Design of thermal-anemometry-based probes for the simultaneous measurement of velocity and gas concentration in turbulent flows

Abstract

Although thermal anemometry has been employed for the simultaneous measurement of velocity and gas concentration, the underlying theory and techniques to do so are not well established. To rectify this situation, the present work uses theory and experiments to investigate the design of thermal-anemometry-based probes capable of making such measurements, specifically focusing on those for use in helium/air mixtures. It is demonstrated that an interference probe, which consists of two hot-wires placed close enough together that one is located in the thermal wake of the other, can be used to simultaneously measure velocity and helium concentration. The performance of the probe is increased when (i) the separation distance (s) between the wires is small (, where is the diameter of the upstream wire), and (ii) the downstream wire overheat ratio is low. Furthermore, a short downstream wire is recommended to ensure that the separation distance remains small while the wires are being operated.