A High-pressure Bi-directional Cycloid Rotor Flowmeter

Flow rate is one of the most important parameters in industrial automation, and flowmeters are the most widely used instruments for measuring this parameter. Positive displacement meters are considered to have a high accuracy and robustness, due to many advantages, such as good stability, insensitivity to upstream velocity distribution and fluid viscosity, easy maintenance, PD meters still take up a large proportion in all kinds of flowmeters, especially in custody transfer operations and hydraulic control system. The research of PD meters with high accuracy and high pressure resistance can improve the performance of electro-hydraulic control system and is an impetus for the development of flow transmission and control technologies.This dissertation has focused on the high-pressure bi-directional cycloid rotor flowmeter. With abundant literature reviews, theory analysis, computer simulations and experiments, the following points are studied in depth. Firstly, the structure of the high-pressure bi-directional cycloid rotor flowmeter is proposed, which contains a pair of inner meshed cycloid rotors. This kind of flowmeter has the advantages of concise structure, low pressure loss, high accuracy and smoothly running. There are oil grooves in the top cover and bottom cover to maintain the rotation, and the special shape of the grooves are helpful to increase the flow passage area and decrease the pressure loss. The rotor speed sensors which use the non-contact detection principle and the secondary instrument are designed, which makes the flowmeter can bear high pressure. The dissertation explores the influence of the fluid temperature and elastic modulus, and after that an experiment system is built up to calibrate the prototype. According to the results, the reasons of the relative errors are analysed.In chapter one, the development, working principle and classification of flowmeters are reviewed, especially proposed the innovation of the rotors’shape and the mechanical structure. The research significances, research points and research contents are described generally.In chapter two, the structure of the high-pressure bi-directional cycloid rotor flowmeter is presented. The measuring chamber distorts under high pressure, which leads to the increasing of the measuring error. So a finite element analysis has been done to the covers and shell to make sure that the deformation is small enough when they are bearing a high pressure. Also analysis of fixed bolts strength has been done to make sure the security. At last, an experiment is done to measure the real deformation of the covers when they are under high pressure, and the results of the experiment and the finite element analysis are identical with each other.In chapter three, we focus on the cycloid rotors. The constructing principle of the cycloid rotors teeth is specified, and the meshing process is analyzed including the changing processes of meshing angle and slip rate. The calculation method used to determine the displacement of the cycloid rotor flowmeter has been presented to help design the flowmeter. At last, in order to solve the problem of locked dead lead by multipoint engagement, a modification method of the rotor curves is described.In chapter four, analysis on the rotor speed sensors and the secondary instrument are presented. The rotor speed sensors are made up by permanent magnets and hall sensors. In order to optimize the sensors, finite element analysis of the magnetic field is suggested. A secondary instrument based on MCU is used to change the electrical signals into the display number which is shown on the Nixie Tubes. And this secondary instrument can adjust the flow coefficient easily.In chapter five, the experimental characteristics of the cycloid rotor flowmeter including pressure loss characteristics, the speed fluctuation and internal leakage characteristics are studied in depth. A prototype and an experiment system were fabricated as part of this research. A high accuracy standard oval gear flowmeters with the accuracy of ±0.2% is used to simplify the calibration process. Because the test environment of the oval gear flowmeter and the cycloid rotor flowmeter is different, a converted coefficient is adopted to change the results given by cycloid rotor flowmeter according to the temperature and pressure. After doing modeling and analysis of internal leakage, a modification method is proposed on the basis of least square method to decrease the relative errors below±0.3%.In chapter six, all achievements of the dissertation are summarized and the further research work is put forward.