Types Of Porous Media Research Articles

Temperature Distribution and Evaporation Rate in Porous Media

Various studies have been done to improve solar still performance, especially in water streams. Various methods create thin water flow on the absorbent plate, including using porous media. The research aims to identify temperature distribution and evaporation rate in porous media. The use of porous media as an absorber plate material in solar still applications is investigated in this study. Five types of porous media have been researched, such as concrete consisting of river sand and iron with a particle size of 0.125 and 0.250 mm, and natural stone. A comparison of 5 specimen types is held by conducting evaporation tests. The pore media specimen 5x1x10 cm is heated by an electric heater with a power of 36, 4 W. The bottom side of the specimen is exposed to a constant high salt water reservoir. Data is collected periodically for 2 hours. Research produces specimens at smaller particle sizes with thermal conductivity and greater heat transfer rates. Iron sand concrete as aggregate has better temperature distribution than the specimen of river sand. The largest high-dampened front reduction is obtained on specimen C with a value of 0.051 m. The largest evaporation rate is owned by specimen C with the amount of 2.38 ml in 7200 s. Concrete with an aggregate of iron sand (0.125 mm particle size) is recommended as a solar still absorbent plate material; however, natural stone materials also have a high potential to be used as a solar still absorbent plate material.

Research on NMR Noise Reduction Method Based on Improved CEEMD

Low-field NMR technology has been widely used in many fields, among which the most representative method is the use of CPMG sequence for T2 measurement. Important parameters such as permeability, saturation and fluid type of porous media can be obtained by T2 spectrum inversion calculation of NMR echo sequence signal. However, T2 spectrum inversion calculation is easily affected by noise signals. Improving the signal-to-noise ratio (SNR) of echo signal is one of the key problems with the application of low-field NMR technology. Therefore, in order to obtain more accurate analysis results, it is necessary to develop corresponding noise reduction methods. The past researches on NMR signal noise reduction mainly focus on echo string. In this paper, a complete NMR signal model is constructed, and the problem of the echo and echo string de-noising is discussed. FIR filter and orthogonal modulation filter (OMF) are studied for noise reduction of echo. To solve the problem of echo string de-noising, an improved complementary ensemble empirical mode decomposition (CEEMD) threshold de-noising method is proposed and compared with the heuristic threshold de-noising method based on sym4 wavelet and the previous empirical mode decomposition (EMD) threshold de-noising method. Based on the construction model and practical verification, it is proved that the proposed method can invert the more accurate T2 spectrum while improving the signal-to-noise ratio. The research results of this paper provide a strong support for the application of low-field NMR technology in the environment of strong noise.

Combustion behavior of rotary solid porous burners (RSPB)

The combustion behavior of rotary solid porous burners (RSPB), i.e., temperature (T), exhaust gas (CO and NOx) and combustion efficiency (nc) were investigated. The stainless wire-mesh type of porous media was selected as porous absorber with porosity of 0.82, thickness of 4.2 mm. The rice husk was used as the fuel with the humidity around 12-14%. The experiment showed that the T tends to increase following the rotating velocity (ro) rising around 0.5-1 rpm. When a ro increased to 1.5 rpm, a T had tendency decreasingly. Because, a ro was too high resulting in the fuel in combustion chamber were ejected quickly then the reaction time reduced not enough to burn fuel, leading to incomplete combustion. The air flow rate (Qa) of 40 m3/h and the fuel load input rate (Qf) of 2.3 kg/h, gave the highest of T due to the system become complete combustion. Corresponding to the level of CO, the least level was obtained at ro = 1 rpm, Qf = 2.3 kg/h and Qa = 40 m3/h. The qc yielded highest with 93.7% at the same condition. The NOx in this research was considered as low, not more than 40 ppm in all experimental conditions.

Study the Effect of Granules Type of The Porous Medium on The Heat Transfer Enhancement for Double Pipe Heat Exchanger

The current study includes the effect of the type of porous medium on the heat transfer enhancement for double-pipe heat exchanger. Using the three types of the porous medium of balls (steel, ceramic and glass) with diameters (6.35, 6 and 7) mm respectively. The tests were carried out on a locally manufactured heat exchanger, consisting of a copper pipe with an inner diameter (20mm), an outer diameter (22mm) and a length of (1800mm), fixed inside a pipe made of galvanized iron with the same length of copper pipe with inner diameter (50mm) and thickness (5mm). The heat exchanger is insulated with a layer of glass wool to prevent leakage of heat to the area surrounding the exchanger. The tests carried out on the heat exchanger in four cases, the three cases for porous medium, also the case of exchanger without porous medium, and for all cases identical operating conditions, which is inlet temperature of hot, and cold water determined at (63 and 32)˚C and the number of Reynolds from (1100 to 9750) for cold water and (415 to 7500) for hot water. The experimental results showed that the highest thermal conductivity was obtained when the ceramic balls were used, which was estimated to be approximately (219.302) W/˚C and increased by (105.3%, 10.8%, 4.3%) for cases: without porous medium, glass balls and steel balls respectively. The effect of the pressure drop in the hot water side, was recorded the highest value for pressure drop when the ceramic balls were used and ranged from (0.5 to 19.5) mmHg and increased by (0.95%, 2.25%) when compared with the results of two cases for balls (steel and glass) respectively.

Multidimensional nonlinear pseudo-differential evolution equation with p-adic spatial variables

We study the Cauchy problem for p-adic non-linear evolutionary pseudo-differential equations for complex-valued functions of a real positive time variable and p-adic spatial variables. Among the equations under consideration there is the p-adic analog of the porous medium equation (or more generally, the nonlinear filtration equation) which arise in numerous application in mathematical physics and mathematical biology. Our approach is based on the construction of a linear Markov semigroup on a p-adic ball and the proof of m-accretivity of the appropriate nonlinear operator. The latter result is equivalent to the existence and uniqueness of a mild solution of the Cauchy problem of a nonlinear equation of the porous medium type.

Characteristics of turbulent square duct flows over porous media

Particle image velocimetry measurements have been carried out to assess the fully developed turbulence in square-sectioned porous duct flows. To the bottom duct wall, this study applies two types of porous media whose porosities are approximately 0.8 and ratios of wall-normal to streamwise permeabilities are 0.8 and 7.8. Both over- and under-surface turbulence of the porous layers are discussed at inlet flow Reynolds numbers of and 7500. Cross-sectional secondary flows are detected with an enhanced magnitude of approximately 6 % of the inlet bulk velocity. The secondary flow pattern consisting of four large vortices is observed to be insensitive to the porous structures. Over the porous wall, although turbulence is enhanced by the permeability, it is confirmed that turbulence over and under the porous surfaces is rather insensitive to the wall-normal permeability compared with the streamwise permeability as seen in porous-wall channel flows. In the present range of streamwise permeability Reynolds numbers of , the wall-normal fluctuations become dominant once underneath the porous surface while the streamwise ones become dominant again deep inside the porous layer. Applying streamwise–spanwise plane averaging, which covers a 52 % area in the middle of the duct, to the flow quantities, it is confirmed that the correlations between the pore-scale Reynolds number and the log-law parameters are similar to those seen in a wide range of porous-wall channels. The above characteristics are generally the same as those of porous-wall channels in the same range of porosities and permeability Reynolds numbers even with the enhanced secondary flows. However, from the spectral analysis of flows at the porous walls, it is found that, near the symmetry planes, the wavelengths of the Kelvin–Helmholtz waves become a little shorter than those in turbulent porous-wall channels possibly because of the sidewall boundary layers, particularly at low Reynolds numbers.

Nonlinear diffusion and hyperuniformity from Poisson representation in systems with interaction mediated dynamics

We introduce a minimal model of interacting particles relying on conservation of the number of particles and interactions respecting conservation of the center of mass. The dynamics in our model is directly amenable to simple pairwise interactions between particles leading to particle displacements, ensues from this what we call interaction mediated dynamics. Inspired by binary reaction kinetics-like rules, we model systems of interacting agents activated upon pairwise contact. Using Poisson representations, our model is amenable to an exact nonlinear stochastic differential equation. We derive analytically its hydrodynamic limit, which turns out to be a nonlinear diffusion equation of porous medium type valid even far from steady state. We obtain exact self-similar solutions with subdiffusive scaling and compact support. The nonequilibrium steady state of our model in the dense phase displays hyperuniformity which we are able to predict from our analytical approach. We reinterpret hyperuniformity as stemming from correlations in particles displacements induced by the conservation of center of mass. Although quite simplistic, this model could in principle be realized experimentally at different scales by active particles systems.

Global higher integrability of weak solutions of porous medium systems

We establish higher integrability up to the boundary for the gradient of solutions to porous medium type systems, whose model case is given by \begin{document}$ \begin{equation*} \partial_t u-\Delta(|u|^{m-1}u) = \mathrm{div}\,F\,, \end{equation*} $\end{document} where $ m>1 $. More precisely, we prove that under suitable assumptions the spatial gradient $ D(|u|^{m-1}u) $ of any weak solution is integrable to a larger power than the natural power $ 2 $. Our analysis includes both the case of the lateral boundary and the initial boundary.

Quantification of Uncertainties from Image Processing and Analysis in Laboratory-Scale DNAPL Release Studies Evaluated by Reflective Optical Imaging

Subsurface DNAPL (dense non-aqueous phase liquid) contamination from (un-) intentional spilling typically leads to severe environmental hazards. A large number of studies have demonstrated the relevance of DNAPL source zone geometry for the determination of contaminant plume propagation in groundwater. Optical imaging represents a promising non-invasive method for identifying DNAPL saturation without disturbing multiphase flow dynamics. However, workflow and image analysis methodologies have not been sufficiently developed or described for general application to related experimental efforts. For example, the choice of dye(s) used for phase colorization affects image processing and can bias final estimations of DNAPL saturations. In this study, we perform a series of DNAPL migration and entrapment studies in transparent tanks that are filled with three different types of porous media. Different dyes are used and raw images are acquired. Subsequently, these are used to evaluate a suite of image processing and analysis approaches, which are organized into a workflow. Our approach allows for us to identify key image processing and analysis steps that introduce the most error. Applicable dye configurations led to uncertainties of up to 41% depending on the selection of processing steps. Based on these findings, it was possible to delineate a flexible framework for image processing and analysis that has the potential for transfer and application in other tank experiment setups.

Existence for singular doubly nonlinear systems of porous medium type with time dependent boundary values

In this paper we prove the existence of variational solutions to the Cauchy–Dirichlet problem with time dependent boundary values associated with doubly nonlinear systems $$\begin{aligned} \partial _t \big (|u|^{m-1}u\big ) - {{\,\mathrm{div}\,}}(D_\xi f(Du)) = 0 \end{aligned}$$with $$m>1$$ and a convex function f satisfying a standard p-growth condition for an exponent $$p \in (1,\infty )$$. The proof relies on a nonlinear version of the method of minimizing movements.

Factors affecting the transport of petroleum colloids in saturated porous media

Batch and column experiments were performed to evaluate the responses of attachment and transport of petroleum colloids to the changes in solution chemistry conditions. We found that transport of petroleum colloids was inhibited with increasing the ionic strength or decreasing the pH. This observation can be explained by the increase in particle size of petroleum colloids and the reduction in electrostatic repulsion between colloids and grain surfaces. Meanwhile, the extent of transport inhibition by ionic strength depended on the type of porous media, that is, greater mobility of petroleum colloids could be found in sand rather than in soil at the same ionic strength. This can probably be ascribed to surface chemistry of soil minerals. In the case of divalent ion (e.g., Ca2+), the retention of petroleum colloids was more obvious in soil than in sand resulting from the complexing between the oxygen functional groups from both petroleum colloids and grains, i.e., petroleum colloids could bind to the sand/soil grains through Ca2+ bridging. Additionally, the presence of sodium dodecyl sulfate (SDS, selected as a model surfactant) significantly enhanced the mobility of petroleum colloids as a result of enhanced steric hindrance that remarkably inhibited aggregation of petroleum colloids. Also, a two-site transport model was used to fit the transport data to gain further insights on deposition mechanisms. These findings from this research are helpful to understand the transport and fate of petroleum colloids in subsurface systems.

Global regularity and convergence to equilibrium of reaction\u2013diffusion systems with nonlinear diffusion

We study the boundedness and convergence to equilibrium of weak solutions to reaction–diffusion systems with nonlinear diffusion. The nonlinear diffusion is of porous medium type, and the nonlinear reaction terms are assumed to grow polynomially and to dissipate (or conserve) the total mass. By utilising duality estimates, the dissipation of the total mass and the smoothing effect of the porous medium equation, we prove that if the exponents of the nonlinear diffusion terms are high enough, then weak solutions are bounded, locally Hölder continuous and their L^{infty }(Omega )-norm grows in time at most polynomially. In order to show convergence to equilibrium, we consider a specific class of nonlinear reaction–diffusion models, which describe a single reversible reaction with arbitrarily many chemical substances. By exploiting a generalised logarithmic Sobolev inequality, an indirect diffusion effect and the polynomial in time growth of the L^{infty }(Omega )-norm, we show an entropy–entropy production inequality which implies exponential convergence to equilibrium in L^p(Omega )-norm, for any 1le p < infty , with explicit rates and constants.

Heat transfer and fluid flow characteristics of tubular channel partially filled with grooved metal foams

The metal foam is a type of porous media that can be characterized by high porosity, tortuous flow paths, high strength to weight ratio and high thermal conductivity. Due to these features the metal foam is used in many engineering applications such as heat exchanges. Therefore, a new design of a circular pipe partially filled with a grooved metallic foam is proposed in order to improve the hydraulic and thermal performance, and consequently reduce the pumping power losses and the metal foam volume.In the current work, the non-Darcy laminar forced convection flow is considered under the thermal boundary condition of constant wall heat flux. The governing equations are solved using the finite volume method (FVM) with temperature-dependent water properties. The variable parameters are; the pitch of the helical grooves, the number of helical grooves and the aspect ratio (Ri: diameter ratio of the metal foam to the pipe). The results show that for Ri = 0.55, four helical grooves having two pitches provides the optimal increase in the Nu number (7%) and the PEC is around 1.21 with a reduction in the pumping power and the amount of the metal foam about 25% and 16.74%, respectively, at Re = 1000.

Uniqueness of entropy solutions to fractional conservation laws with “fully infinite” speed of propagation

Our goal is to study the uniqueness of bounded entropy solutions for a multidimensional conservation law including a non-Lipschitz convection term and a diffusion term of non-local porous medium type. The non-locality is given by a fractional power of the Laplace operator. For a wide class of nonlinearities, the L1-contraction principle is established, despite the fact that the “finite-infinite” speed of propagation (Alibaud (2007) [1]) cannot be exploited in our framework; existence is deduced with perturbation arguments. The method of proof, adapted from Andreianov and Maliki (2010) [9], requires a careful analysis of the action of the fractional laplacian on truncations of radial powers.

Mechanical and Acoustic Emission Characteristics of Coal at Temperature Impact

Coal and rock mass constitute a type of porous medium. This study investigated the influence of temperature impact on the mechanical properties and acoustic emission (AE) characteristics of coal. A mechanism analysis was performed from the perspective of microstructure. The results show that the temperature impact causes the development of pores and cracks in the coal, which reduces the strength of coal. The elastic modulus of coal generally decreases with increasing temperature gradient. AE parameters increase with the increase in the load and reach the maximum value at the peak stress. AE parameters and cumulative parameters decrease with increasing temperature gradient. Not only does temperature impact change the fracture structure of the coal surface, but also the internal fracture structure of the coal is significantly affected. After temperature impact, the cracks expand and new cracks are initiated, and the fracture volume of the coal increases. Temperature impact causes the volume and specific surface area of small pores and meso-pores in coal to increase, and promotes the opening of the necking pores within the coal. The impact causes macro-pores to penetrate through to form cracks, which increases the transport of coal gas and significantly improves the permeability of coal. The thermal stress generated by coal under temperature impact is greater than its tensile strength, which promotes the cracking of coal, along with the initiation, widening, extension, and expansion of crack networks, which significantly change the fracture structure of coal. The research results lay a certain theoretical and experimental foundation for further study of mechanical properties of coal affected by liquid nitrogen.

Cotransport of graphene oxides/reduced graphene oxides with BPA in both bare and iron oxides coated quartz sand

This study investigated the cotransport behaviors of graphene oxides (GO) and reduced graphene oxides (RGO) with bisphenol A (BPA) in porous media in both NaCl (1 and 10 mmol/L) and CaCl2 solutions (0.5 and 1.5 mmol/L) at pH 6.5. Both bare and iron oxides-coated quartz sand were employed as porous media in present study. We found that under all examined solution conditions, the presence of BPA (100 µ/L) did not have obvious influence on the transport of both GO and RGO (8 mg/L as TOC) in both bare and iron oxides-coated quartz sand. Although the dissolved BPA was the major form dominating the transport behaviors of total BPA in the presence of GO/RGO, yet the GO/RGO-associated BPA (due to the adsorption of BPA onto GO/RGO surfaces) also had some contribution to the transport of total BPA in the presence of GO/RGO in two types of porous media. Overall, due to the different transport behaviors of GO and RGO under different solution conditions, we found that the presence of GO/RGO decreased the transport of total BPA under all examined solution conditions in two types of porous media with the smallest decrease in 1 mmol/L NaCl solutions and the largest in 1.5 mmol/L CaCl2 solutions. The results of this study clearly indicated that when BPA was co-present with GO/RGO, the transport behaviors of GO/RGO in porous media would have great influences on the fate and transport of BPA in natural environments due to their adsorption onto GO/RGO.

The self-improving property of higher integrability in the obstacle problem for the porous medium equation

We prove local higher integrability of spatial gradients for obstacle problems related to porous medium type equations.

Characterization of Capillary Pressure–Saturation Relationships for Double-Porosity Medium Using Light Transmission Visualization Technique

Capillary pressure saturation (Pc–Sw) relationship plays a central role in the description of fluid flow in porous media. In this research, the light transmission visualization (LTV) technique was applied to characterize the Pc–Sw relationship in a double-porosity medium. Four experiments were conducted in two-dimensional (2-D) flow chambers packed with a double-porosity medium composed of a mixture of silica sand and sintered kaolin clay spheres. In each experiment, a different volumetric fraction of macropores and micropores was used. The experiment was also repeated by compacting the flow chamber with silica sand only to represent single-porosity medium. Variable saturations of water across the height of the system were applied by controlling the capillary pressure. Images of the 2-D model were collected using a digital camera and analyzed pixel by pixel to determine water saturation in the double-porosity medium. Results from the LTV technique showed that the Pc–Sw relationships for all experiments in double-porosity soil medium were similar in shape but varied depending on the porous media composition. Comparison with the pressure cell test results showed that the Pc–Sw curves for all experiments consistent comparable to those obtained by the LTV technique. The Pc–Sw curves were also fit to van Genuchten model for comparison and validation. For double-porosity media, the best-fit parameters were consistent with published data for sandy clay. Moreover, little variability was observed in the best-fit α and n values for the different double porosity. Overall, this study proves that the LTV technique is a noninvasive laboratory tool that can provide high-resolution spatial data for water saturation distribution in different types of porous media and is capable of producing highly resolved Pc–Sw relationships.

Free convection heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a porous complex shaped cavity with MHD and thermal radiation effects

PurposeThe present study aims to address the flow and heat transfer of MgO-MWCNTs/EG hybrid nanofluid in a complex shape enclosure filled with a porous medium. The enclosure is subject to a uniform inclined magnetic field and radiation effects. The effect of the presence of a variable magnetic field on the natural convection heat transfer of hybrid nanofluids in a complex shape cavity is studied for the first time. The geometry of the cavity is an annular space with an isothermal wavy outer cold wall. Two types of the porous medium, glass ball and aluminum metal foam, are adopted for the porous space. The governing equations for mass, momentum and heat transfer of the hybrid nanofluid are introduced and transformed into non-dimensional form. The actual available thermal conductivity and dynamic viscosity data for the hybrid nanofluid are directly used for thermophysical properties of the hybrid nanofluid.Design/methodology/approachThe governing equations for mass, momentum and heat transfer of hybrid nanofluid are introduced and transformed into non-dimensional form. The thermal conductivity and dynamic viscosity of the nanofluid are directly used from the experimental results available in the literature. The finite element method is used to solve the governing equations. Grid check procedure and validations were performed.FindingsThe effect of Hartmann number, Rayleigh number, Darcy number, the shape of the cavity and the type of porous medium on the thermal performance of the cavity are studied. The outcomes show that using the composite nanoparticles boosts the convective heat transfer. However, the rise of the volume fraction of nanoparticles would reduce the overall enhancement. Considering a convective dominant regime of natural convection flow with Rayleigh number of 107, the maximum enhancement ratio (Nusselt number ratio compared to the pure fluid) for the case of glass ball is about 1.17 and for the case of aluminum metal foam is about 1.15 when the volume fraction of hybrid nanoparticles is minimum as 0.2 per cent.Originality/valueThe effect of the presence of a variable magnetic field on the natural convection heat transfer of a new type of hybrid nanofluids, MgO-MWCNTs/EG, in a complex shape cavity is studied for the first time. The results of this paper are new and original with many practical applications of hybrid nanofluids in the modern industry.

Yield-stress fluids in porous media: a comparison of viscoplastic and elastoviscoplastic flows

A numerical and theoretical study of yield-stress fluid flows in two types of model porous media is presented. We focus on viscoplastic and elastoviscoplastic flows to reveal some differences and similarities between these two classes of flows. Small elastic effects increase the pressure drop and also the size of unyielded regions in the flow which is the consequence of different stress solutions compare to viscoplastic flows. Yet, the velocity fields in the viscoplastic and elastoviscoplastic flows are comparable for small elastic effects. By increasing the yield stress, the difference in the pressure drops between the two classes of flows becomes smaller and smaller for both considered geometries. When the elastic effects increase, the elastoviscoplastic flow becomes time-dependent and some oscillations in the flow can be observed. Focusing on the regime of very large yield stress effects in the viscoplastic flow, we address in detail the interesting limit of ‘flow/no flow’: yield-stress fluids can resist small imposed pressure gradients and remain quiescent. The critical pressure gradient which should be exceeded to guarantee a continuous flow in the porous media will be reported. Finally, we propose a theoretical framework for studying the ‘yield limit’ in the porous media.