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Title: The freezing and charging of water drops
Author: Johnson, David Alan
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1967
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This thesis describes an experimental study of freezing water drops about one millimetre in diameter, It is well known that under certain conditions the expansion which occurs when water freezes can cause freezing drops to fracture in such a way that fragment 6 of ice are ejected It is shown how the ejection of such ice splinters from drops freezing in the atmosphere could be of importance in increasing precipitation by the Bergeron - Findeisen process and also in separating electric charges which may be significant in the generation of electric fields in thunderclouds. Previous work on the shattering of freezing drops failed to simulate atmospheric conditions in a number of respects, and the need for further work to determine more precisely the conditions under which drops fracture on freezing is clearly demonstrate& Experimental observations of freezing drops showed that whether or not drops fracture on freezing depends on the conditions under which the drops are nucleated and on the nature of the environment in which they freeze° All the results indicate that a drop does not fracture unless the heat transfer from the drop is distributed in such a way that a strong shell of ice forms around the drop. A semi-quantitative theory suggests that the earlier during freezing the shell of ice forms, and the smaller the amount of dissolved gas present in the drop, the more likely the drop is to fracture, It is plausible that, under certain well defined conditions, ice splinters can be ejected when cloud droplets are accreted by a larger ice crystal: and further work is suggested. The electric charges separated when drops fractured during freezing were measured. Charges of both signs and variable magnitude were detected when small ice splinters were ejected from freezing drops, Experiments on the freezing of drops of pure water and of dilute solutions suggest that neither the steady state thermoelectric effect nor the Workman - Reynolds effect is capable of explaining all the results, and alternative mechanisms are suggested.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available