化工原理流量计性能实验教学的新探索

以化工原理实验中流量计性能实验的计算为例,讨论了1stOpt软件在化工原理实验中的应用。通过1stOpt软件计算出了体积流量和压差之间的关系。1stOpt软件具有简便、准确和可靠等优点。将1stOpt软件应用于流量计性能实验,不但能有效提高学生处理实验数据的技巧,而且也能使学生利用工程的观点来解决化工原理实验中遇到的问题。

常用流量计性能虚拟实验的设计与开发

虚拟实验是现代辅助教学技术之一,已广泛应用于学校和社会教育。本文首先阐述了虚拟实验的优点,然后论述了以flash作为开发平台,设计与开发常用流量计性能虚拟实验的思路,最后对虚拟实验系统的具体设计、实现过程进行了详细说明。

流量计性能受流量稳定性影响实验

流量波动是影响流量计性能的重要因素之一.为了测试流量计测量性能受流量稳定性的影响,通过控制水泵转速模拟了10种不同的流量稳定性状况,对4种典型的流量计进行了测量性能实验.以仪表系数或流量系数相对偏差、线性度和重复性为评价指标.实验结果表明:流量计性能受流量波动影响的大小,不但与流量波动的幅度和周期相关,而且与流量计本身特性相关;均速管流量计流量系数发生偏移,测量重复性变差,流量系数与差压平方根的倒数成正比,测量时间内取流量平均和差压平均的方法不能减弱该影响;涡轮流量计在小流量点处仪表系数明显偏小,仪表系数发生偏移,线性度变差;电磁流量计仪表系数发生偏移,测量重复性变差;科氏质量流量计仪表系数发生偏移;对使用转换器的流量计,提高其信号采样频率和运算速度,可以提高流量计测量精度.

一种高性能涡街流量计的研究与设计

涡街流量计因其具有电路先进、功耗微低、量程比宽、结构简单、阻力损失小、坚固耐用、用途广、使用寿命长、工作稳定、便于安装调试等特点,被广泛应用于石油、化工、冶金等工业部门以及市政建设和环保工程,主要实施对气体、液体、蒸汽的流量计量、检测和控制。及时根据市场需求,积极开展对涡街流量计转换器的优化设计,选用微功耗集成电路芯片,通过LC无源滤波、抗浪涌、温压分时复用、模拟信号处理电路优化等技术,提高了涡街流量计抗电磁干扰能力~([1]),实现对被测介质标准体积流量更精准的测量。

Influences of cavity leakage on the design of low flow coefficient centrifugal impeller

The low flow coefficient centrifugal impeller(LFCCI)gives a relatively low efficiency and a special treatment is required for the design of this kind of impeller.This paper investigates the influences of cavity leakage on the performance prediction and design of LFCCI based on Computational Fluid Dynamics(CFD)techniques.The results show that,the reduction in the effi-ciency of impeller due to the introduction of cavity leakage varies with the blade shape of impeller in a wide range since there is a strong and complex interaction of main flow and leakage flow in the LFCCI.To get a credible optimization result,the backside and foreside cavities should be considered in the CFD-based design of LFCCI.

Performance Test and Flow Measurement of Contra-Rotating Axial Flow Pump

An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows： （1） The pump is inherently designed as smaller sized and at lower rotational speed. （2） A stable head-characteristic curve for flow rate with negative slope appears. （3） As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows： （1） The structure of double shaft system becomes complex. （2） The pump performance is inferior at over flow rate as the rear rotor loading is weakened. （3） The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields.

The Effect of Diffuser Angle on the Discharge Coefficient of a Miniature Critical Nozzle

Many researches on critical nozzles have been performed to accurately measure the mass flow rate of gas flow,and to standardize the performance as a flow meter.Recently,much interest is being paid on the measurement of very small mass flow rate in industry fields such as MEMS applications.However,the design and performance data of the critical nozzles obtained so far have been applied mainly to the critical nozzles with comparatively large diameters,and the works available on miniature critical nozzles are lacking.In the present study,a computational fluid dynamics method has been applied to investigate the influence of the diffuser angle on discharge coefficient of the miniature critical nozzles.In computations,the throat diameter of critical nozzle is varied from 0.2 mm to 5.0 mm and the diffuser angle is changed from 2 deg to 8 deg.The computational results are validated with some experimental data available.The results show that the present computational results predict appropriately the discharge coefficient of the gas flows through miniature critical nozzles.It is known that the discharge coefficient is considerably influenced by the diffuser angle,as the throat diameter of nozzle becomes small below a certain value.This implies that the miniature critical nozzles should be carefully designed.

Performance Analyses for a Cyclone Type Filter

Flow characteristics inside a cyclone filter were investigated by the use of computational fluid dynamics(CFD). For computations, SST model was adopted. Parametric study was carried out considering the filtering performance. Revolution speeds were changed from 100 to 550 with 50 increments. A skirt is the driving source for cyclone operation. The influence of several design factors, such as the skirt length, the skirt gap and the return length to filtering performance was investigated under the particle diameter 100μm of debris material(Al, s.g.=2.7). The filtering performance was also investigated with the skirt length 28 mm changing the debris diameters from 1μm to 50μm. The flow rate of the working fluid was maintained at 0.55kg/s. It has been verified that the most influential factors to the filtering efficiencies was the skirt gap between the cyclone generator and the cyclone vessel.