جستجوی مقالات مرتبط با کلیدواژه "particle size distribution" در نشریات گروه "مکانیک"
تکرار جستجوی کلیدواژه «particle size distribution» در نشریات گروه «فنی و مهندسی»-
Computational particle fluid dynamics method is utilized to study the influence of polydisperse and monodisperse particle size distribution, fuel addition, and biomass mixing ratio on the gas-solid flow behavior in a pilot-scale circulating fluidized bed (CFB). Numerical results show that a polydisperse system with different particle sizes can enhance the fluidization quality and the uniformity of the particle volume fraction in comparison with a monodisperse system with uniform particle sizes. When fuel is present in the CFB, the disturbance at the circulation inlet is eliminated and the particle aggregation effect at the wall is reduced. Furthermore, the particle volume fraction, pressure, and particle velocity distributions change only slightly as the biomass increased from 0% to 20% or from 50% to 100% of the total fuel mass. However, as the biomass ratio increases from 20% to 50%, the pressure drop in the riser decreases and the back-mixing degree at the riser wall weakens.Keywords: CPFD, Hydrodynamics, Circulating Fluidized Bed, Particle Size Distribution, Multiple Particles Mixing
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The technique of numerical inversion of the Laplace transform is applied to solve the population balance equation (PBE). The model considers the dispersed phase systems in which nucleation and heterogeneous condensation are present. The studied phenomena model corresponds to a nonlinear integro-partial-differential equation. Test cases are solved considering two different collision mechanisms, the first-order removal mechanism and the effect of simultaneous coagulation and growth. Numerical results are compared with the analytical solution and with the literature. Based on these results, the technique applied in this work demonstrates to be a tool to solve problems in particulate systems, particularly for aerosol modeling where coagulation is the most important inter-particle mechanism affecting the size distribution.Keywords: Aerosol modeling, numerical inversion of the Laplace transform, Particle size distribution
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The synergetic effect of amine functionalized multiple graphene layers (AMGL) and multi-walled carbon nanotube (AMWCNT) nano-fillers mixed with epoxy resin is investigated on the particle size distribution (PSD) and tensile properties of hybrid composites. The hybrid composites with an equal ratio of nano-fillers at a weight percent of 0.25, 0.50, 1, and 2 wt % are fabricated. The particle size analysis (PSA) is performed by the dynamic light scattering (DLS) technique and image analysis (IA) method; both verify PSD for composites. This is further verified by the analyses of scanning electron microscopy (SEM) images using Image J software. The optimum composite particle size of 6.8 µm and homogeneous mixture with a poly-dispersity index (PI) of 0.74 is investigated for a sample having filler content of 0.5 wt %. Tensile stress and elastic modulus is also found to be maximum at 0.5 wt %, which is 49.91 MPa of 2302 Mpa, respectively. The chemical composition of composite affecting its PSD is characterized by energy dispersive X-ray (EDX) process. Dimensional analysis of particle size in the domain of epoxy matrix provides deep insights to the researchers and may also provide them a direction for selecting an appropriate material for a particular application.Keywords: Particle size distribution, Hybrid composite, Image analysis, Tensile strength, Elastic modulus
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This paper summarized some common grading curves of ballast layers and found that the content of 16-32 mm ballast particles ("middle-size particles" in this paper) had a significant effect on the direct shear performance of the ballast layer. In this paper, the direct shear tests of the ballast layers with different contents of middle-size particles were reproduced using the discrete element method (DEM). Two different compactions of the ballast samples were used, and the reasons for the changes of shear strength of the ballast layers with different size distributions were analyzed from macroscopic and microscopic perspectives. The results showed that the strengthening effect of the ballast due insertion of middle-particles could only be observed for normally compacted ballast, whereas the same insertion with fully compacted ballast would decrease the shear strengths properties. The fully compacted ballast is subjected to the dilation. The reason of the strengthening effect for the normally compacted ballast were the contraction and dilation processes. Insertion of the middle-size particles up to 20-30% at most increase the dilation processes. Thus, the results show that the ballast layers with conventional narrow particle size distribution (narrow PSD) have higher shear strength than wide range particle size distribution (wide range PSD) if the ballast is good fully compacted. Additionally, it should be noted that the number of small particles will increase during the lifecycle of the ballast layer due to corner brakeage and the external contamination. Moreover, the drainage aspects of the wide range PSD should be considered. Therefore, the excessive insertion of middle-size particles is not justified.Keywords: railway, fines-free ballast, Particle size distribution, direct shear test, discrete element method
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Particle size normally varies over wide ranges in any commercial transportation of solids through the pipeline. In the present study, the three-dimensional numerical modeling of the conventional 90o bend transporting multi-sized particulate slurry using granular Eulerian-Eulerian model is performed. The mixture of water and six different sizes of zinc tailing particles ranging from 37.5 µm to 575 µm are considered. The effect of variation in velocity and concentration on pressure drop and flow field of the multi-sized particulate slurry is investigated. The simulations are performed in the velocity range of 2.25 m/s to 3.5 m/s for the weighted solid concentration range of 9.82 to 44.26%. The comparison of pressure drop data from the available experimental results and the present numerical modeling with multisized particulate slurry shows maximum deviation within ±6%. Further, the suspension behavior of different size particles in the multi-sized slurry flow inside the bend is analyzed with the variation in the flow velocity and solid concentration. The particles of different size in the multi-sized slurry showed different suspension characteristics.
Keywords: CFD, Eulerian-eulerian model, Multi-sized particle, Bend, Particle size distribution -
در معادن زغال سنگ، انفجار مخلوط گرد زغال و گاز متان در سال های اخیر باعث اثرات فاجعه باری شده است. اشتعال پذیری و فعالیت های شیمیایی گردوغبار مربوط به اندازه ذرات است. لذا، مکانیسم انفجار گردوغبار زغال سنگ به طور گسترده ای توسط اندازه ذرات زغال سنگ کنترل می شود. در این مقاله، اثر اندازه ذرات گردوغبار زغال سنگ بر روی شدت انفجار گردوغبار زغال سنگ با استفاده از آزمون انفجار در محفظه 2 لیتری مورد بررسی قرار گرفت. نمونه های زغال سنگ مورد آزمایش از سه معدن از منطقه زغالی مهم کشور (البرز شرقی، البرز مرکزی و طبس) جمع آوری شده و به صورت گرد زغال در هشت مقیاس مختلف (149، 125، 105، 74، 63، 53، 44 و 37 میکرون) آماده سازی شده است. نتایج آنالیز سرندی نشان می دهد که تقریبا تمام نمونه گرد زغال های انتخاب شده حداقل غلظت مطلوب انفجار (250 گرم بر متر مکعب) را دارند. شدت انفجار هر نمونه با اندازه گیری حداکثر فشار، حداکثر میزان افزایش فشار و شاخص انفجار طی آزمایش های متعددی مورد ارزیابی قرار گرفت. در این تحلیل، تمامی آزمایش ها در فشار 1/5 بار و دمای اولیه 25 درجه سانتی گراد انجام شد. طبق نتایج به دست آمده، ذرات گرد زغال با ابعاد 44 و 37 میکرون نسبت به سایر ابعاد شاخص انفجاری بالاتری دارند. بنابراین، پارامترهای حداکثر فشار انفجار و حداکثر نرخ افزایش فشار با کاهش اندازه و پراکندگی ذرات، روند افزایشی را در شدت انفجار نشان می دهد. حضور ذرات ریز باعث افزایش سطح موثر و در نتیجه باعث افزایش سرعت انفجار و نرخ ناپایداری می شود که موجب شتاب فرایند انفجار گرد زغال می شود. بنابراین، طبق نتایج به دست آمده، در فرایند بررسی انفجار گرد زغال، علاوه بر غلظت گرد زغال، اندازه ذرات نیز بایستی درنظر گرفته شود. نتایج به دست آمده در این مکانیسم نه تنها در تحقیق و پیشرفت دانش فرایند انفجار گرد زغال مفید است، بلکه در انجام اقدامات لازم برای جلوگیری از انفجار گرد زغال سنگ در معادن زغال سنگ نیز موثر است.
کلید واژگان: گردوغبار زغال سنگ, محفظه احتراق, شاخص انفجار, توزیع اندازه ذرات, پارامترهای انفجاریIn this study, the effect of coal dust particle size on the intensity of coal dust explosion was investigated using an explosion test in a 2-liter chamber. Samples of coal have been collected from various coal mines in the country and they are used for coal dust preparation. To determine the index of explosion capability (KST), the distribution of the explosion intensity of each sample should be evaluated by measuring the maximum pressure (Pmax) and the maximum explosion pressure rise rate (dp/dtmax) in different experiments. Coal dust particles at constant concentrations and different sizes (149µm, 125µm, 105µm, 74µm, 63µm, 53µm, 44µm, 37µm) were evaluated. The results of the sieving analysis show that almost all samples of the prepared coal dust have a minimum optimum explosive concentration (250 g/m3 ). In this analysis, all tests were carried out at 1.5 bar and the initial temperature was 25 °C. According to the results, coal dust particles with dimensions of 44 and 37 microns have higher explosive index than other dimensions. Therefore, both parameters of maximum explosion pressure (Pmax) and the maximum explosion pressure rise rate (dp/dtmax) show an increasing trend with decreasing particle size. Also an increasing concentration of coal dust shows an increasing trend at the first and then a decrease in the intensity of the explosion. The presence of small coal particles increases the effective level, thus increasing the explosion rate and the rate of instability, which accelerates the process of coal dust explosion. Therefore, according to the results obtained in the process of checking coal dust explosion, in addition to the inherent characteristics of coal dust, particle size coal dust should also be taken into account. The results obtained in this mechanism are useful not only in the research and development of knowledge of coal dust blasting processes, but also in taking the necessary measures to prevent the explosion of coal dust in coal mines.
Keywords: coal dust, combustion chamber, explosion index, particle size distribution, explosive parameters
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