Void Fraction Measurement of Cryogenic Two Phase Flow Using a Capacitance Sensor

Abstract

A new capacitance type void fraction sensor was designed, produced, and tested. This sensor applies the difference between the relative permittivity of gaseous hydrogen ( = 1.0) and that of liquid hydrogen ( = 1.2). Following the sensor verification test using light diesel oil and air, a cryogenic experiment using liquid nitrogen was conducted. As a result, the void fraction measured by the sensor showed good agreement with the result obtained by an optical analysis using a high speed camera. One of the key problems on the sensor is an existence of the temperature drift caused by the change of the relative permittivity of the glass tube. In order to reduce the temperature drift, the length of electrodes and material of tubes were changed. Combination of short arc length electrodes and iupilon tube is ideal for reducing the unwanted temperature drift. The sensor which has shorter electrodes reduces the quantity of the temperature drift by 63% compared to the original sensor.