Noise reduction of refrigerant two-phase flow using flow conditioners near the electric expansion valve

Two-phase flow, particularly generated in an expansion device, is a primary cause of refrigerant-induced noise in an air-conditioning system. The indoor unit (IDU) of a multi-split air source heat pump (ASHP) for both heating and cooling must include an electric expansion valve (EEV); therefore, consumers have perceived the increased noise. To reduce this noise, we experimentally investigated the two-phase flow and consequent noise by applying a honeycomb and porous metal as a flow conditioner to the EEV in the IDU of a multi-split ASHP. Flow conditioning near the EEV with the honeycomb and porous metal made the two-phase flow steadier and more uniform, leading to reduced noise and frequency variation for the three heat operation modes of a multi-split ASHP. The noise reduction was also verified in the transient operating modes of a real IDU.