穿孔板噪声谱分析研究

水力空化与超声空化是产生空化的两种主要方法,国内外研究者对超声空化的噪声谱研究的非常多．但对于水力空化,一般仅进行应用方面的实验研究,而疏于声学方面的研究．为进一步了解水力空化的声学特性,本文理论上进行板的振动的计算,并用ANSYS模拟穿孔板的振动,研究其振动频率与测得的空化噪声谱之间的联系．研究结果表明,在特定的条件下,测得的噪声谱呈现明显线状谱分布的超声成分,此时高速水流冲击穿孔板引起了穿孔板的强烈振动,发出超声,但在一般情况下,多孔板水力空化噪声谱并不含超声成分,也不具有明显线状谱特性．     

Energy Consumption in Comminution of Mica with Cavitation Abrasive Water Jet

We have studied the efficiency of energy consumption in the comminution of mica powder with cavitation abrasive water jet technology. The energy required to create new surfaces in the comminution of mica powder with cavitation abrasive water jet was calculated,in order to estimate its efficiency of energy consumption. The particle size distribution and the specific surface area were measured by applying a JEM-200CX transmission electron microscope and an Autosorb-1 automatic surface area analyzer. The study results show that the efficiency of energy consumed in creating new surface areas is as high as 2.92%,or 4.94% with the aid of cavitation in the comminution of mica powder. This efficiency will decrease with an increase in the number of comminutions. After three comminutions,the efficien-cies will become 1.91% and 2.29% for comminution without cavitation and with cavitation,respectively. The abrasive water jet technology is an effective way for comminution of mica powder.     

再热器减温水调节阀运行异常的分析与改进

分析了某600 MW超临界机组再热器减温水调节阀调节性能差、小流量调节时汽蚀冲刷严重、密封严密性差,以及阀门振动大导致定位器失准等问题产生的原因,提出了有针对性的解决方案.通过改造调节阀的阀内件以及优化调节阀的特性曲线,有效地提高了阀门的调节精度,消除了减温水系统的泄漏量,大大减少了设备维护工作量,为火电机组解决同类问题提供了借鉴的经验.     

再热器减温水调节阀异常运行的分析与改进

分析了某600MW超临界机组再热器减温水调节阀调节性能差、小流量调节时汽蚀冲刷严重、密封严密性差、阀门振动大导致定位器失准等问题产生的原因,设计了针对性的解决方案。通过改造调节阀的阀内件以及优化调节阀的特性曲线,有效提高地了阀门的调节精度,消除了减温水系统的泄漏量,大大减少了设备维护工作量,为火电机组解决同类问题提供了值得借鉴的经验。     

气穴中液压油温度随气泡膨胀变化规律

针对液压系统中气穴的产生及其发展过程常伴随着液压油温度变化的现象,研究了液压系统中气穴产生及其发展过程与液压油温度变化的关系。结合液压系统中气穴产生及其发展过程的特点,对气穴中气泡产生、发展过程中的热力学条件进行适当假设,应用热力学原理推导了气穴产生时气泡膨胀阶段气泡半径变化与液压油温度变化之间的关系式,改进了Rayleigh-Plesset方程。应用数值计算方法对气泡半径与液压油温度的关系进行了数值模拟研究,并通过试验进行了验证,得出气穴产生后,在气泡膨胀的整个过程中,多变指数k取1~1.24更符合实际规律。     

Ultrasonic plastification speed of polymer and its influencing factors

The melt filling difficulty in micro cavity is one of the main challenges for micro-injection molding (MIM). An approach employing ultrasound in MIM was proposed. The approach was extensively studied through experiments with a home-made experimental ultrasonic plastification device. The results of the experiments show that polymer ultrasonic plastification speed increases with ultrasonic supply voltage and plastification pressure. When the ultrasonic supply voltage is 200 V and the plastification pressure is 2.0 MPa, the polymer ultrasonic plastification speed reaches the maximum value of 0.111 1 g/s. The results also indicate that the ultrasonic cavitation effect is the most significant effect of all the three effects during polymer ultrasonic plastification process.     

Study of the phase-change coefficients of the cavitation model in cavitation flow fields generated from cone cavitator

The influence of phase-change coefficients variations in the Singhal cavitation model on the calculation results has been numerically studied. By comparing the numerical results and experimental data, the relationship between the coefficients and cavitation numbers is obtained. The calculation results of 2d axisymmetrical cylinder with 45-degree cone cavitator show that under different cavitation numbers, there are three typical kind of cavities, which are respectively main cavity, secondary cavity and rear cavity. The coefficients variations have a great influence respectively on the three type cavities in shape, collapse position, collapse strength, etc, and different cavitation numbers are corresponding to different phase-change coefficients. The cavitation flow field can be divided into three typical zones according to the cavitation number: weak-cavitation zone, secondary-cavitation zone and supercavitation zone. For 45-degree cone cavitator cylinder, the evaporation coefficients will firstly decrease and then increase with the decrease of cavitation numbers in secondary-cavitation zone, while the condensation coefficients keep relatively lower and almost unchanged. In weak-cavitation zone, there only exists the smaller main cavity attached to the model head or there is no obvious cavity. In supercavitation zone, the secondary cavity attached to the model will fall off and merge into the new rear cavity.     

水轮机空化系数的动态测定

水轮机叶片上的空化空蚀破坏造成水电站的频繁检修,利用计算流体力学软件Fluent对HL240型水轮机的设计工况进行数值模拟,模拟结果求出的空化系数与模型试验非常吻合。在一定的时段对机组的运行工况进行数值模拟,利用模拟结果可得到该时段叶片各个区域上的空化系数,从而判断该区域是否发生空化空蚀。把不同时段的结果进行汇总,则可以得到整个叶片上发生空化空蚀的总区域和各区域发生空蚀破坏的程度,从而对水轮机何时进行检修提供理论指导,使水电站经济效益达到最大化。     

超声处理对啤酒酵母影响的研究

以酵母细胞为研究对象,采用平板菌落计数法研究了超声作用时间、超声功率以及菌液初始浓度等条件对微生物存活率的影响.结果表明,超声功率、超声作用时间及菌液浓度均影响杀菌效果,长时间、大功率的超声处理对啤酒酵母具有较好的杀灭效果;当超声频率为28 kHz,超声时间达到30 min时,细菌杀灭率达到了95 %.     

Cavitation Inception in Turbulent Flows Around a Hydrofoil

For most engineering purposes cavitation de-grades performance.Engineering designs are ai med atproducing geometries and operating conditions thatresist cavitation.It is desirable to identify,under-stand,predict,and control the physical mechanismsleading to cavitation inception.One of the centralproblems in cavitation research has been the predic-tion of the onset or inception of cavitation.The cavi-tation occurring in a flow system is related to thepressure field and viscous flowpatterns[1].…