Design of a capacitance sensor for void fraction measurement in annular flows through a vertical pipe

This work develops simple capacitance sensors which can measure the void fraction in the annular flow of a vertical pipe. In this work plate- and ring-type sensors are considered. For the determination of the optimal gap size for each sensor type, several numerical tests are performed and numerical results show that the angle of the gap between 1 and 1.5 rad gives more outstanding performance than others for the plate-type sensor, and in the case of the ring-type sensor the larger gap distance to radius ratio gives better result. Additionally, these numerical trends are successfully compared with static phantom experiments.