Synthesis of Natural-Like Snow by Ultrasonic Nebulization of Water: Morphology and Raman Characterization

Abstract

The current devices used to produce massive amounts of snow (i.e., snow machines) can be improved with concern to both the energy efficiency and the quality of snow. Here we investigate an alternative snow production method based on the ultrasonic nebulization of water and its subsequent condensation on the cold surfaces of a refrigerator. Inspection of the snow samples with a stereo optical microscope shows both dendritic and granular snow morphologies. The characterization of the samples by Raman spectroscopy shows a behavior consistent with that of a natural, low-density snow. Our results indicate that ultrasonic nebulization of water is an effective strategy for producing natural-like snow at the laboratory scale.

Keywords: OH-stretching; Raman spectroscopy; artificial snow; dendritic snow; laboratory snow; water nebulization.

Figure 1

(a) Picture of a double and a single dendritic snow crystal grown on the internal surface of the freezer. Microscopic pictures of double (b) and single (c,d,e) dendritic snow crystals. Black and white bars are 1 cm and 500 µm long, respectively. The angle between the light blue lines displayed on the crystal branches is 60°.

Figure 2

Microscopic picture of granular snow. Inset: snow accumulation produced after 3 h of deposition. Black and white bars correspond to 10 cm and 500 µm, respectively.

Figure 3

(a) Raman spectra taken at −2 °C across the OH-stretching band of bulk ice (black), fresh snow collected on field (blue), and laboratory snow (red). Shaded areas under the curves represent the integration intervals of Equation (1) for the three cases. The S values of the three spectra are reported in the inset. (b) S values of bulk ice (black line), fresh snow (blue triangles), and laboratory snow (red circles). The small red circles are the S values for all the laboratory snow spectra. The red box plot is obtained by grouping for a given T₀ temperature the S values measured on laboratory snow over the temperature interval T₀ − 0.25 °C < T < T₀ + 0.25 °C.

Figure 4

Schematization of the snow-making device. Ultrasonic nebulizer (1), liquid water supply (2), stream of nebulized water droplets (3), refrigerating fluid (4) that circulates around the freezer walls, Styrofoam plate (5), and snow deposit (6) that grows on the freezer internal surface. Magnification: mechanism of the generation of the snow dendrites on the metallic plates of the freezer. The blue arrow indicates the direction of the heat flow.