Two-phase flow distribution in a refrigerant distributor having four indoor-unit connections of a variable refrigerant flow system

In a variable refrigerant flow (VRF) system, the refrigerant is supplied from one outdoor unit to multiple indoor units through a header or refrigerant distributor. When the two-phase refrigerant flows into the distributor, uneven distribution occurs and deteriorate system performance. An experimental apparatus simulating the refrigerant distributor of a VRF system was constructed and air-water two-phase flow distribution characteristics were investigated. The air-water two-phase flow was more mal-distributed as the void fraction increased. A change in void fraction affected the distribution more than a change in mass flow rate in the experimental range. The flow distribution in the header was little affected by variation of the downstream flow resistance. Previous empirical correlations were investigated to predict the air-water two-phase flow distribution measured in this experiment, but performance was poor. To estimate the refrigerant two-phase flow distribution, computational fluid dynamics (CFD) simulations were performed using R410A as a working fluid. The mal-distribution of R410A appeared to be mitigated compared with air-water flow due to the large vapor phase density of R410A. (c) 2021 Elsevier Ltd and IIR. All rights reserved.

Automated summary

The study found that in VRF systems, the distribution characteristics of air-water two-phase flow are significantly influenced by void fraction, with void fraction changes having a larger impact on distribution than changes in mass flow rate. The distribution in the header is minimally affected by variations in downstream flow resistance. Previous empirical correlations were ineffective in predicting two-phase flow distribution accurately, while the use of R410A as a working fluid appeared to mitigate refrigerant mal-distribution compared to air-water flow.