It has been reported that lubricating oil has a significant influence on the cooling heat transfer of supercritical carbon dioxide. In this study, numerical analysis of the flow pattern of a carbon dioxide (CO_2)-oil mixture in a gas cooler was conducted to analyze the change in oil film thickness and heat transfer coefficient against bulk temperature. Simulations were conducted using FLUENT software, and the volume-of-fluid (VOF) model was applied to capture the interface of the lubricating oil and CO_2. The compatibility of lubricants was found to have a dramatic influence on cooling heat transfer. The flow regime changes due to CO_2 dissolving into the oil causing changes in viscosity, surface tension, and density of the oil film. The comparison of simulated heat transfer coefficients with experimental results showed that the numerical simulation is an effective approach to analyze the characteristics of the flow and heat transfer of supercritical CO_2-oil mixture, and the numerical approach proposed could be further extended to the actual gas cooler design.
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