Design of Ice-free Nanostructured Surfaces Based on Repulsion of Impacting Water Droplets

This paper reviews the background to and the current status of analyses developed to address the problem of icing on aircraft. Methods for water droplet trajectory calculation, ice accretion prediction, aerodynamic performance degradation and an overview of ice protection system modelling are presented. The paper addresses the issues involved in the development of icing analyses including problem formulation and assumptions, solution techniques, validation and the incorporation of empirical inputs where a purely theoretical approach is not feasible. Results are presented to illustrate the capabilities of the analyses when applied to practical design problems. Recommendations are made for further research.

Freezing of water droplets on solid surfaces: An experimental and numerical study

A diffusion-enhancing icing theory for the freezing transition of supercooled large water droplet in impact

Experimental and numerical study on freezing process of water droplets under surfaces with different wettability

Freezing dynamics of supercooled micro-sized water droplets

Numerical and experimental analysis of rapid solidification considering undercooling effect during water droplet impact on a substrate

A microscope method was used to study the freezing of individual water droplets 9 to 33 microns in diameter formed by condensation on various surfaces and protected with a film of silicone oil. The lowest freezing temperatures were found to be independent of the six surfaces used but dependent upon the volume of the water droplets and the rate of cooling. The results were correlated with those of other observers and it was concluded that homogeneous nucleation occurred in the lowest freezing droplets. Values of the surface free energy for a water-ice interface were calculated.

Anti-icing property of bio-inspired micro-structure superhydrophobic surfaces and heat transfer model

The collision behavior and ice formation of a water droplet are affected by its falling process. In this paper, the two-phase flow of air and a water droplet at a specific temperature is adopted to investigate the processes of falling and freezing of a single water droplet. To track the air–water droplet interface and the temperature distribution, the level-set method and the non-isothermal flow coupling method are used, and the freezing model is added into the water’s control equations. The numerical results indicated that with the initial temperature at 283.15 K and the spherical shape, the water droplet changes to the shape of a straw hat at 293.15 K and a drum at 293.15 K but an oval face in freezing temperatures at 0.10 s. There is an obvious drop in the downward velocity when the water droplet falls in mild temperatures at 0.09 s. The downward velocity of the water droplet in air at sub-zero temperatures has a continuous increase during the time span from 0 s to 0.10 s. There is also an obvious difference when the water droplet impinges on the solid bottom. Lastly, the freezing of sessile water droplets attached on the horizontal surface is helpful to reveal the unique phase change process of water droplets in cold air.

The freezing of water droplets placed on metallic surfaces and surfaces lubricated with various silicone oils was studied. The freezing of water droplets placed on inclined and upside-down planes, both bare and coated with silicone oil (that completely coated the water droplets) was also studied. We established that the opening angle of the freezing cone did not depend on neither the spatial orientation of the substrate nor on the coating of the frozen droplet with the silicone oil. The geometrical axis of the freezing cones coincided with the normal to the inclined surface. The opening angle of the freezing tip was not influenced by the volume of the droplet, contact angle hysteresis, the pinning of the triple line, the surface tension of the cloaked droplet, the viscosity of the silicone oil and the spatial orientation of the substrate. The paper supports the universal mechanism of the formation of the freezing tip, based on purely geometrical considerations.

Experimental study on freezing characteristics of water droplets on cold surfaces

An experimental investigation on the unsteady heat transfer process over an ice accreting airfoil surface

Freezing characteristics of deposited water droplets on hydrophilic and hydrophobic cold surfaces

The in-flight ice formation and accretion are highly dependent on weather conditions that essentially affect the heat transfer capability. When the temperature is sufficiently cold, the heat transfer is adequate to remove all of the latent heat from the collected water. The rate of rime ice accretion is controlled by the droplet collection efficiency. Otherwise, when the heat transfer is inadequate to remove all of the latent heat in collected water, the rate of glaze ice accretion is essentially controlled by the local convective heat transfer, which determines the amount of latent heat removal from the collected water. To better understand the physical details during an ice accretion process, time resolved heat transfer information is important and strongly desired. In this study, a methodology based on infrared thermography was developed to achieve nonintrusive measurements of unsteady heat transfer process over an ice accreting NACA 0012 airfoil. Comprehensive 2-D surface temperature distribution measurements under various icing conditions (e.g. air temperature, liquid water content, and wind speed) were performed in an icing wind tunnel. A heat balance model was formulated based on the current measurement model. The dynamic surface temperature distribution variations were characterized based on the measurements. The temperature variation history at different chordwise positions during ice accretion process was fully recorded and illustrated. Based on the temperature variation history along the airfoil surface, the heat transfer evolution in chordwise direction was evaluated. Finally, The effects of the liquid water content on the heat transfer process were elucidated based on the measurement results.

Freezing and melting of a sessile water droplet on a horizontal cold plate