Pore Parameters Research Articles

Experimental Investigation of Airfoil Instability Tonal Noise Reduction Using Structured Porous Trailing Edges

Reducing the tonal noise from airfoil instabilities has attracted significant interest from the aeronautical community in the past few years. The aim of this paper is to investigate the effect of structured porous trailing edges on the tonal noise reduction performance of a symmetrical NACA 0012 airfoil. Detailed parametric testing was performed in an open-jet wind tunnel between the baseline solid trailing edge and seventeen structured porous trailing edges with different sub-millimeter-scale pores. The experimental results demonstrate that structured porous trailing edges can reduce the noticeable tonal noise of the symmetrical NACA 0012 airfoil. Moreover, the design parameters for the structured porous edges have slightly different impacts on the tonal noise reduction performance between a zero angle of attack (α = 0°) and a non-zero angle of attack (α = 10°): better airfoil tonal noise reduction is due to the porous parameters of small pore coverage, small-to-moderate chordwise spacing, and moderate spanwise spacing at α = 0°. On the other hand, the optimal combination of the structured porous edge at α = 10° is the configuration with larger pore coverage, smaller chordwise spacing, and spanwise spacing.

Investigation of Melting Heat Transfer in Viscous Nanofluid Flow Including Micro-Organisms and Entropy Generation Due to an Inclined Exponentially Stretching Sheet

This study investigates melting heat transfer and entropy production in viscous nanofluid flow consisting of micro-organisms over an inclined exponentially stretching permeable sheet. The flow is considered via porous medium. Impacts of heat transport characteristics are invoked in the energy equation. In concentration equation we have included chemical reaction impact. The regulating PDEs are transformed into nonlinear ODEs in non-dimensional form using adequate similarity transformation relations. The analytical solution of the problem is obtained utilizing HAM. Various plots are drawn to exhibit impacts of the regulating parameters (Prandtl number, Porous medium parameter, Thermal Grashof number, Mass Grashof number, Micro-organism Grashof number, Thermophoresis parameter, Radiation parameter, Bio-convection Levis number, Brownian motion parameter, Chemical reaction parameter, Suction parameter, Peclet number, and Melting parameter) occurred in the problem on relevant fields (flow, temperature and concentration distribution) and entropy production and discussed. Further values of significant physical quantities skin friction coefficient, Nusselt number, Sherwood number, and motile microbes density computed using MATLAB based bvp4c function and HAM are displayed in tabular mode and found in excellent agreement. For validity of the results skin friction coefficient and Nusselt number values are compared to prior research, apparently good agreement is found. The effect of melting surface parameter is found to reduce the fluid flow and temperature field. Entropy production lessens with rising values of slip parameters but effects of radiation and porous medium parameters are found to upsurge it. It is also noticed that bioconvection Lewis number and Peclet number reduce the micro-organism density profile. Inclusion of entropy analysis is a novel feature of the study. The solution methodology also enriched the novelty of the investigation. The results of the study may be applied to improve the efficiency of thermal, fluid flow and energy systems. This study may also find applications in bio-nano-coolant systems and heat transfer devices.

Carbon dots encapsulated in (YGd)2O3:Eu3+ nanophosphors for thermal sensing, advanced forensic and information security applications

The outstanding optical characteristics of carbon dots (CDs) make them an extremely promising class of multifunctional nanomaterials based on carbon. The incorporation of hydrothermally prepared Aloe vera carbon dots (AVCDs) into europium doped yttrium gadolinium ((YGd)2O3:Eu3+) mixed oxide nanophosphors ((YGO):Eu3+ NPs) synthesized through the solution combustion (SC) method. The resulting (YGO):Eu3+@AVCDs nanocomposite (NCs) demonstrates a broad excitation band, with the intense peak at ∼395 nm, aligning with the emission wavelength (350–420 nm) of n-UV LED chips. Notably, the (YGO):Eu3+@AVCDs (5 wt %) NCs exhibits a 4 fold increase in photoluminescence (PL) intensity compared to (YGO):7Eu3+, attributed to the fluorescence resonance energy transfer (FRET) between AVCDs and Eu3+ ions. Remarkably, even at an elevated temperature of 423 K, the thermal stability of (YGO):Eu3+@AVCDs (5 wt %) remains exceptional, retaining 88.31 % of its initial luminescence intensity. The internal quantum efficiency (IQE) is measured at a notable 74.16 %, while the optimized composite achieves a remarkable color purity of 99.59 %. Latent fingerprints (LFPs) are effectively developed on different surfaces using the optimized NCs via a simple powder dusting technique, and these fingerprints (FPs) revealed under 365 nm UV light. The study also examines various pore parameter namely size, shape, number, position, type, and inter-distance. Moreover, a transparent anti-counterfeiting (AC) ink is fabricated using optimized NCs providing effective AC features through its red emission under 365 nm UV light. This study not only offers solutions for overcoming the self-quenching effect of CDs but also underscores the potential applications in white light emitting diodes (w-LEDs), latent fingerprints, lip prints (LPs), and anti-counterfeiting.

Approaches of Combining Machine Learning with NMR-Based Pore Structure Characterization for Reservoir Evaluation

Tight gas, a category of unconventional natural gas, relies on advanced intelligent monitoring methods for their extraction. Conventional logging for reservoir evaluation relies on logging data and the manual setting of evaluation criteria to classify reservoirs. However, the complexity and heterogeneity of tight reservoirs pose challenges in accurately identifying target layers by using traditional well-logging techniques. Machine learning may hold the key to solving this problem, as it enables computers to learn without being explicitly programmed and manually adding rules. Therefore, it is possible to make reservoir evaluations using machine learning methods. In this paper, the reservoir quality index (RQI) and porous geometric parameters obtained from the optimized inversion of the spherical–tubular model are adopted to evaluate the reservoir. Then, three different machine learning approaches, the random forest (RF) algorithm, support vector machine (SVM) algorithm, and extreme gradient boosting (XGB) algorithm, are utilized for reservoir classification. The selected dataset covers more than 7000 samples from five wells. The data from four wells are arranged as the training dataset, and the data of the remaining one well is designed as the testing dataset to calculate the prediction accuracies of different machine learning algorithms. Among them, accuracies of RF, SVM, and XGB are all higher than 90%, and XGB owns the highest result by reaching 97%. Machine learning based approaches can greatly assist reservoir prediction by implementing the well-logging data. The research highlights the application of reservoir classification with a higher prediction accuracy by combining machine learning algorithms with NMR-logging-based pore structure characterization, which can provide a guideline for sweet spot identification within the tight formation. This not only optimizes resource extraction but also aligns with the global shift towards clean and renewable energy sources, promoting sustainability and reducing the carbon footprint associated with conventional energy production. In summary, the fusion of machine learning and NMR-logging-based reservoir evaluation plays a crucial role in advancing both energy efficiency and the transition to cleaner energy sources.

Effect of the pore parameters of the perforated baffle on the control of liquid sloshing

The phenomenon of liquid sloshing inside a tank has a significant negative impact on the safety of the vessel. Installing perforated baffles is considered an effective means of mitigating liquid sloshing. This study investigated the influence of pore parameters on the anti-sloshing effectiveness of baffles. The simulations were performed using STAR-CCM+. In the numerical simulation of the tank sloshing, we have adjusted the factors in the k-ε model to obtain more approximate results compared to the experiments. By changing variables such as the porosity, degree of porosity, and pore distribution of the baffles, the results of the numerical simulations were compared to analyze their performance. Different combinations of porosity and porosity degree parameters have varying effects on sloshing factors such as the wave height, pressure, and rolling moment of the liquid tank. The perforated baffle performed well at restraining the slamming load. The findings also indicate that the effects of porosity are greater than those of the pore distribution. In most cases, an even pore distribution is more effective. These results can provide guidelines for the optimal design of vertical porous baffles.

Comprehensive Comparison of Lacustrine Fine-Grained Sedimentary Rock Reservoirs, Organic Matter, and Palaeoenvironment: A Case Study of the Jurassic Ziliujing Formation and Xintiangou Formation in the Sichuan Basin

Lacustrine sedimentary formations potentially contain hydrocarbons. The lacustrine sedimentary rocks of the Ziliujung and Xintiangou Formations have been investigated for their hydrocarbon potential using low-pressure nitrogen adsorption (LP-N2A), low-field nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), total organic carbon (TOC), rock-eval pyrolysis (Rock-Eval), gas chromatography (GC), gas chromatography–mass spectrometry (GC–MS), X-ray fluorescence spectrometry (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). The results show that the normalized difference of the pore parameters between the two formations is less than 10%, and the pores are mainly slit-like mesopores with high porosity. Macropores and micropores are often developed in the quartz skeleton, while mesopores often occur among organic matter, clay minerals, carbonate minerals, and pyrite particles. The organic matter abundance of the Ziliujing Formation is relatively high. Additionally, the organic matter types of the two formations are mainly type II and type III, and the sources of the organic matter are plankton and bacteria which have reached the mature gas production stage. The palaeoenvironmental differences between the depositional periods of the two formations lie within 10% of each other. The warm and humid climate promotes the development of quartz minerals to further enhance the proportion of both micropores and macropores, and the clay minerals, carbonate minerals, and pyrite carried in the terrigenous detritus are closely associated with the total organic carbon (TOC), which promotes the development of mesopores to enhance the porosity. The reservoir, organic matter, and palaeoenvironmental characteristics of fine-grained sedimentary rocks in the two formations are similar, and both of them have good potential for development. The above results provide a basic geological theoretical basis for unconventional oil and gas exploration in the northeastern margin of the Sichuan Basin.

Microscopic Factors Affecting the Performance of Pervious Concrete.

The impacts of various aggregate particle sizes and cement contents on the internal structure of pervious concrete were investigated. Accordingly, test blocks with different aggregate particle sizes and cement contents were dissected and photographed. Subsequently, the captured images were processed using the ImageJ software (1.53i) to analyze the profiles of the test blocks and identify the internal mesoscopic parameters of the pervious concrete. This study discusses the relationship between microscopic parameters and macroscopic factors based on experimental results. It also fits functional equations linking the permeability coefficient with pore parameters, matrix parameters, and compressive strength. The results indicated that, as the aggregate size increased, the internal pore diameter of the pervious concrete increased, whereas the total area and width of the cement matrix decreased. This resulted in a low permeability coefficient and high compressive strength of the test block. Increasing the cement content in pervious concrete reduced the porosity and increased the width and area of the internal matrix. Consequently, the permeability coefficient decreased, and the compressive strength of the test block increased.

Evaluation of Permeability Models for Foundry Molds and Cores in Sand Casting Processes

Predicting the permeability of different regions of foundry cores and molds with complex geometries will help control the regional outgassing, enabling better defect prediction in castings. In this work, foundry cores prepared with different bulk properties were characterized using X-ray microtomography, and the obtained images were analyzed to study all relevant grain and pore parameters, including but not limited to the specific surface area, specific internal volume, and tortuosity. The obtained microstructural parameters were incorporated into prevalent models used to predict the fluid flow through porous media, and their accuracy is compared with respect to experimentally measured permeability. The original Kozeny model was identified as the most suitable model to predict the permeability of sand molds. Although the model predicts permeability well, the input parameters are laborious to measure. Hence, a methodology for replacing the pore diameter and tortuosity with simple process parameters is proposed. This modified version of the original Kozeny model helps predict permeability of foundry molds and cores at different regions resulting in better defect prediction and eventual scrap reduction.

The effect of pore size distribution on the fractal evaporative interface in porous media

This article aims to comprehensively analyze the heat and mass transfer and fractal evaporative interface in porous media with different pore size distribution through experiments and simulations of water. Weierstrass-Mandelbrot(W-M) function is used to establish a fractal evaporative interface based on fractal dimension and scaling parameter, which are determined by parameters of pore. The evaporative interface at the pore level is observed in the experiment with aluminum and nickel porous media, which shows reliability of model. The simulation results reveal that when the mass flow rate enlarges, the average Nusselt number, RMS and STD gradually grow, and the average temperature, vapor volume fraction, and velocity reduce, which indicates better thermal protection. As the initial temperature of the bottom improves, the trends in these variables are opposite except for STD, which means more irregular of evaporative interface. These findings have potential applications in transpiration cooling with high temperature in aerospace field and technologies requiring a stable evaporative interface, such as seawater desalination.

Entropy analysis for two-dimensional double-diffusive mixed convective flow of a Williamson nanofluid through a porous medium

The problem of double-diffusive convection is investigated by considering the MHD effect on non-Newtonian Williamson fluid flowing over a porous medium. The nature of fluid flow and the amount of heat and mass transfer are studied by the variation of MHD and porous parameters. The flow equations are coupled having more than one independent variable which can be transformed into a single independent variable by introducing similarity variables and solved numerically with the utilization of builtin MATLAB bvp4c package. The Brownian motion and thermophoresis effects on flow equations are studied graphically and the irreversibility of flow is considered. The presence of the Prandtl number in the momentum equation and its effect on physical parameters are taken into account. The variation of Williamson parameter on velocity, temperature, nanoparticle concentration, and concentration profiles are analyzed. The primary innovation of our research is shown in tables that contrast the acquired outcomes with the earlier conclusions found in the literature. The behavior of energy and concentration profiles are shown through graphs by differing numerical values of physical parameters.

Changes in Pore Structure and Fractal Characteristics of Solvents Pretreated High-Rank Coal under Supercritical CO2

CO2 injection in coal seams, which is a significant initiative to mitigate environmental problems caused by greenhouse gases, often leads a sequence of changes in the physical properties of coal reservoirs. To look into how the pore structure changes in the process of CO2 sequestration, we selected fresh coal from Huoerxinhe coal mine in China as the object. Then, acid treatment and SC-CO2 extraction were used to dissolve Organic and inorganic components in coal. Thus, by using SEM, LTGA-N2 apparatus and XRD, the characteristics of pore parameter and fractal dimension variation were discussed. The research results show that, the APS of samples THF, HCL-HF and Y-C increase, while the total PV decreases and the pore connectivity deteriorates. The pore connectivity of Samples THF and HCL-HF is improved (THF-C, HCL-HF-C), but the total pore volume continuously reduces. In addition, solvents treatment and SC-CO2 extraction mainly act on the microporous fraction. After solvents pretreatment, the changes in the pore size distribution curves are mainly manifested in the reduction of number of micropores, especially in the micropores around 3–4 nm. There is a small increase in micropores for samples Y-C and HCL-HF-C, with the pore size mainly concentrated around 4 nm, while the pores of the sample THF-C mainly show an increase within the scope of 3–16 nm. Generally, solvent pretreatment and SC-CO2 extraction help to simplify pore structure. However, the sample HCL-HF-C shows opposite change characteristics. In a short period of time, the larger pore fractal dimension, the less beneficial it is to the flow of CO2, while pore fractal dimension becomes progressively less useful in assessing pore connectivity with increasing time.

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The primary goal of this investigation is to examine the heat and flow characteristics of a hybrid nanofluid consisting of silver (Ag) and aluminum oxide (Al2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}O3)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3})$$\\end{document} nanoparticles over an unsteady radially stretching sheet embedded in porous medium. The investigation is conducted under the influence of several key parameters, namely joule heating, viscous dissipation, porous, slip, and suction. The technique of similarity transformations is used to transform the governing system of PDEs into nonlinear ODEs and the bvp4c solver is used to solve them numerically. The present study examines the influence of sphere and platelet shape nanoparticles on the temperature and velocity profiles. The outcomes are discussed through graphs and tables. A rise in the porous, slip, and suction parameters makes the velocity profile decrease gradually. The temperature escalates when Biot number, magnetic parameter, and Eckert number increase. As compared to sphere shapes, platelet-shaped nanoparticles exhibit the greatest heat transfer and flow. Results reveal that by using Ag-Al2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{3}$$\\end{document}/H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{2}$$\\end{document}O hybrid nanofluid with a volume fraction of 5%, the heat transfer enhancement of platelet shape nanoparticles increased by 11.88% than sphere-shaped nanoparticles. Overall, the platelet shape of nanoparticles offers distinctive advantages in various engineering applications, primarily due to their large surface area, anisotropic properties, and tunable surface chemistry. These properties make them versatile tools for improving the performance of materials and systems in engineering fields. The findings can contribute to the design and optimization of nanofluid-based systems in various engineering applications, such as heat exchangers, microfluidics, and energy conversion devices.

Pore structure characterization of sandstone under different water invasion cycles using micro-CT

The meso-structural changes of rocks during repeated cycles of water invasion are the fundamental cause of macroscopic physical property damage. In this paper, based on the computed tomography scan images of rock samples under different numbers of water invasion cycles, a three-dimensional pore network model was constructed to analyze the changes in pore structure under the action of water invasion. The damage variable was introduced to quantitatively characterize the parameter damage of each pore and reveal the evolution of rock meso-damage. The results show that 81% of the pore radius is less than 10 μm under 0 water invasion cycles and that 76% of the pore radiuses are less than 10 μm after 10 water invasion cycles. After 10 water invasion cycles, the peak range of the pore radius distribution enlarged from the initial range of 2–4 μm to that of 4–6 μm and the proportion of pore throats with a radius less than 10 μm decreased from an initial 82–72%. With an increase of water invasion cycles, the proportion of large pores increased and the connectivity among pores enhances gradually. The damage variable of each pore parameter changed the most during 2–5 water invasion cycles. After 10 water invasion cycles, the maximum degree of damage that the pore volume reached was up to 41.44% and the minimum degree of damage of the pore coordination number was 5.80%. The test results helped to reveal the pore structure changes and the damage of rock samples during water invasion cycles.

Effect of 3D-Printed Porous Titanium Alloy Pore Structure on Bone Regeneration: A Review

As a biomedical material, porous titanium alloy has gained widespread recognition and application within the field of orthopedics. Its remarkable biocompatibility, bioactivity, and mechanical properties establish it as a promising material for facilitating bone regeneration. A well-designed porous structure can lower the material’s modulus while retaining ample strength, rendering it more akin to natural bone tissue. The progression of additive manufacturing (AM) technology has significantly propelled the advancement of porous implants, simplifying the production of such structures. AM allows for the customization of porous implants with various shapes and sizes tailored to individual patients. Additionally, it enables the design of microscopic-scale porous structures to closely mimic natural bone, thus opening up avenues for the development of porous titanium alloy bone implants that can better stimulate bone regeneration. This article reviews the research progress on the structural design and preparation methods of porous titanium alloy bone implants, analyzes the porous structure design parameters that affect the performance of the implant, and discusses the application of porous medical titanium alloys. By comparing the effects of the parameters of different porosity, pore shape, and pore size on implant performance, it was concluded that pore diameters in the range of 500~800 μm and porosity in the range of 70%–90% have better bone-regeneration effects. At the same time, when the pore structure is a diamond, rhombohedral, or cube structure, it has better mechanical properties and bone-regeneration effects, providing a reference range for the application of clinical porous implants.

Analysis of Surgical Masks Adverse Effects on Facial Skin in Long Term Usage During COVID-19 Pandemic.

During the coronavirus disease-2019 pandemic, masks have become mandatory for protection against the virus transmitted by breathing. This study examined the impact of surgical masks used daily on civilian facial skin. Moisture, elasticity, pore, melanin, acne, wrinkle, and sensitivity parameters of 83 volunteers were measured numerically using an API-100 skin analyzer and camera recordings. Numerical values were compared following the device's algorithm calibrated according to age, gender, and race. Finally, the obtained data were statistically evaluated and compared with the averages. Pore, melanin, acne, and wrinkle parameters were higher without gender discrimination, whereas moisture and elasticity parameters were low. While a significant increase was observed in women for sensitivity, the increase was not statistically significant in men. The negative effects of long-term daily wearing of surgical masks on facial skin were statistically significant. Therefore, taking outdoor breaks during mask use, washing the face intermittently, using moisturizing and purifying cosmetic products, and anti-wrinkle effects have been proposed to reduce the possible defects.

An improved porous media model for simulating the flow–nets interaction

This study presents an improved porous media model for simulating the interaction between the fixed aquaculture nets and flow. The fluid motion is computed based on the Reynolds time-averaged Navier–Stokes equations on the regular Eulerian mesh. The porous media model simulates the nets, where the interface between the complex shapes of the nets and the fluid is determined by the continuous forced immersed boundary (IB) method. The fluid volume fraction is defined and embedded in the porous media coefficients and porosity equations to set the porous media parameters at IB. Several cases validate the model, including the flow interactions with the single net panel, gravity net cage, and offshore aquaculture platform. Meanwhile, the effects of incoming velocity, attack angle, solidity, and the shape of the net on the simulation are investigated. The numerical model can reasonably predict the hydrodynamic of the nets with a relative error of less than 8%. Moreover, the computational efficiency of the hydrodynamic of complex shaped nets is significantly improved, with a maximum of about 11.54 times.

Permeability prediction of porous aerostatic bearings through 3D morphology and fractal calculation method

AbstractPorous ceramics for aerostatic bearing restrictors were fabricated using carboxymethyl cellulose and polystyrene microspheres as pore formers. The three‐dimensional morphology of the porous ceramics was nondestructively obtained using laser scanning confocal microscopy, and the processing information was eliminated by fitting the pore area fractal dimensions at different heights. A mathematical model was developed based on the assumption of elliptical tortuous capillaries to relate microstructural pore parameters to permeability by combining fractal theory, Darcy's law, and the gas conservation equation. The calculated permeability closely matched the experimental results, with an error of less than 3.5%. This method has promising potential as an alternative to pressure drop experiments. Moreover, the capacity of the fractal calculation model to establish a correlation between microstructural parameters and permeability paves a new way to design future porous aerostatic bearings.

Pore parameter selection for fused deposition modeling of gas diffusion layers in proton exchange membrane fuel cells

AbstractBecause of the global energy crisis, many researchers have focused their efforts on fuel cells. The gas diffusion layer (GDL) is a fundamental component of proton exchange membrane (PEM) fuel cells. The manufacturing procedures for traditional carbon‐based GDLs are sophisticated and energy‐intensive, and have design flexibility constraints, making it difficult to build complicated forms and structures. Additive manufacturing is widely used in a variety of fields, with the fused deposition modeling (FDM) technique being the most popular method. Prior to conducting systematic research on the printed GDLs, it is necessary to investigate the pore parameters with the support of FDM technique. In this research, the initial step involves material selection, FDM printer selection, and modeling. Subsequently, printing analysis and sample characterization are conducted to select an acceptable pore shape. A water drainage test determines the appropriate pore size, followed by additional tests for acceptable porosity range. The square pore shape is determined to be more suitable. A pore side length of 1.0 mm is identified. Furthermore, a suitable pore range of 10.9%–30.3% is identified. Next step, the printed GDLs will undergo further testing to investigate their suitability to be used in PEM fuel cells.

Effect of porous fin parameters on the turbulent natural convection heat transfer in the side-heated cavity containing the internal heat source

In order to study the effect of porous fin parameters on the natural convection heat transfer in the side-heated cavity containing the internal heat source, the influence of the structural parameters of porous fins (length of porous fins l, installation position of porous fins s, Installation angle of porous fins θ) and the physical property parameters of porous fins (effective thermal conductivity Ke, Darcy number Da) on the natural convection heat transfer in the cavity was numerically analyzed by arranging a porous fin on the hot wall. The effect of the coupling effect of the structure parameters of porous fins was analyzed by the response surface method, and it was found that the coupling effect of the installation position and installation angle of porous fins had the most significant effect on the convective heat transfer in the cavity, the combination of the structural parameters of porous fins with the optimal convective heat transfer effect is l = 0.053 H, s = 0.373 H, and θ = 93.21°, which increases the average Nusselt number of the hot wall by 38.72% compared with no-fin structure; The effect of Darcy number and effective thermal conductivity of porous fins on the average Nusselt number of the hot wall surface is analyzed. The results of the study can guide the study of solar radiation in buildings, the internal temperature control of automobiles, and the study of the thermal performance of electronic components.

Effects of void defects on the mechanical properties of biphasic calcium phosphate nanoparticles: A molecular dynamics investigation

Porous biphasic calcium phosphate (BCP) ceramics are widely used in bone tissue engineering, and the mechanical properties of BCP implants must be reliable. However, the effects of pore structure (e.g., shape and size) on the mechanical properties are not well understood. In this study, we used molecular dynamics simulations to investigate the influence of pore shape and size on the mechanical behavior of BCP nanoparticles. BCP void models with cylindrical and cuboid pores ranging from 2 to 16 nm in diameter were constructed, and the elastic moduli were calculated. In addition, uniaxial tensile and compressive tests were performed on the models. We found that the pore size had a more significant impact on the mechanical properties of BCP than pore shape. Further, the elastic moduli decreased nonlinearly with increasing pore size. In addition, the tensile and compressive strength also decreased with the increase in pore size, but the ductility improved. Furthermore, deformation and fracture were more likely to occur near the pores and at the phase interfaces as a result of high atomic local strain in the calcium-deficient hydroxyapatite area. The results of this work reveal the effects of pore parameters on the mechanical properties of porous BCP at the nanometer level, which may aid the design of improved porous and multiphase CaP-based biomaterials for bone regeneration.