MEASUREMENT OF GAS-PHASE CHARACTERISTICS USING NEW MONOFIBER OPTICAL PROBES AND REAL-TIME SIGNAL-PROCESSING

Single optical or impedance phase detection probes are able to measure gas velocities provided that their sensitive length L is accurately k nown. In this paper, it is shown that L can be controlled during the m anufacture of optical probes: Besides, for a probe geometry in the for m of a cone + a cylinder + a cone, the corresponding rise time/velocit y correlation becomes weakly sensitive to uncontrollable parameters su ch as the angle of impact on the interface. A real-time signal process ing performing phase detection as well as velocity measurements is des cribed. Since its sensitivity to the operator inputs is less than the reproducibility of measurements, it is a fairly objective tool. Qualif ications achieved in air/water flows with various optical probes demon strate that the void fraction is detected with a relative error less t han 10%. For bubbly flows, the gas flux is accurate within +/- 10%, bu t this uncertainty increases when large bubbles are present in the flo w. (C) 1998 Elsevier Science S.A. All rights reserved.