VOID FRACTION DETECTION WITH A MICRO OPTICAL PROBE INSIDE CAPILLARY CHANNELS FOR THERMAL MANAGEMENT IN SPACE

This study examines the results of void fraction measurements in a two-phase flow inside a capillary channel by means of an optical probe. The purpose of such research is to assess the reliability of the optical measurement technique for two different fiber shapes, a conical lens and a 90° lens. The optic probes are tested in a vertical pipe in which an upward co-current gas-liquid flow was stimulated through a pump and a syringe. The probe signal was detected by a photodiode and implemented by a control hardware, Crio. The output signal was analysed and post-processed with a Matlab script. A high-speed camera, Ximea xiQ, was used to compare the fiber signal output with a digital camera signal, obtained by the post-process of the photo-sequences. Excellent results were obtained regarding the probe capability to detect the local void fraction and its accuracy, still it was not possible to evaluate any analytic velocity relationship