Study Of Ultrasonic Flow Measurement In The Circulation Water

Flow measurement of large-diameter circulating water pipes has been a difficult problem in the power plant,and it’s of great significance for energy saving of thermal power units.By measuring propagation time of the ultrasonic wave along the channels, the ultrasonic transit-time method is a way to obtain flow measurement of large-diameter pipes.However,due to elbows、 valves and other pieces of local resistance contained in the pipes,and lack of straight pipe length in the downstream of local resistance,so it is difficult to ensure the flow velocity distribution in fully developed,and existing methods of measurement can not obtain satisfactory measurement accuracy.So for the problem of low accuracy in non-ideal flow field conditions of the ultrasonic flowmeter, the research had been launched from the following three aspects:Based on different turbulence models and the mesh densities,the simulation solutions had been designed. The results of different simulation schemes were compared by the experimental data of national engineering laboratory.A thermal power unit had been used as the research object, and CFD simulation method was used to model the actual recycled water pipes.The flow of the fluid in the circulating water pipes were analyzed by Tecplot.For a multi-channel measuring conditions,different ultrasonic measurement solutions were designed.The relationship between the measurement data and installation location、number of channels、numerical integration algorithms、channel rotation angle had been studied.The results showed that,the changing of installation location、number of channels、numerical integration algorithms and channel rotation angle can improve measurement accuracy. The paper can get at least two methods to control the measurement accuracy within 1% in the measurement location.For when the conditions are not available for multichannel measurement,the changing of installation location and rotation angle can improve measurement accuracy of the mono ultrasonic flowmeter,but the measurement accuracy within 1% can not be obtained.To solve the problem that mono ultrasonic flowmeter had a low accuracy,the model for solving flow sensor coefficient based on generalized regression neural networks was propose.The relationship between the network output and the training samples,spreads had been studied.The results show that the accuracy of adjusted results can be increased significantly.Then the correction software of mono ultrasonic flowmeter had been designed by the way of VB and Matlab Mixed Programming.