Velocity measurement in critical flow nozzle and its response using recovery temperature anemometry (RTA)

Abstract

Gas flow measurement is indispensable for social activities. Critical flow nozzles used for flow standards have been improved in ISO 9300 in 1990 and 2005. However, there are still issues regarding their rational shape. The main reason is that it is difficult to measure the flow velocity in the nozzle with low disturbance and high accuracy, although various velocity measurement methods have been proposed.In this paper, we developed a recovery temperature anemometry (RTA) to measure the flow velocity from micrometer-order temperature sensors. The validity of RTA was verified through experiments and numerical simulations. It was confirmed from the experimental results that the difference between RTA and the reference was within 5% in the velocity range from 60 to 95 m/s. The supersonic flow in the critical flow nozzle measured using RTA agrees with the numerical simulations. In addition, the sensor part of the thermometer has a small heat capacity, and a test to confirm the temperature response was also conducted. As a result, a temperature response of about 30Hz was confirmed.