Electric Effect during the Fast Dendritic Freezing of Supercooled Water Droplets

Abstract

An electrical phenomenon consisting of two alternating voltage peaks of up to 6 V amplitude was observed during the rapid dendritic freezing phase of supercooled water droplets in the millimeter size range with supercoolings ΔT in the range of 5 to 20 K. For correlation of the dendritic freezing front with the electric potential, a fast recording oscilloscope was combined with a high-speed camera operating at up to 5000 frames per second. The strength of the effect is roughly proportional to the supercooling and dendritic freezing speed. Furthermore, during the subsequent second freezing phase, which is much slower than the dendritic, a qualitatively different electric potential evolution of similar magnitude has been found which resembles the well-investigated Workman-Reynolds freezing potential (WRFP). The experiments show clear evidence that the first rapid dendritic freezing stage significantly influences direction and amount of the electric potential during the second slow freezing stage. Compared to the WRFP, which takes place for much smaller supercoolings of ΔT ≪ 5 K, the evolution of the presented dendritic freezing potential occurs about 10(4) times faster, is about 10 times smaller in view of the maximum voltage, and shows similar break off concentrations but remarkably does not vanish at low foreign ion concentrations. This phenomenon has direct relevance to atmospheric freezing processes of the Earth, other planets, and satellites.

Critical Radius of Supercooled Water Droplets: On the Transition toward Dendritic Freezing

“…The theoretical studies of Weiss et al and Rozmanov and Kusalik indicate a qualitatively similar characteristics of which the Weiss study is in better agreement with the experimental results of Pruppacher et al . and our results presented here and in refs and . Compared to the Pruppacher data which reached to supercoolings up to about −16 °C with no evident relative maximum, our measurements cover data up to −24 °C supercooling and seem to demonstrate a relative maximum of the freezing rate at around −17 to −19 °C supercooling, (see Figure ).…”

“…For monitoring the freezing process of supercooled water droplets and especially the velocity of the stage one (dendritic) freezing front, vacuum-isolated cooling and climate chambers have been used in combination with highspeed monitoring. , Droplets with a diameter of 1–3 mm have been positioned within an ultrasonic levitator (20 kHz and 58 kHz) or between two thin wire loops in the cooling chamber. − The freezing process was recorded with a high-speed camera MotionPro Y4 of firm IDT/Imaging Solutions at frame rates in the range of 500–5000 frames per second. Two short-arc lamps with Y-shaped optical fibers and focal lenses have been used to illuminate the droplet from four directions.…”

“…In other cases a bigger cooling chamber with a 500 L volume has been used, which included the complete recording and illumination technique together with an additional infrared camera for temperature monitoring. Further details of the experimental setup is described in refs , , , and .…”

“…The freezing of bigger supercooled water droplets (Δ T > 5 K) in the micrometer to millimeter size range splits into two stages: first, a fast adiabatic stage (kinetically controlled, during milliseconds) where a dendritic network is formed within an aqueous vicinity while the droplet is heated toward the melting point; this occurs asymmetrically from one side to the other. Second, a slow quasi-isothermal stage (limited by heat transport, during seconds) where the droplet completely freezes from outside to the interior; this proceeds symmetrically from the outer surface into the interior of the droplet. ,,− …”

Substrate Dependence of the Freezing Dynamics of Supercooled Water Films: A High-Speed Optical Microscope Study

“…Despite that, water droplets in the atmosphere still predominantly freeze at supercooling temper-atures lower than −5 °C. The freezing process of supercooled water droplets has been studied for decades, 6 and the process has been traditionally described as being split in two stages if the droplet is large enough (micrometer to millimeter size 7 ): first, a fast quasi-adiabatic stage, where a dendritic ice network is formed, keeping the rest of the droplet still in a liquid state; then, a slow quasi-isothermal stage where the droplet completely freezes (from the outside to the interior if the droplet is suspended in cold air 8,9 or inside another cold liquid 10 and perpendicular to the interface if the droplet is in contact with a cold surface 11 ). The first stage happens on the order of milliseconds and it is kinetically controlled while the droplet is heated to the melting point.…”