Ultrasonic gas flow and concentration measurement in hydrogen and nitrogen gas mixtures

Ultrasonic flowmeters are useful for hydrogen flow and concentration measurement in fuel cells. However, the presence of reacted water necessitates a water-tolerant flow path design, leading to the use of non-ideal flow correction curve. In such designs, measuring gas mixtures with significantly different kinematic viscosities, such as hydrogen and nitrogen, can cause measurement errors. To achieve high-accuracy measurement, we applied a method to estimate the kinematic viscosity of the gas mixture based on the concentration calculation using speed of sound and then correct the flow rate based on these properties. Using critical nozzles calibrated to the national gas flow rate standards for hydrogen and nitrogen, our experiments confirmed the accuracy of our method for nitrogen and hydrogen gas mixture, with concentration measurement errors within 0.04 vol% and flow measurement errors within 0.5 %.