Test stand and model development for assessing two-phase flow of low-GWP zeotropic refrigerant mixtures with lubricants.

Approximately 40% of US energy is consumed by HVAC&R applications. With the push to reduce direct and indirect CO2 emissions, there is a need to adopt environmentally friendly and efficient refrigerants. Zeotropic mixtures represent an alternative to conventional pure refrigerants, meeting efficiency and environmental needs, but with their own challenges. Their heat transfer efficiency is reduced by temperature suppression, and fractionation in phase change can lead to circulating composition shift and thus system and compressor issues. These issues can be compounded through the presence of lubricants. To experimentally assess zeotropic behavior with and without lubricants, this paper details the development of a condenser test stand designed to assess composition shift of zeotropic mixtures of hydrofluorocarbons (HFCs), hydrofluoroolefins (HFOs), hydrocarbons (HCs), and CO2 with lubricants. Additionally, a physics-based model of two-phase zeotropic flow is introduced. The test stand will be later used to improve and validate the model.