Control of the Particle Size of Submicron HMX Explosive by Spraying in Non-Solvent

Preparation and characterization of cyclotetramethylene tetranitramine (HMX; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) submicron particles by spraying in non-solvent technology at different process parameters was investigated in this article. The results indicated that the process parameters, such as addition of surfactant, slurry, and anti-solvent temperatures; compressed air flow rate; slurry flow rate; stirring the anti-solvent; and nozzle diameter played important roles in controlling the performance of HMX submicron particles, such as particle size, size distribution, etc. The produced HMX particles by spraying in a non-solvent method were identified and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results showed that this method is simple for micronization of energetic materials and would be an effective method for large-scale preparation of submicron particles of HMX explosive. Finally, the optimum condition for the preparation of fine powder of HMX by spraying in a non-solvent method was proposed.     

Preparation and Characterization of Nano-CL-20 Explosive

Nano-CL-20 was prepared via precipitative crystallization by spraying a solution of CL-20 in a solvent (ethyl acetate) into a nonsolvent (isooctane). Scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) were used to characterize the appearance and the size of the particles. The results revealed that nano-CL-20 particles have the shape of spheres or ellipsoids with an average size of 95 nm. Due to their small diameter and high surface energy, the particles tended to agglomerate. Impact sensitivity of nanosize CL-20 was decreased in comparison to micrometer-size CL-20.     

Mathematical modeling of moisture and solute diffusion in the cylindrical green bean during osmotic dehydration in salt solution

In this study, mass transfer during osmotic dehydration of cylindrical cut green beans in salt solution was investigated. The osmotic solution concentrations used were 10%, 20% and 26.5% (w/w) NaCl, osmotic solution temperatures used were 30 °C, 40 °C and 50 °C, the solution-to-green bean mass ratio was more than 20:1 (w/w) and the process duration varied from 0 to 6 hr. A two-parameter mathematical model developed by Azuara et al. (1992) was used for describing the mass transfer in osmotic dehydration of green bean samples and estimation of the final equilibrium moisture loss and solid gain. Effective radial diffusivity of moisture as well as solute was estimated using the analytical solution of Fick's second law of diffusion in the cylindrical coordinates. For above conditions of osmotic dehydration, moisture and salt effective diffusivities were found to be in the range of 1.776 × 10⁻¹⁰-2.707 × 10⁻¹⁰ m²/s and 1.126 × 10⁻¹⁰-1.667 × 10⁻¹⁰ m²/s, respectively. Moisture and solute distributions as a function of time and location in the radial direction were plotted by using the estimated equilibrium moisture and solute concentrations and also moisture and solute diffusivities.     

Mechanical and thermal stresses in a functionally graded rotating disk with variable thickness due to radially symmetry loads

Rotating disks have many applications in the aerospace industry such as gas turbines and gears. These disks normally work under thermo mechanical loads. Minimizing the weight of such components can help reduce the overall payload in aerospace industry. For this purpose, a rotating functionally graded (FG) disk with variable thickness under a steady temperature field is considered in this paper. Thermo elastic solutions and the weight of the disk are related to the material grading index and the geometry of the disk. It is found that a disk with parabolic or hyperbolic convergent thickness profile has smaller stresses and displacements compared to a uniform thickness disk. Maximum radial stress due to centrifugal load in the solid disk with parabolic thickness profile may not be at the center unlike uniform thickness disk. Functionally graded disk with variable thickness has smaller stresses due to thermal load compared to those with uniform thickness. It is seen that for a given value of grading index, the FG disk having concave thickness profile is the lightest in weight whereas the FG disk with uniform thickness profile is the heaviest. Also for any given thickness profile, the weight of the FG disk lies in between the weights of the all-metal and the all-ceramic disks.     

Transient and thermal contact analysis for the elastic behavior of functionally graded brake disks due to mechanical and thermal loads

In this paper, the transient and contact analysis of functionally graded (FG) brake disk is presented. The analysis was carried out using ANSYS parametric design language (APDL). The FG brake disk is made of metal–ceramic material. The material properties vary in radial direction with the values from full-metal at the inner radius to that of full-ceramic at the outer radius. In the analysis, FG brake disk is in contact with one pure pad disk and coulomb contact friction is considered as heat source. The non-dimensional results are obtained for specific value of grading index (n = 1) by considering different material property divisions of 25, 50, 100 and 200. The results presented are for the pressure distribution, total stress, pad penetration, friction stress, heat flux and temperature during contact, for different values of contact stiffness factor, F_kn, which depends on the property gradation of FG brake disk with 200 material property divisions. The results show that the contact pressure and contact total stress increase with increasing values of F_kn, and hence it can be concluded that gradation of the metal–ceramic has significant effect in the thermomechanical response of FG brake disks.     

Thermo elastic analysis of functionally graded rotating disks with temperature-dependent material properties: uniform and variable thickness

A thermo elastic analysis is presented for axisymmetric rotating disks made of functionally graded material (FGM) with variable thickness. Material properties are assumed to be temperature-dependent and graded in the radial direction according to a grading index power law distribution. The temperature field considered is assumed to be uniformly distributed over the disk surface and varied in the radial direction. Semi-analytical solutions for the displacement field are given for solid disk and annular disk under free-free and fixed-free boundary conditions. The effects of the thermal field, the material grading index and the geometry of the disk on the displacement and stress fields are investigated. Results of this study emphasize on the crucial role of the temperature-dependent properties in a high temperature environment. A comparison of these results with the reported ones in the literature that is temperature-dependent versus temperature-independent suggests that a functionally graded rotating disk with concave thickness profile can work more efficiently than the one with uniform thickness irrespective of whether the material properties are assumed to be temperature-dependent or temperature-independent.     

Conversion of syngas to liquid hydrocarbons via a sorption-enhanced dual bed reactor

Fischer–Tropsch synthesis (FTS) plays an important role in the production of clean liquid transportation fuels, chemicals, and other hydrocarbon products. This study proposes a novel dual bed configuration of FTS reactor in which Zeolite 4A, with the composition of Na₁₂ (Si₁₂Al₁₂O₄₈)?27H₂O, is considered as water adsorbent inside the first reactor. In the second converter, the heat of reaction is used to pre-heat the synthesis gas to the first bed. The simulation results show an enhancement in the gasoline production, a main decrease in undesirable product formation (CO₂ and CH₄), and a favorable temperature profile along the proposed concept rather than the conventional reactor. This paper shows how the concept of in-situ water adsorption is feasible and beneficial for dual bed FTS.     

Simultaneous heavy paraffin dehydrogenation and hydrogenation of nitrobenzene in a linear alkyl benzene plant

In the current study, a novel thermally coupled reactor with radial-flow pattern named as Radial Flow-Coupling Reactor (RF-CR) is modeled for heavy paraffin dehydrogenation. In this novel structure, the cross-section area of the Radial Flow-Tubular Reactor is sliced into some subsections. The necessary heat for heavy paraffin dehydrogenation in the endothermic side is supplied by the catalytic nitrobenzene hydrogenation in the exothermic side. The results of modeling represent 12.4 tons per day enhancement in the olefin production rate in comparison with non-coupling configuration using the same catalyst loading and duty. Besides, aniline as an additional valuable product is produced ～17.45 tons per day in exothermic side of RF-CR.     

Investigation of the filtration rate of silica in aluminum fluoride production from silicic acid

The effect of some influencing parameters such as temperature, initial concentration of flusilicic acid, rate of addition of Al(OH)₃ powder, agitation speed and aging time of slurry and their mixed effects on the filtration rate of silica precipitates have been investigated. Moreover, a suitable model is presented to describe the formation mechanism of aggregated silica precipitates which can well explain the effect of different factors on the filtration rate of the silica precipitates.