Simulation method for modeling the operation of magnetic flowmeters

We study the problems of testing magnetic flowmeters for liquid metals and determine their metrological characteristics. The existing flow measuring test beds for liquid metals are unsuitable for the experimental evaluation of the components of errors and, therefore, it is necessary to use simulation methods for modeling the operation of magnetic flowmeters. In order to perform the tests, it is necessary either to have liquid-metal test benches or apply the methods capable of investigation of the flowmeters without benches and reproducing the flow rate of metals in various operating modes. By analogy with the simulation method of examination of the water flowmeters, we develop a simulation method aimed at modeling the operation of magnetic flowmeters for liquid metals. The proposed method enables us to estimate the error of magnetic flowmeters under the operating conditions. The components of the measurement error of magnetic flowmeters caused by the violations of the geometry of primary converter (the sizes and locations of the electrodes and the design of the inductor coils), variations of the hydrodynamic conditions, and temperature dependence of the shunting effect of pipeline walls, are analyzed. We deduce an expression for the signal of the primary converter in the form of an integral (over the inner surface of the pipe) of the product of the radial component of magnetic field by the surface weighting function. The deduced integral expression serves as a basis of the proposed imitation method used for modeling of the operation of magnetic flowmeters. It can be interpreted as a magnetic flux through an induction coil located on the inner surface of the channel whose turns are directed along the level lines of the surface weighting function. If this coil is inserted into the flowmeter channel, then the time-integrated voltage induced in the coil becomes proportional to the voltage acting between the electrodes of the flowmeter. Note that the surface weighting function depends on the geometry of the channel, the kinematic structure of the flow, and the ratio of conductivities of the wall and the liquid. Therefore, the metrological characteristics of the flowmeter can be studied by the simulation method in the cases where each of the factors mentioned above varies individually or all these factors vary together. To do this, in modeling induction coil, it is sufficient to take into account the surface weighting function that reflects the behavior either of any investigated factor or of their combinations. We used the simulation methods to study the dependences of the flowmeter signals on the distribution of the velocity in the channel and the shunting effect of the pipeline wall.