The Electrofreezing of Supercooled Water Drops
The Electrofreezing of Supercooled Water Drops
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过冷水滴的电冷冻
DOI：
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发表时间：
1969
期刊：
影响因子：
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通讯作者：
J. Latham
中科院分区：
文献类型：
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作者：
M. A. Abbas;J. Latham
研究了在0°C至-45° C的环境中，悬挂在绝缘支架上的半径为0.106 cm至0.134 cm的过冷液滴的冻结。发现如果液滴表面被电力或机械力破坏以产生从局部破裂区域发出的液体细丝，则液滴在0至-22 ° C的温度范围内在固定时间间隔内冻结的概率明显更大。例如，对于五分钟的测试间隔，如果液滴被电场破坏，则在-5 ° C、-10° C、-15 ° C和-20 ° C的温度下冻结的所研究的液滴的分数分别为0.44、0.62、0.75和0.88，如果表面被绝缘纤维或导线在与液滴相同的温度下穿透，则分别为0.50和0.58，但如果液滴表面在此间隔期间未被破坏，则分别仅为0、0.02、0.07和0.18，但保持不受干扰，位于刚好低于衰变阈值的强电场中，或在其支撑物上剧烈摇动。这些观察结果与Pruppacher（1963 a，B）推导的电冻结发生的判据完全不一致，即电冻结现象总是与三相边界的运动有关。然而，这些观察结果与Loeb（1963）的建议一致，即发生电冻结的最基本条件是一部分液滴被拉出成为细丝; Loeb等人（1938）先前已经表明，这样的细丝可能含有分子聚集体，这些分子聚集体充当极好的冻结核。这些结论得到了高速照片的支持，照片显示冻结来自中断区域。在破碎过程中释放到液体中的气泡对冻结概率的影响是次要的。对自然云观测的回顾表明，虽然没有明确的证据表明存在电冻结现象，但大量间接信息强烈表明，电冻结是在过冷云中观察到的极高温度下存在冰粒的原因。所观察到的冷冻颗粒的特性是一致的，这将是预期从电冷冻。
Studies have been made of the freezing of supercooled drops of radii ranging from 0.106 cm to 0.134 cm suspended from insulating supports in an environment whose temperature could be varied from 0°C to -45° C. It was found that the probability of a drop freezing within a fixed interval of time was appreciably greater over the temperature range 0 to -22°C if the surface of the drop was disrupted by either electrical or mechanical forces to produce a filament of liquid emanating from the localised area of rupture. For example, for a five-minute test-interval the fraction of drops studied that froze at temperatures -5°C, -10° C, -15°C and -20°C were 0.44, 0,62, 0.75 and 0.88 respectively if the drop wasl disrupted by means of an electric field, 0.25, 0.44, 0.50 and 0.58 respectively if the surface was penetrated by an insulating fibre or conducting wire at the same temperature as the drop, but only 0, 0.02, 0.07 and 0.18 respectively if the drop surface was not disrupted during this interval, but remained undisturbed, was situated in a strong electric field just below the disintegration threshold, or shaken violently on its support. These observations are totally inconsistent with the criterion for the occurrence of electrofreezing deduced by Pruppacher (1963 a, b), namely that the phenomenon is always associated with the movement of a triple-phase boundary. However, the observations are in agreement with the suggestion of Loeb (1963) that the most essential condition for the occurrence of electrofreezing is that a portion of the drop be drawn out into a thin filament; Loeb et al. (1938) had previously shown that such a filament may contain molecular aggregates which act as excellent freezing nuclei. These conclusions were reinforced by high-speed photographs demonstrating that freezing originated from the area of disruption. The influence upon the freezing probability of air-bubbles released into the liquid during the disruption process was shown to be secondary. A review of observations that have been made on natural clouds indicates that although no definitive evidence exists for the occurrence of electrofreezing, a considerable body of indirect information suggests strongly that electrofreezing was responsible for the observed existence of ice particles at extremely high temperatures within supercooled clouds. The characteristics of the observed frozen particles are consistent with those which would be expected from electrofreezing.