Two phase pressure losses of R134a in microchannel tube headers with large free flow area ratios

Abstract This paper presents the results of an experimental investigation of two-phase pressure loss of R134a in microchannel headers. Novel experimental techniques and test sections were developed to enable the accurate determination of the minor losses without obfuscating the problem with a lengthwise pressure gradient. This technique represents a departure from approaches used by other investigators that have extrapolated minor losses from air–water experiments and the combined effects of expansion, contraction, deceleration, and lengthwise pressure gradients. Pressure losses were recorded over the entire range of qualities from 100% vapor to 100% liquid. In addition, the tests were conducted for five different refrigerant mass fluxes between 185 and 785 kg/m 2  s. Approximately 450 data points were recorded to obtain a comprehensive understanding of the effects of mass flux and quality on the minor pressure losses. High accuracy instrumentation such as Coriolis mass flowmeters, RTDs, pressure transducers, and real-time data analyses were used to ensure accuracy in the results. The results show that many of the commonly used correlations for estimating two-phase pressure losses significantly underpredict the pressure losses found in compact microchannel tube headers.