Porous Inserts Research Articles

Influence of the Form of Porous Insert in the Flow of a Viscous Liquid in a Plane Pipe

Filtration of an incompressible liquid (gas) in a non-deformable porous medium is investigated. The results of numerical simulation of the hydrodynamic features of the flow arising after the passage of the liquid through a layer of an immobile porous medium are presented. An interpenetrating model of multiphase media is used to describe such flows. Kozeny-Karman relations are used as the interaction force. The influence of the geometrical shape of the bulk layer on the nature and magnitude of the inhomogeneity of the flow velocity around the obstacle is shown. The shape of the porous medium significantly affects the flow parameters. Numerical simulation results are compared with experimental data. The shape of the porous medium significantly affects the flow parameters. Numerical simulation results are compared with experimental data. The effects of non-uniformity of the fluid velocity field arising due to the shape of the layer surface are investigated by the methods of a computational experiment. A qualitative comparison is made of velocity inhomogeneities when a fluid flows through a porous obstacle. For the numerical implementation of the filtration equation of the interpenetrating model, a SIMPLE-like algorithm was used.

Mathematical model of gas dynamics of a nozzle channel with a gas-dynamic method of thrust vector control using a porous insert

The ability to change the magnitude and direction of the thrust vector is a fundamental parameter of the propulsion systems of aircraft. A wide range of methods for controlling these quantities has been developed, which are used depending on the design schemes. The article discusses the organization of the gas-dynamic method of thrust vector control, carried out using distributed gas injection through a porous insert.

Forced convection enhancement of air flowing inside circular pipe with varying the pitch (P) of wire-mesh porous media

The forced convective heat transfers on a circular pipe with varying the pitch (P) of stainless wire-mesh porous media for the constant case of surface temperature have been investigated experimentally. The examined parameters were Nusselt number (Nu), friction factor (f), and performance evaluation criteria (PEC). The circular test pipe’s wall temperature was maintained at a constant 25 °C. The porous inserts were made of SUS 304 stainless wire mesh with a pore per inch (PPI) of 8, and the working fluid was airflow rate expressed as Reynolds number (Re) changing from 6000 to 55,000. Five pitch distances (P) were examined: 25, 50, 75, 100, and 125 mm. The test section consisted of two horizontal concentric pipes through which heated air flowed in one direction (a test pipe or inner pipe) and cold water flowed in the opposite direction through the annulus. The dimension of the circular test pipe yielded 100 mm long, 25.4 mm inner diameter (Di), and 3 mm thick were adopted. From the experiment, the Nu increased with Re, but the result was reversed by raising P. As decreasing Re and P, the f decreased. It was described by a higher material volume of the solid skeleton of porous media leading to gain more energy absorption from hot air due to the higher effective thermal conductivity (ETC) and, then, to generate higher pressure drop with many the obstruction. The maximum PEC was given at P=75 mm because this may be a proper condition for enhancing forced convective heat transfers on a circular test pipe with stainless wire-mesh porous media placed for the constant situation of surface temperature.

The effect of an Al-based cellular structure on the thermal performance of a zeolite-based hybrid heat accumulator

The heat accumulator designed for the purposes of this study consists of two chambers with metal foam structures and honeycomb segments casted by the means of investment casting from an AlSi alloy. The cellular metal castings, characterized by a relatively large coefficient of thermal conductivity, provide rapid transport of heat energy from the source to the heat storage materials (paraffin or zeolite). In order to simulate the conditions of solar heating, two outdoor halogen reflectors were used for the heating stage. Multiple long-term cycles of charging and discharging of this heat accumulator, with and without porous metallic inserts to improve the thermal conductivity and increase the heat transfer area, were conducted and subsequently analysed. The metal foams are suitable for enhancing heat transfer in a zeolite bed, whereas the durable honeycomb casting is preferable for phase change material. Additionally, the porous foam improves the conditions for transporting vapour during dehydration/hydration. The application of cast inserts in the zeolite chamber helped to decrease the temperature gradient to below 50 °C. The overall amount of energy stored in the hybrid TES unit equaled 7676.4 kJ (2.14 kWh).

Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction

Lattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at zero angle-of-attack. A partially blocked insert is considered by adding a solid partition between 84 % and 96 % of the aerofoil chord. The regular porous insert achieves a substantial noise reduction at low frequencies, although a slight noise increase is found at high frequencies. The partially blocked porous insert exhibits a lower noise reduction level, but the noise emission at mid-to-high frequency is slightly affected. The segment of the porous insert near the tip plays a dominant role in promoting noise mitigation, whereas the solid-porous junction contributes, in addition to the rough surface, towards the high-frequency excess noise. The current study demonstrates the existence of an entrance length associated with the porous material geometry, which is linked to the pressure release process that is responsible for promoting noise mitigation. This process is characterised by the aerodynamic interaction between pressure fluctuations across the porous medium, which is found at locations where the porous insert thickness is less than twice the entrance length. Present results also suggest that the noise attenuation level is related to both the chordwise extent of the porous insert and the streamwise turbulent length scale. The porous inserts also cause a slight drag increase compared to their solid counterpart.

Thermo-hydraulic analyses of the absorber tube with molten salt-based nanofluid and porous medium inserts

In this work, a new combination technique of molten salt-based nanofluid and porous medium inserts is presented for the thermo-hydraulic performance improvement of the absorber tube. The effects of porous medium configurations, porosities, nanoparticle concentrations, materials, and Reynolds numbers are discussed in terms of the flow and heat transfer characteristics as well as the performance evaluation criterion (PEC). According to the results, the enhanced tube inserted with wall attached type porous medium can achieve much better heat transfer performance. Molten salt-based nanofluid shows considerable heat transfer performance inside the tube with a porous medium, compared with pure molten salt flow inside a smooth tube. Among the four kinds of materials, the best one for the porous medium is copper. The combination for the best thermo-hydraulic performance is proposed with the 0.125% (mass fraction) molten salt-based nanofluid and the absorber tube with copper metal foam (porosity of 0.9005), after systematically comparing the simulation results. This combination accomplishes the best heat transfer enhancement with 12.44 times of Nusselt number higher than pure molten salt inside the smooth tube at the Reynolds number of 1×104. The peak PEC value of 5.98 is reached at the Reynolds number of 6×104. Finally, the improvement of the thermo-hydraulic performance of this combination technique was proved through physical discussions based on the temperature and velocity profiles.

Thermal performance evaluation of a microchannel with different porous media insert configurations

PurposeThis paper aims to numerically investigate the thermal performance evaluation of a microchannel with different porous media insert configurations.Design/methodology/approachHeat transfer and pressure drop of fluid flow through a three-dimensional (3D) microchannel with different partially and filled porous media insert configurations are investigated numerically. The number of divisions and positions of porous material inside the microchannel for 12 different arrangements are considered. A control volume method is used for single-phase laminar flow with the Darcy–Forchheimer model used for the porous media. The geometry of the problem consists of a microchannel with a rectangular cross-section of 0.4 mm × 0.2 mm and length 20 mm, with a stainless steel porous material insert with a porosity coefficient of ε = 0.32 and a Darcy number of Da = 2.7 × 10−4.FindingsNumerical results show that when the transverse arrangement is used, as the number of partitions increases, the thermal performance is improved and the heat transfer increases up to 300% compared to that of the plain microchannel. Comparing the obtained results from the microchannels with transverse and longitudinal configurations, at low Reynolds numbers, the transverse arrangement of porous blocks and at high Reynold numbers, the longitudinal arrangement present the best thermal performance which is virtually four times higher compared to the obtained Nu numbers from the plain microchannel. The results show that as the volume of porous material is constant in the cases with various transverse porous blocks, the pressure drop is not changed in these cases. Also, the highest thermal performance ratio is when the porous material is placed along the walls in a longitudinal direction.Originality/valueTo the best knowledge of the authors, in the previous research, the effect of the arrangement and location of the porous medium in the transverse and longitudinal direction in the microchannel and their effect in different states on the behavior of flow and heat transfer has not been numerically investigated. In this study, the porous media configuration and its placement in a 3D microchannel were numerically studied. The effect of porous material layout and configurations in different longitudinal and transverse directions on the pressure drop, heat transfer and thermal performance in the 3D microchannel is investigated numerically.

Transcryptomic Analysis of Human Brain -Microvascular Endothelial Cell Driven Changes in -Vascular Pericytes.

Many pathological conditions of the brain are associated with structural abnormalities within the neurovascular system and linked to pericyte (PC) loss and/or dysfunction. Since crosstalk between endothelial cells (ECs) and PCs greatly impacts the function of the blood–brain barrier (BBB), effects of PCs on endothelial integrity and function have been investigated extensively. However, the impact of ECs on the function and activity of PCs remains largely unknown. Hence, using co-cultures of human brain vascular PCs with human cerebral microvascular ECs on opposite sides of porous Transwell inserts which facilitates direct EC–PC contact and improves EC barrier function, we analyzed EC-driven transcriptomic changes in PCs using microarrays and changes in cytokines/chemokines using proteome arrays. Gene expression analysis (GEA) in PCs co-cultured with ECs versus PCs cultured alone showed significant upregulation of 1′334 genes and downregulation of 964 genes. GEA in co-cultured PCs revealed increased expression of five prominent PC markers as well as soluble factors, such as transforming growth factor beta, fibroblast growth factor, angiopoietin 1, brain-derived neurotrophic factor, all of which are involved in EC–PC crosstalk and BBB induction. Pathway enrichment analysis of modulated genes showed a strong impact on many inflammatory and extracellular matrix (ECM) pathways including interferon and interleukin signaling, TGF-β and interleukin-1 regulation of ECM, as well as on the mRNA processing pathway. Interestingly, while co-culture induced the mRNA expression of many chemokines and cytokines, including several CCL- and CXC-motif ligands and interleukins, we observed a decreased expression of the same inflammatory mediators on the protein level. Importantly, in PCs, ECs significantly induced interferon associated proteins (IFIT1, IFI44L, IF127, IFIT3, IFI6, IFI44) with anti-viral actions; downregulated prostaglandin E receptor 2 (prevent COX-2 mediated BBB damage); upregulated fibulin-3 and connective tissue growth factor essential for BBB integrity; and multiple ECMs (collagens and integrins) that inhibit cell migration. Our findings suggest that via direct contact, ECs prime PCs to induce molecules to promote BBB integrity and cell survival during infection and inflammatory insult. Taken together, we provide first evidence that interaction with ECs though porous membranes induces major changes in the transcriptomic and proteomic profile of PCs. ECs influence genes involved in diverse aspects of PC function including PC maturation, cell survival, anti-viral defense, blood flow regulation, immuno-modulation and ECM deposition.

Mixed convection from a heat source in a channel with a porous insert: A numerical analysis based on local thermal non-equilibrium model

Numerical examination was carried out on mixed convection in a horizontal channel containing a single heat source at the bottom wall with a porous insert placed exactly on the heater surface. It was assumed that the porous insert partially fills the channel. The numerical simulations were carried out using the local thermal non-equilibrium (LTNE) condition and the temperature distribution of solid and fluid phases of porous insert were obtained. The impact of height of the porous insert, porosity of the porous insert, material and diameter of the solid particle of the porous insert, buoyancy force, Reynolds number of the flow on the distribution of temperature were investigated and the influence of these parameters over the applicability of the local thermal equilibrium condition (LTE) was also studied. The results indicate that the effect of buoyancy force is considerable and cannot be ignored at low Reynolds number. Applying the LTNE condition, the optimum thickness of porous insert for the improvement in heat transfer with a considerable pressure drop is found to be equal to half the channel height. The porosity of the porous insert, the particle diameter of the solid phase of the porous insert and the thermal conductivity of the solid phase of the porous insert highly affect the applicability of LTE condition.

Air Permeability of Maraging Steel Cellular Parts Made by Selective Laser Melting.

Additive manufacturing, such as selective laser melting (SLM), can be used to manufacture cellular parts. In this study, cellular coupons of maraging steels are prepared through SLM by varying hatch distance. Air flow and permeability of porous maraging steel blocks are obtained for samples of different thickness based on the Darcy equation. By reducing hatch distance from 0.75 to 0.4 mm, the permeability decreases from 1.664 × 10−6 mm2 to 0.991 × 10−6 mm2 for 4 mm thick coupons. In addition, by increasing the thickness from 2 to 8 mm, the permeability increases from 0.741 × 10−6 mm2 to 1.345 × 10−6 mm2 at 16.2 J/mm3 energy density and 0.14 MPa inlet pressure. Simulation using ANSYS-Fluent is conducted to observe the pressure difference across the porous coupons and is compared with the experimental results. Surface artifacts and the actual morphology of scan lines can cause the simulated permeability to deviate from the experimental values. The measured permeability of maraging steel coupons is regression fit with both energy density and size of samples which provide a design guideline of porous mold inserts for industry applications such as injection molding.

Forced Convection in Wavy Microchannels Porous Media Using TiO2 and Al2O3-Cu Nanoparticles in Water Base Fluids: Numerical Results.

In the present work, an attempt is made to investigate the performance of three fluids with forced convection in a wavy channel. The fluids are water, a nanofluid of 1% TiO2 in a water solution and a hybrid fluid which consists of 1% Al2O3–Cu nanoparticles in a water solution. The wavy channel has a porous insert with a permeability of 10 PPI, 20 PPI and 40 PPI, respectively. Since Reynolds number is less than 1000, the flow is assumed laminar, Newtonian and steady state. Results revealed that wavy channel provides a better heat enhancement than a straight channel of the same dimension. Porous material increases heat extraction at the expenses of the pressure drop. The nanofluid of 1% TiO2 in water provided the highest performance evaluation criteria.

The Clinical Application of Porous Tantalum and Its New Development for Bone Tissue Engineering.

Porous tantalum (Ta) is a promising biomaterial and has been applied in orthopedics and dentistry for nearly two decades. The high porosity and interconnected pore structure of porous Ta promise fine bone ingrowth and new bone formation within the inner space, which further guarantee rapid osteointegration and bone–implant stability in the long term. Porous Ta has high wettability and surface energy that can facilitate adherence, proliferation and mineralization of osteoblasts. Meanwhile, the low elastic modulus and high friction coefficient of porous Ta allow it to effectively avoid the stress shield effect, minimize marginal bone loss and ensure primary stability. Accordingly, the satisfactory clinical application of porous Ta-based implants or prostheses is mainly derived from its excellent biological and mechanical properties. With the advent of additive manufacturing, personalized porous Ta-based implants or prostheses have shown their clinical value in the treatment of individual patients who need specially designed implants or prosthesis. In addition, many modification methods have been introduced to enhance the bioactivity and antibacterial property of porous Ta with promising in vitro and in vivo research results. In any case, choosing suitable patients is of great importance to guarantee surgical success after porous Ta insertion.

On the noise reduction of a porous trailing edge applied to an airfoil at lifting condition

Numerical simulations, using a lattice-Boltzmann technique, have been carried out to study the effect of aerodynamic loading and Reynolds number on the aeroacoustics of a porous trailing-edge insert. The airfoil is a National Advisory Committee for Aeronautics 0018 with the last 20% of its chord being replaceable with porous insert based on a Ni-Cr-Al metal foam with a mean pore diameter of 0.8 mm. The porous insert is modeled as an equivalent fluid region governed by the Darcy's law. The angle-of-attack is set to 7.8°, and the freestream Reynolds numbers based on the airfoil chord are 2.7 × 105 and 5.4 × 105. The amount of noise reduction produced by the porous insert generally decreases as the angle-of-attack or Reynolds number is increased, although the far-field noise directivity remains similar to that of the solid insert case. Unlike for a solid insert, in which noise sources are concentrated at the trailing edge, those on the porous insert are distributed across the porous medium surface, and they promote phase interference effect that causes noise attenuation. This mechanism is realized by the pressure release process, which refers to the interaction between surface pressure fluctuations on both sides of the trailing edge through the porous medium. It is found that the pressure release process is strongly present at the last 25% of the porous insert extent, and thus the upstream segment plays a relatively limited role in noise attenuation. The porous insert also causes velocity deficit, enhanced Reynolds shear stress, and lower convection velocity in the turbulent boundary layer. Nevertheless, since only the flow field surrounding the porous insert is affected, the overall aerodynamic penalty is relatively minor. It has also been found that the effect of mean cross-flow inside the porous medium is almost negligible in the present investigation due to the small surface pressure difference between the two sides of the porous insert.

Controlling the Aerodynamic Drag of a Cylinder with Gas-Permeable Porous Inserts by Regulating Base Pressure

Controlling the Aerodynamic Drag of a Cylinder with Gas-Permeable Porous Inserts by Regulating Base Pressure

FleXert: A Soft, Actuatable Multiwell Plate Insert for Cell Culture under Stretch.

Porous multiwell plate inserts are widely used in biomedical research to study transport processes or to culture cells/tissues at the air-liquid interface. These inserts are made of rigid materials and used under static culture conditions, which are unrepresentative of biological microenvironments. Here, we present FleXert, a soft, actuatable cell culture insert that interfaces with six-well plates. It is made of polydimethylsiloxane (PDMS) and comprises a porous PDMS membrane as cell/tissue support. FleXerts can be pneumatically actuated using a standard syringe pump, imparting tensile strains of up to 30%. A wide range of actuation patterns can be achieved by varying the air pressure and pumping rate. Facile surface functionalization of FleXert's porous PDMS membrane with fibronectin enables adhesion of human dermal fibroblasts and strains developing on FleXert's membrane are successfully transduced to the cell layer. 3D tissue models, such as fibroblast-laden collagen gels, can also be anchored to PDMS following polydopamine coating. Furthermore, collagen-coated FleXert membranes support the establishment of a human skin model, demonstrating the material's excellent biocompatibility required for tissue engineering. In contrast to existing technologies, FleXerts do not require costly fabrication equipment or custom-built culture chambers, making them a versatile and low-cost solution for tissue engineering and biological barrier penetration studies under physiological strain. This paper is an extensive toolkit for multidisciplinary mechanobiology studies, including detailed instructions for a wide variety of methods such as device fabrication, theoretical modeling, cell culture, and image analysis techniques.

Investigation of Vasculogenesis Inducing Biphasic Scaffolds for Bone Tissue Engineering.

Vascularization is the main obstacle for the bone tissue engineering strategies since the defect size is generally large. Incorporation of angiogenic factors is one of the strategies employed in order to accelerate vascularization and improve bone healing. In this study, a biphasic scaffold consisting of fibrous poly(lactide-co-glycolide) (PLGA) and poly(lactide-co-glycolide)-block-poly(ethylene glycol)-block-poly(lactide-co-glycolide) (PLGA-PEG-PLGA) hydrogel loaded with vascular endothelial growth factor-A (VEGF) inducer, GS4012, was constructed. Mesenchymal stem cells isolated from rat bone marrow (rBMSCs) were used for differentiation into osteogenic cells, and endothelial cells isolated from rat peripheral blood (rPBECs) were used to test the in vitro endothelial cell recruitment. The biphasic scaffold was tested for cell proliferation, ALP expression, VEGF induction, expression of osteogenic genes by rBMSCs, and recruitment of rPBECs in vitro and for improved bone healing and vascularization in vivo on critical size rat cranial defects. Endothelial migration through porous insert and VEGF induction were obtained in vitro in response to GS4012 as well as the upregulation of ALP, Runx2, Col I, and OC gene expressions. The biphasic scaffold was also shown to be effective in improving endothelial cell recruitment, vascularization, and bone healing in vivo. Thus, the proposed design has a great potential for the healing of critical size bone defect in tissue engineering studies according to both in vitro and in vivo investigations.

Influence of porous inserts on flow boiling heat transfer in horizontal tubes

In this paper we want to assess the mechanisms by which metal porous inserts influence flow boiling heat transfer in horizontal tubes. For this purpose, measurement data of the local and circumferentially averaged heat transfer coefficient of CO2 flow boiling in horizontal tubes with two different porous inserts are presented. As inserts, different sponges (open-cell network structures) and a wire matrix element are chosen and compared with each other. Different operating conditions were investigated. The mass flux was varied in a range from 25 kg m−2 s−1 to 190 kg m−2 s−1 and the vapor quality from 10% to 100%. Saturation pressures of 12 bar, 19 bar and 26.5 bar and average heat fluxes up to 65 kW m−2 were realized. By comparing the local heat transfer coefficient with empty tube data, wetting and convective heat transfer can be identified as the main influencing factors. Thus, we can obtain guidelines for the development of a model to describe the heat transfer coefficient of two-phase flow in porous inserts. A model derived in this way describes the measurement data of flow boiling of CO2 in horizontal tubes with inserts with a high degree of accuracy. The model is based on established sub-models without any additional fitting parameter. More than 90% of all measured data are predicted with less than 30% deviation

Numerical analysis of the performance improvement of a flat-plate solar collector using conjugated porous blocks

Performance enhancement of a flat-plate solar collector (FPSC) of direct absorption has been studied using porous insertions. The FPSC channel includes three conjugated porous blocks with various levels of permeability near the bottom insulator wall. Both the length and width of the blocks are altered near the inlet and outlet sections. The size of the middle trapezoidal block is aligned with reference to the gap available between the blocks near inlet and outlet. The parametric study focuses on finding the optimum design and arrangement of porous insertion. The height and width of the inlet sections are varied between 0 - H (step of 0.2) and 0-L (step of 0.2), respectively. The permeability of the porous blocks is varied between Da = 10−3 - 10−1. The opensource tool OpenFOAM® is used, and a generic steady-state thermal transport code is modified by the extended Darcy-Brinkman-Forchheimer model for realising porous medium. Numerical results indicate that the overall performance of the flat plate collector channel is improved by using the conjugated arrangement of porous bodies. The approach of placing the bodies near the bottom insulator plate improves heat transfer by promoting thermal mixing. Also, it is seen that more flow deviates towards the top absorber plate, and hence better thermal contact is established with the working fluid. The optimum performance is noticed for lower values of height of the block near the inlet and higher values near the outlet.

Scaling Up Studies on PEMFC Using a Modified Serpentine Flow Field Incorporating Porous Sponge Inserts to Observe Water Molecules.

Flooding of the cathode flow channel is a major hindrance in achieving maximum performance from Proton Exchange Membrane Fuel Cells (PEMFC) during the scaling up process. Water accumulated between the interface region of Gas Diffusion Layer (GDL) and rib of the cathode flow field can be removed by the use of Porous Sponge Inserts (PSI) on the ribs. In the present work, the experimental investigations are carried out on PEMFC for the various reaction areas, namely 25, 50 and 100 cm2. Stoichiometry value of 2 is maintained for all experiments to avoid variations in power density obtained due to differences in fuel utilization. The experiments include two flow fields, namely Serpentine Flow Field (SFF) and Modified Serpentine with Staggered provisions of 4 mm PSI (4 mm × 2 mm × 2 mm) Flow Field (MSSFF). The peak power densities obtained on MSSFF are 0.420 W/cm2, 0.298 W/cm2 and 0.232 W/cm2 compared to SFF which yields 0.242 W/cm2, 0.213 W/cm2 and 0.171 W/cm2 for reaction areas of 25, 50 and 100 cm2 respectively. Further, the reliability of experimental results is verified for SFF and MSSFF on 25 cm2 PEMFC by using Electrochemical Impedance Spectroscopy (EIS). The use of 4 mm PSI is found to improve the performance of PEMFC through the better water management.

Метод управления аэродинамическим сопротивлением цилиндра с газопроницаемыми пористыми вставками путем регулирования донного давления

The results of an experimental and numerical study of a supersonic (M = 7) flow around a hollow cylinder with gas-permeable porous inserts located along the flow are presented. The possibility of controlling the aerodynamic drag of the model by passing a part of the incident flow into the bottom area through gas-permeable porous inserts is shown. The flow rate of air directed to the bottom region to control the resistance was controlled by heating the porous inserts with an electric glow discharge.