Predictions of In-Tube Cooling Heat Transfer Coefficients and Pressure Drops of CO2 and Lubricating Oil Mixture at Supercritical Pressures

Abstract

ABSTRACTThe in-tube cooling heat transfer and flow characteristics of supercritical pressure CO2 mixed with small amounts of lubricating oil differ from those for pure CO2 due to the entrainment of the lubricating oil as well as the sharp property variations of the supercritical CO2 working fluid. In-tube gas cooling flow and heat transfer models were developed in this study for CO2 with entrained polyol ester type lubricating oil in a CO2 gas cooler at supercritical pressures. A “thermodynamic approach,” which treats the CO2–oil mixture as a homogenous mixture was used with the heat transfer coefficients and frictional pressure drops evaluated based on the thermophysical properties of the CO2–oil mixture. Thermophysical property variation correction terms as a function of the wall temperature and the oil concentration were included in the models. The frictional pressure drop correlation predicts more than 90% of the experimentally measured data within ±10%, while the heat transfer coefficient correlation predicts more than 90% of the experimentally measured data within ±20%.