimer extended Darcy model to describe flow within the saturated porous layer. Numerical solutions are obtained using an iterative finite difference method. Key parameters studied include the porous thickness ( 0.0 ≤ S ≤ 1.0 ), the nanoparticle volume fraction ( 0.0 ≤ ϕ ≤ 0.05 ), the thermal conductivity ratio ( 0.5 ≤ R k ≤ 10 ), and the Darcy number ( 10 − 5 ≤ D a ≤ 10 − 2 ). Key findings include the observation that the highest heat transfer is achieved at the highest concentration, regardless of the porous layer configuration, permeability value, or thermal conductivity ratio. Specifically, an augmentation in values of N u ― I up to 22% is obtained as concentration is adjusted from 1% to 5%. Similarly, an augmentation in values of N u ― II up to 25% is obtained as concentration is adjusted from 1% to 5%.

The Fabrication and Characterization of Silicon Surface Grooving Using the CV Etching Technique for Front Deep Metallic Contact Solar Cells

This study experimentally investigated the use of the chemical vapor etching method for silicon surface grooving for regular front deep metallic contact solar cell applications. The thickness of silicon wafers is a crucial parameter in the production of solar cells with front and back buried contacts, because silicon surface grooves result in a larger contact area, which in turn improves carrier collection and increases the collection probability for minority carriers. A simple, low-cost HNO3/HF chemical vapor etching technique was used to create grooves on silicon wafers with the help of a highly effective anti-acid mask. The thick porous layer of powder that was produced was easily dissolved in water, leaving patterned grooved areas on the silicon substrate. A linear dependence was observed between the etched thickness and time, suggesting that the etching process followed a constant etch rate, something that is crucial for ensuring precise and reproducible etching results for the semiconductor and microfabrication industries. Moreover, by creating shorter pathways for charge carriers to travel to their respective contacts, front deep contacts minimize the overall distance they need to traverse and therefore reduce the chance of carrier recombination within the silicon material. As a result, the internal quantum efficiency of solar cells with front deep metallic contacts improved by 35% compared to mc-Si solar cells having planar contacts. The use of front deep contacts therefore represents a forward-looking strategy for improving the performance of silicon solar cells. Indeed, this innovative electrode configuration improves charge carrier collection, mitigates recombination losses, and ultimately leads to more efficient and effective solar energy conversion, which contributes to sustainable energy development in the areas of clean energy resources. Further work needs to be undertaken to develop energy sustainably and consider other clean energy resources.

Analysis of Wave Force and Run-Up Acting on an Impermeable Vertical Circular Cylinder Surrounded by Multiple Thick Porous Layers

Abstract In this work, we analyze the effect of multiple thick porous layers, fitted around a rigid vertical circular cylinder, on the wave forces acting on the rigid structure. Using the eigenfunction expansion method in cylindrical coordinates, we derive the expressions for velocity potentials in the respective domains and finally calculate the wave force acting on the rigid structure by integrating the pressure term. Consideration of the multiple porous layers, each with different porosities, gives rise to a very basic question to answer: what will be the appropriate arrangement of the porous layers to reduce the wave impact? Hence, for numerical study, we consider three different arrangements of the porous layers. For such arrangements of the porous layers, we also analyze the effects of the other crucial parameters, such as the number and the thickness of the porous layers, on the wave force. The key finding of the analysis is that the wave force acting on the rigid structure can be minimized by increasing the number of porous layers with decreasing porosity from the innermost layer to the outermost layer. The wave breaking and forced oscillations for certain values of the porous impedance parameter are some of the interesting observations. The present model is also verified against an existing work in the literature which shows an excellent agreement.

Boulder distribution, circular polarization, and optical maturity: A survey of example lunar polar terrains for future landing sites

Boulder occurrence at the southern polar regions of the Moon was analysed to see connections between optical, radio, spectral, and topography-related roughness datasets. On optical images, boulders tend to concentrate in groups (the groups are 0.9–1.8 km diameter and cover about 9% of the surveyed regions; while boulders inside these groups have up to 6 boulder/100 m2, e.g., 60,000 boulder/km2 (54% of areal coverage), while outside these groups around 7 boulder/km2 (0.06% areal coverage). The correlation between optical boulder density and Circular Polarization Ratio: CPR (0.26) and Optical Maturity: OMAT (0.38) values are weak, while CPR and OMAT distribution patterns are elevated around fresh craters with elevated boulder density. While fresh craters with boulders coincide with elevated CPR values, but in some cases, elevated CPR is without elevated surface boulder occurrence, indicating shallow subsurface boulders. A good correlation between CPR values and surface roughness (0.68) indicates boulder exhumation at topographic differences of craters. OMAT and CPR values of fresh craters (with elevated and sharp rims) show elevated values above the adjacent regions. OMAT is elevated up to 1–3 times the crater diameter, while CPR is elevated at a smaller area than OMAT values. The CPR might partly come from boulders that could not be ejected as far as smaller regolith grains indicated by OMAT-related freshness. Boulder occurrence at fresh impact craters indicates a thickness of the loose top porous regolith layer of 6–11 m, not far from those gained by another author (5–18 m) for terrain areas.

Research on the permanent deformation mechanism and dynamic meso-mechanical response of porous asphalt mixture composite structure using the discrete element method

This study proposed a heterogeneous 3D virtual rutting model to investigate the rutting evolution mechanism and the dynamic meso-mechanical response of a porous asphalt mixture composite structure. The 3D virtual rutting test model incorporated a three-phase asphalt mastic-aggregate-airvoids system with grain size distribution and genuine aggregate morphology. Innovative algorithms were developed for cyclic rolling loading to reflect repetitive wheel loading. In contrast to the indoor rutting tests, the 3D virtual rutting tests exhibited greater rutting deformation and weaker dynamic stability in the range of 3.16%–10.17% and 2.65%–11.77%, respectively. Shear forces were predominant in the virtual rutting tests. As the porous asphalt mixture composite structure's surface layer thickness increased, the shear contact force increased and the maximum parallel-bond (PB) contact force diminished. The 3D virtual rutting test model was demonstrated to be feasible for simulating rutting deformation and dynamic meso-structural responses in porous asphalt mixtures with cyclic rolling loading algorithms.

Vancomycin-loaded porous chitosan-pectin-hydroxyapatite nanocomposite coating on Ti6Al4V towards enhancing prosthesis antiinfection performance

Cathodic electrophoretic deposition (EPD) was used to fabricate novel porous chitosan/pectin/hydroxyapatite (CS/P/HA) nanocomposite coatings on Ti6Al4V substrates. Rietveld refinement results revealed variations in peak intensity, position, and width, reflecting structural changes resulting from the reduction of the applied voltage from 30 to 10 V. The deposits obtained at 10 V after 1 h of presedimentation exhibited a denser microstructure with narrow pore size distribution compared to the others. The wettability and adhesion strength of coated Ti6Al4V improved with increasing HA content. Release of antibiotic from the composite coating confirmed 40% initial burst release, 50% semi-steady release and 10% residual release. A thick and uniform porous apatite layer was formed on Ti6Al4V after 21 days of immersion in simulated body fluid (SBF). Therefore, CS/P/HA coated Ti6Al4V has the potential for practical antiinfection performance.

Stirred discs from polycaprolactone nanofibers highly doped with graphene for straightforward preconcentration of pollutants in environmental waters

A novel sorbent for solid phase extraction (SPE) based on hybrid nanofibrous polycaprolactone containing graphene nanoparticles has been prepared. The preparation of hybrid polymer nanofibers with a very high 1:1 polymer/graphene ratio was achieved for the first time using alternating current electrospinning. The final appearance of these nanofibers was a thick porous layer that was cut into the shape of easy-to-handle extraction discs. Based on the preliminary study in which the graphene content varied, 30% graphene-doped nanofibers (w/w) exhibited the highest recoveries and enabled a significant increase in the retention of analytes, 2–25 times in comparison to PCL. The incorporation of graphene resulted in a higher surface area of 12 g/m2 compared to 2 g/m2 determined for the native polycaprolactone (PCL) nanofibers. This unique material was applied for a simple stirred disc sorptive extraction and preconcentration of trace levels of emerging organic environmental contaminants, bisphenols A, AF, AP, C, S, Z, 3-chlorophenol, and pesticides fenoxycarb, deltamethrin, and kadethrin from surface waters prior to HPLC-DAD determination. This was accomplished by stirring the unsupported nanofiber disc in a large-volume sample with RSD of five extractions of 3–15%. Recoveries yielded 87–120%, except 52% for bisphenol S due to its high polarity. Optimization of the extraction procedure included conditioning, sample volume, extraction time, and elution solvent. Our novel desorption procedure carried out in a vial used for the direct injection into the HPLC system significantly reduced sample handling and minimized potential human error.

Poroviscoelastic Gravitational Dynamics

AbstractGlobal‐scale periodic deformation has been studied using the (visco)elastic gravitational theory, which assumes a planetary body consists of solid or liquid layers. Recent planetary exploration missions, however, suggest that a global layer of a mixture of solid and liquid exists in several planetary bodies. This study provides a theory of periodic deformation of such a layer unifying the viscoelastic gravitational theory with the theory of poroelasticity without introducing additional constraints. The governing equation system and a formulation suitable for numerical calculation are given. Equations used to calculate the energy dissipation rate are also given. The analytical solutions for a homogeneous sphere are obtained using an eigenvalue approach. Simple numerical calculations assuming a homogeneous sphere reveal that a numerical instability occurs if a thick porous layer, a low permeability, or a high frequency is assumed. This instability can be avoided by choosing an appropriate interior structure model that is numerically equivalent. Different simple numerical calculations adopting a multilayered, radially varying interior profile reveal that the radial profile of the tidal heating rate for a fluid‐saturated porous layer and that for a low‐viscosity solid layer are completely different. In addition, the radial variation in porosity can lead to a factor of ∼100 increase in the local heating rate. These results indicate that future studies should consider a wider variety of detailed interior structure models.

Natural convection in a square cavity partially filled with porous medium and nanofluid using Buongiorno's model

Natural convection is investigated in a square cavity divided in three layers, nanofluid at the middle and the upper and lower parts for porous layer. The cavity is heated from the left and cold from the right at constant temperature Th and Tc respectively. The side walls are well insulated. The Buongiorno’s model was used to evaluate the distribution of nanoparticles and takes account the Brownian and thermophoresis motion. The governing equations are solved by the Galerkin finite element method. The governing parameters are Rayleigh (103≤ Ra ≤ 106), porous layer thickness (0.3 ≤ Lp ≤ 0.05).The result shows that increasing buoyancy forces reinforce circulation flow in the nanofluid layer than the porous layer, the decrease effect of porous layer thickness improve considerably the convective heat transfer. The heat and mass transfer are enhanced.

Oblique wave trapping by a permeable wall breakwater connected with thick surface porous layer

ABSTRACT The reflection of surface gravity waves by a vertical wall breakwater connected with a thick surface porous layer is analysed under the framework of potential flow theory. The thick surface porous layer is placed within the confined space available between the vertical permeable wall and the impermeable seawall. The analytical investigation is progressed by creating the hidden water chamber beneath the surface porous layer. The Matched Eigenfunction Expansion Method (MEEM) is used based on the continuity of velocity and pressure along with orthogonal mode-coupling relation. The hidden water chamber will be helpful to enhance the trapping of incident wave energy and also to reduce the quantity of construction material. The present study results are well agreed with the results available in the literature when a hidden water chamber is absent. The effect of permeable wall porosity, thick surface layer porosity, angle of wave contact, depth of the surface porous layer, thickness of the permeable wall, and hidden chamber spacing on wave reflection against incident wave properties and breakwater physical properties are studied. A comparative study is performed between three different types of porous breakwaters to investigate the integrity of the proposed breakwater. The minor value of wave reflection and gradual reduction of fluid force experienced by the rigid wall is achieved due to the presence of a surface layer, which maximises the incident wave damping, as most of the wave energy propagates near the free surface.

Heat transfer and cold energy capacity properties of crushed-rock layer in cold sandy regions

Addressing the impact of climate warming and anthropic activities, crushed-rock layer (CRL) is a zero-carbon emission technology by using natural cold air to protect infrastructures in permafrost regions. But in cold sandy environment, the issue of its cold energy capacity on account of aeolian sand clogging needs to be solved. Based novel field experiments on Tibet Plateau, the dynamic evolution law and its controlling factors of natural cold energy accumulation of the CRL are quantitatively figured out. Results show that the initially open CRL had a strong forced convection of air in the first two winters, while the cooling effect was failure after the third winter. The filling of aeolian sand caused heat transfer mode of the CRL to change from forced convection to natural convection in cold season, losing the ability of “thermal semiconductor” aimed to mitigate permafrost degradation. The closed CRL represented weak natural convection in cold season and thermal insulation in warm season, which had better long-term cooling effectiveness than other conditions in the aeolian environment. As the thickness of the aeolian sand filling increased, the maximum Rayleigh number and natural convection time of the closed CRL decreased. Accumulation of cooling energy in cold season and thermal insulation in warm season were positive correlation with thickness of porous media layer. It was not recommended to solely adopt crushed rock embankment or crushed rock revetment in aeolian sand environment and regions with higher annual average temperature. The findings solved the scientific evaluation issue of cold energy storage capacity of CRL, and provided constructive engineering implications for its efficient application.

Electrochemical Impedance Spectroscopy Study of Porous Anodic Alumina Films Fabricated at Low Temperature

A method of fabrication of AAO film in 0.3 mol/L H2C2O4 by adding 1,2-propanediol(PROH) and at sub-zero temperature has been proposed. The electrochemical characteristics of the barrier and porous layers of AAO films before and after pore-filling are examined using electrochemical impedance spectroscopy (EIS). It is shown that the high and medium frequency range corresponds to the barrier layer properties and the low frequency ranges reflect the sealed porous layer properties. The calculated thickness of the barrier layer is in the range of 1 ~ 18 nm. The resistance (Rb) and the thickness (δb) of the barrier layer increase and the capacitance of the barrier layer (CPEb) decrease with the volume percentage of PROH increasing from in electrolyte from 25 % to 75 %. The surface non-homogeneity of AAO film goes better by pore-filling, leading to a decrease in the capacitance of the porous layer (CPEp) and an increase in the porous layer thickness.

Influence of the catalyst layer thickness on the determination of the OER activity of Fe3O4@CoFe2O4 core-shell nanoparticles

Transition metal oxides-based catalytic layers often present a complex 3D porous architecture affecting the evaluation of their intrinsic electrocatalytic activity. In this work the oxygen evolution reaction activity of core-shell Fe3O4@CoFe2O4 nanoparticles combining a conductive magnetite core and a catalytically active cobalt ferrite shell was studied at different loading and thickness of the catalytic layer. It was observed that their apparent activity is decreasing and that the Tafel slopes are becoming convex when the loading increases. The activity decay could be attributed to the significant resistance to charge transport in the thick porous catalyst layer. This resistance could be estimated by fitting the electrochemical impedance spectra using the transmission line model. The influence of the layer thickness on the experimental current-potential curves and on their Tafel slopes could be simulated using a simple model based on the Telegrapher's equations. It is concluded that in order to measure accurately the activity and Tafel slopes of an electrocatalyst, thin layers must be used, notably for catalyst layers that are not highly conductive.

In situ characterization of wall linings with perforated facings

The in-situ characterization of acoustic materials is one of the main challenges in room acoustics. Previously, the characterization of a single porous layer backed by a hard wall was successfully done by combining pressure-velocity measurements near the surface of the material with an impedance model fitting approach. In practice however, most porous materials are mounted behind a membrane or a rigid perforated facing. By again combining pressure-velocity measurements and a model fitting procedure, this work studies the possibility to characterize such systems. This was done by measuring a variety of perforated facings and membrane facings, whether in front of an air cavity or backed by a porous layer and comparing the obtained impedance model parameters to the reference values. Good agreement was observed between the retrieved parameters and the references, with error in retrieved moving mass, facing thickness, cavity depth, porous layer thickness and porous layer flow resistivity not exceeding 15%.

Porous top layer optimization of cement concrete slabs for tyre/road noise reduction

The I-STREET CUD-SF project aims at developing an urban pavement made of cement concrete slabs that can be easily removed and replaced for maintenance purposes. These slabs are made of a dense cement concrete body and a functionalized porous top layer ensuring water drainage and sound absorption. In order to optimize the porous layer for tyre/road noise reduction, several mix recipes with different porosity and maximum aggregate size were considered. Recipes with the most interesting absorption properties were preliminary selected based on absorption coefficient measurements performed on cylindrical test specimens with an impedance tube. A second phase was dedicated to evaluation of texture induced coast-by rolling noise levels with the tyre/road noise prediction model HyRoNE from 3D texture scans performed on rectangular laboratory samples. Finally, based on a porous medium model and a propagation model considering the tyre/road noise source as an omnidirectional point source over an impedance plane surface, the porous layer thickness of the selected mix was adjusted to minimize the predicted noise at roadside for different reference rolling speeds. This paper gives an overview of the results obtained at the different stages of the optimization process, prior in-situ assessment of the industrial solution in a near future.

Numerical simulation on pore-scale pool boiling mechanisms of horizontal gradient porous metals

Horizontal gradient porous metals are proposed to solve the problem of nonuniform temperature distribution on the heating surface. The model of horizontal gradient porous metal is established based on the thermal response of metal skeletons. Pool boiling heat transfer performances of horizontal gradient porous metals are studied by phase-change lattice Boltzmann model. Horizontal porous metal layer thickness, wettability and thermal conductivity gradient effects on bubble behavior and heating surface temperature distribution uniformity are statistically analyzed. The results show that porous metals with horizontal thickness gradient can realize liquid-vapor channel separation, reduce the resistance of bubble rising, and improve the fresh liquid supplement. Compared with the uniform porous metal, the horizontal gradient porous metal with lateral hydrophobic surface or higher thermal conductivity has better boiling heat transfer performance and promotes heating surface uniform temperature distribution at low heat fluxes. The results provide a novel solution to improve the chip wall temperature uniformity for the stable operation of electronic equipment.

Preparation of porous silicon Wafers using sun light photo chemical etching (SLPCE)

porous Silicon (PS) Layers were prepared by photochemical etching using Sun Light as a Source of energy for the first time instead of industrial Sources of light Such as Lasers, Halogen and tungsten lamps. That was used to preparation (PS) by photochemical etching. Silicon Wafers n-type (100), resistivity (10Ω.cm), (40%) HF Acid, with different illumination intensities(power density) (1758, 3956, 6182 and 8902)mw /cm2 were obtained using different Lenses with different diameters (40, 60, 75 and 90) mm, focal length (13,18,41,45) cm respectively and constant etching time (60min). The morphology of the surface was studied by using an (atomic force microscope) (AFM) and (scanning electron microscope) (SEM) results shows formation of groups of pores and crystals in (nm)size with different diminution are distributed in etched area in wavy forms. The thickness of porous layers ranged from (50.06 3.68, 3.79 and 3.39) nm and the diameter of the particles are(84.06, 59.42, 51.12 and 34.8)nm respectively. The current voltage characteristics for ALthin/n-si/PS/ALthin device fabricated by sun light photochemical etching technique showed a rectifying behavior which improved with increasing light intensity.

Impact of wavy porous layer on the hydrodynamic forces and heat transfer of hybrid nanofluid flow in a channel with cavity under the effect of partial magnetic field

Abstract This computational analysis focuses on the effects of porous layer on the flow dynamics, heat transfer and hydrodynamic forces of hybrid nanofluid in a channel having an open cavity fixed with bottom wall in the presence of partial magnetic field. The set of PDEs governing the dynamics has been transformed to dimensionless form and simulated using higher order finite element method. In particular, P 3 / P 2 ${\mathbb{P}}_{3}/{\mathbb{P}}_{2}$ finite element pair is employed for the spatial discretization and Crank–Nicolson approach is utilized for the temporal discretization. The obtained equations has been linearized with adaptive Newtons method and linearized systems have been computed using the geometric multi-grid technique. The impact of parameters, for instance, Richardson number, thickness of porous layer and nanoparticle fraction is analyzed in the presence of partial magnetic field and porous layer on the hydrodynamic forces like lift and drag forces on the submerged bodies, being the important part of the fluid flow and heat transfer are also be analysed. It is noticed that the drag and lift coefficients are reduced as the nanoparticle fraction is altered while the local- and average-Nusselt number get higher values.

Влияние наполнителей на структуру силоксановых пленок

The influence of fillers on the structures of siloxane films was studied. Three variants of fillers are considered: ethyl alcohol, chitosan and sodium bicarbonate with its subsequent removal. It is shown that the use of alcohol leads to a change in the surface structure and the formation of numerous pores-“pits”. The use of sodium bicarbonate or chitazan makes it possible to create developed networks of pores intersecting with each other and having access to the surface. The possibility of controlling the thickness of porous layers by changing the concentration of the introduced filler is shown. It is concluded that the studied variants of the modification of the structure of siloxane films open up wide opportunities for creating drug delivery systems or other active agents, including controlled prolonged action.