Channel Porosity Research Articles

Highly porous building ceramics based on «clay-ash microspheres» and «zeolite-ash microspheres» mixtures

The possibility of obtaining highly porous heat-insulating ceramic materials based on compositions of mineral binding components (clay and zeolite rock) with ash-containing waste from the combustion of solid fuel (ash microspheres) is considered.It has been established that the pore-forming effect of ash microspheres in mixtures with low-melting clay is due to both the porous macrostructure of the ash component (the presence of hollow spherical particles) and the nature of physicochemical processes in the “clay – ash microspheres” and “zeolite – ash microspheres” systems (the synthesis of anorthite and mullite proceeding with an increase in molar volume).The creation of highly porous ceramic structures from mixtures of ash microspheres with zeolite rock, in addition to the structural features of microspheres, is also due to the structural (channel) porosity of zeolite minerals. The established pore-forming effect of zeolite rock and ash microspheres made it possible to develop a method for preparing a semi-dry masses from these compositions and to propose a technological scheme for obtaining a highly porous ceramic brick.The use of zeolite rock as a binder in a mixture with ash microspheres in content up 60–95 wt%, modified with zeolite-lignosulfonate slip, makes it possible to obtain a highly efficient constraction and thermal insulation ceramic brick with a compressive strength of 18–30 MPa, volume weight 930–1100 kg/m3 and thermal conductivity 0.22–0.31 W/m·K at a firing temperature of 950–1000 °C.

The Oligocene‐Miocene Guadalope‐Matarranya Fan, Spain, as an Analog for Long‐Lived, Ridge‐Bearing Megafans on Mars

AbstractNumerous sedimentary fans on Mars have been studied to better understand the early martian hydrological system. Of particular interest is to estimate the duration of fluvial activity from alluvial fan size by dividing deposit volume by bankfull sediment flux. However, such a calculation requires an intermittency factor—a parameter relating sediment discharge from channel‐filling (bankfull) floods to the long‐term mean sediment discharge—which is poorly constrained. Here, we investigated fluvial fan deposits from the Oligocene–Miocene Caspe Formation, Spain, as an analog to fans on Mars because it has exhumed channel belts that create sinuous ridges in the modern topography, similar to those observed on Mars that are used for paleohydraulics. We made measurements of the thicknesses of dune and bar cross sets within exhumed channel belts at nine field sites to reconstruct bankfull channel depth (∼1.4 m) and bankfull sediment flux (∼0.48 m3/s). We estimated total bed‐material sediment volume of the fan (362 km3) from stratigraphic thickness, the area containing exhumed channel belts, porosity and sand fraction. Combined with previous constraints on depositional timespan (∼6 Myr), we calculated a sediment‐transport intermittency factor of 0.004 (range: 0.0004–0.04). Our approach can be applied to Mars by using remote sensing measurements of fluvial ridge morphology, which indicates the possibility of long depositional timespans exceeding millions of years for martian fans.

Numerical study on the influence of waveform channel and related design parameters on the cold start of proton exchange membrane fuel cell

In order to enable the proton exchange membrane fuel cell to be used under outdoor conditions, research on the cold start of the fuel cell is essential. In this paper, numerical simulation is used to study the influence of fuel cell cathode channel geometry and porosity on the fuel cell cold start process. By analyzing the internal parameters of the fuel cell at different times, including current density, ice volume fraction, temperature and water content, the optimal fuel cell design was obtained. From a comprehensive comparison, although the current density and temperature rise of the ordinary wave channel fuel cell with higher porosity increase slowly at the beginning of the cold start, the decline process and icing process of it are also relatively slow. Therefore, a fuel cell with an ordinary wave channel and a higher porosity may perform better at cold start. This research contributes to the application and commercialization of fuel cells in a wider range of practical conditions.

Two Cd-MOFs with different types of channels based on phenylimidazole dicarboxylic acids: Synthesis, crystal structure and solid fluorescence properties

The reaction of cadmium(II) nitrate with two phenylimidazole dicarboxylic acids, 2-phenyl-1H-imidazole-4,5-dicarboxylic acid (H3PhIDC) and 2-p-methoxyphenyl-1H-imidazole-4,5-dicarboxylic acid (p-H3MOPhIDC), produce two new cadmium(II) organic frameworks (Cd-MOFs), namely [Cd4(HPhIDC)4(CH3CN)(H2O)]n (1) and {[Cd2(p-HMOPhIDC)2(H2O)2]•DMF}n (2). Structural analyses show that although 1 and 2 are both three-dimensional (3-D) network skeletons formed by the connection of phenylimidazole dicarboxylic acid, their channel types and porosity (8.8% for 1, 25.1% for 2) are different. The channel of 1 is a quadrilateral channel containing six Cd(II) ions, whereas the channel of 2 is a double channel containing ten Cd(II) ions in a staggered arrangement of large and small quadrilaterals. The difference in the structure and size of the channels of Cd-MOFs may be attributed to the bridging mode of the phenylimidazole dicarboxylic acid ligands. In addition, the fluorescence properties of 1 and 2 at room temperature in solid state were also studied.

Interface regulation of mixed matrix membranes by ultrathin MOF nanosheet for faster CO2 transfer

Mixed matrix membranes (MMMs) incorporating porous materials received extensive attention for applications of gas separation, but the one shows significant high permeability and increased selectivity is rare. Here, we report a strategy of interface regulation in two groups of MMMs via formed H-bonding by a newly designed and ultrathin metal organic framework nanosheet (MOFN). The chemically stable MOFN (thickness: 5–8 nm) with lamellae of micrometre lateral dimensions was prepared from [Hf6] cluster and tricarboxylate ligand, where the capping molecule of formic acid coordinates with Hf4+ ion as H-bonding donor toward incorporated polymers and also acts as an anisotropic regulator for MOFN growth. The well-distributed MOFN in two polymers shows sharply promoted CO2 permeability (720 GPU and 2085 GPU), as well as enhanced separation factor, over wide pressure and temperature ranges that are suitable for CO2 capture from natural gas. This is because the H-bonding regulated polymer-MOFN alignments lead to contractile channel and abundant porosity, validated by Raman mapping and positron annihilation lifetime spectroscopy. This work not only gives rise two candidate membranes for selective CO2 removal from naturals gas, but also, more prospectively, deliveries a design philosophy for construction of advanced MMMs.

Osmotic-Capillary Principles for Microfluidic Pumping and Fluid Management for Sweat Sensing Devices

Sweat is an essential biofluid for monitoring individuals’ health as it contains several key biomarkers. However, sampling sweat for analysis is still challenging as most of the commercially available sweat sensing devices are either invasive in nature or work only during active perspiration. These devices may not function under low-sweating conditions and may be incapable of sensing in sweat from sedentary subjects. We demonstrate a new principle for the design of flexible and wearable devices, which are capable of extracting sweat under both resting and actively perspiring conditions using osmotic pressure difference for pumping, and evaporation for liquid disposal (Biomicrofludics, 14, 034112, 2020). The device is composed of silicone, hosting polyacrylamide hydrogel patch, and paper microfluidic conduit with a site of evaporation at the end (evaporation pad). The hydrogel is equilibrated with glycerin, glucose, or NaCl solution to build up the desired osmotic strength to extract fluid from the skin. We investigate their operation using a model biomarker (dye) solution. In-vitro testing with gelatin-based model skin platform revealed that both glucose and glycerin-infused gels facilitate high analyte accumulation on the evaporation pad, with glucose as osmolyte having the highest driving pressure. The cumulative dye collection also depends on the dimensions of the paper channel, hydrogel area and paper porosity. Human trials show potential to extract sweat and analyze it for lactate under both resting and non-resting conditions within a period of two hours. This sweat sampling concept can be integrated in continuously operating wearable devices using enzymatic electrochemical sensors. We used lactate as a concept demonstrator, as sweat appears to be more informative medium for lactate quantification than blood. The ability to measure lactate enables monitoring metabolism and oxidative stress levels in athletes and military personnel.

Improving the Efficiency of Non-Stationary Climate Control in Buildings with a Non-Constant Stay of People by Using Porous Materials.

This article presents the results of experimental research on the non-stationary management of the internal climate of buildings with a non-constant stay of people. During the absence of people, a significant drop in air temperature and corresponding energy conservation in heating is possible. The effectiveness of porous building materials is shown, provided that the appropriate characteristics are selected. Daily fluctuations in the outside temperature are completely extinguished by a layer of foam polystyrene insulation. The absence of channel porosity in the structural material of the wall is a guarantee of the stability of its thermal and humidity regime. This, in turn, prevents the development of mold and mildew.

Calculation of thermohydraulic effectiveness of the porous once-through water steam generators in laminar flow region with boundary conditions of the first kind

The paper presents results of calculations of thermohydraulic efficiency of the porous once-through steam generators with water as a model working fluid in the region of the heat-transfer agent laminar motion and with boundary conditions of the first kind. The smooth-wall cylindrical channels with different diameters were used as the reference surfaces to be compared. The following operating and design parameters were taken as a calculation base: temperature of the liquid on the saturation line at entry into the channel was: Tso = 280 °C, 300 °C, 320 °C, 340 °C, 360 °C. Temperature head, i.e. a difference between the wall temperature and temperature of the liquid at entry into the channel was: ΔT=Tw-To = 1 °C; 2 °C; 3 °C; 4 °C; 5 °C. The Reynolds number at entry into the channel was: Reo = 700; 1000; 1200; 1500; 1700; 2000; 2300. The channel porosity was: θ = 0.7; 0.75; 0.8; 0.85; 0.9. The porous material was metal felt with the copper fiber diameter of 200 microns. The channel diameter was: d =3·10-3 m; 4·10-3 m; 5·10-3 m; 6·10-3 m; 7·10-3m; 10·10-3 m. On the basis of the performed computational studies, it was concluded that for the conditions of the same mass flow rates of the coolant, with laminar mode of motion, and the same channel diameters, it is possible to achieve a significant reduction in the length of the porous once-through steam generator in comparison with the length of the smooth-wall once-through steam generator; however, under these conditions it is not possible to reduce pressure drop in the channels and, accordingly, to reduce power consumption needed for heat-transfer agent pumping. This computational study also made it possible to establish main regularities in behavior of the energy efficiency coefficients and their dependence on the model operating and design parameters. Keywords: thermo-hydraulic efficiency; porous steam-generating channels; heat-transfer agent, water; boundary conditions of the first kind; laminar flow regime.

Efficient design of a wavy channel embedded with porous media for solar air heating

ABSTRACT In this experimental thermal performance investigation, we present a solar air heater design exhibiting a wavy channel embedded with porous media to illustrate the enhanced fluid mixing and heat transfer area, and consequently high thermal performance. In this design, two wavy plates form the air flow channel and wiremesh as a porous media of high porosity is inserted in the wavy channel to maintain the channel porosity. Results of the investigation revealed promising scope for thermal performance enhancement. Thermal and thermohydraulic efficiency of 38–93% and 38–89%, respectively, is obtained for the investigated range of Reynolds number and channel porosity (. Moreover, the obtained result of thermal and thermohydraulic efficiency for 97% channel porosity is 27% and 24%, respectively, high compared to 100% channel porosity. As a part of this work, we also presented the developed correlations for Nusselt number and friction factor to predict the thermal performance of wavy absorber plate embedded with porous media and the effect of Darcy number on the thermal performance.

Structural and sedimentary discontinuities control the generation of karst dissolution cavities in a carbonate sequence, Potiguar Basin, Brazil

Epigenetic karstic systems in carbonate rocks commonly result from progressive dissolution by acidic meteoric waters over thousands to millions of years. The generation of secondary porosity and permeability improvement due to dissolution in carbonate reservoirs of geofluids (e.g., groundwater, hydrocarbons, and CO2) can profoundly impact reservoir storage capacity and subsurface fluid flow. This study investigates the control of structural discontinuities such as stylolites, fractures, and primary sedimentary discontinuities on the generation of multiscale karst dissolution cavities by epigenetic fluid percolation in a Late Cretaceous carbonate sequence (Jandaíra Formation) in the Potiguar Basin, Northeastern Brazil. The study relies on micro- and macroscale analyses such as stratigraphic logs, field structural investigations, rock strength data collected in the field (Schmidt hammer), microtomographic and drone images, thin section analyses, porosity and permeability laboratory measurements. The results show that bed-perpendicular stratabound and non-stratabound stylolites and fractures can be enlarged due to meteoric water percolation until they merge and form a single channel system that crosscuts all sedimentary multilayers. Bed-parallel stylolites are ubiquitous in carbonate sequences overprinting bed interfaces and layers. Where not dissolved, bed-parallel stylolites have low porosity and permeability and thus can act as barriers to vertical fluid flow. Where dissolved, such stylolites can contribute to horizontal fluid flow and form channel porosity. The results of this study led to a formulation of a conceptual model of rock dissolution along structural and sedimentary discontinuities that affects carbonate rock successions in the subsurface.

Hierarchically-porous metallic scaffolds via 3D extrusion and reduction of oxide particle inks with salt space-holders

3D ink-extrusion of powders followed by sintering is an emerging additive manufacturing method capable of creating metallic microlattices. Here, we study the creation of hierarchically porous Fe or Ni scaffolds by 3D extrusion of 0/90° lattices from inks consisting of fine oxide powders (Fe 2 O 3 or NiO, < 3 µm), coarse space-holder particles (CuSO 4, < 45 µm) and a polymer binder within a solvent. After space-holder leaching and debinding of the lattices, a sintering step densifies the metallic Fe or Ni powders created by oxide reduction with H 2 , while maintaining the larger pores templated by the space-holder particles within the printed struts. The resulting Fe or Ni lattices exhibit a hierarchical porosity: (i) open submillimeter channels within the lattice between the printed struts; (ii) open micropores (5–50 µm) within the struts, from leaching of space-holder particles; (iii) closed submicron pores within the micropore walls, from incomplete sintering of the metal microparticles created by oxide reduction. While the channel porosity is defined by the printed geometry, strut porosity is controlled by the sintering temperature, with the finest porosity removed first. Sintering at 873–1373 K for 1 h leads to strut porosities of 38–19% in Fe and 59–29% in Ni. In situ synchrotron X-ray tomography reveals the sintering kinetics and porosity evolution upon debinding, oxide reduction by H 2 and sintering of the porous metal, which, combined, lead to ~50% shrinkage of the scaffolds as compared to the printed state. The space-holder templated pores are not eliminated by sintering and remain in the struts, but they shrink upon reduction and sintering of the surrounding metal matrix (e.g., by 40% in Fe and by 30% in Ni upon sintering at 1173 K for 1 h).

CFD study of the effect of perforated spacer on pressure loss and mass transfer in spacer-filled membrane channels

One way to reduce pressure loss in spiral wound membrane modules is via creating holes within the feed spacer matrix, leading to increased channel porosity and reduced flow resistance. This study modifies conventional spacer geometry (i.e., dual-layer non-woven spacer) by perforating spacer filament and analyses the effect of different perforation aspects of spacers on the membrane performance via CFD. The results show that spacers with perforations near the membrane surface demonstrate similar mass transfer and pressure loss to the case where the perforation is in the middle of the channel (i.e., bulk flow) and the case that considers spacers without perforation, for a Reh range of 50 – 200. Moreover, a large perforation size decreases mass transfer by over 10% through weakening of the flow velocity or suppression of vortex shedding. The main finding is that spacer perforation does not improve mass transfer for the cases simulated using conventional spacers.

The impact of thermodynamic potentials on the design of electrodialysis desalination plants

Electrodialysis desalination (ED) is an efficient method to desalinate brackish water and to mitigate the salinity of high saline resources (>50 parts per thousand (ppt)). Many models were proposed to investigate ED systems; however, these models require detailed simulations. One of the simplest methods is a lumped model, which shows a reasonable and limited accuracy that can only be used for low salinities, i.e., brackish water (<8 ppt). In this paper, an improved lumped model is presented to tackle the salt separation by ED for a wide range of salinities (~200 ppt). Electrochemical equilibrium is implemented in a membrane interface to determine Donnan's potential and concentrations on the membrane surface based on membrane characteristics and bulk solution. The boundary film effect is then calculated based on the pre-calculated concentrations at the membrane and bulk solution. The spacer effect is also included which is important for the separation process in terms of area shading factor and channel porosity more than its contribution in cell pair resistance. Water transport through charged membranes is also considered. The modified model results show a substantial improvement in ED performance values. It could help researchers, engineers, and designers for the design and analysis of desalination plants.

Study of drying process a vertical porous channel by developing a numeric solver in OpenFOAM

In this study, the phenomenon of evaporation in a porous medium of a vertical channel is analyzed. Numerical simulations of the partial evaporation process of the water in porous channel is conducted using an In-house developed code. First, by adding the thermal phase change to the base solver, the solver containing the evaporation phenomenon was generated and then, considering the hydrodynamic and thermophysical characteristics of the porous region, the final solver was obtained. The Initial state of the system consists of a water phase and a porous medium made of copper particles. However, with the partial evaporation of water, the vapor phase appears as the second fluid phase. It was assumed that water and vapor are incompressible and incompatible and the phenomenon of evaporation occurs unevenly. The Volume of fluid method (VOF) governs the interface between phases and the Lee model was used to account for the mass transfer between liquid and vapor phases. For surface tension between phases, the continuous surface force method was considered. Comparison of simulation results with experimental results showed that the new solver could well estimate the evaporation rate in different sections of the channel. The characteristics of this flow were introduced by examining the distribution of water volume fractions, temperature variations, time evolution of the porous channel drying process, porosity, permeability and contact angle between fluid phases and wall.

Novel Surface-Enhanced Raman Scattering Substrate based on Functionalized Silicon Nanowires

This study reports synthesis of a new Surface-Enhanced Raman Scattering (SERS) substrate using Silicon nanowires (SiNW’s) arrays, produced through chemical etching, and functionalized by tailoring their surface chemistry with nitrogen containing groups. From SEM characterization, phenomenon of micro channel formation, porosity and amorphous nature for the as prepared SiNWs was observed. Photoluminescence (PL) spectrum showed that these nanowires have broad emission band in the range of 500-900 nm. Also, change in the surface chemistry of Si nanowires after nitrogen treatment was observed by elemental analysis, EDX and X-ray photoelectron spectroscopy. The data showed that raising the modification temperature also increased the nitrogen content. At high temperature, pyridine and aromatic amines were the dominant functional groups while a small amount of quaternary nitrogen and protonated amide were also present. Methylene blue (MB) was used as a probe molecule to investigate SERS activities of functionalized SiNWs. The enhancement factor was estimated to be 107-109. Interaction of nitrogen containing groups on the surface of SiNWs with MB molecules resulted in high adsorption of MB on the substrate and higher signal detection by SERS.

Experimental investigation of a double pass converging finned wire mesh packed bed solar air heater

Abstract A double pass converging finned wire mesh packed bed solar air heater design is investigated experimentally. Double (Counter) pass of air is provided by forcing the air first through an upper channel which is formed between the lower glass cover and the absorber plate, then through the lower channel created between the absorber and the back plates. Whereas, solar air heater design consists of two glass covers on the top and converging fins in the lower channel. The double glazing reduces the thermal losses to surrounding while the converging fins strengthen the convective heat transfer to the air by increasing heat transfer area and the velocity of the air at a given mass flow rate. Periodic converging sections are provided in the lower channel by utilizing sixteen numbers of fins attached at an angle of about 11° to the bottom and top of the absorber and back plates, respectively. In addition to the finned channel, ten layers of wiremesh screens confer 96% channel porosity in the second channel. Moreover, wire mesh offers high heat transfer area to the exiting jet of the air from the converging region as well as provides thermal energy storage. The maximum thermal and thermohydraulic efficiencies of the solar air heater are obtained as 93% and 80%, respectively, at a mass flow rate of 0.03 kg/s and about 0.023 kg/s, respectively. The best output of the solar air heater is the hot air at a temperature of 55 °C corresponding to the mass flow rate of 0.01 kg/s and solar radiation of about 823 W/m2.

The impact of fossils on diagenetically controlled reservoir quality: the Zechstein Brońsko Reef (Upper Permian, W Poland)

Although the sedimentation and diagenesis of the Polish Zechstein Limestone strata (Ca1, Permian) already have been investigated, relatively little has been done to resolve their petrophysical potential. Therefore, the gap between sedimentological and petrophysical studies was bridged through an integrated analysis of geological and geophysical data. The results of core description, polarized-light microscopy, well log interpretations and laboratory measurements on core samples were combined with previously published nuclear magnetic resonance (NMR) and X-ray microtomography (μCT) data, especially helpful in the recognition of pore geometry. The Ca1 strata of the Bronsko-1 and Bronsko-2 wells, located on the Zechstein Bronsko Reef (West Poland), were studied to determine the influence of fossils on porosity and permeability. It was concluded that greater diversification of the original biota led to an increase in porosity and variation in pore geometry. While encrusting organisms such as foraminifers promoted the development of channel and fracture porosity, the dissolution of the primarily aragonitic bivalve and gastropod shells and the shells of terebratulid brachiopods often gave rise to the formation of cavernous and mouldic porosity. The channels appear to be most common in the bryozoanforaminifer biofacies, representing a shallowing of the depositional environment. Caverns, in turn, corresponded to the organisms of the brachiopod-bryozoan and the lightly karstified bivalve-gastropod biofacies, both of which probably experienced the influence of sabkha conditions, leading to a general decrease in porosity. The bryozoan zoecia tended to enhance both primary intraparticle voids, and after their dissolution, secondary intraparticle pores, which showed limited connectivity in the high-energy Acanthocladia biofacies, where considerable fragmentation of fossils took place, hence decreasing the permeability. Anhydrite cementation was found to be the most pronounced factor controlling porosity destruction, while dolomitization enhanced it significantly, especially for the stromatolitic biofacies, where small, unconnected vugs were formed owing to this process. The permeability is typically below 100 mD, and this is caused by the rich diagenetic history of the reef, that recorded marine, sabkha-related and burial cementation, now represented by the different fabrics of anhydrite, calcite, and dolomite.

CFD Investigation of the Effect of the Feed Spacer on Hydrodynamics in Spiral Wound Membrane Modules

Spacers are designed to create a feed channel, but they are also obstacles to the flow in spiral wound membrane modules. The geometry of the feed spacer influences the flow pattern, which was investigated by using a three-dimensional Computational Fluid Dynamics (CFD) model. For the conventional feed spacer, unavoidable disadvantages were caused by its line contact with the membrane. The pillar-like feed spacer was designed to achieve area contact, which made it possible to enhance the porosity and minimize the adverse effects from the dead zone caused by the transverse filament. Through reductions in the connecting filament’s diameter, the channel porosity reached 0.979. Regarding the maximum porosity, the dimensionless power number was reduced by 47.31% at Reynolds number 150 in comparison with a previously studied commercial spacer. Furthermore, a modified friction factor, as a dimensionless parameter, was employed to investigate the shear stress at the membrane’s surface. At dimensionless power number 106, the enhancement of the modified friction factor increased by approximately 22.27% in comparison with the results of a previous study. Based on the numerical prediction, the homogenization of shear stress distribution, which changed the flow profile near the membrane, was featured through contour plots.

Three dimensional simulation of hydrodynamic and heat transfer behavior of magnetite nanofluid flow in circular and rectangular channel heat sinks filled with porous media

A three dimensional numerical simulation has been carried out to study the effect of porous media on the heat transfer and pressure drop of magnetite (Fe3O4/water) nanofluid flow in two conventional heat sinks; circular and rectangular channel heat sinks. Effects of different parameters such as nanofluid volume fraction and flow rate and channel porosity on the performance of the heat sinks have been investigated. A maximum heat transfer enhancement of 13% and 14% has been achieved by using nanofluid in clear rectangular and circular channel heat sinks, respectively. These values grow up to 450% and 547%, respectively when the heat sinks are filled with the porous media. The heat transfer enhancement due to the insertion of the porous media is accompanied by very large pressure drop. Results indicate that the overall heat sink performance is improved at low flow rates and porosities and high concentrations of the nanofluid.

MHD Natural Convection Slip Flow through Vertical Porous Plates with Time-Periodic Boundary Conditions

In this work, the convective flow of heat generating hydromagnetic fluid through a leaky channel is investigated. Due to channel porosity, the asymmetrical slip conditions are imposed on both walls. The coupled dimensionless partial differential equations are reduced to a system of second-order boundary-value problems based on some flow assumptions and solved by Adomian decomposition method (ADM). Variations in velocity and temperature profiles are presented and discussed in detail. The result of the analysis revealed that increasing Hartmann number decreases the flow velocity while the slip parameters enhance the flow.