• optical fiber
• heat pipe exchange

Two-phase flows within mini channels are now one of the most studied topics for thermal control
in space applications. However, heat exchangers using capillary pipes must be characterized and
optimized. The measurement of the flow rate characteristics is essential for describing the
performances of these devices. This thesis aims to improve the accuracy of void fraction
measurement with a single optical fiber Probe in a bubbly flow. The optical fiber probe is conical
shape tapered at 70 degrees to make sure that all the laser rays will reflect inside the optical fiber.
In particular, it has been designed the implementation of this optical system for void fraction
measurement inside mini channels to be mounted on the plate. This design of this optical probe
sensor is compact and fits in a 300x300 mm aluminum plate to be portable to take measurements
inside a Pulsating heat Pipe for future Space applications. The Light output component of the
fiber has a circular and smooth (homogenized) intensity profile and asymmetrical beam
efficiency, which is very useful, fewer complex optics are needed to generate a circular pump
spot, so there is no need to use special collimators, lenses. Optical Circulators have been used to
allow the light beam to pass from the light source to the tip of the probe and then back to the
photodetector without making any interaction between the forward and back beams.