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

ABSTRACT

The 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%.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No: 51406096), the Research Fund for the Doctoral Program of Higher Education of China (Grant No: 20130002120020), the Key Project Fund from the National Natural Science Foundation of China (No. 51536004), and the Tsinghua University Initiative Scientific Research Program (Grant No: 20151080379). We thank Prof. David Christopher for editing the English.

Additional information

Notes on contributors

Chen-Ru Zhao

Chen-Ru Zhao is an assistant professor in the Institute of Nuclear and New Energy Technology, Tsinghua University. She received her Ph.D. degree in Power Engineering and Engineering Thermophysics from Department of Thermal Engineering, Tsinghua University in 2011. Her research interests are in the field of flow and heat transfer, thermal–hydraulic phenomena to supercritical pressure fluids in power engineering applications.

Zhen Zhang

Zhen Zhang is an assistant professor in the Institute of Nuclear and New Energy Technology, Tsinghua University. She received her Ph.D. degree in Power Engineering and Engineering Thermophysics from Department of Thermal Engineering, Tsinghua University in 2013. Her research interests are in the field of flow and heat transfer, thermal–hydraulic phenomena to supercritical pressure fluids in power engineering applications.

Pei-Xue Jiang

Pei-Xue Jiang is a professor in the Department of Thermal Engineering, Tsinghua University. He received his Ph.D. degree from Department of Thermo-Power Engineering, Moscow Power Engineering Institute in 1991. He then joined the faculty of Tsinghua University and took the professor post in 1997. His main research interests include convection heat transfer at supercritical pressures, trans-critical CO₂ air conditioning systems and heat pumps, convection heat transfer in porous media and enhanced heat transfer, transpiration cooling and film cooling, thermal transport in nanoscale structures. He has published more than 100 papers in international journals and conferences. He is recipient of the National Outstanding Youth Fund from the National Natural Science Foundation of China, 2000, Chang Jiang Scholar of Ministry of Education, China, 2006, the leader of the Foundation for Innovative Research Groups of the National Natural Science Foundation of China, 2013.