Nonporous Systems Research Articles

Numerical study of parabolic trough solar collector’s thermo-hydraulic performance using CuO and Al2O3 nanofluids

The current study aims to boost the thermal and hydraulic performance of a parabolic trough solar collector by modifying the absorber tube with a porous obstacle insertion. The research investigates how porous media and nanoparticles together influence the system's thermal performance, considering factors like outlet temperature, average Nusselt number, average friction factor, thermal performance factor, and thermal efficiency at different mass flow rates. To achieve better thermal performance, the base fluid, water, is substituted with Copper Oxide (CuO)-water and Aluminum Oxide (Al2O3)-water nanofluids at concentrations ranging from 3% to 7% by volume. The experiments are conducted at 800–1000 W.m-2 heat flux on the outside tube surface. The finite element method discretizes the governing equations for 3-D fluid flow simulations conducted in COMSOL Multiphysics 6.1 software. The simulation is carried out considering four altered rates of mass flow, ranging from 0.015 kg.s−1 to 0.060 kg.s−1. The findings show that at a Reynolds number of 1428 and a 7% volume concentration, the maximum thermal performance factor recorded is 1.97 and 1.99 for Al2O3 and CuO nanofluids, respectively. Additionally, the absorber tube achieves maximum thermal efficiency of up to 77.93% and 79.03%. Also, the augmentation in the average Nusselt number ratio is 26.27% and 36.74% when using Al2O3 and CuO nanofluids, respectively, with the tube height-to-diameter ratio (h/D) set at 0.42. The average friction factor ratio was reduced by 2.9% using CuO nanofluids compared to Al2O3 nanofluids. Thermal efficiency was enhanced by 7.2% using a porous obstacle insert in the parabolic trough solar collector system compared to a non-porous system.

Effect of Size and Temperature on Water Dynamics inside Carbon Nano-Tubes Studied by Molecular Dynamics Simulation.

Water transport inside carbon nano-tubes (CNTs) has attracted considerable attention due to its nano-fluidic properties, its importance in nonporous systems, and the wide range of applications in membrane desalination and biological medicine. Recent studies show an enhancement of water diffusion inside nano-channels depending on the size of the nano-confinement. However, the underlying mechanism of this enhancement is not well understood yet. In this study, we performed Molecular Dynamics (MD) simulations to study water flow inside CNT systems. The length of CNTs considered in this study is 20 nm, but their diameters vary from 1 to 10 nm. The simulations are conducted at temperatures ranging from 260 K to 320 K. We observe that water molecules are arranged into coaxial water tubular sheets. The number of these tubular sheets depends on the CNT size. Further analysis reveals that the diffusion of water molecules along the CNT axis deviates from the Arrhenius temperature dependence. The non-Arrhenius relationship results from a fragile liquid-like water component persisting at low temperatures with fragility higher than that of the bulk water.

Simple holistic solution to Archie's-law puzzle in porous media.

In this paper, we account for the many critical exponents derived from the studies of the electrical conductivity in porous media by applying analysis of the well-known relation known as Archie's law. In spite of its seeming simplicity this law is considered to be "poorly understood," and the question that was and still is debated in the literature is whether there is some "hidden physics" in this law, or if it is "strictly a parametrization use for curve fitting with a priori no physical meaning." Our solution to the corresponding long-debated 78 years old puzzle is based on the classical percolation theory, but it also involves a principle that is based on continuum percolation. This principle is that the electrical properties of a percolation system are determined by the interplay between the connectivity of the conducting objects in that system, and the connectivity of the intersections between pairs of them. We thus propose a general concept that we call an electrically affected connectivity, and we predict the corresponding evolvement of the conductivity critical exponent with the increase of the content of the electrically conducting phase. Then, we show that the zerolike threshold that characterizes Archie's law is what enables the observation of this evolution. Combining the above principle and the latter feature, we provide a holistic, yet simple, solution to the longstanding controversy surrounding this law and its practical applications. In contrast with many previous claims that Archie's law lacks a physical basis, and the commonly suggested experiential explanations for it, we provide a solution that is physically based and thus elucidates Archie's law by showing clearly that it represents a bona fide phase transition phenomenon. This conclusion and its generality are strongly supported by the fact that it also explains the behavior of the electrical conductivity exponents in nonporous systems such as composite materials. The predicted ability to extract the long sought microgeometrical information from Archie's-law data, within the framework of the percolation phase transition, is expected to open a new direction in the understanding and the applications of this law.

High Pressure In Situ Single‐Crystal X‐Ray Diffraction Reveals Turnstile Linker Rotation Upon Room‐Temperature Stepped Uptake of Alkanes

The rare availability of suitable single-crystal X-ray diffraction (SCXRD) structural data allows for the direct interpretation of the response of a framework to gas sorption and may lead to the development of improved functional porous materials. We report an in situ SCXRD structural investigation of a flexible MOF subjected to methane, ethane, propane, and butane gas pressures. Supporting theoretical investigations indicate weak host–guest interactions for the crystallographically modelled gaseous guests and, in addition, reveal that a turnstile mechanism facilitates the transport of alkanes through the seemingly nonporous system. Inflections present in the adsorption isotherms are furthermore rationalized as due to gate-opening, but without the expected creation of new accessible space.

Key factors of marine shale conductivity in southern China—Part I: The influence factors other than porosity

The complicated response mechanism of shale gas requires that a systematic pilot study is conducted on the influences of resistivity log responses to help with subsequent experimental design, physical derivations and resistivity simulations. The purpose of this research is to clarify the main controlling factors of the resistivity log responses and their semi-quantitative relationship in certain marine shale gas formations. Comprehensive analyses on large core test datasets, including mineralogical, petrological, geochemical and other data, from the Longmaxi-Wufeng Formation and the corresponding resistivity logging curves are carried out in 4 shale gas areas. This research indicates that in low-porosity systems, the mineral composition directly impacts the resistivity. Carbonates with large intergranular pores and even intragranular pores increase the resistivity. The hydrophilic nature of clay decreases the resistivity. When organic matter is not carbonized, the organic matter and biosilica will further increase the resistivity. Pyrite layers will cause a large drop in resistivity (to less than 5 Ω m). The resistivity is lower where organic matter carbonization has occurred in the studied reservoir. Mineral components, especially clay minerals and organic matter, are the main controlling factors of the conductivity of low-porosity systems. In addition, we propose that elemental logging can be used to characterize the comprehensive effect of low-porosity s systems on the resistivity of the reservoir and can accurately reflect the resistivity. These results will help to develop future studies on the relationship between the electrical conductivity and saturation of shale gas rocks, which is of great significance. • Combining the data of 14 wells in four shale gas blocks, the resistivity characteristics of marine shale are systematically and quantitatively analysed. • Shale mineral composition is the non-porous factor that mainly affects resistivity, among which carbonate minerals and combinations of biosilica and (uncarbonized) organic matter will increase the resistivity. • The layered pyrite greatly reduces the resistivity, but the dispersed pyrite has little effect on the resistivity of marine shale. • A semi-quantitative characterization technology for non-porous systems is proposed (ER curve), and the effect of mineral composition on resistivity is semi-quantitatively characterized.

Numerical analysis of thermal performance of a solar dryer and validated with experimental and thermo-graphical data

Solar drying is a common method for preservation of food materials and improving thermal efficiency of solar collectors is important as the main part of a solar air heating system. One the most used collectors in solar drying system is flat plate collector and in these collectors the main problem is the low heat flux through the absorber plate, which reduces thermal and drying efficiency of the dryer. In this research, the heat transfer process of the solar dryer was investigated at three conditions non-porous system, with porous system and with porous and recycling system with three methods (experimental, computational fluid dynamics (CFD) and thermo-graphical). The flat plate collector was divided into four equal sections and then the amount of heat transfer coefficient, heat flux and total heat transfer from the collector over the time were calculated for each section. The dryer performance was also evaluated using a heat exchanger that placed at the inlet of the collector. Moreover, the air velocity distribution and temperature counters inside the collector were simulated using computational fluid dynamics method. The results showed that the heat transfer for all cases increased from 10:00 and reached to maximum level at around 12:00–13:00. Due to the reduction of heat accumulation at the end of the collector, heat transfer was more homogeneous for porous collector. Moreover, the results showed that the amount of total heat transfer increased about 16.50% in porous system and 21.19% porous and recycling system compared to non-porous system. The average drying efficiency for solar dryer were about 51%, 53% and 54% for non-porous system, porous system and porous and recycling system, respectively. The results of computational fluid dynamics simulation and thermo-graphical test showed a good agreement between the experimental data and the mentioned methods (R2 > 0.96 and R2 > 0.98).

Porous magnetic materials based on EPDM rubber filled with carbonyl iron particles

This paper deals with a possibility to prepare porous magnetic elastomers whose mechanical behavior can be controlled by means of a magnetic field. The elastomers under investigation are based on ethylene propylene diene rubber (EPDM) filled with carbonyl iron particles. The foaming agent based on azodicarbonamide was used at 2 loading levels to control their porous character and the magneto-mechanical behavior was compared with non-porous magnetic EPDM system. The non-porous systems exhibited the highest magnetorheological efficiency even though the porous systems showed lower values of storage modulus in the inactive state. Porous systems also exhibited lower mechanical hysteresis when compared to non-porous one during single-strain measurements with increasing/decreasing magnetic field due to pores which increase a distance between particles and thus lower the strength of magnetic network created at high magnetic fields. Porous systems can be potentially utilized in applications in which conventional magnetorheological elastomers are too tough, thus, porous systems offer magnetorheological material with properties between magnetorheological fluids and solid elastomers.

Slip flow in porous media

The dynamics of fluids and their interaction with surfaces in Unconventional Gas Reservoirs (UGRs) are very different from those in conventional systems. The physics of flow through the matrices of these reservoirs are not well understood. The small size of flow conduits which is comparable to the gas mean free path results in a deviation from Darcy to slip, transition and free molecular flow regimes. Solving Navier–Stokes (N–S) equations with modified boundary conditions has so far been the best practical approach to describe these flow behaviours.In this paper, a study of slip flow in shale gas reservoirs is presented. Several permeability measurements were performed using three shale rock samples to study the slip permeability. The Maxwellian type slip boundary conditions were used in N–S equations to obtain the slip coefficients and tangential momentum accommodation coefficient (TMAC) in porous media from the experimental data. Our results show that slip coefficients in porous media are higher than those in non-porous systems. In addition, it is found that the TMAC is smaller in porous media in comparison to flow in non-porous materials. These observations, which are attributed to greater surface area and roughness, are in agreement with literature data, which are limited to flow through individual micro conduits. The outcomes of this study will be useful for accurate prediction of gas flow rate in shale/tight gas reservoirs when using slip boundary conditions.

Dynamic and Quasi-static Failure Evolution of 3D Woven Cellular Composite Systems

The effects of porosity on the impact response and perforation resistance of 3D woven carbon-fiber reinforced epoxy panels under impact by projectiles and under quasi-static three-point bending were experimentally investigated. The 3D cellular composite systems were fabricated by a new method, where porosity can be controlled. The porous samples absorbed a greater amount of specific energy than the nonporous samples. This may be due to the deflection of matrix cracks by the pores and the greater flexibility of the fibers to absorb energy through tensile straining. The quasi-static experiments also indicate that porosity may exhibit strength comparable to nonporous systems.

Impact-induced deformation fields in 3D cellular woven composites

Abstract The deformation fields and kinematics of nonporous and porous three-dimensional (3D) woven composite material systems were analyzed and characterized under an incident impact energy of 560 J caused by a 78 g projectile at a velocity of 120 m/s. The analysis quantifies experimental observations of the effects of porosity on the impact resistance and behavior of 3D woven composites. The dynamic nonlinear impact solution was obtained by the finite element method, in which contact between the projectile and the target plate was modeled with gap elements. In the present study, we investigated the spatial and temporal evolution of multi-dimensional elastic fields and potential damage modes in the target plates. A unit cell, representative of the 3D woven composite, was used to obtain estimates of the overall elastic moduli. These estimates were then used with two material models to represent the porous system in the finite element analysis of the target plate. One material model, which had explicit geometrical distributions of 3D voids, was used in the impact region, and the other material model, which was based on a representation of smeared voids, was used in regions removed from the impact zone. The analysis indicates that wave propagation effects at the incident energy applied here are significant, and these effects can lead to projectile penetration at the impact face. Localized shear damage in the 3D woven system precedes penetration in both the nonporous and the porous systems. Experimental observations, which indicate that a porous system can dissipate more energy than the nonporous system before penetration, are found to be mainly attributed to the confinement of local damage fields, which emanate from the boundaries of the embedded voids.

Description of Gas Adsorption Isotherms on Porous and Dispersed Systems with the Excess Surface Work Model

We introduced in (2) and (3) the excess surface work (ESW) to describe adsorption isotherms of nonporous materials and of a single phase over the complete pressure range. In this paper this model is extended successfully to adsorption isotherms of porous and finely dispersed materials. In this case capillary condensation may occur and the excess surface work yields more than one minimum. By linearizing the corresponding integral form and calculating the parameters, it is now possible to describe the complete adsorption isotherm as for the simple case of nonporous systems.

Extreme Path Derivatives of a Function with Respect to a Nonporous System of Paths

Extreme Path Derivatives of a Function with Respect to a Nonporous System of Paths

Negative C2 values of inhomogeneous polymer networks measured in elongation

AbstractIt was found that negative slopes of the Mooney‐Rivlin plot (negative C2 values) can be expected for polymer networks prepared by means of a crosslinking polymerization of respective monomers in the presence of large concentrations of a diluent, or for such systems having macroscopic porosity. Some examples are given for swollen poly (2‐hydroxyethyl methacrylate) networks prepared in the presence of high concentrations of water (porous systems), and/or ethylene glycol (nonporous systems), and also for a network of partially hydrolyzed polyacrylonitrile prepared in a similar way. Negative C2 parameters are probably connected with inhomogenous deformations of supramolecular domains in the stressed cross section of the systems studied.