High sensitive Polyimide-based single-walled carbon nanotube thermal film sensor for fluid shear stress measurements

A flexible polyimide-based single-walled carbon nanotube (SWCNT) thermal film sensor has been developed for wall shear stress measurements in both air and water. To ensure high sensitivity, vacuum thermal annealing and electrical aging are conducted to enhance the electric properties of the sensor with low-resistance and the high temperature coefficient of resistivity (TCR). The TCR of sensors can reach to 8040 ppm/°C to the author's knowledge, which is the highest reported value of thermal sensors used for shear stress measurements. In calibration, the output voltage of the sensor is proportional to the one third power of wall shear stress with the sensitivity on the order of mV Pa^-1 in the constant current operation mode. The repeatability error is no more than 1% in both air and water, which confirms the capability of the flexible SWCNT thermal film sensor for fluid wall shear stress measurements with high sensitivity.