Research On Mass Flow Rate Measurement Using Vortex Flowmeter Based On Differential Pressure Principle

Flow is an important parameter in industrial process control. These years flow measurement and instrumentation has rapidly developed due to the demanding of modern industrial manufacture. In practical application flow measurement is more complicated because of complication and variety of the measurement object. There are still many unsolved flow measurement problems up to present time. Among these problems mass flow rate measurement is more important and difficulty. Great efforts should be done to solve this problem.The vortex flowmeter is a device that based on Von Karman vortex shedding principle. Because of the advantages that can not be instead of, vortex flowmeter has rapidly developed since 70 years 20 century and looks highly promising. It is currently applied extensively to the measurement of gases, liquids and steam over a wide range of flow rates. However, when compared for the conventional flowmeter, it still has some limits in theory and practice. Work should be done to closer understanding of the vortex shedding phenomenon, solving weakness of anti-disturbance and low flow rate measurement.Based on the theory of hydrodynamics and the characteristics of vortex flowmeter, a new method using differential pressure principle to detect the vortex signal is proposed in this dissertation. Using this method mass flow rate of different fluid medium such as gases, liquids and steam can be directly measured by vortex flowmeter. This method also has good ability to anti-disturbance.The dissertation mainly focuses on the following contents:(1) Flow measurements especially mass flow rate measurements were briefly summarized. The literatures about vortex flowmeter especially for the mass flow rate measurement were detailed summarized. Based on the generation of vortex shedding and the characteristics of fluid field, a new method using differential pressure principle is proposed. The characteristics, realization and difficulties of this method were analyzed and proposals were brought forward to solve the difficulties.(2) Numerical simulations were carried out to the vortex flowmeter fluid field. According to the Computational Fluid Dynamics (CFD) theory, the physical and mathematical models were established. CFD codes FLUENT were used in the numerical simulations. The emphases of simulation were vibration and average of pressure in the fluid field near vortex shedder. Static pressure on some given pointswere monitored, analyzed and compared. The results of the simulation gave direction to the research on experiments.(3) According to the differential pressure principle proposed in this dissertation, the schemes of experiment were established. Gas and water were used for the fluid medium. The differential pressure sensors were selected for experiments. The signal processing of differential pressure was introduced.(4) Experiments were carried out to the research on mass flow rate measurement using vortex flowmeter. The results of experiment gave the relationship between differential pressure at different positions and flow rate, the vibration of meter coefficient (K-factor). The appropriate positions to detect the differential pressure were determined. At specified positions K-factors of different fluid medium are the same. The results also proved that this method can measure the mass flow rate accurately and realized multi-parameters measurement.(5) Modern signal processing methods were used to deal with the vortex signal. The signal processing methods widely used in vortex flowmeter at present time were introduced. A new recursive Discrete Fourier Transform (DFT) algorithm based on sum-and-difference formula of trigonometrical function was proposed to deal with the vortex signal. The experimental results proved that this method has stronger anti-noise ability, higher efficiency and broader application prospects.The research results show that the method using differential pressure to measure mass flow rate by vortex flowmeter is feasibility and effective. It provides a new method to directly measure mass flow rate.