capacitive sensor, void fraction, headers, microchannel heat exchangers, R134a
This paper presents the design and building of capacitive sensors for measuring void fraction in headers of microchannel heat exchangers with R134a. The capacitive sensors utilize different electrical properties (dielectric constant) between the liquid and vapor phases to measure the void fraction of two-phase flow. The test section (a header) is made of 3D printed partitions with a total length of 185.8 mm and an inner diameter of 15.8 mm (D). It has eleven microchannel-tube protrusions with a depth of half inner diameter. All microchannel tubes are capable of being connected to real aluminum tube-like real heat exchangers in the future study. Eleven capacitive sensors locate between protrusions. Each sensor has two concave-plate electrodes with the axial length of the half inner diameter (D/2). With these eleven sensors, void fractions along the header can be measured spontaneously. Preliminary validation of the sensors is also presented in this paper.