Shape Memory Alloy-Based Sensor for Two-Phase Flow Detection

In contemporary times, Shape Memory Alloys (SMAs) are ubiquitously used as actuators due to their ability to achieve pre-deformed shape upon heating, thus creating a plethora of applications in active shape and vibration control domains. However, use of SMA material as sensing elements need definite exploration. In this study, a novel application of the Nickel Titanium Naval Ordnance Laboratory - NITiNOL based SMA wire sensor (Flexinol NiTi, $100~\mu m$ diameter), to determine two-phase flow characteristics in a gas-liquid Taylor bubble flow is demonstrated, using the principle of significant change in its electrical resistance during its solid-phase transformation (austenite-martensite) which occurs when the heated SMA wire experiences an intermittent flow of gas and liquid over it. Determination of multi-phase (gas or vapour dispersed in liquid) flow parameters such as constituent phase distribution, local velocities and bubble frequency is exhibited. Design challenges include the matching of convective thermal transient time scales with those of the sensor with available control parameters. A preliminary design methodology is outlined and validated. The limitations of this type of sensor platform is also delineated for improving prospects.