Flow visualization and noise measurement of R410A two-phase flow near electric expansion valve for heating cycle of multi-split air-source heat pump

Abstract

Multi-split air-source heat pumps (ASHPs) have been widely used for both heating and cooling. An electric expansion valve (EEV) is frequently positioned in the indoor unit (IDU), leading to an increase in the two-phase flow noise of the refrigerant. In this study, we experimentally investigated the two-phase flow patterns and flow-induced noise of R410A refrigerant near the EEV in an IDU during the heating cycle of a multi-split ASHP with four IDUs. The flow-induced noise and two-phase flow patterns of horizontal and vertical pipe layouts near the EEV were simultaneously measured under a transient operation condition of temperature (24-38 degrees C), pressure (1.7-2.7 MPa), and mass flowrate (6.2-41.9 kg/h). The big noise near the EEV was generated for an intermittent flow and a churn/slug flow pattern at the EEV inlet for both horizontal and vertical pipe layouts, respectively. Unlike refrigerators and cooling air-conditioners, a vertical pipe layout has two-phase flow patterns that are advantageous for noise reduction near the EEV because of the high operating mass flux and pressure for R410A of a heating cycle of a multi-split ASHP. The two-phase flow-induced noise of the refrigerant near the EEV was strongly affected by the flow patterns at the EEV's inlet and outlet. The present study indicates that the flow patterns affected by pipe layout, phase properties, and operating conditions should be considered as one of the important factors in designing a refrigerant system of reduced noise.