جستجوی مقالات مرتبط با کلیدواژه "توزیع اندازه ذرات" در نشریات گروه "مهندسی شیمی، نفت و پلیمر"

The composite solid propellant based on the three main components AP/Al/HTPB containing 19 wt.% of Aluminum has special physical, mechanical and combustion properties due to the high solid load. Increasing the solid load is done in order to improve the performance properties of solid propellant, such as specific impulse and volume combustion heat, which are requirements of space missions. On the other hand, increasing the solid load (reducing the binder system) leads to limitations in the production process, such as increasing the viscosity, reducing the pot life, and reducing the processability of the propellant slurry, and also reducing the quality of other propellant properties such as mechanical properties. In this study, the effect of ammonium perchlorate (AP) as one of the key parameters on the physical, mechanical and combustion properties of composite solid propellant has been studied experimentally. The results showed that by reducing the average size of AP particles, the density does not change significantly, the tensile strength and modulus increase and the elongation decreases, and the burning rate of the propellants increases slightly. The average density of propellants is 1792 kg/m3, For the propellant sample with the NCO/OH ratio = 0.88 and the mass average AP particle size equal to 251 μm, the ultimate tensile strength is 0.523 MPa, the maximum elongation is 35.1%, the modulus is 1.5 Mpa, and the burning rate at 65 bar is equal to 6.9 mm/sec.

Polymer-bonded explosives are widely used in defense and commercial industries. In this type of explosive, very high amounts of explosive crystals (about 90% by weight) are surrounded by a polymeric binder (about 10%), which leads to a decrease in sensitivity and a significant increase in safety during application and storage. These mixtures are molded in different ways, such as pressing, casting, extrusion, and injection. Studying the rheology of these mixtures with a high percentage of solid loading leads to finding the appropriate quality control method at different production stages. The first step was to review studies on alternatives to simulating explosive rheological behavior, such as dechlorane, calcium carbonate, sugar, etc. The general behavior of simulated mixtures, such as yield stress, shear rate dependence, time dependence, etc., is compared with original explosive. The results showed that despite the similarity in some rheological behaviors, it is impossible to predict and study all the rheological behaviors of polymer-bonded explosives using simulating materials. This paper discusses factors affecting the rheology of polymer-bonded explosives, such as particle size distribution, modification of explosive crystal surfaces, and plasticizer. A review of scientific sources showed that using a wide distribution of explosive crystal particles compared to a narrow distribution led to a significant reduction in viscosity and dependence on shear rate and time. The absence of strong interactions between crystal particles and polymer binder leads to no observation of quasi-solid behavior even in 85% by weight of explosive crystals such as octogen in hydroxyl-terminated polybutadiene

One of the challenges in emulsion polymerization over the past two decades has been how to increase the solid content of polymer latex. Compared to conventional latex, high solid content latex (HSC) has a large volume fraction of the monomer dispersed phase, even more than 70% by weight. Increasing the concentration of polymer in latex, has important advantages such as increasing the space-time efficiency of the reactor, reducing the film formation and drying time, as well as reducing its storage and transportation costs. Conventional emulsion polymerization, mini-emulsion polymerization, self-emulsification polymerization, and concentrated emulsion polymerization have all been used to prepare HSC latexes, and good results have been reported in recent years. Production of HSC latexes in a reproducible manner requires precise control of the particle size distribution. To obtain a solid content above 60% or 70% by weight, the particle size distribution must be quite broad or multimodal. In addition, viscosity of HSC latex is highly sensitive to particle size distribution. In this study, the advances of the last few years, which are mainly in the preparation processes of such latexes and their applications are briefly reviewed.

Organic deposits particularly, asphaltenes cause detrimental effect on the petroleum industry, because it causes to decreases produced oil and clogging the oil facilities. Generally, dispersants and inhibitors or asphaltene solvents are using for chemical controlling of asphaltene precipitation. The asphaltenes content in crude oil are stable under the certain conditions, but there is no certainty about the stability of system in another operational condition. So it is important to study the kinetics of asphaltene settling and deposition. In this work, we investigated the kinetics effect of the three dispersants on the stability of asphaltene aggregates using turbidity measurement and particle size distribution methods. Turbidity measurement showed as the dispersant strength rises;moreover, the turbidity of unstable sample containing dispersant less declines versus time. Asphaltene particle size distribution measurements showed that adding dispersant decrease the average diameter of asphaltene aggregates. Also, in this study the kinetics of asphaltene settling using power law model and the relations of the diluted suspensions was developed. The result of model showed the settling velocity of asphaltene has been decreased by adding dispersants.

The particle size distribution (PSD) is one of the most important parameters of emulsion polymerization latexes. This parameter affected the rheological and optical properties, adhesion, film formation and mechanical strength of latexes. Therefore, the modeling of PSD is of utmost importance in terms of application and mechanistic studies. Dynamic evolution of PSD is described by a set of population balance equations which involved various phenomena such as nucleation, growth, and coagulation. The extensive application and especially annually massive production of poly(butylacrylate) and polybutadiene produced by emulsion polymerization, highlights the significant of modeling these processes, which could resulted in better mechanistic knowledge and tailor-made polymer materials. In this paper, a mechanistic model based on population balance equations is developed for butyl acrylate and butadiene emulsion polymerization in a batch reactor. This model is used to predict the evolution of particle size distribution and the finite volume method as a precise technique is used for discritizing PBEs. The simulation results compared with the measured values during the evolution of conversion and average particle diameter for different initial surfactant concentrations.

Water injection process has inevitably been scaling process associated. One of the important discussions in this field is to evaluate formation damage. In the current paper, the effect of some parameters on permeability reduction is investigated. In this study, the fracture effect on formation damage in reservoir rock is studied using a physical model. In addition, injection rate and pressure effects are considered in the physical model. Rock structure and heterogeneity restrict investigating formation damage phenomena. We selected some core samples in one of the oil fields injecting water in aquifer for the simulation of the physical model in laboratory. We tried to perform different scenarios using injected water sample in core flooding process. Although, permeability reduction is observed in no fractured samples, injection pressure increasing is not concluded in injection process in the fractured sample. On the other hand, fracture creation in samples, especially the sandstone sample with weak cementation, can be cause of particle movement or formation damage transfer through reservoir (far from injection well). This subject create problems later after injection especially in production wells where they depend on more parameters e.g. rock structure, texture, pore and particle size distribution, and reservoir heterogeneity.

In the current study, using experimental data from literature, an empirical correlation of phenanthrene solubility in the mixture of supercritical CO2 and toluene and also another equation to correlate its supersaturation rate with pressure (antisolvent addition rate were determined. Afterwards, the kinetic modeling of supercritical antisolvent crystallization process using the Population Balance Equation (PBE) method was fulfilled. Lax-Wendroff and Crank- Nicholson as a combinatorial numerical algorithm was used to solve the PBE. The simulation was performed at 40C and pressure range between 0.34 and 5.63 MPa by changing the main operating parameter, the antisolvent addition rate (system pressure). To determine nucleation rate, crystal growth rate, crystal size distribution, and mean size, discretization method was used and a numerical solution to the PBE was performed. The results showed that drastic decrease of solubility (mole fraction) from 0.27 to 0.16 was the result of pressure increase from 0.1 to 0.34MPa which followed by high supersaturation generation from 1 to 1.6. By adding the antisolvent, the highest supersaturation was at 6 Mpa. The primary nucleation was superior at 0.3 MPa while the second nucleation increased by the antisolvent addition and the solute precipitation and reached the maximum at 6 Mpa. The particle size distribution showed to have one pick located within small sized particles (class sizes lower than 20) upto 1.79 MPa. By the pressure increase a second pick gradually was appearing and the diagram was changing to binomial.

A major problem in the chemical industries is the separation of waste material produced in the chemical processes. There has been a number of attempts to find a solution to this problem. One of these methods is sedimentation; however, the major drawback of this method is the low velocity of natural sedimentation. By adding particles with larger mass to this system, waste material could be absorbed on their surface and thus increasing the removing rate of the waste material. For this purpose, surface of massive material should be modified for adsorption of the waste material. However, sedimentation velocity is a function of hydrodynamic forces, particle-matrix interaction and particle-particle interaction so that change in surface properties can affect the sedimentation velocity. In this study, a model is developed to predict the effect of particle matrix interaction on sedimentation velocity. A method is also devised to measure sedimentation velocity and to obtain an estimate of particle size distribution. From this study, it is concluded that particle-matrix interaction could be used to increase sedimentation velocity.

In this research, a lithography ink formulation based on the Maleic and Alkyd resin has been prepared and its rheological parameters such as viscosity vs. shear rate, thixotropy cycle, storage and loss modules and dynamic viscosity were studied. It was observed that viscosity values augmented severely by increasing the pigments concentration and reducing the particle size distribution. Time dependence thixotropy values were significant in samples containing small particle size and high pigment concentration. Structural networking and association of carbon black particles as well as particle-particle and particle-binder interaction are reasons for this behavior. Storage and loss modules were increased with reduction of particle size and/or increasing of pigment concentration. Besides, the differences between dynamic parameters in low frequencieswere obvious. J. Color Sci. Tech. 4(2010), 91-103© Institute for Color Science and Technology.

Particle size distribution measurement tools are generally offline, expensive and slow. So, it is very important to design an observer with the ability to estimate particle size distribution in emulsion polymerization. In this paper, a non-isothermal model based on population balance equations (Zero-one model) including nucleation, particle growth, and coagulation is chosen for estimation of particles size distribution. Then a reduced observer is presented for estimation of particle size distribution with the assumption of having free active surface material density. It is shown that in case of presence of immeasurable turbulence and modeling error, the observer’s performance is better than wide open circuit observer. In addition, by measuring conversion percentage made possible by use of density measurement, the observer performance will be enhanced. As it is hard to measure concentration of free active surface material directly, it will be measured using an electrical conduction method. The results show that in case of presence of immeasurable turbulence, performance of observer by use of electrical conduction measurement is better than wide open circuit observer, but in case of presence of modeling error, no considerable enhancement were observed compared with wide open circuit observer

Water based acrylic resins are type of resins that are used as basic material for production of paints and coatings which have desirable coating properties and environmental friendly. These advantages cause developments and increasing production of these materials, recently. In this work it was attempted to present a review on the synthesis, mechanism and properties of water based acrylic resins and effective parameters influenced improvement of the properties.According to the studied different operational parameters it is revealed that temperature, mixing intensity, rate of feeding and concentration of the monomers have significant effect on the properties of the resin such as particle size distribution, glassy transition temperature (Tg) of dry latex film, average molecular weight and morphology of the latex particles, and by adjusting these variables we can approach to desirable end-use properties.At the final part of this study, the rate of development in the world science 2002 to 2007 has been tabulated, and discussed to give an insight to the future demands of these products.