Effect of impeller reflux balance holes on pressure and axial force of centrifugal pump

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5 m3/h, H=60 m, n=2950 r/min was selected to be designed with eight axial reflux balance holes with 4.5 mm in diameter. The simulated Q-H curve and net positive suction head(NPSH) were in good agreement with experimental results, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic; however, it showed to little superiority in head and efficiency. The pressure in rear pump chamber at 0.6 times rate flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rate flow and 28.33% at 1.4 times rate flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreases as flow rate increases. Radical reflux balance holes chosen to be 5.2 mm and 5.9 mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics was conducted based on momentum equations and standard turbulence model(κ-ε). It is found that axial force of pump with radical reflux balance holes of5.2 mm and 5.9 mm in diameter is significantly less than that with radical reflux balance holes of 4.5 mm in diameter. Better axial force balance is obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.

Effect and sensitivity analysis of the rotational speed on the fluid-induced force characteristics of the straight-through labyrinth gas seal

The effects of the rotational speed on the fluid-induced force characteristics of a straight-through labyrinth gas seal( STLGS) are numerically investigated using the steady computational fluid dynamics( CFD) method based on a three-dimensional model of the STLGS. The fluid-induced force characteristics of the STLGS for five rotational speeds at a pressure drop of △P = 5000 Pa with and without eccentricity are computed. The grid density analysis ensures the accuracy of the present steady-CFD method. The effect and sensitivity analysis show that the changes in rotational speed affect the pressure forces,viscous forces and total pressure distributions on the rotor surface,velocity streamlines,leakage flow rates,and maximum flow velocities. The results indicate that the rotational speed inhibits the pressure forces,leakage flow rates and maximum flow velocities and promotes the viscous forces and total pressure on the rotor surface.

Microstructures in Centrifugal Casting of SiC_p/AlSi9Mg Composites with Different Mould Rotation Speeds

Two ingots were produced by centrifugal casting at mould rotational speeds of 600 rpm and 800 rpm using 20 vol%SiC p /AlSi9Mg composite melt,respectively.The microstructure along the radial direction of cross-sectional sample of ingots was presented.SiC particles migrated towards the external circumference of the tube,and the distribution of SiC particles became uniform under centrifugal force.Voids in 20 vol%SiC p /AlSi9Mg composite melt migrated towards the inner circumference of the tube.The quantitative analysis results indicated that not only SiC particles but also primaryαphases segregated greatly in centrifugal casting resulting from the transportation behavior of constitutions with different densities in the SiC p /AlSi9Mg composite melt.In addition,the eutectic Si was broken owing to the motion of SiC p /AlSi9Mg composite melt during centrifugal casting.

Effect of the Density of Molten Metal on the Raining Phenomenon in Horizontal Centrifugal Casting

In this work the influence of the density of the molten metal on the emergence of the raining phenomenon in the horizontal centrifugal casting process is numerically studied. Transient 2D numerical simulations were carried out using Computational Fluid Dynamics software. Three molten metals with different density, namely aluminum, iron and lead, and three angular frequencies, namely 50, 66 and 77 rad/s were considered. It is found that the density of the molten metal significantly affects the emergence, transient or permanent, of the rain phenomenon. However, the magnitude and duration of the rain phenomenon depend on the angular frequency of the rotating mold. Likewise, since gravitational forces affect the metal according to its density, the value of the critical rotation speed of the mold is also affected.

Experimental Study of Cavitation Phenomenon in a Centrifugal Blood Pump Induced by the Failure of Inlet Cannula

Cavitation of centrifugal blood pump is a serious problem accompany with the blocking failure of short inlet cannula. However, hardly any work has been seen in published literature on this complex cavitation phenomenon caused by the coupling effect of inlet cannula blocking and pumps suction. Even for cavitation studies on ordinary centrifugal pumps, similar researches on this issue are rare. In this paper, the roles of throttling, rotation speed and fluid viscosity on bubble inception and intensity in a centrifugal blood pump are studied, on the basis of experimental observations. An adjustable throttle valve installed just upstream blood pump inlet is used to simulate the throttling effect of the narrowed inlet cannula. The rotation speed is adjusted from 2 600 r/rain to 3 200 r/min. Glycerin water solutions are used to investigate the influences of kinetic viscosity. Bubbles are recorded with a high-speed video camera. Direct observation shows that different from cavitation in industrial centrifugal pumps, gas nuclei appears at the nearby of vane leading edges while throttling is light, then moves upstream to the joint position of inlet pipe and pump with the closing of the valve. It＇s found that the critical inlet pressure, obtained when bubbles are first observed, decreases linearly with viscosity and the slope is independent with rotation speeds; the critical inlet pressure and the inlet extreme pressure which is obtained when the throttle valve is nearly closed, fall linearly with rotation speed respectively and the relative pressure between them is independent with rotation speed and fluid viscosity. This paper studies experimentally on cavitation in centrifugal blood pump that caused by the failure of assembled short inlet cannula, which mav beneficial the desima of centrifugal blood Dumo with inlet cannula.

Effect of centrifugal counter-gravity casting on solidification microstructure and mechanical properties of A357 aluminum alloy

To investigate the influence of Centrifugal Counter-gravity Casting(C3) process on the solidification microstructure and mechanical properties of the casting, A357 aluminum alloy samples were produced by different process conditions under C3. The results show that C3 has better feeding capacity compared with the vacuum suction casting; and that the mechanical vibration and the convection of melts formed at the centrifugal rotation stage suppress the growth of dendrites, subsequently resulting in the refinement of grains and the improvement of mechanical properties, density and hardness. A finer grain and higher strength can be obtained in the A357 alloy by increasing centrifugal radius and rotational speed. However, casting defects will appear near the rotational axis and the mechanical properties will decrease once the rotational speed exceeds 150 r·min-1.

A NEW CENTRIFUGAL ATOMIZATION TECHNIQUE OF SPRAY ROTATION FOR POWDER PREPARATION

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A Device that can Produce Net Impulse Using Rotating Masses

This paper describes a device capable of producing net impulse, through two synchronized masses, which move along a figure-eight-shaped orbit. In addition to the detailed description of the mechanical components of this device, particular attention is paid to the theoretical treatment of the innovative principle on which the device is based. In more details, the mechanical system consists of two independent but simultaneous rotations, the former being related to the formation of the figure-eight-shaped path and the latter to an additional spinning. Based on the parametric equations of motion of the lumped masses, and considering semi-static tensile deformation of the connecting rods carrying them, it was found that the resultant impulse towards the direction of the spin vector includes a non-vanishing term that is linearly proportional to the time. In addition, reduced but encouraging experimental results are reported. These findings sustain the capability of the proposed mechanism to achieve propulsion.

一种超高转速风机转频噪声分析与控制

高转速风机具有体积小,效率高,可靠性高等优异特性,在家用产品、高端制造以及航空航天等领域应用前景广阔。随着转速的提高,风机的激励力和噪声将发生很大变化,高转速对噪声设计提出了更高的要求。本文对某型15万转风机的转频噪声进行研究,首先对风机转子系统不平衡力进行分析,随着转速升高转子不平衡力对其振动噪声的影响越发显著,风机低噪设计需要转子系统偏心质量更小,同时指出对转子系统和叶轮进行整体动平衡操作,可以有效降低系统不平衡激励,转频噪声降噪效果更优。进一步地,针对风机进风口来流状态对转频噪声的影响进行讨论,发现进风口不均匀来流会激发叶轮-转子系统产生不平衡激励,从而导致风机转频噪声恶化。因此风机与整机系统匹配设计时,必须考虑风机进风口结构的影响。最后综合风机转子系统的整体动平衡方案及进风口来流均匀设计等措施,该高转速风机转频噪声下降明显,收到良好的降噪效果。

聚苯硫醚离心分离实验研究

硫化钠合成聚苯硫醚是聚苯硫醚主流生产方法,该方法出来的缩聚产品一方面含有低聚物,一方面盐容易包裹在产品中。工业上多采用多次洗涤来消除产品中低聚物和盐。实验采用翻袋离心机对含约8.69%聚苯硫醚,9.6%无机盐的聚苯硫醚浆料体系进行NMP一次洗涤和脱离子水多次洗涤实验。实验结果显示:经过1次NMP洗涤和8次脱离子水洗涤可得到灰分质量分数<0.2%的PPS纯产品,PPS滤饼湿质量分数45%,溶剂NMP基本置换为水,满足聚苯硫醚生产的洗涤分离要求。该实验结果为进一步开展聚苯硫醚浆料体系离心分离工程化的研究工作提供基础数据支持。

离心泵变频技改的节能量测算探讨

在离心泵变转速节能技改项目中,由于泵流量不满足相似定律的比例条件,不宜采用比例定律计算有关参数及节能效果。依据泵流量不变的条件,通过相似理论导出泵扬程、泵效率随泵转速变化的关系式,有效减小预测值与实际节能效果的偏差。

引信安全执行机构高精度转速离心测试系统

高精度转速大型离心机是用于引信安全执行机构测试的专用设备,针对引信安全执行机构过载环境下解除保险测试过程中,直径大于1 m的离心机转速精度不满足现有测试需求的情况,提出一种引信安全执行机构测试用大型离心机的设计。通过对离心机控制系统电机、支撑座及刚性轴的改进设计,增强了离心机强度、动平衡和轴系精度,实现了高精度转速引信测试用大型离心机的研制。建模和仿真测试结果表明,离心机回转速率精度和速率稳定性从10^(-3)提升到了10^(-4)数量级。

篦齿封严结构高速旋转碰磨实验研究

针对压气机铜银锌封严环在航空发动机转子高速旋转过程中与篦齿之间发生的碰磨现象,利用最高转速45000 r/min的高速旋转实验台进行实验研究,得到了封严环碰磨区域的表面形貌以及磨损槽尺寸,并获得了封严环初始温度、篦齿径向侵入深度对封严环碰磨区域径向与轴向温度分布以及碰磨力的影响规律。实验结果表明:在篦齿径向侵入速率V_(r)≥0.04 m/s时,碰磨过程中铜银锌涂层会发生塑性变形,在磨损槽两侧产生毛刺;碰磨过程中封严环碰磨区域温度会急剧升高,距封严环内壁面径向距离越近的位置温度越高,但在同一径向距离的不同轴向位置温度基本接近;碰磨力和温升随封严环初始温度的升高而减小,而篦齿径向侵入深度的增加则导致碰磨力和温升增大;相同工况条件下,篦齿径向侵入时的碰磨力和温升变化要比轴向侵入时更剧烈,碰磨产生的径向力显著大于轴向力。

浅谈离心脱水机运行模式

文章介绍了杭州萧山供水有限公司江东水厂污泥脱水工艺,总结了离心脱水机运行中存在的主要问题,如污泥水水质波动、脱水机运行参数调整、PAM药剂配套等,并提出了相应的解决办法,以保证离心脱水机正常、高效运行,供相同工艺和流域的污泥脱水单位参考。

航空航天高速轴承保持架的优化设计

讨论了航天航空高速轴承保持架的基本原理、材料特性对比、以及不同保持架类型的特点。尤其强调了高速轴承保持架在承受离心力、高温及动态载荷时的材料和结构要求。通过实例分析,展示了优化设计如何增强保持架的自润滑性和热稳定性,从而提高整个轴承系统的性能和可靠性。为高速轴承保持架的设计和改进提供了理论依据和实践指导。

基于有限元的高速旋转主轴过盈配合研究

主轴是高速机床的核心部件 ,机床主轴与电机转子间过盈配合特性是影响主轴性能的重要因素。离心力的存在 ,使得过盈配合特性发生了很大的变化 ,尤其当主轴高速旋转时 ,其影响更加明显 ,成为影响过盈配合特性的主要因素。借助于弹塑性接触有限元法 ,建立了高速旋转主轴与电机转子间过盈配合的有限元模型 ,仿真模拟了过盈量、旋转速度 (离心力 )对过盈配合面间的应力、位移、接触应力的影响。

浓海水冷冻脱盐技术研究

通过实验室冷冻离心实验,研究了浓海水的冷冻脱盐技术。实验研究了离心转速对冰冻的浓海水的脱盐和脱除钙镁离子的影响,并对多步冷冻脱盐前后余冰和浓海水的盐度分别进行分析,以及利用ICP-MS对其主要离子含量进行测定。实验结果表明,离心转速变化对冰冻浓海水脱盐、脱除钙镁离子的影响显著。各实验离心转速条件下,脱盐和脱除钙镁离子均有较好效果,脱除率均达到88.5%和87.4%以上。随着离心转速的提高,脱盐率提高,转速4000r/min达到最大,但是其变化幅度减小,进一步提高转速对脱盐率和钙镁离子脱除率的提高影响不大。经过多步冷冻脱盐发现,一次冷冻离心分离,得到的余冰的盐度脱除达到99.0%。通过与原浓海水离子含量相比,钾钙钠镁等主要离子含量降低为原浓海水的3%以下。而多步离心分离之后,得到的浓海水的盐度达到原浓海水的3.3倍。每步实验,均有低盐度、低离子含量的冰生成,冰的产量达到被处理的浓海水总体积的2/3以上。

高速机床电主轴过盈配合量的计算

电主轴是高速机床的核心部件，电机转子与机床主轴间过盈配合量的大小是影响主轴性能的重要因素。本文根据材料力学和弹性力学理论，对电主轴的配合特性进行了分析，分别推导出电主轴在静态和高速运转条件下，主轴过盈量和应力分布的理论公式。最后，根据理论公式计算出ＧＤ－Ⅱ型电主轴的过盈配合量，研究结果表明，采用理论公式设计的过盈配合能较好地满足高速电主轴的需要。

离心泵调速运行节能效果试验

为了给离心泵调速节能研究提供理论依据,利用变频器在离心泵开式试验台上对BX50-31型泵进行变频调速运行测试试验,得到了其在恒定扬程、变扬程及试验室装置条件下的性能参数,并对所得试验数据进行了分析,得出了其在相对流量为50%的调节流量下,相对节能效果高达87.52%.

全附体潜艇模型回转运动流场数值模拟

为研究潜艇的回转运动,在RANS方程中引入旋转坐标系科氏力和艇体惯性离心力,并采用分块结构化网格技术,对全附体潜艇模型回转运动的流场进行了CFD数值模拟。首先,推导了旋转坐标系下流场计算的控制方程,给出了科氏力和艇体惯性离心力的表达式,并将其引入到动量方程中;然后,采用RNGk-ε湍流模型以及用户自定义函数方法设置了计算边界条件,数值模拟了全附体潜艇模型(DRAPA SUBOFF)的操舵定常回转运动流场;最后,分析了所计算流场的速度、压力和涡的分布及形态,分析表明计算结果符合其规律性。