Search

This study investigates pressure gradient dynamics within a porous medium in the context of two-phase fluid flow, specifically water and sand particle interactions. Using experimental data, we refine pressure correction coefficients within a numerical solution framework, employing the Semi-Implicit Method for the Pressure-linked Equations algorithm. Our findings highlight the relative nature of pressure gradient phenomena, with particle size and volume fraction emerging as crucial determinants. Graphical representations reveal a clear trend: an increase in volume fraction, up to 40%, across varying Reynolds Numbers, leads to a transition towards non-Newtonian behavior in the two-phase fluid system. Unlike the linear pressure gradient seen in single-phase fluid flow, the interplay between liquid and solid phases, along with drag forces, imparts a distinctly nonlinear trajectory to the pressure gradient in two-phase fluid flow scenarios. As the two-phase flow enters a porous medium, numerous factors come into play, resulting in a pressure drop. These factors include changes in cross-sectional geometry, alterations in boundary layer dynamics, and ensuing momentum fluctuations. Interestingly, an increase in porosity percentage inversely correlates with pressure gradient, resulting in reduced pressure gradient with higher porosity levels. [ABSTRACT FROM AUTHOR]

This study investigates pressure gradient dynamics within a porous medium in the context of two-phase fluid flow, specifically water and sand particle interactions. Using experimental data, we refine pressure correction coefficients within a numerical solution framework, employing the Semi-Implicit Method for the Pressure-linked Equations algorithm. Our findings highlight the relative nature of pressure gradient phenomena, with particle size and volume fraction emerging as crucial determinants. Graphical representations reveal a clear trend: an increase in volume fraction, up to 40%, across varying Reynolds Numbers, leads to a transition towards non-Newtonian behavior in the two-phase fluid system. Unlike the linear pressure gradient seen in single-phase fluid flow, the interplay between liquid and solid phases, along with drag forces, imparts a distinctly nonlinear trajectory to the pressure gradient in two-phase fluid flow scenarios. As the two-phase flow enters a porous medium, numerous factors come into play, resulting in a pressure drop. These factors include changes in cross-sectional geometry, alterations in boundary layer dynamics, and ensuing momentum fluctuations. Interestingly, an increase in porosity percentage inversely correlates with pressure gradient, resulting in reduced pressure gradient with higher porosity levels.

Nowadays, the design of porous bone scaffolds represents a crucial issue in orthopedical applications. In this article, the mechanical properties of a multi-component scaffold with different porosity percentages were investigated. Mori–Tanaka equations were used to estimate various properties of calcium phosphate (CaP) bone cement reinforced by strontium nitrate nanoparticles (NPs) based on porosity percentages in both cases; before and after samples placement in simulated body fluid (SBF) solution. With the support of these equations, the mechanical properties of bone cement material without porosity were estimated to be used in finite element analysis (FEA); so then to assess structural stability and stress distribution, the experimental compression tests on the scaffold were simulated with the ABAQUS engineering package. The mechanical properties observation indicates that the grain and particle size increased by nitrate addition to the bone cement. The approach in this manuscript allows quantifying the effect of porosity on mechanical properties of CaP cements reinforced by the strontium nitrate NPs, to be fabricated based on the patient's needs. [ABSTRACT FROM AUTHOR]

Treatment of tissue defects commonly represents a major problem in clinics due to difficulties involving a shortage of donors, inappropriate sizes, abnormal shapes, and immunological rejection. While many scaffold parameters such as pore shape, porosity percentage, and pore connectivity could be adjusted to achieve desired mechanical and biological properties. These parameters are crucial scaffold parameters that can be accurately produced by 3D bioprinting technology based on the damaged tissue. In the present research, the effect of porosity percentage (40%, 50%, and 60%) and different pore shapes (square, star, and gyroid) on the mechanical (e.g., stiffness, compressive and tensile behavior) and biological (e.g., biodegradation, and cell viability) properties of porous polycaprolactone (PCL) scaffolds coated with gelatin have been investigated. Moreover, human foreskin fibroblast cells were cultured on the scaffolds in the in‐vitro procedures. MTT assay (4, 7, and 14 days) was utilized to determine the cytotoxicity of the porous scaffolds. It is revealed that the porous scaffolds produced by the bioprinter did not produce a cytotoxic effect. Among all the porous scaffolds, scaffolds with a pore size of about 500 μm and porosity of 50% showed the best cell proliferation compared to the controls after 14 days. The results demonstrated that the pore shape, porosity percentage, and pore connectivity have an important role in improving the mechanical and biological properties of porous scaffolds. These 3D bioprinted biodegradable scaffolds exhibit potential for future application as polymeric scaffolds in hard tissue engineering applications. [ABSTRACT FROM AUTHOR]

Objects touched by patients and healthcare workers in hospitals may harbor pathogens, including multi-drug resistant (MDR) staphylococci, enterococci (VRE), Escherichia coli, Acinetobacter, and Pseudomonas species. Medical devices contaminated by these pathogens may also act as a source of severe and difficult-to-treat human infections, thus becoming a critical public health concern requiring urgent resolutions. To this end, we recently reported the bactericidal effects of a cationic copolymer (CP1). Here, aiming at developing a bactericidal formulation possibly to be used either for surfaces disinfection or to treat skin infections, CP1 was formulated as a hydrogel (CP1_1.1-Hgel). Importantly, even if not cross-linked, CP1 formed the gel upon simple dispersion in water, without requiring gelling agents or other additives which could be skin-incompatible or interfere with CP1 bactericidal effects in possible future topical applications. CP1_1.1-Hgel was characterized by attenuated-total-reflectance Fourier transform infrared (ATR-FTIR) and UV-Vis spectroscopy, as well as optic and scanning electron microscopy (OM and SEM) to investigate its chemical structure and morphology. Its stability was assessed by monitoring its inversion properties over time at room temperature, while its mechanical characteristics were assessed by rheological experiments. Dose-dependent cytotoxicity studies performed on human fibroblasts for 24 h with gel samples obtained by diluting CP_1.1-Hgel at properly selected concentrations established that the 3D network formation did not significantly affect the cytotoxic profile of CP1. Also, microbiologic investigations carried out on two-fold serial dilutions of CP1-gel confirmed the minimum inhibitory concentrations (MICs) previously reported for the not formulated CP1.Selectivity indices values up to 12 were estimated by the values of LD50 and MICs determined here on gel samples. [ABSTRACT FROM AUTHOR]

To evaluate and compare the flexural strength, surface roughness and porosity percentage of acrylic denture base material modified with two antimicrobial agents, Thymoquinone (TQ) and Silver nanoparticles (AgNP). A total of 90 specimens were fabricated and divided into groups A, B and C with 30 specimens each. Of the 30 specimens, 10 specimens measuring 65mmx 10mmx 2.5 mm were used to study the flexural strength, 10 specimens measuring 10 mm × 20 mm × 3 mm to study surface roughness and 10 specimens measuring 10 mm × 20 mm × 3 mm to study porosity percentage. Group A specimens were made of unmodified denture base resin, group B and C were modified with 2.5% AgNP and 1% TQ respectively. The specimens were processed in the conventional manner. A universal testing machine was used to measure flexural strength and a profilometer was used to measure surface roughness. Porosity percentage was evaluated with help of a desiccator. The data obtained was subjected to statistical analyses using One-way ANOVA and the Tukey-post hoc test, with statistical significance at p ≤ 0.05. Addition of 2.5% AgNP and 1% TQ to acrylic denture base resin significantly reduced flexural strength and increased the porosity percentage (p < 0.01) but within clinically acceptable limits. No significant difference was found in the surface roughness between the various groups tested. Heat cured acrylic denture base resins modified with 2.5% AgNPs,1% TQ exhibited clinically acceptable flexural strength and surface properties and could be incorporated into the denture base material as an antimicrobial agent. [Display omitted] [ABSTRACT FROM AUTHOR]

Logging operation by skidders can lead to soil compaction, rutting and erosion of skid trails. Therefore, in order to restore the soil physical properties of skid trails, it is necessary to perform improvement treatments. In this study, four compaction improvement treatments were investigated on one-year-old skid trails with two slope classes of low slope (0-20) and high slope (over 20) and 5 replications. 360 soil samples were taken, half of them before applying the treatments and the other half a year after the treatments application, and were analyzed to evaluate the improvement effect of the treatments. Results of low slope class showed that there was a significant difference between soil bulk density and porosity percentage in improvement treatment plots and control plots of forested area. Treatments of orthogonal groove, diagonal groove and logging residuals showed no significant difference with the control skid trail, and only the use of the combined treatment was able to significantly reduce bulk density and increase porosity percentage compared to the control skid trail. For high slope class, all soil improvement treatments showed a significant difference with control plots; however, compared to the control skid trail, none of the mentioned treatments could cause significant differences. Among the studied treatments, the combined treatment had the best performance in restoring soil physical properties in both low and high slope classes.

In this study the parameters affecting the foaming process of pure commercial aluminum for preparing of light products are investigated. Titanium hydride (TiH2) powder as a foaming agent (0/5 to 2/5 wt%) added to the aluminum melt. The temperature range of 620 to 660°C was selected. The proper holding temperature and foaming agent content lead to production of foamed aluminum with high porosity percentage and cell structure uniformity. Results show that by adding 1 wt% of TiH2 at foaming temperature of 640°C, cells with 2-6 millimeter in diameter and uniform distribution with 86% porosity are achieved. [ABSTRACT FROM AUTHOR]

Modern architects often adopt the use of façades on new buildings or to improve the appearance of an existing old building. Among various types of facades, ones with porous skins are increasingly popular. The porous features can not only improve the aesthetic of design but can also significantly lower wind loads on the inner building. This research investigates the filtering performance of various exterior porous façades on the surface pressures of an ordinary building based on systematical wind tunnel tests. Three target parameters, the porosity percentage of the façade, the gap distance between the façade and the building surface, and the opening shape of the pores, are investigated in this study. Preliminary results show that the Reynolds number makes little difference to the measured mean and root-mean-square values of fluctuating pressures. Subsequent results show that the façade skin porosity and gap distance together contribute to any amplification or reduction of surface pressures measured on the inner building. Different reduction or amplification levels are also found highly related to the upstream or downstream region over the side faces for the mean and the fluctuating pressures. For a limited area near the building corners, an amplification in negative local pressures was found due to the flow entering the façade cavity on the windward face and being channeled between the façade and sidewall of the building. A channel-effect phenomenon is also indicated with the presence of the exterior skin in certain regions, instead of just the reducing effect from the pores. • This study investigates the filtering effect of porous façade skins on wind loads over the building surface. • Reynold number effect on the filtered wind loads is shown to be less sensitive when it is greater than the 6 × 104. • Porosity percentage and gap distance dominate the amplification or reduction effects over different surface regions. • A channel-effect phenomenon is observed due to the exterior skin, implying a mixed filtering mechanism. [ABSTRACT FROM AUTHOR]