Quantitative Visualization of CO2-Oil Mixtures in CO2 Expansion Flows

Quantitative visualization of CO2-oil mixture flows through channels that simulate CO2 expansion devices was pursued. The existence of traces of lubricant oil (specifically polyolester (POE)) in the working medium makes the flow amenable to laser-induced fluorescence (LIF) diagnostics. This technique is used to visualize the flow of CO2-oil mixtures through an optically accessible test section under various operating conditions. 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.). Further flow visualization was accomplished using high-speed cinematography, which revealed information about the oil film structure as a function of oil circulation rate and CO2 flow rate. Further experiments using laserbased shadowgraph were conducted and the need for a square cross-section was established due to refraction in the round tubing. 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.Air Conditioning and Refrigeration Project 19