Lixin Cheng

Beijing Key Laboratory of Heat Transfer and Energy Conversion, 

Beijing University of Technology, Beijing 100124, P. R. China

Department of Engineering and Mathematics, Sheffield Hallam University,

 City Campus, Howard Street, Sheffield S1 1WB, UK

Dr. Lixin Cheng has worked at Sheffield Hallam University since 2016. He obtained his Ph.D. in Thermal Energy Engineering at the State Key Laboratory of Multiphase Flow at Xi’an Jiaotong University, China in 1998. He has received several prestigious awards such as Alexander von Humboldt Fellowship in Germany in 2006, an ERCOFTAC Visitor Grant in Switzerland in 2010 and a Distinguished Visiting Professorship of the City of Beijing, China in 2016-2021. His research interests are multiphase flow and heat transfer and thermal energy engineering. He has published more than 100 papers in journals and conferences, 9 book chapters and edited 10 books. He has delivered more than 60 keynote and invited lectures worldwide. He has been the chair of the World Congress on Momentum, Heat and Mass Transfer (MHMT) since 2017. He is one of the founders and co-chair of the International Symposium of Thermal-Fluid Dynamics (ISTFD) series since 2019. He is associate editor of Heat Transfer Engineering, Heat Transfer Research and Journal of Fluid Flow, Heat and Mass Transfer, and international advisor of Thermal Power Generation (a Chinese journal).

Title: Effect of the Reduced Pressure on Flow Boiling Heat Transfer of CO2 in Macro- and Micro-channels 

Abstract：This lecture focuses on the effect of the reduced pressure on CO2 flow boiling heat transfer and mechanisms in macro- and micro-channels. First, flow boiling heat transfer behaviors of CO2 at high and low reduced pressures were simulated using the Cheng et al. [L. Cheng, G. Ribatski, J.R. Thome, New prediction methods for CO2 evaporation inside tubes: Part II—An updated general flow boiling heat transfer model based on flow patterns, Int. J. Heat Mass Transfer, 51 (2008) 125-135] general mechanistic heat transfer model for flow boiling CO2 to analyze the heat transfer behaviors and mechanisms at low and high reduced pressures. Then, the simulated heat transfer coefficients were compared to an experimental database at the reduced pressure from 0.1332 to 0.9082 (the corresponding saturation temperature from -40.6 to 26.77C), the tube diameter from 0.529 to 9.52 mm, the heat flux from 2 to 72 kW/m2 and the mass flux from 100 to 1500 kg/m2s. The model predicts 81.3% of the data before the dryout inception within ±30% while it only predicts 21% of data in the dryout and mist flow regimes within ±30%. The poor prediction of the heat transfer coefficients in the dryout and mist flow regimes are because the model does not capture the dryout inception and completion. Furthermore, the heat transfer mechanisms are discussed from the standpoint of the flow regime variations and unstable flow boiling phenomena in macroscale and microscale tubes. According to the analysis, recommendation has been made to the research of flow boiling of CO2 in future. New mechanisms should be investigated to understand the unstable and transient evaporation processes. The mechanisms should be incorporated in the improvement of the model for better prediction of heat transfer coefficients at a wide range of conditions. Furthermore, effort should be made to develop new prediction methods by considering the unstable and transient two-phase flow and flow boiling of CO2 as well.