ESTIMATION OF THE SYSTEMATIC UNCERTAINTY OF ULTRASONIC FLOWMETER IN A NONISOTHERMIC FLOW
When measuring the flow rate of a time-of-flight ultrasonic (US) flowmeter, an additional systematic uncertainty of the induced inhomogeneity in the velocity distribution of sound is possible. Based on the refined theory of sound propagation in an inhomogeneous flow, a mathematical model is developed for calculating the acoustic ray trajectories in a time-of-flight ultrasonic flowmeter. The analysis of the influence of various factors on the trajectories of ultrasound is carried out. It is shown that the displacement of trajectories in a nonisothermal flow increases with increasing D c / c 0, M and decreases with increasing Re. The displacement of trajectories causes additional systematic uncertainty. It is shown that it is necessary to introduce correction coefficients depending on the Mach number of the flux. It is established that with an increase in Re the additional systematic uncertainty decreases, and with increasing M and D c / c 0 increases. The determination of the velocity from different equations leads to a different uncertainty. The obtained data allow performing quantitative estimates of the allowable inhomogeneity of the temperature field.