Analysis of powder behaviour in bin blending processes at different scales using DEM

Obtaining a desired content uniformity with satisfactory flowability is one of the main challenges during blending process of the pre-mixture with lubricants. In this study, Discrete Element Method (DEM) simulations were implemented to examine blending time and mixing behaviour during the blending process on the lab and industrial scales. The main goal was to investigate the possible influence of operational conditions on the blending behaviour and the change in powder cohesivity during the scale-up process. The effects of rotational speed and filling mass on the particles' travelled distance, velocity, shear stress and blending time were studied in the simulations. Based on the simulations, blending time and particle exposure to shear during the blending process were calculated for different scales. It was observed that the system's mass significantly influences them, and the effect of rotational speed could be neglected. The novelty of this paper is connecting particle exposure to shear from DEM to the flow function coefficient (ffc) of powder from experiments. It was done to define a critical range of exposure to shear that changes the powder flowability in different scales.     

Study of powder flow patterns in a Couette cell with axial flow using tracers and solid fraction measurements

We present different aspects of dense granular flows in a Couette geometry using a variety of particulate materials with shape and size distributions. Tracer studies point to an apparent coupling of particle size with flow and stress field gradients. While there is a clear industrial motivation to use “real” materials as a means to expand basic physical and engineering research in granular dynamics, the current study suggests additional academic motivations. Indeed, particles with distributed characteristics uncover rich interactions between flow and stress fields that might otherwise go un-noticed with model materials such as spherical glass beads. Distribution of size and shape play a strong role in how stress is transmitted in granular media (Kheiripour Langroudi et al. in Powder Technol 203:23–32, 2010) and how particle pattern arrangements evolve. Direct solid fraction measurements, using a capacitance probe, show that dense particle flows exhibit significant variations in solid fraction in both sheared and stagnant layers. Furthermore, these measurements also show different dependence of the solid fraction on shearing rate: solid fraction decreases in sheared layers and increases in stagnant layers as the shear rate is increased. From these results the thickness of the shear band could be estimated and was found to vary as a function of particle shape and the roughness of the container walls. The main result is that shear stress (or torque) (see also Kheiripour Langroudi et al. in Powder Technol 197:91–101, 2010) and solid fraction profiles depend on particle shape and whether or not an extra degree of freedom in their movement is provided so that the system can dilate under various shear states in the Couette cell. This extra degree of freedom is assured in the present experimental work by allowing a slight axial outflow from the Couette device while the driven shear fields are in the radial and tangential directions.     

Three-dimensional measurement of a gas flow temperature field using far-infrared band CT techniques

Emission spectral tomography (EST) can be utilized to reconstruct three-dimensional (3D) physical parameter distributions of gas flow fields. Mostly, the radiant energy of the visual and near-infrared bands is received by a video camera in EST, so it is difficult to examine a low/medium-temperature gas flow field by normal EST. However, the far-infrared radiant energy of a low/medium-temperature gas flow field is strong enough to be received by a far-infrared detector. Based on EST, a far-infrared band computed tomography (FICT) approach is proposed that focuses on far-infrared spectral emission and band emission tomography. Both low- and medium-temperature blackbody furnaces were adopted to calibrate the relation between infrared thermal image intensity and radiant exitance. The 3D temperature reconstruction of an alcohol blow lamp was carried out. According to the results of multiple measurements, the relative error of the FICT approach is less than 20%. The experimental results prove the feasibility of the FICT approach.     

两种不同结构空调器轴流风机内流及性能分析

应用Navier-Stokes方程和RNGκ-ε湍流模型对空调器用轴流风机系统的内流特性进行三维数值模拟。针对匹配同一室外机时出现的不同叶片数目的叶轮,采用数值模拟与外部性能实验相结合的方法,对不同结构的两/三叶片风轮使用时的内部流场及气动性能进行详细分析。实验分析结果显示,两/三叶片叶轮各具特点,三叶片风轮匹配室外机时,风轮出口的轴向速度变化梯度较小,且气流扰动较小,能够有效地降低风机的相对湍流强度,改善气动噪声,实现降低噪声2.2dB（A）。而两叶片风轮用材少,质量轻,电功率消耗比三叶片风轮降低3.25%-6.06%,表明其具有良好的节能效果。     

Analysis of powder flow and in-system rheology in a horizontal convective mixer with reclining blades

A prototypal convective mixer, designed and built for this work, allows investigating powder rheology under various geometrical configurations. The configuration chosen here is a horizontal vessel with four rectangular blades. Two blade inclinations (0–33°) and three filling ratios are studied for two powders of different kind: a free-flowing powder (semolina) and a cohesive powder (lactose). For the smaller agitation speeds, the flow regime of the powder is rolling and is characterized by surface powder avalanches. For greater agitation speeds, the flow regime is cataracting, with particle projections that follow the blade movement. These flow regimes are identified for both powders and do not depends on the filling ratio. Rheological measurements evidence that the blade inclination has little impact on the mechanical power needed to stir the free-flowing powder. It has an impact observable on cohesive powders, especially for high filling ratios. A correlation between the power number and the Froude number is established and compared to previous results obtained on a different technology. It is of the form: N_p?=?a.F_r^b. The dependencies of the coefficients a and b on the powder type and on the flow regime are quantified.     

A study on defect controlled morphology of Organic/Inorganic composite nanofibers with different heat flow rates

One dimensional nanofibers of organic and inorganic materials have been used in filters, optoelectronic devices, sensors etc. It is difficult to obtain ultra fine fibers of inorganic materials having lengths in the order of millimeter as they tend to break during formation due to thermal and other mechanical stresses. In this study, we have investigated the mechanism to prevent the defect formation and the breaking ZnO nanofibers by using optimized heat flow rates. ZnO nanofibers were obtained by heat treating the PVA composites fibers formed by electrospinning. The morphology and structural characteristic of prepared samples were investigated by Scanning electron microscopy and X-ray diffraction. It was found that the morphology of the composite and annealed nanofibers could be influenced by the concentration of the polymer content and heat flow rate during thermal treatment respectively. A lower concentration favors the formation of defects along the fiber and the number of defects reduces when the concentration is increased. The reasons for the formation of defects and their reduction, and the observed structural changes of ZnO nanofibers during heat treatment are also discussed.     

Numerical study of flow field in new design cyclones with different wall temperature profiles: Comparison with conventional ones

In this paper, numerical study of flow field in the new design cyclones with five different wall temperature profiles are investigated. The new design cyclone is based on the idea of improving cyclone collection efficiency and pressure drop by increasing the vortex length. In this paper, the five wall temperature profiles are as follows: (A) cooling with uniform distribution, (B) without temperature change, (C) heating with uniform distribution, (D) incremental linear heating, (E) reduction linear heating. Results are compared in new design and conventional cyclones. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW).Results show that generally, heating the bottom zone of the cyclones can improve the collection efficiency and reduce the pressure drop while heating the top zone of the cyclones marginally affects the flow field. Moreover, cooling the cyclones reduces the efficiency and causes a higher pressure drop. Among five different wall temperature profiles, C and E profiles can increase the efficiency about 8% and profile C reduces the pressure drop by about 9%. The mentioned values in different conditions including particle diameter, flow rate, etc. can be different.     

Scheduling of a no-wait two-machine flow shop with sequence-dependent setup times and probable rework using robust meta-heuristics

This paper investigates the scheduling of a no-wait two-machine flow shop considering anticipatory sequence-dependent setup time and a probable rework for both machines to minimise mean completion time (MCT). To tackle the problem, a robust meta-heuristic algorithm, namely the adapted imperialist competitive algorithm (AICA), has been proposed and is compared with two common and popular meta-heuristic algorithms (i.e. genetic algorithm (GA) and population-based simulated annealing (PBSA)). In this study, we have adapted a traditional imperialist competitive algorithm (ICA) with some considerable changes. First of all, a revolution procedure is added to the algorithm for imperialists similar to colonies. Furthermore, the revolution is only performed when the new solution is better than the previous solution, and chief among them for preservation of premature convergence, the concept of global war is applied. However, the performance of AICA is sensitive to the choice of the best parameter values. Thus, to obtain optimal performance, a comprehensive calibration methodology called response surface methodology is employed to obtain the best combination of parameter values. In order to evaluate the effectiveness and efficiency of proposed algorithms, several test problems are generated and the results obtained from algorithms are then compared in terms of relative percentage deviation. Computational experiments indicate that AICA outperforms GA and PBSA in the MCT performance measure, and GA outperforms the others in terms of computational time.     

The effect of submergence ratio on flow pattern around short T-head spur dike in a mild bend with rigid bed using numerical model

Spur dikes are hydraulic structures frequently applied to protect rivers’ banks. Since flow pattern around a spur dike located in a rivers’ bend is particularly complicated due to the existence of secondary flow and helical flow, the effect of submergence ratio on flow patterns around a short T-head spur dike located in a 90° bend has been monitored numerically in this study. The numerical data are verified with experimental data obtained under non-submerged conditions, which indicate the numerical results are in accordance with experimental data. In this research, the numerical simulation based on various submergence ratios is done using FLOW-3D software to analyze. The results showed an increase in dimensions and the number of vortices associated with an increase in submergence ratio so that for the amount of 50% submergence, two vortices form around outer wall and an area downstream of the wing of spur dike, at bed level. Moreover, the length and width of separation zones were estimated to be 1.6 and 1.5 times larger compared to non-submerged condition, respectively.