Relationships between Surface Properties and Snow Adhesion and Its Shedding Mechanisms

Jamie Heil,Behrouz Mohammadian,Kevin Bruns,Hossein Sojoudi,Mehdi Sarayloo

doi:10.3390/app10165407

Abstract

Understanding the mechanisms of snow adhesion to surfaces and its subsequent shedding provides means to search for active and passive methods to mitigate the issues caused by snow accumulation on surfaces. Here, a novel setup is presented to measure the adhesion strength of snow to various surfaces without altering its properties (i.e., liquid water content (LWC) and/or density) during the measurements and to study snow shedding mechanisms. In this setup, a sensor is utilized to ensure constant temperature and liquid water content of snow on test substrates, unlike inclined or centrifugal snow adhesion testing. A snow gun consisting of an internal mixing chamber and ball valves for adjusting air and water flow is designed to form snow with controlled LWC inside a walk-in freezing room with controlled temperatures. We report that snow adheres to surfaces strongly when the LWC is around 20%. We also show that on smooth (i.e., RMS roughness of less than 7.17 μm) and very rough (i.e., RMS roughness of greater than 308.33 μm) surfaces, snow experiences minimal contact with the surface, resulting in low adhesion strength of snow. At the intermediate surface roughness (i.e., RMS of 50 μm with a surface temperature of 0 °C, the contact area between the snow and the surface increases, leading to increased adhesion strength of snow to the substrate. It is also found that an increase in the polar surface energy significantly increases the adhesion strength of wet snow while adhesion strength decreases with an increase in dispersive surface energy. Finally, we show that during shedding, snow experiences complete sliding, compression, or a combination of the two behaviors depending on surface temperature and LWC of the snow. The results of this study suggest pathways for designing surfaces that might reduce snow adhesion strength and facilitate its shedding.

Highlights

The freezing process of liquid water droplets in the atmosphere and adhering to surfaces is known as atmospheric icing [1,2]
Many air gaps can occur at the surface because the snow is dry and this can result in lower contact area between the snow and the substrate, leading to lower snow adhesion strength
To the best of our knowledge, this is closest attempt in forming artificial snow comparable to natural snow, considering the limited size of our freezing room and the lack of temperature gradients that real snow experiences falling from the atmosphere

Summary

Introduction

The freezing process of liquid water droplets in the atmosphere and adhering to surfaces is known as atmospheric icing [1,2]. Wet snow results when dry snowflakes rapidly metamorphize at negative air temperatures in supercooled clouds. These snowflakes pass into a positive temperature air layer, allowing melting to occur, causing an increase in the liquid water content [20]. Finstead and co-workers suggested that wet snow occurs when air temperatures are between −2 and 5 ◦ C and the critical percent relative humidity is more than 85.1 − 5.3 × Ta [22] Under these conditions snow can adhere to surfaces. We show how infiltration of the snow’s free liquid water into the surface roughness depends on temperature and plays a significant role in snow adhesion or shedding. The results of this work can be helpful in identifying snow mitigation strategies on bridge cables, solar panels, and camera lenses of autonomous vehicles

Experimental Section

Experimental

Results and Discussion

Conclusions