Two-phase refrigerant distribution improvement by a new vertical multi-stream header in micro-channel heat exchangers

Abstract

The Micro-channel heat exchangers (MCHXs) suffer from the non-uniform distribution of two-phase refrigerant due to the combined effects of inlet phase separation and differences in flow resistance, which becomes accentuated when faced with a large number of microchannel flat tubes. A multi-stream radial-tunnel header (MSRH) is presented to divide the refrigerant into several streams by radial-distributed tunnels and reduce the number of microchannels per stream, improving the distribution uniformity. The numerical models of conventional cylinder header (CCH) and MSRH are established and validated experimentally. Results show that the two-phase flow variation along the flow path is reduced by the radial tunnels with relatively equal flow resistance in MSRH. However, the two-phase separation and deflection will occur in the inlet bend due to the large gas–liquid density difference. Then, the MSRH with two rectifying structures is further proposed to mitigate the inlet phase separation. The average standard deviation of liquid refrigerant flow rate is reduced from 23.75 % to 9.4 % and 1.61 %, respectively. Furthermore, the design method of key parameters is also presented to provide guidance for various working conditions in actual application.