具有工业以太网接口的差压质量流量计研究

研究了一种具有工业以太网接口的差压质量流量计。该质量流量计利用差压、压力、介质温度组成的复合多功能传感器,以及管道中节流装置进行质量流量测量,通过DSP对差压、压力和介质温度信号进行处理,得到流体的瞬时质量流量和累积质量流量;进行了工业以太网(MODBUS/TCP)接口模块的电路设计和相应的软件设计。最后以水为介质,在不同的节流件孔径条件下进行了质量流量测量,不确定度均为±1%左右。     

背靠管式差压气体流量计

根据差压流量计的测量原理,设计了背靠管式差压气体流量计,采用背靠管式节流体结构使得迎风取压孔和背风取压孔处产生了较大的压力差,利用设计的单片机测量系统对压力信号进行采集、放大、滤波和模数转换处理后,实现了对较低气体流速的流量测量。通过试验证明:该流量计的测量下限低于0.5 m/s,测量误差小于1%。     

一种基于频率的光纤光栅小型流量计研究

提出了一种基于频率的光纤光栅小型流量计用于流体流量测量的设计方案。该流量计基于卡门涡街原理,利用发生体后产生脉动流体,通过测得其振动频率来测流体流量。通过对涡街流场二维仿真和三维仿真建模进行了理论分析并确定了Bragg光纤光栅粘贴的位置,实验表明,该流量计具有良好的可行性。     

脉动流对差压式流量计测量误差影响的研究

基于脉动流场中差压式流量计的计量特性，本文分析了差压式流量计在各种脉动流频率和幅度下的流量测量误差。针对不同脉动频率和脉动幅度的脉动流，在自行设计的实验装置中使用响应时间不同的差压式流量计进行流量测量的研究，获得了流量计响应时间、流体的脉动幅度和频率与流量测量误差间的变化对应关系。研究结果表明，通过减少脉动幅值和缩短流量计的响应时间可有效地减少流量测量误差。     

长喉颈文丘里喉部取压位置对湿气测量模型影响的试验研究

文丘里流量计广泛应用于湿气流量测量领域。为探索长喉颈文丘里管喉部取压位置对其湿气测量模型的影响,从理论上对其各个部分压力降进行研究。设计内径为50 mm、节流比为0.4的文丘里试验样机,取压位置距离喉部入口分别为喉部直径的0.5倍、3.75倍和7倍。在天津大学流量实验室双闭环中压湿气装置上进行试验验证。试验压力为0.2~0.8 MPa,干度为0.5~1。根据试验数据,针对不同的喉部取压位置,分析虚高梯度与L-M参数之间的关系;同时分析差压比K参数灵敏度与液气质量比qml/qmg之间的关系,发现虚高和K参数均受喉部取压位置的影响。建立基于K参数、Froude数、气液密度比的虚高模型和液气质量比模型,通过迭代算法求出气相和液相流量。分析基于不同取压位置的测量模型对湿气两相流气相和液相流量预测结果误差和不确定度的影响,得出取压位置为距离喉部入口3.75倍喉部直径时效果最好的结论,该位置模型气相测量不确定度为5.06%,液相为2.15%。     

智能化差压式双向流量计的研究

本文介绍了一种新研制的新型智能化差压式双向流量诸，它包括差压式双向流量传感器，测量电路和单片机系统，能将流量信号转换成电量的变化，通过单片机处理后，用ＬＥＤ显示流量，并对流量计测试测试。结果表明，该传感器能测量正，反向流量，具有较好的线性，也能进行一定的动态流量测量。     

温压补偿型超声气体质量流量计

对超声时差法进行算法改进后，结合气体密度公式推导出超声质量流量方程，据此设计出温压补偿型超声气体质量流量计，给出了流量计核心系统及温压补偿部分的硬件设计。将只用于流体体积流量测量的超声流量计推广到气体质量流量测量领域，使超声流量计趋向理想化。经实验证明此流量计在测量常压空气时精度可达1．42％。     

一种新型硅压阻式流速流向传感器的设计

本文设计了一种基于体微机械加工技术、SU-8-光刻胶工艺和压阻检测的新型硅压阻式流速流向传感器.该传感器由立柱和支撑梁构成,这种结构将流体的流速流向信息转化为立柱的倾斜和相应的梁的变形,通过4根正交梁端部的压阻应变计来测量梁的变形.通过测量压电电阻的阻值变化就可以得到流体的流速和流向.利用惠斯通电桥来获得正弦电压输出.理论分析了器件的结构变形和电压输出,并用有限元方法进行了验证.为该传感器设计了一套基于键合技术的体微机械加工工艺.     

双钝体涡

涡街流量计测量应用广泛,但小流量信噪比低、抗干扰性能差.本论文提出以双钝体组合强化流体振动,从而降低涡街流量计的计量下限,提高其抗干扰性能.通过实验研究获得了优化的双钝体组合,表明双钝体组合能达到强化流体振动和提高流量计信噪比的目的.     

双钝体涡街流量计流体振动特性研究

涡街流量计测量应用广泛,但小流量信噪比低、抗干扰性能差。本论文提出双钝体组合强化流体振动,从而降低涡街流量计的计量下限,提高其抗干扰性能。通过实验研究获得了优化的双钝体组合,表明双钝体组合能达到强化流体振动和提高流量计信噪比的目的。     

A study of mass flow rate measurement based on the vortex shedding principle

Mass flow rate measurement is very important in the majority of industry processes because the mass of fluid is not affected by ambient temperature and pressure as the volume will be. Conventional mass flow rate is normally derived from the volumetric flow rate multiplied by fluid density. The density can be obtained by a densitometer or calculated according to the temperature and pressure measured by a thermometer and pressure gauge respectively. However the measurement accuracy is not always satisfactory. Flowmeters directly measuring mass flow rate have been studied and developed recently, such as Coriolis and thermal flowmeters. Unfortunately they still have some limits in practical applications. A new method in which mass flow rate can be directly measured based on the vortex shedding principle is presented in this paper. As a vortex flowmeter, von Kàrmàn vortex shedding is generated by a bluff body (vortex shedder), leading to a pressure drop and pressure fluctuation. A single differential pressure sensor is employed to detect the pressure difference between upstream and downstream sides of the vortex shedder. Both vortex shedding frequency and pressure drop are contained from the output signal of the differential pressure sensor, so that the mass flow rate can be obtained from the pressure signal. Numerical simulation has been done to analyze the characteristics of the fluid field and design the measurement device. The Computational Fluid Dynamics (CFD) codes Fluent were used in the numerical simulation. Experiments were carried out with water and gas, and the results show that this method is feasible and effective to measure the mass flow rate. This method has also robustness to disturbances such as pipe vibration and fluid turbulence.     

Performance evaluation of piezoelectric and differential pressure sensor for vortex flowmeters

Piezoelectric and transient differential pressure sensors are two among the most widely employed sensors for vortex flowmeter application. The present study evaluates the performance of these two techniques under fully developed and disturbed flow conditions. Firstly, the location of the transient differential pressure sensor is optimized to obtain high amplitude signals and good linearity in Strouhal number. Empirical mode decomposition method in combination with autocorrelation decay is successfully employed at high Reynolds numbers to identify the vortex shedding frequency in presence of hydrodynamic noise. The performance of the differential pressure sensor deteriorates significantly under disturbed flow conditions at low Reynolds number due to the presence of low frequency components. This deterioration in the signal quality limits the lower operating range of the flowmeter with differential pressure sensor. The output signals of the piezoelectric sensor and differential pressure sensor under no flow condition are compared to obtain the background noise due to piping vibrations and electrical interferences. These results will help a designer to suggest robust signal processing algorithms for vortex frequency detection.     

Mass flowmeter detecting fluctuations in lift generated by vortex shedding

Indirect measurement of mass flow rate has been widely used, combining volumetric flowmeters with the temperature and/or pressure compensation of fluid density. However, this approach has disadvantages, such as a complicated compensating algorithm, and is only applicable to ideal gases, except for highly pressurized and other gases. A flowmeter for direct measurement of mass flow is more suitable for overcoming the disadvantages of indirect measurement. The authors propose one approach to direct measurement using a vortex flowmeter. That is, Karman vortices are generated by a vortex shedder, and fluctuations in the lift and their frequency are detected by stress sensors built into the vortex shedder. The amount of lift is divided by the frequency to yield signals proportional to the mass flow rate. The proposed approach to sensing features simplicity both in principle and in sensor construction. Satisfactory results are obtained from applying this approach to water, air and other gases.     

Influence of blockage and upstream disturbances on the performance of a vortex flowmeter with a trapezoidal bluff body

Experimental investigations are conducted on vortex flowmeter with the differential wall pressure measurement method. The bluff body employed is trapezoidal in shape and water is used as the working fluid. Three different blockages (0.14, 0.24 and 0.3) are considered in this study. The performance of the vortex flowmeter is studied both under fully developed condition and in the presence of flow disturbances. The flow disturbance is created using 45° swirl generator and gate valve placed at different upstream distances. The performance of the flowmeter is also evaluated in the presence of a Laws Vanes flow conditioner placed downstream of the swirl generator. The blockage ratio of 0.3 is found to be the best among all the blockages studied under both disturbed and undisturbed conditions.     

一种新式差压流量计的设计与应用

该文分析了影响蒸汽流量准确计量的主要因素,介绍了传统的蒸汽流量计如孔板流量计和涡街流量计的使用局限性,详细介绍了一种基于皮托管原理的新式差压式流量计的设计原理、结构特点及其标定方法,通过实例给出了典型蒸汽工况下选择流量计的考虑因素,以及应用这种新式差压式流量计的选型和计算过程。     

基于HART协议的温压补偿型涡街流量计的设计

在传统涡街流量计的基础上，设计出符合HART协议的两线制一体化温压补偿型涡街流量计。介绍了传感器工作原理和温压补偿方法，给出系统的设计结构和硬件电路组成。着重阐述了HART协议在涡街流量计中的软硬件实现方法．并通过HART调制解调器实现了仪表与上位机之间的双向数字通讯。     

Influence of blockage and shape of a bluff body on the performance of vortex flowmeter with wall pressure measurement

Experimental and numerical investigations are carried out with various bluff body shapes to identify an appropriate shape which can be used for vortex flowmeter application. In both the cases vortex shedding frequency is inferred from the fluctuation of wall pressure. The numerical simulations are carried out with cylindrical and triangular bluff bodies to understand the vortex shedding phenomenon and to identify an appropriate turbulence model for this class of flows with wall pressure measurement. The simulations reveal that the k-ε RNG model predicts the Strouhal number closer to the experimental results than other models. The experimental investigations are carried out with several bluff body shapes, such as triangular, trapezoidal, conical, cylindrical and ring shapes, with water as the working medium. In this context, the effects of sampling rate, tap location and blockage effects are explored. The results suggest that the axisymmetric tapping is better than differential pressure tapping in terms of signal amplitude. The non-dimensional location of the static pressure tap is found to be 0.714 times diameter of pipe times blockage. The trapezoidal bluff body is found to be the best among all the bluff bodies investigated in terms of signal amplitude and constancy of Strouhal number. The vortex flowmeter performance is also measured under disturbed flow conditions created by using gate valve and bends. These results are significant because they provide an optimum bluff body shape and blockage, and also present the performance of vortex flow meter under disturbed flow conditions which is rather seldom reported in the literature.     

Static and dynamic characteristics of a hydraulic Wheatstone bridge mass flowmeter

The hydraulic Wheatstone measuring bridge is a potential linear-flowmeter solution for direct mass flow measurements. In a concrete example of the flowmeter, four matched orifices are used as the local flow restrictors in the bridge network. This paper presents an analysis of the nonlinearity of the static measuring characteristics of the hydraulic measuring bridge, which results from the impact of the flow rate on the local pressure loss coefficient of the orifices. The results of the experimental analysis were confirmed with solutions of the physical–mathematical model of the flowmeter. Another objective of this study was to evaluate the suitability of this flowmeter for pulsating flow measurements. For this reason, a dynamic model of the flowmeter was built by upgrading the steady-state flow model with the effects of fluid compressibility and inertia. Since the flowmeter’s characteristic is linear, it was found to be unaffected by the square root errors, which is the case with standard pressure differential flowmeters. On the other hand, the flowmeter’s frequency characteristic exhibited a typical resonance, the value of which depends on the fluid and the dimensional properties of the bridge.     

Novel liquid flow sensor based on differential pressure method

In this article, a novel liquid flow sensor which is composed of a special structure conduit main body and a differential pressure sensor was designed, fabricated, and calibrated. The conduit main body includes an inlet channel section with a branch conduit connecting one end of the pressure sensor, a throat channel section, and an outlet channel section with a branch conduit connecting another end of the pressure sensor. The basic principle is to employ a differential pressure sensor to measure the pressure difference between the inlet channel and outlet channel of the conduit main body when fluid passes through it. The pressure difference between the two ends of the differential pressure sensor (i.e., the two branch conduits located in the inlet and outlet channel sections) is of either forward or backward flow and directly interrelates with the volume flow rate (mass flow rate or flow velocity) via the conduit main body, so the volume flow rate or mass flow rate or flow velocity can be calculated and the flow direction can be determined from the detected pressure difference. This liquid flow sensor is characterized by using only one differential pressure sensor of a simple structure, the error of which is less than 1%.