The use of two-phase ejectors to recover expansion work to improve COP of transcritical R744 systems hasbeen the subject of numerous investigations during the past decade. However, there is little understanding asto how oil in circulation in different parts of the system is affected when a two-phase ejector is used toreplace the expansion valve. This paper presents detailed measurement results conducted on a transcriticalR744 ejector system using polyalkylene glycol (PAG) oil, demonstrating that at the same test condition, theoil circulation rates (OCRs) in different parts of the system can easily vary by an order of magnitude. Thehighest OCRs of approximately 10% by mass were measured close to the evaporator inlet. The influence ofcompressor speed, ejector motive nozzle needle position and evaporator inlet metering valve opening on theOCRs was investigated and it is explained why these condition changes will result in variation of oil incirculation.
展开▼
