Experimental and numerical investigation on the performance of small-sized cavitating venturis

Cavitating venturis (CVs) are simple devices which can be used in different industrial applications to passively control the flow rate of fluids. In this research the operation of small-sized CVs is characterized and their capabilities in regulating the mass flow rate were experimentally and numerically investigated. The effect of upstream and downstream pressures, as well as geometrical parameters such as the throat diameter, throat length, and diffuser angle on the mass flow rate and critical pressure ratio were studied. For experimental data acquisition, three CVs with throat diameters of 0.7, 1 and 1.5 mm were manufactured and tested. The fabricated CVs were tested at different upstream and downstream pressures in order to measure their output mass flow rate and to obtain their characteristic curves. The flow inside the CVs was also simulated by computational fluid dynamics. The numerical results showed agreement with the experimental data by a maximum deviation of 5–10% and confirmed that the numerical approach can be used to predict the critical pressure ratio and mass flow rate at cavitaing condition. It is found that despite the small size of venturis, they are capable of controlling the mass flow rate and exhibit the normal characteristics. By decreasing the throat diameter, their cavitating mode became more limited. Results also show that increasing the diffuser angle and throat length leads to a decrease in critical pressure ratio.     

基于模糊PID控制器的流量控制设计

现今流量控制系统很多都使用常规PID控制器,这样虽然比较方便,但不能在线整定参数,因而不能很好地控制非线性等复杂系统.在本系统中,采用模糊PID控制器来设计控制流量.模糊PID控制器将PID控制和模糊控制两种方法结合起来,既能消除稳态误差,又能对复杂系统进行简单有效的控制,从而达到控制要求.     

A novel technique of using a thyristor driven pump as the final control element and flow indicator of a flow control loop

In the present paper, design of a flow control loop using a thyristor driven pump as final control element has been described. In this technique, the load current of a thyristor driven pump motor has been utilized as a mass flow sensing parameter of a fluid passing through a pipeline. This thyristor driven pump has been utilized as a final control element of a flow control loop and the speed of the pump has been selected as the manipulated variable. The non-linearity between the thyristor input signal and pump output has been eliminated by using a modified PID control technique with inverse derivative control action. Thus without using any conventional flow meter and control valve only the thyristor driven pump has been utilized both as the final control element and flow indicating device by using the proposed technique. The whole system has been designed, fabricated and tested by using tap water as the flowing liquid through a pipe line. The experimental results along with the theoretical analysis are compared and reported in the paper.     

Development of a transfer standard with sonic Venturi nozzles for small mass flow rates of gases

We have developed a transfer standard system with sonic Venturi nozzles for small mass flow rates of gases. The system is composed of a newly developed automatic pressure controller, two pressure sensors and one temperature sensor to measure the flow conditions in the upstream and downstream sides of a nozzle. The whole system is packed in a portable aluminum trunk. The data are sent to a laptop computer, and the results are displayed on the screen and are written to files. The system can calibrate a flow meter in the flow rate range from 10 mg/min to 100 g/min using ten different sonic Venturi nozzles with the expanded standard uncertainty (k=2) being less than 0.2% for nitrogen. Examples of mass flow controller calibrations are given.     

温差为源信号的流量控制器

本文介绍一种温差为源信号的流量控制器．是用于采暖供热系统中调控同轴差速式热量表两个固定式叶轮腔中流量的控制装置。由设置于进．出水流腔体内的一对装有饱和蒸汽工质的密闭腔体通过同轴密封联接的弹性波纹管带动串联于卸流旁路中的节流阀的阀芯相对阀壳滑动．从而改变节流阀的开度，达到用两个流体腔内的温度差间接控制出水流道中的流量，使进、出水流道产生相应的流量差．以达到准确热计量的目的。控制器由机械组件构成，自动运作，不依赖外部能量，工作稳定可靠。     

Optimal design and development of electromagnetic linear actuator for mass flow controller

In this paper, we constructed the analytic model of control valve as a function of electric and geometric parameters, and analyzed the influence of the design parameters on the dynamic characteristics. For improving the dynamic characteristics, optimal design is conducted by applying sequential quadratic programming method to the analytic model. This optimal design aims to minimize the response time and maximize force efficiency. By this procedure, control valve can be designed to have fast response in motion.     

配电站直流系统控制器设计

以PLC为核心处理器,实现对配电站直流系统进行自动化管理.具体分析了该系统的组成与功能,以及系统通信功能的实现,介绍了PLC的部分控制程序.     

Development of a flow meter for instantaneous flow rate measurements of anaesthetic liquids

An instrument has been developed for instantaneous flow rate measurements of anaesthetic liquids. For periodically time-varying flows, the instantaneous flow rate is reconstructed from the axial velocity time series measured on the centre-line of a pipe. The theoretical background for the method is given and it is demonstrated that fast variations of flow rate can be measured. The instrument is based on a laser Doppler anemometer (LDA) to record the instantaneous velocity on the axis of a capillary; an ultraviolet laser permits velocity measurements with good signal-to-noise ratio from tracer particles in the submicrometer range present in anaesthetic liquids.     

Uncertainty estimation of a liquid flow standard system with small flow rates

A liquid flow standard system is used to calibrate liquid volume of fuel–oil flow meters at small flow rates between 50 L/h and 700 L/h. However, the system has not been used to calibrate volume flow rate because the system is only operated with the standing-start-and-finish mode. In this study, the liquid flow standard system was rebuilt to provide a calibration service of volume flow rate by attaching two flow diverters, which can operate the system with the flying-start-and-finish mode. To evaluate its performance for volume flow metering, several techniques were introduced. First, diverter timing errors were estimated by linear regression. Second, covariance between buoyancy correction factor and water density was obtained to consider interdependency between the two measurands. Third, calibration and measurement capability (CMC) was evaluated by setting a fixed value of collected weight or elapsed time for flow diversion. Finally, several CMCs were compared to find the best measurement condition. As a result of the above approach, the CMC of the liquid flow standard system was found to be (0.10–0.52)% (k = 2) for (50–700) L/h with a minimum collected weight at 10 kg.     

Wiegand传感器原理及应用

在介绍Ｗｉｅｇａｎｄ传感器工作原理的基础上,阐述了其在椭圆齿轮流量计中的应用。     

二维模糊控制器在小型轮式机器人中的应用

为了提高小型轮式机器人电机系统的运行性能,设计了一种带修正函数的二维模糊控制器.首先阐述模糊控制器的基本结构,并结合具体控制对象设计了fuzzy论域和模糊控制规则;其次设计了实现该控制器的嵌入式平台.最后给出了实验结果,实验证明了该模糊控制器的有效性.     

电磁流量计的使用及电磁兼容性分析

介绍利用面板及智能终端进行电磁流量计参数设置和组态的方法,以及提高电磁流量计的电磁兼容性技术。电磁流量计的干扰源主要包括工频电磁干扰、流体电化学干扰噪声和电源干扰噪声。目前电磁流量计主要采用低频或双频矩形波励磁技术、同步采样技术、输入保护、接地技术等来降低干扰。实际应用表明,这些技术有较好的抗干扰效果。     

Experimental and numerical investigation of the cavitation-induced choked flow in a herschel venturi-tube

Due to their simple geometry, cavitating Venturi nozzles (CV) are a long time subject of experimental as well as numerical investigations. However, research mostly focused on certain aspects like the comparison of experimental data with numerical cavitation models or the spray development of diesel injection nozzles, but rarely on the choked flow condition itself, especially with regard to liquid flow measurement.If the pressure decreases due to the local acceleration of the flow to the respective vapor pressure, a choked flow condition similar to the well-known critical flow Venturi-nozzles (CFVN) develops. For the purpose of gaining further insight into the choked flow condition with respect to liquid flow measurement, high-speed camera investigations of a transparent Herschel Venturi-tube configuration, also known as classical Venturi-tube, were performed. Together with pressure and flow rate measurements, they demonstrated the overall stable flow behavior under choked conditions. With additional numerical investigations, phenomena during the onset of the choked condition were clarified. Furthermore, a simple correlation for the calculation of the actual flow rate during the choked condition, including a temperature correction was proposed.     

PLC可编程序控制器在铝锭码垛机中的应用

铝锭码垛机是一个较复杂的生产线,将可编程序控制器用于该生产线,极大地简化了电器控制过程,且灵活性大为提高。     

矢量谐振控制器在并联有源滤波器中的应用

针对并联有源滤波器(SAPF)补偿电流的控制问题,分析了比例积分(PI)控制器和矢量谐振(VR)控制器对SAPF补偿电流控制的优势和不足之处,提出了这两种控制器并联的电流控制策略,具体将PI控制器、VR控制器分别用于在同步旋转坐标系下无静差地调节基波电流分量和相应频率次的谐波电流分量,介绍了SAPF的数学模型及其特点,并基于零极点对消的方法,详细分析了PI控制器和VR控制器的电流闭环频率特性,论证了并联电流控制方法的可行性,并在Matlab/Simulink模块中搭建的SAPF仿真系统和SAPF实验样机中进行了应用验证。仿真和实验结果都表明,采用该方法的SAPF对主要次的谐波电流有良好的补偿效果。     

塑料挤吹型胚控制器的设计

分析了目前对塑料制品的需求增加,塑料制品结构多样化等现状,提出了具有壁厚控制功能的吹塑成型控制器.并分别从软件系统和硬件系统角度出发,对挤吹成型控制器进行了设计,实现了挤吹成型"高可靠性、高适应性、高效率"的要求.     

智能IC卡水表控制器的设计与应用

本文详细介绍了智能IC卡水表及售水管理系统的组成、功能:主要对智能IC卡水表控制器工作原理及软硬件设计进行了详细阐述,最后讨论了IC卡水表的应用.     

输油气管道自动化系统常用控制器的研究

现管道系统应用的控制器主要有三种:常规P ID控制器、高级控制器和模糊控制器。作者对这三种控制器的控制功能和工作原理进行了阐述,并对其实现方式、使用性能、工程成本等方面进行了比较分析,希望对控制器的工程应用有所借鉴。     

自力式压差控制阀在空调系统中的应用

结合中央空调系统的调节特点及电动二通调节阀的工作特性,采用自力式压差控制阀配合电动二通调节阀使用,发挥了电动二通调节阀的调节优势,实现空调水系统根据用户需求变流量,从而达到舒适和节能的目的。     

基于单片机的脉冲式运动控制器的开发与研究

运动控制器作为机电一体化的核心,在工业生产中得到了广泛的应用,在科技进步的同时,市场需求决定了高性能、低成本的运动控制器将具有广阔的发展前景。在分析数控系统组成的基础上,以具有DSP功能的16位单片机SPCE061A作为核心处理器,以松下数字式交流伺服电机及配套驱动器为控制对象,设计了一款经济实用的脉冲式多轴运动控制器。结合单片机外围定时计数器,通过脉冲方式对电机进行控制,可同时对四轴伺服电机或步进电机进行控制。试验结果表明该系统电路设计合理、结构简单、运行稳定可靠、性价比高,可用于数控机床、机器人、自动导航小车等领域。