Measurement of gas phase characteristics using new monofiber optical probes and real-time signal processing Original Research Article

Single optical or impedance phase detection probes are able to measure gas velocities provided that their sensitive length L is accurately known. In this paper, it is shown that L can be controlled during the manufacture of optical probes. Besides, for a probe geometry in the form of a cone+a cylinder+a cone, the corresponding rise time/velocity correlation becomes weakly sensitive to uncontrollable parameters such as the angle of impact on the interface. A real-time signal processing performing phase detection as well as velocity measurements is described. Since its sensitivity to the operator inputs is less than the reproducibility of measurements, it is a fairly objective tool. Qualifications achieved in air/water flows with various optical probes demonstrate that the void fraction is detected with a relative error less than 10%. For bubbly flows, the gas flux is accurate within ±10%, but this uncertainty increases when large bubbles are present in the flow.