Prototyping and modeling of the centrifugal casting process for paraffin waxes

Centrifugal casting is a technology used for manufacturing hybrid rocket paraffin grains. This technology helps avoiding voids formation inside the solid paraffin as it cools. Voids are formed because of air bubbles being entrapped while pouring and because the liquid wax shrinks by 17–19% upon cooling. In this work, the centrifugal casting process for the manufacturing of paraffin cylinders was prototyped at two different scales considering critical casting issues. The effects of process parameters (rotational speed, melt temperature, and flow rate) on the tensile properties of the manufactured grains were analyzed. The results of the optimization conducted at the lower scale (2.5?kg) were up scaled to manufacture 25?kg grains. The resulting mechanical properties complied with the design specifications, and they were better than those characterized from the gravity cast wax. A numerical model of growth and dissolution of bubbles during the process was then developed to predict the quality of the castings. The numerical results showed how increasing the mold rotational speed up to 1800?rpm reduced the removal time. However, compared to grains solidification time, the predicted removal times were much shorter, proving the advantage of centrifugal casting in counteracting voids formation.     

限矩式离心联轴器

提出一种新型限矩式离心联轴器,说明了设计要点。该联轴器结构简单,有较好的应用前景。     

双声学共振腔体蜗舌降低离心式风机噪声的研究

论述了双声学共振腔体蜗舌降低离心式风机噪声的新方法,进一步提出了双声学共振腔体蜗舌的解析模型。经实验验证,当采用双声学共振腔体蜗舌时,可降低基频噪声２５２ｄＢ（Ａ）。降低一次谐波噪声１６３ｄＢ（Ａ）,总声压级下降９７ｄＢ（Ａ）,比单声学共振腔体蜗舌总声压级多下降３４ｄＢ（Ａ）,风机气动力性能基本不受影响。     

板制小流量叶轮的设计

介绍适合用板料制作小流量的叶轮结构以及这种叶轮的设计计算方法。     

Characterization of centrifugally atomized Al-12Si-5Fe-3Cu-1Mg(wt%) alloy powder and extruded rod

The Al-12Si-5Fe-3Cu-1Mg(wt%) alloy was rapidly solidified by centrifugal atomization. The microstructural characteristics of rapidly solidified powder and the microstructure changes with heat treatment were investigated in terms and related to powder size. The microstructures of the powder consisted of dendritic -Al, eutectic phase, Cu-rich phase, and needle-like intermetallic compounds. These phases were much finer than that of ingot cast structure and the size decreased with increasing cooling rate. The X-ray diffraction of the atomized powders revealed the presence of non-equilibrium 3-(AlFeSi) intermetallic phase. This phase appeared to transform to an equilibrium -(AlFeSi) phase by heating at temperatures above 470°C. The extruded rod which was hot extruded at 360°C with an extrusion ratio of 40:1 also revealed the presence of the -(AIFeSi) intermetallic phase. Using DSC, the exothermic peak due to precipitation from the supersaturated -Al matrix was observed in the range of 200–250°C during continuous heating of atomized powder, and the size of the peaks increased with decreasing powder size.     

离心泵蜗壳内压力脉动特性数值分析

为揭示离心泵蜗壳流道内的压力脉动变化规律,采用雷诺时均方法(RANS),对3种工况下的离心泵内部三维非定常湍流流场进行数值计算,分析同一蜗壳断面不同位置以及沿蜗壳周向不同点的压力脉动特性。结果表明:蜗壳流道内具有非常明显的压力脉动,在各种工况下压力脉动的主频均是叶片通过频率;同一蜗壳断面上的压力脉动从蜗壳底部到蜗壳背面先减小后增大,蜗壳底部监测点的高频脉动成分较多;沿蜗壳周向,随着圆周角的增大,压力脉动减弱,隔舌附近压力脉动幅度最大,且高频脉动成分明显增加。     

低比转速离心泵内部流场数值模拟

采用三维定常雷诺时均Navier-Stokes方程和Spalart—Allmaras湍流模型,对复合叶轮离心泵内部三维流场进行整机定常数值模拟,得到了复合叶轮离心泵内部流场的速度分布和压力分布。分析在不同流量点下复合叶轮和蜗壳内部流场,揭示离心泵内部的重要流动特征,证实了过流部件间相互作用引起的离心泵内部流场的不对称性。数值模拟结果表明,复合叶轮离心泵的整机数值模拟分析能够较准确地预测出离心泵内部的流场结构及性能参数。     

细粒煤重介质离心分选脱硫试验研究

在重介质条件下利用Falcon离心重力分选系统,研究了-500μm不同窄粒级南桐细粒煤的脱硫降灰效果.采用可燃体回收率、脱灰率、脱硫率、脱硫效率4个指标,对比分析了Falcon重介离心分选和常规浮选对南桐细粒高硫煤各粒级的分选效果,结果表明:对于-500μm细粒级煤,脱灰率低于常规浮选,而其余3个指标均高于浮选.125μm是分选效果的显著分界粒度,500～125μm粒级煤的脱硫率、脱灰率高于浮选,而可燃体回收率低于浮选.-125μm粒级煤的脱硫率、脱灰率低于浮选,而可燃体回收率高于浮选.     

不同组合桨搅拌器搅拌特性的数值研究

采用Fluent软件的多重参考系(MRF)及标准k-ε湍流模型,针对双层平直桨叶、双层45°折叶涡轮桨和两者组合搅拌桨这3种搅拌桨,研究了不同桨叶类型搅拌槽内的流动混合特性和加料位置,结果表明:45°折叶涡轮桨和平直叶桨的上下组合桨可以增强搅拌器内流体的上下湍动,促进混合,其搅拌功率较双层平直叶桨下降37.91%,混合时间减少50.48%;选择上层桨叶尖端加料可以缩短搅拌器内液体的混合时间,提高搅拌效率.     

基于CFD的低比转速离心泵叶轮切割性能分析

根据现行的低比转速离心泵切割定律,对MH-46-100型低比转速离心泵叶轮外径进行3次切割,以分块非结构六面体网格划分计算区域。采用有限体积法对雷诺时均Navier-Stokes方程进行数值离散,选用RNGk-ε湍流模型结合SIMPLEC算法求解,对各个模型进行了叶轮和蜗壳相耦合的数值模拟。对性能预测结果与现行的低比转速离心泵切割定律进行对比,证明了切割定律的准确性和基于切割定律的各模型流动的相似性。同时得到了低比转速离心泵叶轮外径减小而效率升高的特点,并对比分析各个模型的流动状况。