基于FLUENT干冰清洗喷嘴气固两相流场仿真研究

本文利用FLUENT软件对圆柱型喷嘴的自由射流流场进行了仿真研究,分析了喷嘴轴线上压力及速度的变化原因以及干冰颗粒的运动情况,发现膨胀波和斜激波的交替出现是影响干冰颗粒速度的变化的最主要原因。结合模拟干冰清洗的碰撞过程的仿真结果,分析了板激波出现的原因,为确定干冰清洗最优靶距提供理论依据。     

惰性粒度对焦炭强度的影响

高强度焦炭的生产技术有很多,其中有煤粉碎粒度控制技术.一般来说,炼焦煤粉碎得越细,焦炭强度越大.但是如果过度粉碎,煤的装入密度降低,会导致装煤量和焦炭强度降低.要防止过度粉碎并提高焦炭强度,准确把握惰性煤颗粒尺寸和焦炭强度的关系十分重要.本文将惰性煤的粒度调整为0.1～0.3mm、0.3～0.6mm、0.6～1.2mm、2.0～4.0mm、5.0～7.0mm以及10～15mm,并且按照一定的比例进行配料生产焦炭.通过焦炭显微镜分析,实际测量了惰性煤的尺寸,研究了惰性煤尺寸对焦炭强度(转鼓强度指数DI6和DI6-15)的影响.     

喷嘴进料对提升管进料段内颗粒浓度分布的影响

在提升管冷模实验装置上考察了喷嘴进料对颗粒浓度径向分布的影响规律. 结果表明,提升管进料段内存在3种形式的颗粒浓度径向分布,在距喷嘴较近的轴向区域,颗粒浓度沿径向呈明显的W形分布,喷嘴进料对颗粒流动的影响很强;在距喷嘴较远的轴向位置,颗粒浓度沿径向呈环-核分布,喷嘴进料对颗粒流动的影响很弱;在二者之间,颗粒浓度沿径向呈弱W分布,喷嘴进料对颗粒流动具有一定影响. 随着喷嘴气速的增加或预提升气速的减小,颗粒浓度逐渐由W形分布转变为环-核分布,喷嘴进料对颗粒流动的影响逐渐减弱. 采用喷嘴射流动量与预提升来流动量比Mj/Mr考察了操作参数及装置结构尺寸对提升管进料段内颗粒浓度径向分布的综合影响. 在实验范围内,动量比对进料段内颗粒浓度径向分布及颗粒流动行为具有明显的影响规律,随着动量比的增加,颗粒浓度逐渐由W形分布转变为环－核分布,操作参数及装置结构尺寸对颗粒流动的影响逐渐减小. 在动量比小于4.21时,操作参数及装置结构尺寸对颗粒流动的影响在H=0.675~1.075 m间的轴向位置基本结束;在动量比增大为4.21时,操作参数及装置结构尺寸对颗粒流动的影响在H=0.375~0.675 m间的轴向位置便已基本结束.     

氢氧化铝晶体颗粒强度的数值模拟分析

利用有限元方法对氢氧化铝晶体叠合形成的氢氧化铝颗粒进行了静力分析,得到了氢氧化铝晶体叠合角度与叠合形成的氢氧化铝颗粒强度的关系,计算了叠合氢氧化铝晶体尺寸与氢氧化铝颗粒强度变化之间的规律. 研究发现：(1) 当氢氧化铝晶体间叠合角度在60o~80o时,氢氧化铝颗粒所受应力最大,强度最小;(2) 叠合的氢氧化铝晶体尺寸较小(约5 mm)时,氢氧化铝颗粒所受应力较小,强度较大;(3) 叠合的氢氧化铝晶体尺寸较大(20~40 mm)时,叠合晶体尺寸越大,氢氧化铝颗粒所受应力越大,强度越小;(4) 大晶体间镶嵌有细小晶体的叠合方式,形成的氢氧化铝颗粒强度有明显优势.     

超细碳酸钙颗粒的离心分级

用一种工业型的牒式离心机对粒度小于8 μm的超细碳酸钙颗粒进行湿法分级.采用统计方法研究了与该离心机相关的主要工艺参数,如:离心力强度、牒类型、喷嘴尺寸、分流率和给料速率等.结果表明:这种牒式离心机可以有效地分级质量分数达到40%的微米粒级的物料,并可获得较窄颗粒粒度分布的超微细产品.离心分级效果与所用的主要参数呈经验关系.     

气流粉碎过程中激波的产生、影响及防止研究

分析了气流粉碎过程中激波产生的原因,采用数值计算方法,讨论了激波对气流磨中颗粒的冲击速度的影响,并提出了防止激波产生的措施。     

气流粉碎过程中激波的产生、影响及防止研究

分析了气流粉碎过程中激波产生的原因,采用数值计算方法,讨论了激波对气流磨中颗粒的冲击速度的影响,并提出了防止激波产生的措施。     

新型蒸汽喷嘴数值模拟研究

根据蒸汽喷射器中出现的各种新型喷嘴,针对整流喷嘴、调节锥喷嘴、维托辛斯基曲线喷嘴和双层喷嘴进行研究,采用Workbench平台的Fluent软件,水蒸气为介质对同一拉法尔喷嘴基本尺寸模型下的各种新型喷嘴的内部流动在同样的工艺条件下进行了数值模拟;研究得出整流喷嘴、调节锥喷嘴、维托辛斯基曲线喷嘴和双层喷嘴出口速度依次增大。结果表明双层喷嘴提速效果好,维托辛斯基曲线喷嘴消除激波效果好,调节锥喷嘴可方便的调节流量及出口速度,而整流喷嘴不能消除激波且增加整流段长度会增加阻力损失。为喷嘴的合理选择及使用提供了一定依据。     

超音速气流粉碎机喷嘴的模拟与实验研究

采用Matlab软件,利用工程热力学的知识设计实验室气流粉碎装置的喷嘴结构和参数,用Fluent流体模拟软件对所设计喷嘴进行流场模拟,并以此对所设计喷嘴的效果进行检验.讨论了顶锥角对超音速喷嘴的影响.通过模拟比较得到,入口压力3.5MPa、入口直径为6mm的喷嘴为设计的最佳喷嘴.对于设计出的超音速喷嘴,顶锥角在8°～12°之间变化时,对喷嘴的性能影响不大.用所设计的喷嘴对重质碳酸钙进行粉碎实验的研究,证明了所设计的喷嘴的粉碎能力,同时得到了其粉碎重质碳酸钙的最佳工艺参数:即在入口压力为3.8MPa,靶距为25mm,管距为1 mm的工艺条件下,可将平均粒径为300μm的重质碳酸钙粉碎至20μm以下.     

中央扩散型喷嘴颗粒分散调节特性的实验研究

建立了几何尺寸相似比为1:5的中央扩散式精矿喷嘴冷态模型装置,用石英砂模拟精矿粉,用Matlab软件绘制接粒称重冷态实验颗粒分布云图,研究了反应塔内颗粒分布均匀性随分散锥、投料速度、工艺风和分布风变化的规律. 结果表明,塔内颗粒分布均匀性可调控,分散锥和投料速度对颗粒分布均匀性影响小;随工艺风流量Qpro增加或分布风流量Qdis减小,颗粒向塔中心区域聚集,表征颗粒分布均匀性的颗粒质量偏析函数增加. 实验范围内各工况Qdis和Qpro与颗粒质量偏析函数px之间的关系可拟合为px=(-0.00025+0.3176/Qdis)Qpro-1.51,拟合规律与文献和冶炼现场操作参数配置基本吻合.     

Engineering Model of Friction of Gas‐Solids Flow in a Jet Mill Nozzle

In this study we develop a model for estimating particle friction against the wall of a jet mill nozzle. The computation is reduced to a definition of conventional force acting on particles in a polydispersed stream. It is assumed that energy losses due to friction are caused by multiple particle collisions against the nozzle walls. The proposed model is oriented to calculating jet mill nozzles and is much simpler than previously applied methods. A parametric study of the proposed model was carried out and the effect of particle friction on particle and gas velocities was derived.     

Parameter effects on dry fine pulverization of alumina particles in a fluidized bed opposed jet mill

The paper presents the experimental results on dry fine pulverization of alumina particles in a fluidized bed opposed jet mill. The effect of operating parameters (i.e., feed load, inlet air pressure and the distance between nozzle outlet and jet meeting point) on the grinding results was investigated in detail. The breakage behaviors of alumina particles with respect to the effects of different parameters were discussed via the selection and breakage functions calculated by the first Kapur function method. In addition, the product size distributions could be simulated by a proposed model.     

An experimental investigation of the convective instability of a jet

This paper is an experimental study of the convective instability of a jet. It is well known that a jet issuing forth from a nozzle is unstable due to surface tension forces that cause it to break downstream into drops. We apply a disturbance of a given frequency at the nozzle tip. This applied frequency determines the wavelength and the growth rate of the growing disturbances and, thereby, the drop size. We measure the wavelength and the growth rate by fitting the entire digitized image of a jet to the functional form suggested by the linear theory. Thus, it makes use of the entire profile instead of the small number of points used in previous studies. Also, in contrast to previous work, we independently measure the jet velocity and the wave speed. At high non-dimensional jet velocity, the experimental results for the growth rates and the wave numbers agree with the linear stability theory of an infinite jet in the absence of gravity. At very low velocity (low Froude number) gravity is important and the agreement is not good.     

Designing a Jet Mill Nozzle of Maximum Efficiency

A method of calculation for an accelerating jet mill nozzle profile which provides a maximum kinetic energy for solid particles at the nozzle outlet, is developed. The gas‐solid flow in the nozzle is described by a well‐known one‐dimensional model. The effect of both solid loading and particle size on the optimal nozzle profile, as well as on the main flow parameters is studied. Distribution of particle velocities in the computed optimal nozzle is compared to that in a conical convergent‐divergent nozzle of the same length. Computations demonstrated that optimized nozzles are profitable for fairly low solid loadings. The kinetic energy of solids at the optimized nozzle outlet is about 50% higher than that in a conical nozzle if the solid/gas mass flow ratio equals unity.     

超声速气体浸没射流的数值计算和实验

从实验和数值计算两方面研究了超声速气体射流在水中的喷射过程.用高速摄影机拍摄了三维水下超声速气体射流的流场.针对实验工况,基于VOF方法,建立水下超声速气体射流的二维轴对称数值计算模型,并开展了相关数值模拟.成功模拟了射流初期气泡运动演化的复杂过程;分析了水下超声速气体欠膨胀射流的流场结构,包括流场的压力和速度等参数分布以及变化规律.数值结果与实验结果对比得知数值计算结果不仅与实验数据吻合较好,而且给出了实验中没有发现的激波、膨胀波等流场结构.     

用对流磨粉碎石灰石的试验研究

本文扼要介绍了对流磨的结构与粉碎原理，及粉碎石灰石的试验研究。研究的主要内容是给料粒度与粉碎产物细度和能量效率的关系，以及喷嘴形状与能量效率的关系。     

Effective comminution of diatomaceous earth in a vertical type jet mill

Comminution characteristics of diatomaceous earth have been investigated in a vertical type jet mill of pilot plant scale; the diameter of the chamber of mill is 26.3 cm. Fluidization of the particles in the chamber has been proposed to enhance the comminution efficiency of the jet mill by promoting the effective contacting of powders with compressed air as well as the chamber wall. Effects of the pressures or densities of pulverizing-air and fluidizing-air and comminution time on the mean size of the particles and the rate of comminution have been examined. The statistical analysis of pressure fluctuations in the chamber of the mill has been utilized to predict the characteristics of the vertical-type jet mill taking advantage of the fluidization technique. The particle size and comminution rate have been correlated with the operating variables, respectively.     

熔体直写电纺聚己内酯纤维有序沉积工艺

目前聚合物熔体电纺技术制备的纤维大多以杂乱无序的无纺布形式存在,限制了电纺技术在组织工程支架以及机器人等需要有序结构领域的应用。本文将熔体电纺技术与三维运动平台相结合,采用自主设计的熔体电纺可控成型实验装置,对聚己内酯（PCL）进行熔体直写静电纺丝,获得了有序纤维。研究了喷头移动速度、接收距离和纺丝电压对熔体直写电纺纤维沉积形貌的影响。结果表明,纤维直径随着喷头移速、接收距离和纺丝电压的增大而减小,其中接收距离的改变对直径的影响最为显著;接收距离的增大虽然有利于纤维的细化,但是距离过大会使纤维沉积的有序性变差;当射流下落速度与喷头移动速度相匹配时,射流才能实现有序沉积;增大接收距离和纺丝电压会引起射流鞭动,需要相应地增大喷头移动速度才能实现有序沉积。