A thermal-calorimetric gas flow meter with improved isolating feature

This paper presents design and characterization of a novel thermal-calorimetric flow-meter using suspended-cantilever-structure. There is an air gap between the heater and each individual thermistor providing a good thermal isolation. Due to the suspended-structure which consists of three cantilevers, the thermal convection effect is present on both sides of the active area. Also the velocity boundary layer thickness of the cantilever is much less than closed-membrane one. This characteristic enhances the sensitivity of sensor. The simulation results indicate that the average temperature difference between upstream and downstream thermistors are 36.5 and 1.04 K for flow rate of 1 m/s and the worst case of 0.1 m/s respectively. This solution significantly improves the sensitivity compared to the closed-membrane-structures. The maximum temperature difference causes 94 mV at the output of Wheatstone bridge with 3 V of voltage supply. The calculated and simulated results show that the maximum power consumption of sensor is 4.7 mW at the maximum flow velocity of 1 m/s. The operational range of the designed flow meter is from 0 to 1 m/s. The features of the device are analytically evaluated and simulated under various conditions.