On the possibility of expanding the studied dynamic ranges in thermal anemometry

The paper presents the results of a study of the possibility of expanding the dynamic ranges of hot-wire methods. The relevance of the work is due to the demand in new methods for measuring the thermal and hydrodynamic parameters of high-speed gas flows for the purposes of scientific instrumentation. The novelty of the presented technical solution lies in the use of two hot-wires anemometers with significantly different thermal inertia for simultaneous measurement of the flow velocity and the heat transfer coefficient in it. The theoretical basis of the proposed method is based on the phenomenon of the inertia of the response of any thermodynamic system under a stepwise thermal effect on it. The method consists in placing in the investigated flow two bodies of the same shape and size which have significantly different thermal inertia. The bodies are subjected to a stepped thermal effect, and the non-stationary temperature delay of the bodies relative to each other is recorded. Using the maximum value of the temperature delay, the value of the heat transfer coefficient of the bodies with the investigated flow can be evaluated by calculation. The flow rate is found from the value of the moment of time corresponding to the maximum temperature delay while using the calibration characteristic previously obtained on the reference flow. The new thermal anemometry method is scientifically substantiated, the measurement equation of the method is obtained, the measurement algorithm and the generalized scheme of the device implementing the method are developed, and the value of the expected uncertainty of the measurement results is given. The simulation results showed that the relative uncertainty provided by the presented method does not exceed 1.5 %. The developed method makes it possible to significantly increase the accuracy and expand the studied dynamic ranges of the required values for a wide range of gas flows. The method can be used in the flow measurement of gas-air flows.