Flow rate independent sensing of thermal conductivity in a gas stream by a thermal MEMS-sensor - Simulation and experiments

- We present a thermal system measuring thermal conductivity in a flowing fluid.
- Constant power mode is used to determine thermal conductivity.
- Due to the sensor design a temperature plateau is obtained, which is flow independent but gas sensitive.
- The distance between heater and temperature sensor is a design parameter to shift the temperature plateau.
- Experimental results confirm the simulation results.

A thermal system for measuring thermal conductivity in a streaming gas is presented. The system features a heating element and a downstream temperature sensor on a membrane area surrounded by a substrate serving as heat sink. Simulations predict a flow independent region by use of the FEM heat transfer model in all directions in a laminar flow profile. Both simulation and experimental results show that the temperature of the downstream element is sensitive toward the gas type but insensitive toward the gas flow over a wide range. Furthermore, the findings show that the temperature of the downstream element in the flow independent region only depends on the gas' thermal conductivity. The distance between the heater and the downstream temperature sensor is found to be a design parameter in order to shift the flow independent region according to the requirements of the application. The experimental results correspond very well to the theoretical predictions.