Design and Calibration of Capacitive Sensors for Measuring Void Fraction in Vertical Headers of Microchannel Heat Exchangers

Abstract

ABSTRACT This paper presents new capacitive sensors built and calibrated to measure cross-sectional void fraction between tubes in vertical headers of microchannel heat exchangers (MCHEs). Eleven individual sensors are assembled into one test header to measure local capacitance independently in real-time. A calibration procedure based on visualization, pressure drop, signal patterns, and mass measurement (quick-closing valve technique, QCV) is proposed. After the calibration, most void fraction data predicted by all eleven sensors fall into ±10% deviations of the experimental results by QCV. The sensors are ready to be utilized to measure local void fraction along vertical inlet or intermediate headers of MCHEs in future studies.