SPEED OF SOUND MEASUREMENTS IN HUMID AIR USING AN ULTRASONIC FLOW METER

Abstract – This paper presents results from experiments using an ultrasonic gas flow meter measuring the speed of sound in air at varying air velocities, humidities and temperatures. The meter utilises the sing-around technique. The transducers in the meter are silicon-based ultrasonic transducers with a centre frequency of 800 kHz. In order to investigate the performance of the flow meter it was tested in a novel gas flow facility connected to a calibration facility for flow meters used for liquids. The Reynolds ’ numbers for the investigated flow velocities ranged from 0 to 3,2·104, the relative humidity varied from 40 % to 80 % RH and the temperature varied from 20°C to 46°C. It was found that the experimentally measured speed of sound corresponded well with the speed of sound obtained from theory. It is also concluded that the flow meter could potentially be used in determining the relative humidity in flowing air at atmospheric pressures using speed of sound and temperature measurements