Flash gas bypass in mobile air conditioning system with R134a

This paper demonstrates that the performance of a mobile air conditioning system (with a microchannel evaporator modified to be single pass) operating normally with R134a in direct expansion mode can be significantly improved when switched to flash gas bypass (FGB) mode. When operated at the same compressor speed, the system in FGB mode produces about 13%–18% more cooling capacity at 4%–7% higher COP than DX mode. When the compressor speed was adjusted to maintain the same cooling capacity, the COP improved 37%–55%. Two main reasons are identified and discussed: 1) improved refrigerant distribution and 2) reduction of refrigerant pressure drop.

► Flash gas bypass method improves (up to 57% in COP) performance of an MAC system.
► The actual value depends on the evaporator design, quality and size of the system.
► Two major benefits of the flash gas bypass method are identified.
► FGB improved refrigerant distribution (sending liquid only to the inlet header).
► FGB reduced pressure drop on refrigerant side (lower flow rate and inlet quality).