Quantitative Visualization of CO2 -Oil Mixtures in CO2 Expansion Flows

We report the construction of an optically accessible flow test section made of quartz to simulate carbon dioxide flow through throttling devices in refrigeration systems. The existence of traces of lubricant oil (specifically Polyolester (POE)) in the working medium makes the flow amenable to Laser Induced Fluorescence (LIF) diagnostics. The molecular structure of these lubricants is rich in carbon – oxygen bonds which can cause fluorescence when excited by a laser in the near ultra-violet region of the spectrum. This technique was used to visualize the flow of CO2-oil mixtures through an optically accessible test section under various operating conditions. Upstream pressures as well as oil flow rates are the independent parameters of the experiment. The results of the measurements provide data on the concentration of the lubricant that is entrained by CO2 in the expansion device as well as information about the form with which the oil is transported through the ejector (liquid films, droplets, mist, etc.). Results from these experiments will guide the design of practical ejector geometries and will also indicate the extent to which various flow models may be employed in the investigation of CO2 refrigeration systems with ejectors.