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- Author or Editor: J. V. Iribarne x
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Abstract
The electrification accompanying the breakup of large drops falling in air in the absence of an electric field has been studied. A closed circuit vertical tunnel has been used, and the chemical composition of the drops has been carefully controlled. The results obtained for the average charge separation between the large and small fragments are non-specific regarding the nature of the ions present (except for surface-active species), but strongly dependent on the electrolytic conductivity. The magnitude of the effect goes from about +10−2 esu per breakup (5 × 10−2 esu cm−3) for pure water to −10−2 esu for concentrated solutions, reversing sign at about 10−5 Ω−1 cm−1 (concentrations ∼10−4 N). It was shown that these results can be interpreted on the basis of two competing processes, one of which is the shelling of the electrical double layer on the water–air interface while the air develops the characteristic liquid film bag or bubble.
Abstract
The electrification accompanying the breakup of large drops falling in air in the absence of an electric field has been studied. A closed circuit vertical tunnel has been used, and the chemical composition of the drops has been carefully controlled. The results obtained for the average charge separation between the large and small fragments are non-specific regarding the nature of the ions present (except for surface-active species), but strongly dependent on the electrolytic conductivity. The magnitude of the effect goes from about +10−2 esu per breakup (5 × 10−2 esu cm−3) for pure water to −10−2 esu for concentrated solutions, reversing sign at about 10−5 Ω−1 cm−1 (concentrations ∼10−4 N). It was shown that these results can be interpreted on the basis of two competing processes, one of which is the shelling of the electrical double layer on the water–air interface while the air develops the characteristic liquid film bag or bubble.
Abstract
Droplets in the size range of 40 to 120 µm diameter were accelerated in a small wind tunnel and accreted onto an ice target connected to an electrometer that measured the charging effect. The experiments were performed with environment temperatures between −6 and −14C and impact velocities between 1 and 30 m sec−1, both in the absence of an external field and with fields up to 2.5 × 105 V m−1.
It was found that in the absence of field, significant charging occurs only above a threshold velocity, of the order of 10 m sec−1 for 100-µm droplets. The sign and magnitude of the effect were critically dependent on the liquid composition, the sign being negative for NACl solutions and positive for (NH4)2SO4 solutions and pure water. The magnitude increased with droplet size and with impact velocity, reaching a maximum in the order of 1–3 fC (average charge per droplet) at about 25 m sec−1, for 100-µm droplets. No evidence of ice splintering was found, and the effect appeared associated with splashing. An explanation based on the mechanism of double layer shearing (which implies that the Workman-Reynolds effect is active) is proposed. External fields induce charge separations proportional to their intensity, with proportionality constants increasing with droplet size and impact velocity; this effect becomes predominant for fields in the order of 104 V m−1 or higher. Consequences of the experiments for the theory of thunderstorm electrification are drawn.
A separate series of experiments, dealing with the electrification associated with the splashing of 370- and 500-µm droplets, is reported in an Appendix.
Abstract
Droplets in the size range of 40 to 120 µm diameter were accelerated in a small wind tunnel and accreted onto an ice target connected to an electrometer that measured the charging effect. The experiments were performed with environment temperatures between −6 and −14C and impact velocities between 1 and 30 m sec−1, both in the absence of an external field and with fields up to 2.5 × 105 V m−1.
It was found that in the absence of field, significant charging occurs only above a threshold velocity, of the order of 10 m sec−1 for 100-µm droplets. The sign and magnitude of the effect were critically dependent on the liquid composition, the sign being negative for NACl solutions and positive for (NH4)2SO4 solutions and pure water. The magnitude increased with droplet size and with impact velocity, reaching a maximum in the order of 1–3 fC (average charge per droplet) at about 25 m sec−1, for 100-µm droplets. No evidence of ice splintering was found, and the effect appeared associated with splashing. An explanation based on the mechanism of double layer shearing (which implies that the Workman-Reynolds effect is active) is proposed. External fields induce charge separations proportional to their intensity, with proportionality constants increasing with droplet size and impact velocity; this effect becomes predominant for fields in the order of 104 V m−1 or higher. Consequences of the experiments for the theory of thunderstorm electrification are drawn.
A separate series of experiments, dealing with the electrification associated with the splashing of 370- and 500-µm droplets, is reported in an Appendix.
Abstract
Drops in the size range 1.2 to 1.9 mm were frozen while floating in a nitrogen stream. Frequency of split-ting and cracking was found to be 80–90% when the gas was dry and 57% when it was saturated with water vapor. During freezing, about half of the drops acquired charges (of both signs) in the order of several tenths of a picoColumb and the same proportion (in separate experiments) produced splinters, giving an average of σ10 splinters per frozen drop.
Abstract
Drops in the size range 1.2 to 1.9 mm were frozen while floating in a nitrogen stream. Frequency of split-ting and cracking was found to be 80–90% when the gas was dry and 57% when it was saturated with water vapor. During freezing, about half of the drops acquired charges (of both signs) in the order of several tenths of a picoColumb and the same proportion (in separate experiments) produced splinters, giving an average of σ10 splinters per frozen drop.
Abstract
The freezing characteristics of supercooled droplets of electrolytic solutions were studied for a set of 22 electrolytes and for concentrations of 10−2, 10−2 and 10−1 N. Ethyl alcohol was also tested. The freezing curves were found to be similar to those of water. The mean freezing temperature was compared in each case with that of the water sample used as a solvent. The differences were interpreted for the more diluted solutions in terms of the theory of heterogeneous nucleation.
Abstract
The freezing characteristics of supercooled droplets of electrolytic solutions were studied for a set of 22 electrolytes and for concentrations of 10−2, 10−2 and 10−1 N. Ethyl alcohol was also tested. The freezing curves were found to be similar to those of water. The mean freezing temperature was compared in each case with that of the water sample used as a solvent. The differences were interpreted for the more diluted solutions in terms of the theory of heterogeneous nucleation.
Abstract
The influence of eddies on crystal orientation has been examined. Extrapolation of experimental determinations of the power spectrum of eddies in turbulent clouds indicates that turbulence is unable to destroy the preferred orientation of falling ice crystals.
Abstract
The influence of eddies on crystal orientation has been examined. Extrapolation of experimental determinations of the power spectrum of eddies in turbulent clouds indicates that turbulence is unable to destroy the preferred orientation of falling ice crystals.
