Fabrication, Structure, Performance, and Application of Graphene-Based Composite Aerogel

Graphene-based composite aerogel (GCA) refers to a solid porous substance formed by graphene or its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), with inorganic materials and polymers. Because GCA has super-high adsorption, separation, electrical properties, and sensitivity, it has great potential for application in super-strong adsorption and separation materials, long-life fast-charging batteries, and flexible sensing materials. GCA has become a research hotspot, and many research papers and achievements have emerged in recent years. Therefore, the fabrication, structure, performance, and application prospects of GCA are summarized and discussed in this review. Meanwhile, the existing problems and development trends of GCA are also introduced so that more will know about it and be interested in researching it.

Nanofluidic thermal-fluid transport in a split-driven porous system working under a magnetic environment

Purpose This study aims to focus on a thermo-fluid flow in a partially driven cavity (PDC) using Cu-water nanoliquid, magnetic field and porous substance. The cooling and sliding motion are applied on the upper half of the vertical walls and the bottom wall is heated. Thermal characteristics are explored to understand magnetohydrodynamic convection in a nanoliquid filled porous system from a fundamental viewpoint. The governing parameters involved to cater to the moving speed of the sidewalls and partial translation direction are the relative strength of thermal buoyancy, porous substance permeability, magnetic field intensity, nanoparticle suspension and orientation of the cavity. Design/methodology/approach The coupled transport equations of the problem are solved using an in-house developed finite volume-based computing code. The staggered nonuniform grids along the x and y directions are used. The SIMPLE algorithm technique is considered for the iterative solution of the discretized equations with the convergence check of the continuity mass defect below 10–10. Findings The present study unveils that the heat transfer enhances at higher Ri with the increasing value of Re, irrespective of the presence of a porous substance or magnetic field or the concentration of nanofluid. Apart from different flow controlling parameters, the wall motions have a significant contribution to the formation of flow vortices and corresponding heat transfer. Orientation of the cavity significantly alters the transport process within the cavity. The upward wall velocity for both the sidewalls could be a better choice to enhance the high heat transfer (approximately 88.39% at Richardson and Reynolds numbers, respectively, 0.1 and 200). Research limitations/implications Considering other multi-physical scenarios like porous layers, conducting block, microorganisms and the present investigation could be further extended to analyze a problem of complex flow physics. Practical implications In this study, the concept of partially driven wall motion has been adopted under the Cu-water nanoliquid, magnetic field, porous substance and oblique enclosure. All the involved flow-controlling parameters have been experimented with under a wide parametric range and associated thermo-flow physics are analyzed in detail. This outcome of this study can be very significant for designing as well as controlling thermal devices. Originality/value The convective process in a partially driven cavity (PDC) with the porous medium has not been investigated in detail considering the multi-physical scenarios. Thus, the present effort is motivated to explore the thermal convection in such an oblique enclosure. The enclosure is heated at its bottom and has partially moving-wall cold walls. It consists of various multi-physical conditions like porous structure, magnetic field, Cu–H2O nanoliquid, etc. The system performance is addressed under different significant variables such as Richardson number, Reynolds number, Darcy number, Hartmann number, nanoliquid concentration and orientation of cavity.

Magnetohydrodynamic mixed bioconvection of oxytactic microorganisms in a nanofluid-saturated porous cavity heated with a bell-shaped curved bottom

Purpose This study aims to investigate thermo-bioconvection of oxytactic microorganisms occurring in a nanofluid-saturated porous lid-driven cavity in the presence of the magnetic field. The heating is provided through a bell-shaped curved bottom wall heated isothermally. The effects of the peak height of the curved bottom wall, bioconvection Rayleigh number (Rb), Darcy number (Da), Hartmann number (Ha), Peclet number (Pe), Lewis number (Le) and Grashof number (Gr) on the flow structure, temperature and the iso-concentrations of oxygen and microorganisms are examined and explained systematically. The local and global, characteristics of heat transfer and oxygen concentration, are estimated through the Nusselt number (Nu) and Sherwood number (Sh), respectively. Design/methodology/approach The governing equations of continuity, momentum, energy and additionally consisting of species transport equations for oxygen concentration and population density of microorganisms, are discretized by the finite volume method. The evolved linearized algebraic equations are solved iteratively through the alternate direction implicit scheme and the tri-diagonal matrix algorithm. The computation domain has meshed in non-uniform staggered grids. The entire computations are carried out through an in-house developed code written in FORTRAN following the SIMPLE algorithm. The third-order upwind and second-order central difference schemes are used for handling the advection and diffusion terms, respectively. The convergence criterion for the iterative process of achieving the final solution is set as 10–8 and 10–10, respectively, for the maximum residuals and the mass defect. Findings The results show that the flow and temperature distribution along with the iso-concentrations of oxygen and microorganisms are markedly affected by the curvature of the bottom wall. A secondary circulation is developed in the cavity that changes the flow physics significantly. The Nu increases with the peak height of the curved bottom wall and Da; however, it decreases with Ha and Rb. The Sh increases with Da but decreases with Ha and the peak height of the curved wall. Research limitations/implications A similar study of bioconvection could be extended further considering thermal radiation, chemical attraction, gravity, light, etc. Practical implications The outcomes of this investigation could be used in diverse fields of multi-physical applications such as in food industries, chemical processing equipment, fuel cell technology and enhanced oil recovery. Originality/value The insights of bioconvection of oxytactic microorganisms using a curved bottom surface along with other physical issues such as nanofluid, porous substance and magnetic field are addressed systematically and thoroughly.

Magnetohydrodynamic bioconvection of oxytactic microorganisms in porous media saturated with Cu–water nanofluid

Purpose The purpose of this study is to address magnetohydrodynamic (MHD) bioconvection caused by the swimming of oxytactic microorganisms in a linearly heated square cavity filled with porous media and Cu–water nanofluid. The effects of different multiphysical aspects are demonstrated using local distributions as well as global quantities for fluid flow, temperature, oxygen concentration and microorganisms population. Design/methodology/approach The coupled transport equations are converted into the nondimensional partial differential equations, which are solved numerically using a finite volume-based computing code. The flow of Cu–water nanofluid through the pores of porous media is formulated following the Brinkman–Forchheimer–Darcy model. The swimming of oxytactic microorganisms is handled following a continuum model. Findings The analysis of transport phenomena of bioconvection is performed in a linearly heated porous enclosure containing Cu–water nanofluid and oxytactic microorganisms under the influence of magnetic fields. The application of such a system could have potential impacts in diverse fields of engineering and science. The results show that the flow and temperature distribution along with the isoconcentrations of oxygen and microorganisms is markedly affected by the involved governing parameters. Research limitations/implications Similar study of bioconvection could be extended further considering thermal radiation, chemical attraction, gravity and light. Practical implications The outcomes of this investigation could be used in diverse fields of multiphysical applications, such as in food industries, chemical processing equipment, fuel cell technology and enhanced oil recovery. Originality/value The insight of the linear heating profile reveals a special attribute of simultaneous heating and cooling zones along the heated side. With such an interesting feature, the MHD bioconvection of oxytactic microorganisms in nanofluid-filled porous substance is not reported so far.

The Movement of CO2 Through the Frozen World of Sea Ice

Every winter, a frozen blanket known as sea ice completely covers the Arctic Ocean. For centuries, sea ice has been viewed as a solid lid on the ocean that acts as a boundary to block gases traveling between the ocean and the atmosphere. However, scientific discoveries over recent years have shown that sea ice is more like a sponge, a porous substance that is also home to microscopic life forms. The pores in sea ice are filled with very salty liquid called brine that is rich in carbon dioxide (CO2). These liquid pockets create a network of tubes or channels that move gases like CO2, similar to the way veins and arteries move blood in our bodies. In this article, you will discover how CO2 enters, exits, and is transformed in one of the harshest environments on Earth.

Thermo-bioconvection of oxytactic microorganisms in porous media in the presence of magnetic field

Purpose This study aims to explore magnetohydrodynamic (MHD) thermo-bioconvection of oxytactic microorganisms in multi-physical directions addressing thermal gradient, lid motion, porous substance and magnetic field collectively using a typical differentially heated two-sided lid-driven cavity. The consequences of a range of pertinent parameters on the flow structure, temperature, oxygen isoconcentration and microorganisms’ isoconcentration are examined and explained in great detail. Design/methodology/approach Two-dimensional governing equations in a two-sided lid-driven porous cavity heated differentially and packed with oxytactic microorganisms under the influence of the magnetic field are solved numerically using the finite volume method-based computational fluid dynamics code. The evolved flow physics is analyzed assuming a steady laminar incompressible Newtonian flow within the validity of the Boussinesq approximation. The transport of oxytactic microorganisms is formulated by augmenting the continuum model. Findings The mechanisms involved with MHD-mixed thermo-bioconvection could have potential benefits for industrial exploitation. The distributions of fluid flow, temperature, oxygen and motile microorganisms are markedly modified with the change of convection regime. Both speed and direction of the translating walls significantly influence the concentration of the motile microorganisms. The concentration of oxygen and motile microorganisms is found to be higher at the upper portion of the cavity. The overall patterns of the fluid flow, temperature and the oxygen and microorganism distributions are markedly affected by the increase of magnetic field strength. Research limitations/implications The concept of the present study could be extended to other areas of bioconvection in the presence of gravity, light or chemical attraction. Practical implications The findings of the present study could be used to multi-physical applications like biomicrosystems, pollutant dispersion in aquifers, chemical catalytic converters, geothermal energy usage, petroleum oil reservoirs, enhanced oil recovery, fuel cells, thermal energy storage and others. Originality/value The MHD-mixed thermo-bioconvection of oxytactic microorganisms is investigated under different parametric conditions. The effect of pertinent parameters on the heat and mass transfers are examined using the Nusselt number and Sherwood number.

USE OF RESINOUS SUBSTANCES BY THE EARLY NEOLITHIC POPULATION IN THE FOREST-STEPPE ISHIM AREA

In this study, the author set out to determine the chemical composition and possible use of a substance, which remnants were found on a tile fragment made of soft brown shist. This item was discovered in the occupa-tion layer of a Neolithic settlement belonging to the Boborykino culture (Mergen 3), located on the terrace of Lake Mergen in the forest-steppe of the Ishim area (south of Western Siberia). By analogy with the complexes of the Boborykino culture in the Tobol area — Yurtobor 3 (7701 ± 120 BP (UPI 559)) and Tashkovo 1 (7440 ± 60 BP (LE 1534)) — which age was determined using carbon-14 dating, the Mergen 3 settlement can be attributed to the second half of the 7th millennium Cal. BC. The fragment measuring 3.0 × 2.1 × 0.55 cm has a spherical indenta-tion in the centre measuring 2.0×2.0×0.2 cm with a volume of 0.118 cm3 (0.118 ml). The whole item probably had a square shape with rounded and slightly raised edges. A visual analysis of the spot was carried out using an MBS-10 binocular microscope at a magnification of 16×. The analysis revealed a brown substance on the edges of the indentation, which looked like a dark porous carbon-like spot in the centre. These remnants were studied using a Bruker ALPHA FT-IR spectrometer with an Eco-ATR module — a single reflection ATR sampling module equipped with a zinc selenide crystal (ZnSe) that allows you to analyse liquid, solid and powder samples without preliminary sample preparation. The measurements were performed in the wavenumber range of 300–4000 cm-1 at a resolution of 4 cm-1. Some of the most significant absorption bands (709; 975; 1,024; 1,027 cm-1) were ob-served, which characterise vibrations bending and stretching the bonds in the skeleton of an organic molecule containing single С–С and С–О bonds. The obtained spectra are most consistent with the IR absorption spectra of resin acids, in particular, dehydroabietic acid that is present in resin obtained from coniferous trees. Consider-ing the small volume of the above-mentioned substance and the limited of its burning, the author excludes the use of this tile as a lamp, the use of the substance for the preparation of glue that held together the parts of complex tools, as well as the use of the substance for healing wounds and for cosmetic purposes, which involved addi-tional ingredients. Signs of burning indicate the use of the artefact for rituals, in particular for obtaining finely dis-persed soot employed when applying tattoos. The conducted experiment showed that the soot from a burnt drop of fresh resin covered 4 cm2 of the wrist area. Soot formed at the very beginning of the combustion process (probably combustion of volatile components), then the substance was oxidised without noticeable emissions. The remnants of the porous substance on the tile confirm the importance of the moment of resin burning with the abundant production of soot. However, the possibility that there were other unknown areas of application of gali-pot obtained from coniferous trees is not excluded. In any case, it is safe to say that the early Neolithic population living in the Ishim area purposefully used natural resins in their activities.

INVESTIGATION OF HEAT-HUMIDITY TRANSFER IN HIGH-POROUS GAS-FILLED POLYMERS TO CALCULATE ITS HEAT CONDUCTIVITY

A method for calculating the effective thermal conductivity of moisture-containing highly porous foamed polymers is proposed. In this method a non-additive scheme for taking into account the effect of steam diffusion on heat transfer is used. The sequential binary systems (interstitial substance from a liquid and a vapor- gas mixture, as well as a polymer skeleton and an intra-porous substance) are described by models of structures with interpenetrating components and isolated inclusions. The conditions for the transition from one model of structure to another are defined and there is not necessity to define empirical coefficients. A geometric model of wet foamed polymer has been developed, that allows us to find a way to determine the value of the boundary moisture content of pores or wetting angle at which the transition from partial wetting of the surface of the pores with liquid to full wetting and vice versa occurs. A mathematical description of the process of heat transfer in the model structure of a wet foamed polymer has been made, taking into account the diffusion of water vapor in the pore space.

Experimental determination of the kinetics of sorption and gas filtration in coal

The paper presents tests set-ups for experiments on sorption kinetics and gas filtration kinetics in a porous medium. It was observed that two phenomena occur in these processes: transportation of gas into the porous solid and settling of gas molecules on the walls of the solid or within its volume. An experiment was carried out in which a thin resistance thermometer was quickly taken out of an argon stream and placed in carbon dioxide or the other way round. The measurement made it possible to determine the sorption time constant. It was demonstrated that the sorption rate is much higher than the filtration rate. Thus, filtration is the process describing the rate at which gas molecules penetrating the porous substance are adsorbed or desorbed. The sorption time constant is not >50 m.In the second experiment, the author determined the rate at which gas is liberated from coal grains. The measurement method was based on measurement of the pressure of desorbing gas in constant volume. The experiment involved measurement of the pressure of the gas liberated from the coal grains in a closed chamber. The kinetic curves obtained in this way were used to determine the carbon dioxide coefficient in coal grains. During the experiment, particular focus was put on the initial stage of gas liberation (up to 0.4 s).The slower process of gas transporting in the porous structure of coal is the transporting of gas through a coal briquette. Experimentally implemented variety of boundary conditions allowed for a more complete verification of the assumed theoretical model and possibly for the exact determination of filtration parameters. The experimental set-up built for this purpose, allows for pressure and temperature measurement on the briquette side surface.

Enhancement diesel oil degradation by using biofilm forming bacteria on biochar

Biochar is defined as a carbon-rich, fine-grained, porous substance, which is produced by pyrolysis biomass with little or no oxygen. Biochar is usually produced from crop residues, wood biomass, animal litters, and solid wastes. Recently, biochar is increasingly receiving attention as an environmental-friendly approach, especially as a climate change mitigation strategy. Biochar is especilly demonstrated to remove diesel oil (DO) from soil and water. In this report, 4 biofilm forming bacteria including Klepsiellasp. VTD8, Pseudomonas sp. BQN21, Rhodococcussp. BN5 and Stenotropomonassp. QND8 were used to attach to biochar produced from husk to estimate the capacity of their DO removal. As the results, removal efficiency of biofilm formed by each strain VTD8, BQN21, BN5 and QND8 were 67, 73, 75 and 68 % with initial concentration of 39 g/l, respectively. On the other hand, mix species biofilm attached to husk carrier and without carrier degraded 98 and 78 %. Using husk without bacteria as absortion control, the amount of DO removal was 23 %. These results gave hint that using biochar produced from husk as carrier for biofilm forming bacteria to attach may increase efficiency of DO pollution treatment. Than sinh học (biochar) là một chất xốp có các gốc carbon và có nguồn gốc từ quá trình nhiệt phân sinh khối các loại chất thải, động, thực vật,… dưới điều kiện hạn chế oxy hoặc không có oxy.Hiện nay biochar đã được ứng dụng rộng rãi trong xử lý môi trường. Đặc biệt các biochar còn được chứng minh là có thể xử lý dầu diesel (diesel oil - DO) có trong đất và nước. Trong nghiên cứu này, chúng tôi sử dụng 4 chủng vi khuẩn tạo màng sinh học tốt là Klepsiella sp. VTD8, Pseudomonas sp. BQN21, Rhodococcus sp. BN5 và Stenotropomonas sp. QND8 để gắn lên chất mang là biochar làm từ trấu nhằm đánh giá hiệu quả xử lý DO của chúng. Kết quả cho thấy, sau 7 ngày, các chủng VTD8, BQN21, BN5 và QND8 có khả năng phân hủy 67, 73, 75 và 68 % DO với hàm lượng ban đầu là 39 g/l. Trong khi đó, hiệu suất của màng sinh học tạo thành bởi hỗn hợp các chủng này khi không có chất mang biochar trấu và khi có chất mang biochar trấu lần lượt là 78 và 98 %. Còn sử dụng chất mang biochar trấu không có vi sinh vật làm đối chứng thì thu được hiệu suất hấp phụ DO là 23 %. Như vậy, kết quả này mở ra tiềm năng ứng dụng biochar trấu làm chất mang cho các chủng vi khuẩn tạo màng sinh học để nâng cao hiệu quả xử lý ô nhiễm dầu.