Evaporating heat transfer characteristics of R744 -relation between the evaporating heat transfer and flow pattern of refrigerant with oil

This paper describes evaporating heat transfer characteristics of a refrigeration cycle. Using R744 as working refrigerant, the effect of the oil mixing rate on the thermal and hydraulic characteristics were investigated. The main test section was a stainless tube an ID of 3.0 mm and the length of 500 mm, which was directly heated by electricity from an electric pole. Further, in order to visualize the flow pattern of the mixture of refrigerant and oil, we placed behind the evaporator sight glass made of acrylic block of 3.0 mm in ID and 135mm in length. Throughout experiments, it was recognized that oil was a significant factor of the heat transfer deterioration and of the increase of pressure drop. In addition, it was observed that the transition of the flow pattern was accelerated as oil concentration increases. Finally, it was concluded that the transition of the flow pattern was influenced by the mass flux and the oil concentration.