Evaluation of ultrasonic sensing of methanol concentration for direct methanol fuel cell

This investigation evaluates the effectiveness of the ultrasonic sensing of methanol concentration and establishes two regression models based on measurements of sound propagation speed against methanol concentration. Uncertainty analysis reveals that propagation distance and equipment sampling rate affect the accuracy of sound speed measurement. An ultrasonic blind region is present because sensitivity declines at a temperature of approximately 63 °C. The accuracy of measurement of the speed of sound is increased by the calibration of transducer distance because of variations in temperature. Increasing the transducer distance to 20 mm reduces the error between the theoretical and experimental speed of sound to 0.59 m/s. If the transducer distance is well calibrated, then the range of temperatures associated with ultrasonic blindness is reduced to 2–6 °C. Frequency shift and attenuation in the blind temperature range are also investigated, indicating that these two parameters are insensitive to methanol concentration.