This paper presents void fraction and flow regimes determined by three methods: visualization (high speed camera), mass measurement (quick-closing valves) and a newly developed capacitance sensor. In a way, this is a calibration process for a capacitance sensor. It is shown that new sensor can characterize flow patterns in low mass flux range and measure void fraction for horizontal and vertical tubes. A calibration procedure of void fraction measurement is based on a mass measurement (quick-closing valves). Two calibration curves for measuring void fraction in horizontal and vertical tubes are developed. With calibration curves, sensors with similar configurations can be directly utilized to measure void fraction in further studies
