scope:

ABSTRACT

The growing applications of variable-speed and tandem compressors, coupled with emerging refrigerant-oil combinations, can lead to higher levels of oil retention in vapor-compression systems, especially at lower refrigerant mass flow rates. To develop better designs and mitigation strategies, it is important to have methods for accurately measuring oil circulation ratio (OCR). High levels of OCR reduce the efficiency of heat exchangers (i.e., evaporators and condensers) and cause the compressor's oil level to reduce, which may ultimately affect its efficiency and life span. However, measuring OCR within a vapor-compression cycle is challenging due to various factors, such as the phase change of the working fluid at different locations, miscibility between the oil and refrigerant, and varying flow regimes. The objective of this study was to develop a noninvasive, in-situ method to measure OCR in real time, which involves minimal human intervention. An OCR measurement method is presented using an oil separator and a level measurement sensor. The approach has been validated with two different methods, one of which is an ASHRAE standard. The relative differences in the OCR measurement between the liquid level probe and ASHRAE standard methods are less than 12%.