Correspondence analysis and establishment of evaluation model of classification performance indices for a turbo air classifier

The operational parameters of a turbo air classifier including feeding speed, rotor cage's rotary speed and air inlet velocity affect its classification performance directly, such as cut size, classification precision, classification efficiency, fine powder yield, particle fineness and degree of dispersion. Current methods of optimizing operational parameters and improving the classification performance of a turbo air classifier are almost single objective decision only for one of the classification performance indices. In this paper, the multi‐objective programming (MOP) model on classification performance for a turbo air classifier is established to evaluate these performance indices comprehensively and achieve optimal classification performance. To minimize the effect of repeatability within these classification performance indices, correspondence analysis is applied to determine the evaluation indices of this MOP model. According to correspondence analysis on the fine talc classification experimental data as well as the calcium carbonate classification experimental data, there is a very strong correlation between cut size and D90; there is also a very strong correlation between cut size and fine powder yield. Thus D90 and fine powder yield are filtered out and they aren't discussed in the evaluation model. The variation coefficient method is introduced to calculate weights of the evaluation function, and the dimensionless transformation method is used to eliminate the effects of different dimension. Thus, the optimal solution among the experimental data is obtained through solving the evaluation function. For the talc classification experiments, the optimal operational parameter combinations are: the feeding speed is 40 kg · h^–1, the air inlet velocity is 5 m · s^–1 and the rotor cage's rotary speed is 1200 ? min^–1. The classification performance indices are: cut size is 16.5 μm, classification precision index is 0.59, Newton classification efficiency is 57% and degree of dispersion is 2.13. For the calcium carbonate classification experiments, the optimal operational parameter combinations are: the feeding speed is 92 kg · h^–1, the air inlet velocity is 12 m · s^–1 and the rotor cage's rotary speed is 1200 ? min^–1. The classification performance indices are: cut size is 31.4 μm, classification precision index is 0.74, Newton classification efficiency is 74% and degree of dispersion is 1.27. This evaluation model avoids the limitation of evaluation for the single classification performance index and incomplete information got by the means of single factor experiment of operational parameters. It also provides the quantitative evaluating criteria for classification performance of a turbo air classifier, which offers a theoretical basis for effective production. This multi‐objective programming optimizing method and evaluation model on classification performance can be applied to other dynamic air classifiers as well.     

Classification performance comprehensive evaluation of an air classifier based on fuzzy analytic hierarchy process

The classification performance evaluation goal for an air classifier is usually limited to one of the classification performance indices including cut size, classification precision, Newton classification efficiency and degree of dispersion. This method hardly evaluates these performance indices of an air classifier comprehensively and suitably. In order to evaluate the classification performance truly and synthetically, Fuzzy Analytic Hierarchy Process is used to calculate the weights of the classification performance indices after determining the hierarchical model in the present paper. The dimensionless transformation eliminates the effect of the different dimensions. Then, the comprehensive evaluation value of the classification performance for each experiment is obtained using the linear weighted method. The maximum value corresponds to the best classification performance among these evaluation values. In the present study, a turbo air classifier is used as the classification system and talc powders are used as materials. The best classification performance indices are a cut size of 16.5 μm, a classification precision of 0.59, a Newton classification efficiency of 57%, and a degree of dispersion of 2.13. The corresponding optimal operational parameter combinations are: the feeding speed is 40 kg·h^–1, the air inlet velocity is 5 m·s^–1 and the rotor cage's rotary speed is 1200·min^–1. This assessment method avoids the limitation of evaluating a single classification performance index and the incomplete information derived from single factor experiments. Furthermore, the method also provides quantitative evaluation criteria for the classification performance of an air classifier. In the proposed method, the classification performance indices can be selected and the precedence relation matrix of Fuzzy Analytic Hierarchy Process can be set flexibly according to production requirements.     

Effect of rotor cage's outer and inner radii on the inner flow field of the turbo air classifier

The effects of rotor cage's outer and inner radii on flow field of the turbo air classifier are comparatively analyzed by numerical simulation using ANSYS-FLUENT. The results of quantitative analysis show when the rotor cage's outer and inner radii are increased, the tangential velocity, radial velocity and upward axial velocity decrease in the annular region and near the entrance of the rotor cage. However, when the rotor cage's outer and inner radii are too large or too small, the tangential velocity and radial velocity will be fluctuated greatly. Moreover, the rotor cage's outer and inner radii directly influence the radial velocity distribution in the rotor cage channel. The rotor cage's outer and inner radii should not be too large or too small. Therefore, in the seven contrast rotor cage models, model 100–70 and 90–60 are selected to carry out the calcium carbonate classification experiments due to their small tangential velocity and radial velocity fluctuations and well-distribution in the rotor cage channel. The experimental results reflect the characteristics of the numerically simulated flow field in the classifier.     

CFD simulation and optimization of the flow field in horizontal turbo air classifiers

This paper mainly presents a numerical study of the gas flow in horizontal turbo air classifiers. The effect of the air-inlet direction on the performance of classifier was also investigated through powder classification experiments. The simulated results show that the vertical vortex is the dominant flow in conical part of the classifier and there exists the horizontal vortex in the classifying chamber. The tangential velocity profile resembles a Rankine vortex inside the rotor cage. The vertical vortex intensity increases with increasing the inlet air velocity, while the rotor cage speed has limited effect on the control of gas pathlines in the classifying chamber. Horizontal turbo air classifiers are divided into four quadrants according to the air-inlet direction. For classifiers in quadrants I and III, a double-layer flow with opposite directions generates around the rotor cage which causes a secondary vortex. The secondary vortex is eliminated and the airflow becomes uniform in the classifier that belongs to quadrant Π or IV. The experimental results with fluidized catalytic cracking catalysts and fly ash demonstrate that cut sizes of this classifier decrease averagely by 5 μm and 2.2 μm respectively, and the classification accuracy increases by 7.5–10.3%.     

Effect of the rotor cage chassis on inner flow field of a turbo air classifier

As the connection between the center of rotor cage and the coarse powder collecting cone, rotor cage chassis of the turbo air classifier directly influences airflow movement in the classifier. In order to study the effect of rotor cage chassis on the inner flow field of a turbo air classifier, the flow fields of four rotor cage chassis structures with different opening size are simulated and compared using ANSYS-FLUENT 17.0. The simulation results show that there is “bypass flow” phenomenon for the classifier with the open rotor cage chassis, compared with the closed rotor cage chassis. The “bypass flow” phenomenon can change the airflow velocity distribution of the annular region. For the open rotor cage chassis, its opening size has no significant effect on the flow field distribution and the airflow velocity. However, the open or closed rotor cage chassis has great effect on the flow field distribution and the airflow velocity. The calcium carbonate classification comparative experiments are carried using the open and closed rotor cage chassis structures. The experiment results show that the open rotor cage chassis can decrease the cut size, and the closed rotor cage chassis can improve the classification accuracy.     

CFD simulation and performance optimization of a new horizontal turbo air classifier

A new horizontal turbo air classifier equipped with two inclined air inlets has been introduced. The flow field and classification performance of the classifier have been investigated using CFD method and response surface methodology (RSM). Simulation results show that the flow field is composed of the primary swirling flow and the secondary upward washing air, and the uniformly distributed swirling flow occupies the classifying chamber. The tangential gas velocity reaches the maximum value on the outer surface of the rotor cage, generating strong centrifugal force for the particle classification. The discrete phase model (DPM) can predict the cut sizes, but cannot present the fish-hook phenomenon. The desirable experimental condition by targeting the cut size of 20 μm and minimizing the classifying accuracy index is, rotor speed of 1373.6 rpm, primary air volume flow rate of 261.8 m³/h and secondary air volume flow rate of 42.4 m³/h. The corresponding fine and coarse fraction loss are less than 1.42% and 7.24%, respectively. This study provides a new strategy to design the horizontal turbo air classifier.     

涡流空气分级机的分级特性

通过对重质碳酸钙和石英在CF型涡流分级机不同转速下进行分级实验,并利用计算流体力学软件对分级特性进行数值模拟。结果表明,随着转速增加,粒度d50和d90都减小,分级效率先增大后减小;在相同的参数下,不同物料的分级效果是不同的;随着转速的增加,涡流分级机流场的涡流现象增强,当转速增加到一定的程度时,出现了反流现象,使已经分离出的细粒又返回到分级区,从而影响分级机的分级效率。     

Modeling and multi-objective optimization of an M-cycle cross-flow indirect evaporative cooler using the GMDH type neural network

A model was presented to determine product air properties of dew-point indirect evaporative coolers with cross flow heat exchanger, M-cycle CrFIEC. In this regard, the most powerful statistical method known as the group method of data handling-type neural network (GMDH) was employed. Then the developed GMDH model was implemented for multi-objective optimization of a prototype CrFIEC and the average annual values of coefficient of performance (COP) and cooling capacity (CC) were maximized, simultaneously, while working to air ratio (WAR) and inlet air velocity were decision variables of optimization. Accordingly, features of the proposed system were optimized at twelve diverse climates of the world based on Koppen–Geiger's classification. Results implied that the optimized inlet air velocity for all climates varied between 1.796 and 1.957 m.s⁻¹, while the optimum WAR was 0.318 for “A” class cities. Moreover, the mean values of the COP and CC were improved 8.1% and 6.9%, respectively.     

Effects of Process Variables on the Size,Shape, and Surface Characteristics of Microcrystalline Cellulose Beads Prepared in a Centrifugal Granulator

Preparation of microcrystalline cellulose (MCC) beads with a laboratory-scale centrifugal granulating apparatus was studied, and the pharmaceutical quality of the beads was characterized with respect to the subsequent drug layering. Five process parameters of potential importance, including rotor rotation speed X₁, slit air X₂, spray air pressure X₃, spray air rate X₄, and height of nozzle setting X₅, were evaluated using a fractional factorial design (FFD 2^5-2) as the experimental design. The responses evaluated were expected yield, mean size, size distribution, shape characteristics (including roundness, circularity, elongation, rectangularity, and modelx), and friability. All five process parameters studied were found to have an influence on the selected properties of the beads, but the effects of rotor rotation speed, slit air flow rate, and spray air rate were statistically significant (p <. 05). The effect of the rotor rotation speed was found to be the most potent on all the responses studied. The results also show some significant interactions between the parameters tested. The most significant interactions were between rotor rotation speed and slit air, rotor rotation speed and spray air, and slit air and spray air.     

基于迅速分级原理的涡流选粉机分级区研究

通过分析涡流选粉机转子周围自由涡对分级过程的影响,应用迅速分级原理设计具有异形导流结构的分级区域,使进入分级区域的气流速度与转子外边缘线速度相当,消除自由涡对颗粒的干扰,颗粒可迅速进入转子叶片间的强制涡流区参与分级,实现迅速分级,减少颗粒在分级区域内的滞留时间以减少团聚。并采用RSM应力方程模型和随机颗粒轨道模型对该分级区域进行气固两相数值模拟,确定实现迅速分级的最优参数。试验表明,装有该异形导流结构的分级区有利于提高分级精度和分级效率。     

铁路轨道除沙车抛沙板参数优化

为了研究铁路轨道除沙车抛沙板参数对抛沙高度及抛沙距离的影响,提出一种离散元正交试验方法,用于优化抛沙板参数,以改善抛沙板的抛沙高度和抛沙距离。通过多因素正交试验和基于离散元法的仿真试验,分析抛沙板的转速、弯折角度、弯折位置以及前进速度对抛沙高度及抛沙距离的影响;通过灰度分析法与极差分析法对试验结果进行分析,得出最佳参数组合,并在试验平台进行试验验证。仿真结果表明,转速对抛沙高度及抛沙距离的影响最大;在抛沙板半径不变的情况下,最佳参数组合：转速为2 r/s,弯折角度为170°,弯折位置为5/6,前进速度为1 km/h。试验结果表明抛沙板参数优化后,除沙车的抛沙高度降低了8.64%,抛沙距离减小了32.3%,这说明优化后的除沙车在满足设计需求的同时既降低了能耗又减少了沙粒对挡沙板的冲击。研究结果可为轨道除沙车的研制提供理论依据。     

Effects of process variables on the size, shape, and surface characteristics of microcrystalline cellulose beads prepared in a centrifugal granulator

Preparation of microcrystalline cellulose (MCC) beads with a laboratory-scale centrifugal granulating apparatus was studied, and the pharmaceutical quality of the beads was characterized with respect to the subsequent drug layering. Five process parameters of potential importance, including rotor rotation speed X1, slit air X2, spray air pressure X3, spray air rate X4, and height of nozzle setting X5, were evaluated using a fractional factorial design (FFD 2(5-2)) as the experimental design. The responses evaluated were expected yield, mean size, size distribution, shape characteristics (including roundness, circularity, elongation, rectangularity, and modelx), and friability. All five process parameters studied were found to have an influence on the selected properties of the beads, but the effects of rotor rotation speed, slit air flow rate, and spray air rate were statistically significant (p < .05). The effect of the rotor rotation speed was found to be the most potent on all the responses studied. The results also show some significant interactions between the parameters tested. The most significant interactions were between rotor rotation speed and slit air, rotor rotation speed and spray air, and slit air and spray air.     

CXM型超细分级磨风口环气相流场的数值模拟

为探究CXM型超细分级磨风口环处结构参数与操作参数对粉碎区粉碎效果的影响,采用标准k-ε两方程湍流模型及多重参考系MRF模型对粉碎室内气相流场进行数值模拟。结果表明:在相同空气进风量及同一转速下,减小径向间隙有利于破坏物料环流层,当间隙为5～10 mm时,所形成的上升气流有助于物料的粉碎与分级。转盘转速的大小,一方面考虑转盘材质对转速的限制,另一方面应根据物料的物化特性结合生产经验确定转盘转速,以达到能量利用率最高。     

岩土工程磁力模型实验土体相似材料的研制

岩土工程磁力模型利用电磁力场来模拟重力场进行岩土工程问题的研究,模型中模型尺寸缩小n倍,重力加速度增加n倍,材料的容重、粘聚力、内摩擦角、弹性模量和泊松比等力学参数均可采用原型参数。基于正交实验设计方法研制了一种可用于磁力模型的磁敏性土体相似材料,材料选用石英砂为骨料,膨润土和双飞粉为胶结料,铁氧体为掺料。实验表明,新材料的容重为19～25kN/m2;粘聚力为0～54kPa,内摩擦角7～31°,可在地质力学与岩土工程磁力模型实验中模拟范围较广的土体材料。对相似材料进行力学实验,研究了磁粉含量与材料力学指标的变化关系。     

重质碳酸钙颗粒气流粉碎与表面改性的一体化处理

研究重质碳酸钙颗粒在气流粉碎与表面改性一体化处理过程中,改性剂溶液流量、改性剂溶液浓度、粉碎气流温度对重质碳酸钙粉出料速度、改性效果以及粒度的影响趋势。研究表明,在气流粉碎的同时进行表面改性处理,可以提高重质碳酸钙粉体的出料速度,选择最佳的粉碎与改性参数后,重质碳酸钙的粉碎出料速率由21.0 g/min提高到56.7 g/min,出料速率提高了170%,并与液体石蜡具有良好的相容性。     

Effects of mechanical activation on the parameters of talc quality for ceramics production – Chemometric approach

Talc is broadly used in the ceramic materials industry, either as a basic raw material, or as filler, due to its chemical inertia, fragmentation proneness, thermal stability, and refractoriness. The mechanical activation is frequently employed in the direct enhancement of talc properties, and thereby in the design of talc based composites with advanced performances. The differences in the set of the process parameters measured before and after talc activation via ultra-centrifugal mill Retsch ZM-1, and their influence on the grain-size distribution related characteristics have been investigated. The mechanical treatments are energetically unsustainable procedures, therefore the talc activation was optimized on basis of assessment of the process variables (number of rotor revolutions, current intensity, activation period, circumferential rotor speed and mill capacity) effect on the final quality of product parameters (mesh sizes, cumulative oversizes, average grain size, level of micronization kinetics, mesh size appropriate to 95% micronized product cumulative undersize and specific surface area). The activated product parameters in all experimental sequences were obtained by the analytical procedure based on Rosin-Rammler-Sperling equation. Response surface method, standard score analysis and principal component analysis were used as a means of the optimization. Developed models showed r² values in the range of 0.714–0.908 and they were able to accurately predict quality parameters in a wide range of process parameters. Standard score analysis highlighted that the optimal sample was obtained using sieve mesh of 120 μm set of processing parameters (SS = 1.0). Multiple comparison tests revealed that the optimal variation in the processing parameters could reduce the negative effect of talc samples inherent properties on the final score and improve the activation procedure energetic and economic sustainability.     

Effect of welding parameters on microstructure and mechanical properties of friction stir welded joints of AA7039 aluminum alloy

A high strength Al–Zn–Mg alloy AA7039 was friction stir welded by varying welding and rotary speed of the tool in order to investigate the effect of varying welding parameters on microstructure and mechanical properties. The friction stir welding (FSW) process parameters have great influence on heat input per unit length of weld, hence on temperature profile which in turn governs the microstructure and mechanical properties of welded joints. There exits an optimum combination of welding and rotary speed to produce a sound and defect free joint with microstructure that yields maximum mechanical properties. The mechanical properties increase with decreasing welding speed/ increasing rotary speed i.e. with increasing heat input per unit length of welded joint. The high heat input joints fractured from heat affected zone (HAZ) adjacent to thermo-mechanically affected zone (TMAZ) on advancing side while low heat input joints fractured from weld nugget along zigzag line on advancing side.     

The working process of an oil‐free claw vacuum pump

Mathematical model of oil free claw vacuum pump is presented. The model is based on energy balance differential equations of thermodynamic system of variable mass working body. Using the equations of coordinates transformation and contact line of rotors continuity condition, equations for geometry of claw pump working chamber on condition of rotors point connection are obtained. To evaluate the leakage through the rotor mechanism channels, their existence graphs are plotted and geometric parameters of the channels depending on rotors position are determined. As a result of modeling, dependence of pressure and temperature in suction and compression‐discharge chambers on rotation angle at different rotary speeds and on different inlet pressures and relationship between pumping speed and inlet pressure are obtained. The comparison between calculated values and experimental data obtained for one‐stage claw pump with identical rotors is carried out. The maximal difference between the calculated and experimental values does not exceed 15 %. The developed mathematical model is recommended for analysis of influence of rotors geometry on the working process parameters and pumping characteristics of an oil free claw pump.     

β-SiC微粉的气流分级工艺

采用生产型流化床对喷式气流粉碎分级机对β-SiC微粉进行气流粉碎分级实验研究,通过探讨不同的工艺参数对分级效果的影响,确定最佳进料速率、每一个粒级的产物所对应的最佳分级轮转速和进料粒度,并优化工艺流程.结果表明,最佳进料速率为42 kg/h;针对不同粒度的产物确定了最佳的分级轮转速;采用优化工艺能够高效地、稳定地获得不同粒径的分级产品,可实现粒度大于W2.5产品的β-SiC微粉的精细分级,分级产物粒度分布窄,颗粒形貌均匀.     

Design of the new guide vane for the turbo air classifier

The guide vane is a common guide part in a turbo air classifier. However, there is a lack of a theoretical design basis and an analogy method is often used to design the guide vanes. The guide vanes’ effects of improving the flow field distribution are obtained by means of comparison of the flow field of the classifiers with and without guide vanes. However, the guide vane of a 15° setting angle should be optimized due to the non-uniform airflow circumferential distribution in the annular region. To obtain a well-distributed flow field of a turbo air classifier, a design method for the guide vane is provided based on the airflow trajectory in the volute and a new guide vane of a 10° setting angle is designed under the operating condition of 12–1200. The numerical simulation results show that the standard deviation of circumferential radial and tangential velocity is decreased. Besides, the trajectories of the particles with the same size in different circumferential positions show their classification results are consistent. This guide vane design method is feasible and provides the design references for the turbo air classifiers.