Low-power micro-fabricated liquid flow-rate sensor

We have constructed micro-fabricated flow sensors that can measure water flow rates of 0.1 to 2.0 gallons per minute (GPM), and the experimental results we obtained are in good agreement with those from COMSOL simulations. Two identical sensors were fabricated on each device with an upstream sensor functioning as a temperature sensor, and the voltage difference between the two sensors indicating the water flow rate. The sensors were constructed on glass substrates, chosen for their low price, efficient thermal isolation, and compatibility with current water supply systems. The variation of water temperature of the flowing fluid from 10 to 50 degrees C was accounted for by normalizing the voltage readings. The dimensions of the sensors ranged from 71 mm by 80 mm to 430 mm by 480 mm with the smaller sensors having a higher sensitivity. Sensitivity also increased with increasing input power up to the point when boiling occurred. The optimized sensor, which was 71 mm by 80 mm on a 3 mm by 3 mm glass substrate, could be operated with only 2.75 mW of power in 10 to 50 degrees C water, providing an economic and energy efficient method to measure large water flow rates of 0.1-0.5 GPM.