A macroscopic viscoelastic model of magnetorheological elastomer with different initial particle chain orientation angles based on fractional viscoelasticity

In this paper, a macroscopic viscoelastic modeling method for magnetorheological elastomer (MRE) based on fractional derivative model is presented to describe the dynamic viscoelastic properties of MRE with different initial particle chain orientation angles. The angle between the particle chain and the applied magnetic field is used as an indicator to describe the directionality of the particle chain. MRE samples with different initial inclination angles have been designed and fabricated. The dynamic viscoelastic properties of different MRE samples under shear working mode were measured using a parallel plate rheometer. The dynamic viscoelastic properties of MRE with different initial inclination angles are analyzed under the test conditions of different strain amplitude, frequency and magnetic flux density. The test results show that the initial inclination angle of the particle chain in the MRE has significant effect on the dynamic viscoelastic properties of the MRE. A polynomial function is used to describe the relationship between the initial particle chain orientation angle and the magneto-induced modulus of MRE. A phenomenological model of magneto-induced modulus is established based on the fractional derivative model. The model parameters are identified using the nonlinear least square method. The predicted values of the model are in good agreement with the experimental results, indicating that the model can well describe the dynamic viscoelastic properties of MRE.

Particle dynamics in drying colloidal solution using discrete particle method

We study particle dynamics in drying colloidal solutions using the numerical simulation with discrete particle method (DPM). Simulations of two different systems were conducted; the drying dynamics of monodispersed and binary mixture of colloidal solution, and compared with those from the previous studies. In the monodispersed colloidal solution, the time evolution of particle concentration profile for varying Péclet number was simulated with the same initial particle concentration. In the binary colloidal solution, when the particle size ratio α is 3, three different stratification modes were observed varying Péclet number and initial particle concentration. By comparison, our method was in a good agreement with the existing methods. Additionally, because of the mesh-based Eulerian approach in our model, other various multi-physical phenomena, such as effect of thermal Marangoni or chemical reaction, can be included in an easy way. From the results, we expect that this work can provide a physical insight for predicting the quality of colloidal drying in a complicated situation.

Practical Limits for Two Fundamental Approaches to Designing Particle Size Distributions to Address a Specific Physical Property like Viscosity

It has previously been shown that optimum particle size distributions with a maximum packing fraction can be achieved from a straight line plot of the accumulated sum of particle volume fractions versus the square root of particle size. This study addresses practical limits for two dominant fundamental approaches to designing particle size distributions to address the effect on a specific physical property such as viscosity. The two fundamental approaches to obtain such a straight line would include: the first design approach would be generated utilizing the same initial particle size, Dmin, but by using different ultimate particle sizes, Dmax. The second design approach would be generated where each distribution starts with the same initial particle size, Dmin, and ends with the same ultimate particle size, Dmax. The first design approach is particularly useful to identify the possible slopes available based on the smallest and largest particle sizes available. The second design approach can be utilized to identify the preferred ratio between particles, Z, and the number of different particle sizes, n, to be utilized in the final particle blend. The extensive empirical experimental evaluations of particle size distributions generated by McGeary were then utilized to confirm the limits.

Study on Deposition Motion of Naturally Circulating Particulate Matter in Supercritical Water Based on Factor and Correspondence Analysis

It is very important to study the deposition of particles in natural circulation of supercritical water to ensure the safe and stable operation of supercritical water reactor. The data of natural circulation loop calculated by ANSYS-CFX simulation software were analyzed by factorial analysis method, and the effects of axial distance, initial particle volume fraction, heating power and particle size on particle deposition were obtained. The results show that the contribution rate of particle size to the deposition rate is the largest, about 36.3%, and the contribution rate of initial particle concentration to the deposition rate is about 15.1%; the interaction between axial distance and heating power is the most obvious, and the interaction effect is the pipe temperature distribution. Through correspondence analysis, the main influencing factors of particle deposition rate at each level were analyzed. The results show that: when the deposition rate is small, the small change of axial distance will also have a greater impact on the deposition of particles; when the deposition rate is further increased, the change of initial particle volume fraction will significantly affect the deposition of particles; when the deposition rate is large, the particle size plays a leading role in the deposition of particles. Both of the two analysis methods show that: in the influence on the deposition of particles in supercritical water natural circulation, the influence degree is particle size > concentration > axial distance > heating power. Based on the two analysis methods, an analysis regression model is established and the volume proportion of particles in natural circulation is predicted.

Development of the Method for Forecasting and Calculating the Operation of Sorption Systems for Purifying the Generator Gas Based on Dolomite Use. Part I

A trend towards energy diversification creates the expansion of small energy facilities that involve the production of solid fuel generator gas, rather than its direct combustion. The economic indicators of such facilities significantly depend on the efficiency of the generator gas purification. A promising sorbent for the purification of the generator gas is dolomite. When working as a sorbent, dolomite particles usually form a layer, through which the generator gas that is heating them is filtered. The objective of the study is to determine kinetic parameters of the thermal decomposition of dolomite, depending on the size of the sample. It was achieved using the thermogravimetric study of the thermal decomposition of single dolomite particles under static conditions at various temperatures. The most significant scientific result was that a dependence of the kinetic parameters of the gross reaction on the size of the initial particle is revealed, and a regression equation was proposed for its quantitative assessment. In addition, since the heat treatment process of the material was fairly long lasting, and the sizes of the particles allowed them to be referred to thermally thin bodies, it was inferred that the effect of a grain size on the reaction kinetics should be explained through the description of the evacuation process of gaseous reaction products from the material. The significance of the results of the study lies in the fact that a particle size must be considered as a factor that affects the progress of the technological process, which increases the reliability of the calculation of sorption-catalytic systems based on the use of dolomite.

Effects of Concentration of Pore Solution on Stability of Ion-Absorbed Rare Earth Ore Aggregate

The continuous change in solution concentration in ore pores during in situ mineral leaching influences the stability of ore aggregate. In this study, influences of the concentration of ammonium sulfate ((NH4)2SO4) solution on the interaction forces between ore particles were calculated. On this basis, the mechanism by which (NH4)2SO4 solution concentration influences the stability of ore aggregate was analyzed. Furthermore, an empirical formula for estimating the critical (NH4)2SO4 solution concentration for aggregation and dispersion of ore body aggregates with different grain composition was proposed. Some major conclusions were drawn. First, for ore bodies with an initial particle size of less than 0.075 mm, the interaction force between particles was net attraction, with the distance range of this force increasing as the concentration of (NH4)2SO4 solution increased from ≤0.001 to 0.16 mol·L−1, aggregation of ore particles occurring within this distance range. Secondly, for ore bodies with initial particle size of less than 0.075 mm, the interaction force between particles was net attraction, but with the distance range of this force decreasing when the (NH4)2SO4 solution concentration increased from 0.16 to 0.28 mol·L−1, dispersion of ore particles occurring beyond this distance range. Thirdly, for ore bodies with particle sizes of less than 0.038, 0.075 and 0.1 mm, the cation exchange capacity (CEC) was 9.13, 8.96, and 8.8 cmol·kg−1, respectively, and the critical (NH4)2SO4 solution concentration affecting the aggregation and dispersion of ore bodies was 0.12, 0.16, and 0.20 mol·L−1, respectively.

Distribution of non-spherical nanoparticles in turbulent flow of ventilation chamber considering fluctuating particle number density

The Reynolds-averaged general dynamic equation (RAGDE) for the nanoparticle size distribution function is derived, including the contribution to particle coagulation resulting from the fluctuating concentration. The equation together with that of a turbulent gas flow is solved numerically in the turbulent flow of a ventilation chamber with a jet on the wall based on the proposed model relating the fluctuating coagulation to the gradient of mean concentration. Some results are compared with the experimental data. The results show that the proposed model relating the fluctuating coagulation to the gradient of mean concentration is reasonable, and it is necessary to consider the contribution to coagulation resulting from the fluctuating concentration in such a flow. The changes of the particle number concentration M0 and the geometric mean diameter dg are more obvious in the core area of the jet, but less obvious in other areas. With the increase in the initial particle number concentration m00, the values of M0 and the standard deviation of the particle size σ decrease, but the value of dg increases. The decrease in the initial particle diameter leads to the reduction of M0 and σ, and the increase in dg. With the increase in the Reynolds number, particles have few chances of collision, and hence the coagulation rate is reduced, leading to the increase in M0 and σ, and the decrease in dg.