Mengjie Song is a Professor in the Department of Energy and Power Engineering, as well as a Teli Young Scholar and the Director of the Frost Lab in the School of Mechanical Engineering at the Beijing Institute of Technology, China. He is also the Editor-in-Chief of Recent Patents on Mechanical Engineering (EI, Scopus), Associate Editor of Frontiers in Energy Research (SCI, IF=2.746). He also works as DECRA Research Fellow at the Sustainable Buildings Research Centre (SBRC) in the Faculty of Engineering and Information Sciences at the University of Wollongong, Australia, and as a Guest Professor of Tomas Bata University in the Czech Republic. Prof. Song has worked for over a decade on the mechanism study of heat and mass transfer coupled with flow. On the topic of frosting and defrosting for air source heat pump, he proposed a series of definitions to describe thermophysical phenomena, such as even/uneven frosting/defrosting, and frosting/defrosting evenness value. His current research interests include solidification of water droplets at different scales and (anti-/de)icing for aircraft surface, and frosting and defrosting for a multi-circuit heat exchanger in refrigeration systems. He has published 122 journal articles and participated in projects from China, Hong Kong, Singapore, Japan, and Australia, handling a total of over 17 million yuan in funding, including 12 as PI. Recently, he was selected for the World’s Top 2% Scientists 2021 (Singleyr) list. Doctor Long ZHANG is an Assistant Professor in the Department of Energy and Power Engineering at the Beijing Institute of Technology, China. He received his Ph.D. degrees from both The Hong Kong Polytechnic University and Harbin Institute of Technology, China. His research interests are the coupling mechanism and application research of heat and mass transfer and flow, especially the phase change problems such as frosting, icing, and the key technology research of heat pumps. He has published more than 50 SCI journal articles, including 32 ones as lead/corresponding author and 2 ESI ones. He also published 2 books and 2 chapters for Elsevier, applied for 8 Chinese patents, and made 6 invited presentations at international and Chinese conferences around frosting and icing topics. Additionally, he holds more than 10 projects, including the National Natural Science Foundation of China.

• 1. Introduction2. Freezing of sessile non-deformed water droplet under natural convection at early frosting stage in an ASHP unit3. Freezing of sessile deformed water droplet under natural convection at early frosting stage in an ASHP unit4. Frosting on surface of horizontal cold plate under natural convection in an ASHP unit5. Frosting on surface of non-horizontal cold plate under natural convection in an ASHP unit6. Frosting on surface of horizontal cold flat plate under forced convection in an ASHP unit7. Measurement and calculation of frost characteristics on cold surfaces8. Experimental study of frosting on surface of finned tube heat exchangers in an ASHP unit9. Numerical study of frosting on surface of finned tube heat exchanger in an ASHP unit10. Frosting on surface of micro-channel heat exchanger in an ASHP unit11. Reverse cycle defrosting for multi-circuit outdoor coil in an ASHP unit12. Conclusions and future work