A comprehensive analysis of capacitive signals of two-phase R134a characteristics in a microchannel heat exchanger header with and without a distributor.

The maldistribution of refrigerant in header has a serious impact on the performance of the microchannel heat exchanger (MCHX). This study investigated using to obtain an improved flow distribution distributor in a MCHX. The tested inlet vapor quality covered from 0.2 to 0.6. Mass flow rate was 10 g/s. In the heat exchanger header, the two-phase distribution was quantified using a capacitance sensor for with and without distributor cases. The capacitive signals were comprehensively analyzed in the time, amplitude and frequency domains. Probability density function (PDF) and Fast Fourier Transform (FFT) of the capacitive signals were used to characterize flow patterns. The local vapor qualities calculated by the correlation was used to quantify two-phase distribution. This comprehensive analysis improved the accuracy of capacitive signal processing of two-phase flow characteristics. In the Fast Fourier Transform of capacitive signals, the more violent the two-phase flow, the greater fluctuation on the amplitude. The improvement of two-phase distribution by distributor and the two-phase flow characteristics at the distribution hole were discussed. At low inlet vapor quality(xin ≤ 0.3), the distributor had a better effect on the maldistribution. At high inlet vapor quality(xin = 0.6), alternate vapor-liquid distribution would occur at the distribution hole. In this paper, the capacitive signals were comprehensively analyzed in the time, amplitude and frequency domains in the MCHX header for the first time. The two-phase flow state was specifically evaluated through the capacitive signal characteristics.