Local Flow and Heat Transfer of Supercritical CO₂ in Semicircular Zigzag Channels of Printed Circuit Heat Exchanger during Cooling

Abstract

Understanding and predictions of the local thermal-hydraulic performance of supercritical CO₂ in channels of printed circuit heat exchanger geometries are of great importance to the design and optimization of the pre-cooler and recuperators in supercritical CO₂ cycle. The local flow and heat transfer of supercritical CO₂ in horizontal semicircular zigzag channel during cooling near the critical or pseudo-critical point have been numerically investigated in this paper. The effects of thermophysical property variations, mass flux, and the channel geometrical parameters on the flow and heat transfer are discussed. It is found that the extrude angle in the zigzag channel impedes the bulk flow and generates secondary flow, which induces asymmetric flow and temperature distribution, and enhances fluid mixing and mitigates the temperature stratification. A dimensionless secondary flow velocity is adopted to evaluate the influence of secondary flow on the heat transfer, which is more enhanced for cases with relatively large mass flux and in channels with relatively large inclined angle and small pitch length, however, the pressure drop increases meanwhile. Finally, pitch-averaged local flow and heat transfer correlations have been developed based on the numerical results and mechanism analysis accounting for the thermophysical property variations and the channel geometrical parameters.

Acknowledgment

We specially thank Ministry of Education, China.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Key Project Fund from the National Natural Science Foundation of China (grant no. 51536004).

Notes on contributors

Zhuo Ren

Zhuo Ren was a Master student in the Institute of Nuclear and New Energy Technology, Tsinghua University. He received his Master’s degree in Nuclear Energy and Nuclear Technology Engineering from Institute of Nuclear and New Energy Technology, Tsinghua University in 2019. His research interests are in the field of thermal-hydraulic phenomena to supercritical pressure fluids in nuclear power engineering applications.

Li Zhang

Li Zhang is a senior engineer in the Institute of Nuclear and New Energy Technology, Tsinghua University. She received her Master’s degree from Department of Precision Instrument, Tsinghua University in 2007. Her research interests are in the field of thermal-hydraulic and mechanic engineering in nuclear engineering applications.

Chen-Ru Zhao

Chen-Ru Zhao is an Associate 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 and two-phase flow in nuclear and power engineering applications.

Pei-Xue Jiang

Pei-Xue Jiang is a Professor in the Department of Energy and Power Engineering, Tsinghua University, China. He received his Ph.D. in the Department of ThermoPower Engineering of 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 in porous media and enhanced heat transfer, convection heat transfer at supercritical pressures, transpiration cooling and film cooling, thermal transport in nanoscale structures, trans-critical CO₂ air conditioning systems, and heat pumps.

Han-Liang Bo

Han-Liang Bo is a Professor in the Institute of Nuclear and New Energy Technology, Tsinghua University. He received his Ph.D. degree in reactor engineering and safety from School of Energy and power engineering, Xi’an Jiaotong University in 1992. He joined the faculty of Tsinghua University in 1994. His main research interests are in the field of reactor thermal hydraulics and reactor equipments.