Analytical and experimental study of two-phase ejectors considering the influence of lubricant oil

Abstract

The use of traditional refrigerants such as HCFCs and HFCs has a significant impact on global warming. On the other hand, natural refrigerants have little environmental impact with essential characteristics such as low global warming potential (GWP) and zero ozone depletion potential (ODP). Among various natural refrigerants, carbon dioxide is used as an alternative natural refrigerant due to its excellent heat transfer efficiency in a supercritical state. However, its COP is low due to its inherent high compressor work. To reduce this high compressor work, additional components such as ejectors are used for carbon dioxide cycles. In this study, a two-phase ejector was investigated. In particular, ejector analysis was performed in consideration of the influence of lubricant oil. In vapor compression cycle, lubrication is essential. This lubricant oil is discharged to the system through a compressor. When oil flows to system and enters the ejector, it forms a layer that can obstruct the flow inside the ejector. Oil circulation ratio (OCR) change can affect the mass flow rate of the ejector as if the inner diameter of the ejector is reduced. Therefore, it is essential to consider effects of OCR in a two-phase ejector analysis. As a result of the simulation, considering the effect of oil, a lower mass flow rate was predicted compared to existing analysis. Compared to previous studies without considering oil, there was an average mass flow rate difference of 13.6%. This simulation result was validated through experiments.