Search Results (22)

Variable-flow displacement has been effectively used to enhance oil recovery; however, it has rarely been investigated for coalbed methane production, and the CH₄ diffusion laws in this process are not clear. In this paper, we carried out a study on the CH₄ diffusion law in the bidirectional diffusion process displaced by variable-flow gas injection. The emission and desorption quantity of CH₄ under variable-flow gas injection, the displacement effect under the principle of equal time and quantity, and the applicability of the CH₄ diffusion model for the bidirectional diffusion process were analyzed. The results indicate that the variable-flow injection modes emit more CH₄ compared to constant flow injection. The CH₄ emission and desorption quantities for each injection mode are as follows: step-changed > sinusoidal-changed > constant flow. Secondly, the order of CH₄ emission and desorption quantity in each gas injection mode is as follows: step-changed > sinusoidal-changed > constant flow. When CO₂ is the injection gas source, the outlet CH₄ emission and desorption quantity are larger than N₂ injection. Thirdly, through the analysis of the principle of equal time and equal quantity, the variable-flow injection modes consume less gas for each volume of emitted CH₄, resulting in a more effective displacement. Finally, the diffusion fitting effect of the bidisperse model for CH₄ in the bidirectional diffusion process is better than that of the unipore model, and the bidisperse diffusion model can better fit the m_t/m_∞ curve of CH₄ diffusion during the variable-flow gas injection replacement process. Full article

Microfluidic-chip based hydrodynamic filtration is one of the passive sorting techniques that can separate cell or particle suspensions into subpopulations of different sizes. As the branch channels and side channels play an important role in maintaining particle focusing, their rational design is necessary for highly efficient sorting. A model framework involving multiple side and multiple branch channels has been developed by extending the analytical analysis of three-dimensional laminar flow in channel networks, which was previously validated by comparison with numerical simulations. Objective parameters were identified as the number of branch channels and each length of individual branches. The presence of multiple side channels causes an increase in the average fluid velocity in main and branch channels as the branch point shifts toward the end of the main channel, which differs from the behavior observed in a single side channel. The number of branches and their individual lengths decrease distinctly in the case of branch channels consisting of narrow and wide sections, which enables the compact design of a microfluidic-chip, being operated by a lower pressure drop under the same throughput. Sorting of bidisperse particles was accomplished with an optimally designed chip to verify this framework by achieving very high recovery and purity. Full article

In this work, the influence of gas–solid drag and heat transfer coefficient models on the prediction capacity of the Euler–Euler approach to simulate reactive bubbling fluidized bed flows is studied. Three different cases are considered, a non-reactive bidisperse bubbling fluidized bed flow (Case 1), and two reactive polydisperse flows in bubbling fluidized beds, one for biomass gasification (Case 2), and the other for biomass pyrolysis (Case 3). The Gidaspow, Syamlal–O’Brien, and BVK gas–solid drag models and the Gunn, Ranz–Marshall, and Li–Mason gas–solid heat transfer correlations are investigated. A Eulerian multiphase approach in a two-dimensional Cartesian domain is employed for the simulations. Computational results for the three cases are compared with experimental data from the literature. The results obtained here contribute to a better understanding of the impacts of such closure models on the prediction ability of the Euler–Euler approach to simulate reactive flows. The results indicate that, for the simulation of reactive flows in bubbling fluidized bed reactors, the kinetic modeling of the reactions has a global effect, which superposes with the influence of the drag and heat transfer coefficient models. Nevertheless, local parameters can be noticeably affected by the choice of the interface closure models. Finally, this work also identifies the models that lead to the best results for the cases analyzed here, and thus proposes the use of such selected models for gasification and pyrolysis processes occurring in bubbling fluidized bed reactors. Full article

When using magnetopolymer composites in high-precision industrial and biomedical technologies, the problem of predicting their properties in an external magnetic field arises. In this work, we study theoretically the influence of the polydispersity of a magnetic filler on a composite’s equilibrium magnetization and on the orientational texturing of magnetic particles formed during polymerization. The results are obtained using rigorous methods of statistical mechanics and Monte Carlo computer simulations in the framework the bidisperse approximation. It is shown that by adjusting the dispersione composition of the magnetic filler and the intensity of the magnetic field at which the sample’s polymerization occurs, it is possible to control the composite’s structure and magnetization. The derived analytical expressions determine these regularities. The developed theory takes into account dipole–dipole interparticle interactions and therefore can be applied to predict the properties of concentrated composites. The obtained results are a theoretical basis for the synthesis of magnetopolymer composites with a predetermined structure and magnetic properties. Full article

An in-depth analysis of the flow patterns and mixing dynamics in a twin-paddle blender with bi-disperse non-spherical particles was investigated using the discrete element method (DEM) and experiments. This study aimed to explore the mixing efficiency of a twin-paddle blender containing two different shapes of non-spherical particles. The study focussed on the demonstration of the applicability of the GPU-based DEM model. To achieve this, calibration tests were performed using a classical rotary drum to validate the accuracy of the DEM model. The next step was to examine the impact of various operating parameters on the mixing performance, such as impeller rotational speed. The relative standard deviation (RSD) was employed as a measure of mixing performance. Results revealed that the rotational speed of the impellers had a significant impact on the mixing performance. Full article

Despite a wide set of experimental data and a large number of studies, the quantitative description of the relaxation mechanisms involved in the disorientation process of bidisperse blends is still under discussion. In particular, while it has been shown that the relaxation of self-unentangled long chains diluted in a short chain matrix is well approximated by a Constraint Release Rouse (CRR) mechanism, there is no consensus on the value of the average release time of their entanglements, ${\tau }_{obs}$, which fixes the timescale of the CRR relaxation. Therefore, the first objective of the present work is to discuss the different approaches proposed to determine this time and compare them to a large set of experimental viscoelastic data, either newly measured (poly(methyl-)methacrylate and 1,4-polybutadiene blends) or coming from the literature (polystyrene and polyisoprene blends). Based on this large set of data, it is found that with respect to the molar mass of the short chain matrix, ${\tau }_{obs}$ follows a power law with an exponent close to 2.5, rather than 3 as previously proposed. While this slight change in the power law exponent does not strongly affect the values of the constraint release times, the results obtained suggest the universality of the CRR process. Finally, we propose a new description of ${\tau }_{obs}$, which is implemented in a tube-based model. The accurate description of the experimental data obtained provides a good starting point to extend this approach to self-entangled binary blends. Full article

A method of simulating the drying process of a soft matter solution with an implicit solvent model by moving the liquid-vapor interface is applied to various solution films and droplets. For a solution of a polymer and nanoparticles, we observe “polymer-on-top” stratification, similar to that found previously with an explicit solvent model. Furthermore, “polymer-on-top” is found even when the nanoparticle size is smaller than the radius of gyration of the polymer chains. For a suspension droplet of a bidisperse mixture of nanoparticles, we show that core-shell clusters of nanoparticles can be obtained via the “small-on-outside” stratification mechanism at fast evaporation rates. “Large-on-outside” stratification and uniform particle distribution are also observed when the evaporation rate is reduced. Polymeric particles with various morphologies, including Janus spheres, core-shell particles, and patchy particles, are produced from drying droplets of polymer solutions by combining fast evaporation with a controlled interaction between the polymers and the liquid-vapor interface. Our results validate the applicability of the moving interface method to a wide range of drying systems. The limitations of the method are pointed out and cautions are provided to potential practitioners on cases where the method might fail. Full article

A drawback of magnetorheological fluids is low kinetic stability, which severely limits their practical utilization. This paper describes the suppression of sedimentation through a combination of bidispersal and coating techniques. A magnetic, sub-micro additive was fabricated and sequentially coated with organosilanes. The first layer was represented by compact silica, while the outer layer consisted of mesoporous silica, obtained with the oil–water biphase stratification method. The success of the modification technique was evidenced with transmission electron microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. The coating exceptionally increased the specific surface area, from 47 m²/g (neat particles) up to 312 m²/g, which when combined with lower density, resulted in remarkable improvement in the sedimentation profile. At this expense, the compact/mesoporous silica slightly diminished the magnetization of the particles, while the magnetorheological performance remained at an acceptable level, as evaluated with a modified version of the Cross model. Sedimentation curves were, for the first time in magnetorheology, modelled via a novel five-parameter equation (S-model) that showed a robust fitting capability. The sub-micro additive prevented the primary carbonyl iron particles from aggregation, which was projected into the improved sedimentation behavior (up to a six-fold reduction in the sedimentation rate). Detailed focus was also given to analyze the implications of the sub-micro additives and their surface texture on the overall behavior of the bidisperse magnetorheological fluids. Full article

Concrete has a large environmental impact due to CO₂ emissions related to cement manufacturing and the consumption of natural aggregates. More sustainable concretes can be developed, replacing part of the cement with mineral admixtures or natural aggregates with recycled ones. However, recycled materials are less regular than natural ones, and using new deposit changes concrete properties, which necessitates the re-optimization of mixture proportions. For small/medium-size waste deposits, the expensive experimental work needed to adapt concrete formulation containing these particular wastes is not profitable, which prevents from their valorization. The aim of this study is to develop a numerical model to optimize the mixture proportions of concentrated suspensions based on very limited entry data. In the model, spheres of small radii are seeded in the porosity and allowed to swell until reaching a target radius/density. On monosized suspensions, it is shown that the ratio between the number of random displacements to the number of particles varies with density, following a classical viscosity–density relationship, which allows identification of the packing fraction. The model is extended to bidisperse systems, with the viscosity of the whole suspension calculated by combining the viscosities of each granular class. The model is applied to bidisperse systems of size ratios 4:1 and 2:1 with varying proportions of large particles. The optimum proportions identified numerically are compared successfully to experimental results from the literature. Full article

The study on the adsorption and micropore filling of water vapor in coal is significant for predicting coalbed methane content in coal seams. The primary purpose of this study is to explain the effects of coal pore structure and its surface chemistry on water vapor monolayer adsorption, micropore filling, and diffusion coefficient. First, X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) analyzed inorganic mineral components of two kinds of coal samples and pore fissures structures. Then, we divide pores and fissures according to the theory of fractal dimensions. Furthermore, we carried out the water vapor adsorption and desorption experiments on two kinds of coal; in particular, we set 14 points of relative pressure between 0 and 0.2. Guggenheim–Anderson–de Boer (GAB), Frenkel–Halsey–Hill (FHH), and Freundlich models were used to analyze the data of water vapor adsorption to obtain the boundary pressure points of the monolayer, multilayer adsorption, and capillary condensation. Finally, the parameters of the models were obtained by fitting the adsorption data of water vapor according to the combined GAB, Freundlich, DA, and bidisperse adsorption (BDA) models to analyze the interaction mechanism between coal and water. We explain why the strongly adsorbed water minerals, such as pyrite, illite, and nacrite coal, can improve water vapor’s adsorption and diffusion capacity in coal pore fissures. Full article

In this study, flow and heat transfers in bidisperse gas–solid systems were numerically investigated using the computational fluid dynamics–discrete element method (CFD–DEM). Three different models to close the gas–solid heat transfer coefficient for each species of bidisperse systems were compared in the simulations. The effect of the particle diameter ratio and particle number ratio between large and small particles on the particle mean temperature and temperature distribution of each species were systematically investigated. The simulation results show that differences in the particle mean temperature and temperature distribution profiles exist among the three heat transfer models at a higher particle number ratio. The differences between the effects of three heat transfer models on heat transfer properties in bidisperse systems with particle diameter ratios of up to 4 are marginal when the particle number ratio between small and large particles is 1. Full article

The analysis of phenomena related to gas transport in hard coal is important with regard to the energetic use of coal bed methane (CBM), the reduction of greenhouse gas emissions to the atmosphere (CO₂) and the prevention of natural hazards such as methane hazards and gas and rock outbursts. This article presents issues concerning the feasibility and scope of applying the unipore and bidisperse diffusion models to obtain knowledge concerning the kinetics of methane sorption and its diffusion in the carbon structure, depending on its petrography. Laboratory tests were carried out on coal samples which varied in terms of petrography. Quantitative point analyses were carried out, based on which content of groups of macerals was determined. The degree of coalification of coal samples was also determined based on measurements of vitrinite reflectivity R₀ and the volatile matter content V^daf. Sorption kinetics were also investigated, and attempts were made to adjust the unipore and bidisperse models to the real sorption kinetic courses. This allowed the identification of appropriate coefficients controlling the course of sorption in mathematical models. An attempt was also made to assess the possibility of applying a given model to properly describe the phenomenon of methane sorption on hard coal. Full article

Increasing the efficiency of using gypsum binders can be carried out by using not natural gypsum raw materials, but calcium sulfate-containing waste from various industries (phosphogypsum, borogypsum, citrogypsum, etc.). As the main source material in the work, we used gypsum-containing waste from a faience factory in the form of waste molds for casting dishes, souvenirs and plumbing fixtures. It has been established that the optimal binding system is formed by mixing powders of dihydrate technogenic gypsum from a coarse and fine earthenware factory with average particle diameters of 3.473 microns and 3.065 microns in a percentage ratio of 30:70, respectively. Using a computer software developed by the authors, which makes it possible to simulate the microstructure of a raw mixture taking into account the contact interaction of particles and calculate the average coordination number, models of binary packing of particles were constructed at various ratios of their diameters. Studies of the strength of composites obtained on the basis of bidisperse systems have shown the presence of an extremum in the region of mixtures containing 30% coarse powder. With optimal packing, a large number of phase contacts are formed due to the regulation of the grain composition of the bidisperse system. It was revealed that a brick based on the waste of two-water gypsum from earthenware production has 2.5–5 times better characteristics of compressive strength than traditional building wall products based on natural gypsum. At the same time, the strength immediately after molding is more than 3 times higher than that of traditional gypsum products. Even higher indicators are achieved when adding microcalcite in addition to the waste of earthenware production, in this case, the compressive strength is 3–6 times higher, and the strength immediately after molding is almost 3 times higher than that of traditional gypsum products. Full article

Axial segregation of polydisperse granular mixtures in rotating drums have been observed in several experimental and discrete particle simulation studies reported in the literature. A common thread to both experimental and numerical studies is the formation of (alternating) bands which eventually coarsen in the long-time limit due to logarithmic merging. Models to explain the experimental observations are generally limited to bidisperse mixtures, and often unable to reproduce band coarsening. One such mechanism for bidisperse mixtures argues that the grains eventually diffuse into axial bands as a consequence of concentration fluctuations in the free surface layer caused by friction-limited mobility. We generalise this model to multi-species mixtures and show that the solution produces banding that evolves more complexly than binary mixtures, with sinusoidal-like variations of the band structure that evolves non-linearly in time. In addition, we successfully recover band coarsening with time—an observation that is generally difficult to reproduce, even experimentally. Contrary to literature findings, the configurations herein did not produce bands within bands for ternary and quaternary mixtures. Full article

The diffusion–adsorption behavior of methane in coal is an important factor that both affecting the decay rate of gas production and the total gas production capacity. In this paper, we established a pore-scale Lattice Boltzmann (LB) model coupled with fluid flow, gas diffusion, and gas adsorption–desorption in the bi-dispersed porous media of coalbed methane. The Knudsen diffusion and dynamic adsorption–desorption of gas in clusters of coal particles were considered. Firstly, the model was verified by two classical cases. Then, three dimensionless numbers, Re, Pe, and Da, were adopted to discuss the impact of fluid velocity, gas diffusivity, and adsorption/desorption rate on the gas flow–diffusion–adsorption process. The effect of the gas adsorption layer in micropores on the diffusion–adsorption–desorption process was considered, and a Langmuir isotherm adsorption theory-based method was developed to obtain the dynamic diffusion coefficient, which can capture the intermediate process during adsorption/desorption reaches equilibrium. The pore-scale bi-disperse porous media of coal matrix was generated based on the RCP algorithm, and the characteristics of gas diffusion and adsorption in the coal matrix with different Pe, Da, and pore size distribution were discussed. The conclusions were as follows: (1) the influence of fluid velocity on the diffusion–adsorption process of coalbed methane at the pore-scale is very small and can be ignored; the magnitude of the gas diffusivity in macropores affects the spread range of the global gas diffusion and the process of adsorption and determines the position where adsorption takes place preferentially. (2) A larger Fickian diffusion coefficient or greater adsorption constant can effectively enhance the adsorption rate, and the trend of gas concentration- adsorption is closer to the Langmuir isotherm adsorption curve. (3) The gas diffusion–adsorption–desorption process is affected by the adsorption properties of coal: the greater the p_L or V_m, the slower the global gas diffusivity decay. (4) The effect of the gas molecular adsorption layer has a great impact on the kinetic process of gas diffusion–adsorption–desorption. Coal is usually tight and has low permeability, so it is difficult to ensure that the gas diffusion and adsorption are sufficient, the direct use of a static isotherm adsorption equation may be incorrect. Full article