Developing the next generation of dual-tip phase-detection probes for air-water flow experiments

Abstract: Self-aeration is a fascinating phenomenon that commonly occurs in high Froude-number flows in natural or human made environments. The most common air-water flow measurement instrument to characterize such flows is the intrusive dual-tip phase-detection needle probe, which identifies phase changes around the needle tips due to a change of resistivity (phase-detection conductivity probe) or light refraction (phase-detection fiber optical probe). Phase-detection conductivity probes are typically custom made for research purposes, with current design dating back to the 1980ies. In the present study, the next generation of dual-tip conductivity probes is developed and validated against a state-of-the-art system. The novel probe design comprises two main features, including (1) a printed circuit board of the sensor's electrodes and (2) a detachable sensor head. These features offer many advantages over the classical needle-type design. For example, the circuit boards can be manufactured with high precision and the sensor head can be easily replaced in case of damage or deterioration. As such, it is anticipated that this relatively cheap and robust design will enable a better repeatability of air-water flow experiments, combined with an enhanced accessibility for the air-water flow research community.