Fluid-compensated thermal flow sensor

Thermal flow meters are widely spread in research, industry and daily life because of their simple handling and their cost efficiency. However, the signals of thermal flow meters are highly fluid-dependent. In fact, a conventional thermal flow meter can often not distinguish if the fluid or the flow has changed. A fluid-independent thermal flow meter is still a challenge in research. This article presents a new approach of a fluid-compensated thermal flow meter using a combination of the 3-Omega-method and constant temperature anemometry (CTA). The 3-Omega-method is used to characterize the fluid properties and CTA is used to characterize the flow. A key element of the proposed method is the combination of the theoretical models of the 3-Omega-method and CTA to obtain a fluid-compensated flow. This method has been characterized theoretically and experimentally, and it could be shown that it can determine the flow rate within 9 %, independent of the type of the fluid.