Research On Measurement Characteristics Of Vortex Flowmeter Under Different Fluid Conditions

Vortex flowmeter is a kind of novel velocity-type flowmeter with the advantages of stabilization, low pressure loss and wide measurement range, so it is widely used in chemical industry, petroleum, metallurgy, light industry, food industry and other flow industry. Because the field and fluid conditions of vortex flowmeter used is complex, it is significant for researching the measurement characteristics of vortex flowmeter under different fluid conditions to improve the measurement accuracy and the field of application.The mainly research works of this thesis are as following.1. The problem and shortage of comparing the vortex flowmeter's pressure loss with orifice plate's by computing is analyzed. Pressure loss of vortex flowmeter is investigated and the result of experiment is compared at a same flow area with orifice plate flowmeter. As a result, their pressure loss ratio is not so much as given in some papers.2. With setting different gas pressure in pipe, the pressure loss coefficient of vortex street flowmeter is investigated in fluid lab in school Electrical Engineering and Automation of Tianjin University. Results show that the change of gas pressure in pipe can affect the pressure loss coefficient by processing a mass of experimental data.3. It is presented how to successfully simulate the phenomenon of Karman vortex street when fluid passes by vortex flowmeter by using CFD software. By comparing the vortex generating frequency with test data, the error is less than 10%. It shows that this is a good method to improve and optimize the vortex flowmeter by CFD software. Based on simulation and test, the optimal pressure tapping position is determined for 2.8 times of cut-off face after vortex generating body.4. The measurement characteristics of vortex flowmeter changing with liquid phase fraction are studied. The experiment is proceeded by the two methods of pulse count and spectrum. The result approved that the spectrum is better than pulse count under vesicular fluid condition.5. The measurement uncertainty, error and the signal quality of vortex flowmeter is investigated under fog two-phase flow. The phenomenon of experiment is explained by numerical method. 6. The present statuses of the research on the structure and transferring mechanics of vortex streets is studied comprehensively. The mathematical model about Strouhal number changing with liquid phase fraction is founded. The experiment proved the validity of mathematical model.