Characterization of two-phase flow distribution in microchannel heat exchanger header for air-conditioning system

• Published in: Experimental thermal and fluid science 2019-09, Vol.106, p.183-193
• Main Authors: Redo, Mark Anthony, Jeong, Jongsoo, Giannetti, Niccolo, Enoki, Koji, Yamaguchi, Seiichi, Saito, Kiyoshi, Kim, Hyunyoung
• Format: Article
• Language: English
• Subjects: Air conditioners; Air conditioning; Correlation; Evaporation; Evaporators; Experiment; Flow distribution; Flow rates; Froude number; Headers; Heat exchangers; High speed cameras; Microchannel heat exchanger; Microchannels; Multiphase flow; Tubes; Two phase flow; Vapors; Vertical header; Visualization
• ISSN: 0894-1777; 1879-2286
• DOI: 10.1016/j.expthermflusci.2019.04.021

•Flow distribution behaviour in an actual microchannel heat exchanger was clarified.•Effect of wider range of inlet mass flowrate, and vapor quality were investigated.•Clear visualization videos were able to provide liquid level reach and flow regime.•Development of new empirical correlation covering dominant forces. The two-phase flow distribution behavior of R410A within the vertical header of a microchannel heat exchanger with multiple horizontally oriented microchannel flat tubes was investigated and is reported in this paper. Unlike most previous studies, which examined the distribution at lower flowrates applicable mostly to automobile applications, this work evaluated higher flowrates relevant to actual air conditioning evaporator applications with larger size headers. The following operating conditions, were utilized: an inlet mass flowrate that varied from 40 to 200 kg h−1 (mass flux of 27–250 kg m−2 s−1 in the header), vapor qualities of 0.1, 0.2, and 0.6, and evaporating temperatures of 10 and 15 °C. The tube protrusion depth into the header was set at 0 and 50%. Flow distribution profiles derived from the experiment measurements and clear visualization images captured by a high speed camera showed that the distribution improves for increased inlet mass flux at low vapor quality, while a 5 °C difference in evaporating temperature does not yield a substantial distribution change. A 50% protrusion produces higher inertial forces pushing the liquid level towards the top section. A correlation was developed to predict the liquid distribution by relating the portion of liquid exiting the branch tube to the liquid at the immediate header as a function of the liquid Froude number.