# Relationships between Surface Properties and Snow Adhesion and Its Shedding Mechanisms
###### 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 \(\upmu\)m) and very rough (i.e., RMS roughness of greater than 308.33 \(\upmu\)m) 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 \(\upmu\)m with a surface temperature of 0 \({}^{\circ}\)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. s 2020 10 5407 29 July 2020 5 August 2020 8 July 2020 5 August 2020 8 July 2020 29 July 2020 5 August 2020 8 July 2020 29 July 2020 5 August 2020 8 July 2020 29 July 2020 5 August 2020 8 July 2020 29 July 2020 29 July 2020 5 August 2020 8 July 2020  
from the surface [4; 5]. Precipitation icing includes freezing rain, and snow [6]. Freezing rain occurs when supercooled water droplets freeze upon impact to a surface [6; 7]. Snow, due to its high stickiness and capability of applying high loads to structures, can be problematic. Snow events occur naturally in many areas in the world such as North America, Europe, Russia, Japan, Greenland, and others. Safety concerns arise when snow accretes on bridge cables, power lines, telecommunication structures, wind turbines, sensors of autonomous vehicles, and solar panels. Snow accretion on structures can result in failures due to overloading, while its shedding and detachment could be damaging to pedestrians and vehicles [2; 8]. Snow covering the sensors of autonomous vehicle sensors causes loss of data to the system, which could lead to fatal vehicular accidents [9; 10]. Solar panels experience a significant reduction in power production when covered with snow, which sometimes may last for days [11; 12; 13]. It was initially reported that snowfall occurs when wet bulb temperatures are below 0 \({}^{\circ}\)C and moisture is present in the atmosphere [14]. Later findings indicated snow formation even at wet bulb temperatures greater than 0 \({}^{\circ}\)C [15]. Snow particles are formed in clouds as a result of nucleation of water droplets around small particles. The most observed snow particle structures are plate-like, columnar, needle, and dendritic. The size and shape of the snow particles are dependent on the temperature and supersaturation of the environment [16]. A snow layer is a mixture of ice particles, air, and water. Liquid water content (LWC) is a snow property that describes the amount of water in the snow and is defined by the mass ratio of the liquid water in the snow to the total mass of snow [17]. Dry snow is composed of air and ice.