Experimental and theoretical study of an on-wall in-tube flexible thermal sensor

We propose a novel type of on-wall in-tube flexible thermal sensor, which is able to measure the flow rate under both developing and fully developed flow conditions. We fabricated the thermal flow sensor on a flexible polyimide film by using polymer MEMS technologies and formed a ring-shaped on-wall in-tube sensor configuration by inserting the sensor into a tube. The resistance of the sensor linearly changed with the change in temperature. Its temperature coefficient of resistance is 0.0026 K−1. We obtained a constant and stable output signal of the sensor even though the sensor position was near the tube entrance region where the flow is developing a hydraulic flow condition. We concluded that the proposed sensor is able to measure the flow rate under both the developing and the fully developed hydraulic flow conditions.