A thermal flow sensor with liquid characterization feature

An enhanced flow sensor is under development at IMTEK to enable simultaneous measurement of thermal properties of a fluid and its flow velocity. AC heating is used to obtain more and detailed information on the fluid properties. Here, we present the flow characteristics of our sensor for liquids and show the influence of thermal conductivity of the fluid on the temperature amplitude at the central thermistor using calibration liquids. We further discuss the influences of fluid thermal properties and flow velocity on the phase of each thermistor signal. Experimental results suggest that phase shift on any thermistor location strongly depends on flow velocity for liquids. They also show that thermal conductivity of liquids can be determined with a minimum accuracy of 85% of their literature values using a linearly interpolated temperature amplitude characteristic of the closest thermistor to the heater.