Yuan Wang 

College of Aerospace Science and Engineering, National University of Defense Technology

Hunan, Changsha, China

E-mail: y.wang@nudt.edu.cn

Yuan Wang, Ph.D., Associate Professor. College of Aerospace Science and Engineering, National University of Defense Technology.

Research Interests include air precooling technology for combined cycle propulsion systems, engine thermal protection, and heat transfer enhancement.

Title: Icing and anti-icing on cold surfaces of cryogenic air precoolers

Abstract: Knowledge of droplet icing and the following crystal growth mechanisms is of great importance in many aspects such as infrastructure, medicine, engineering, aviation, etc. Growing attention has been paid to the icing and frosting on aerospace vehicles as well as the cryogenic air-precoolers for hypersonic turbine engines. Surface hydrophobicity is crucial for ice nucleation and frost deposition. The feasibility of using the hydrophobic/hydrophilic surfaces for anti-icing is still under debate and waiting to be further clarified. 

Experimental and numerical investigations are conducted to explore droplet freezing and the early frost growth on sub-zero surfaces with various structures. Hydrophobic surfaces are fabricated to suppress surface icing and/or frosting. Effects of surface structure, air temperature, relative humidity, and flow velocity on the anti-icing properties are investigated. 

Besides, the heat and moisture transfer characteristics of the forced convection process of air near low-temperature surfaces are simulated. The characteristics and influencing factors of the distribution of the condensation region and frosting region near the cold surfaces are clarified. The anti-icing property of the micro-structured surfaces can be explained based on our simulation. High-speed zones are formed near the leading lip of the micro-pillars. Meanwhile, the air is almost stagnated in the inter-pillar regions, which provides a large thermal resistance between the cold surface and the air. The increase in air velocity would remarkably reduce the local relative humidity. Therefore, the potential for frost growth is suppressed on the micro-structured surfaces. The outcomes of the present study are instructive for the frosting prediction in air precoolers.