The influence of viscothermal effects on calibration measurements in a tube

The Microflown, a novel acoustic flow sensor that is capable of measuring particle velocity in a fluid, can easily and accurately be calibrated in a standing-wave tube. This calibration method in the standing-wave tube is generally most favorable. Even very low frequencies can be measured with this simple setup. It is, therefore, important to analyze the limits of validity of the calibration method. In this paper the effects of the viscous and thermal properties of the fluid on the measurements of the transfer function, when calibrating sensors, are considered. It is shown both theoretically and experimentally for the broad-frequency spectrum that these viscothermal effects are relatively small