Chimie Question #7759
Philip Steernberg (Genre: mâle, Àge: 15 années) de l'Internet sur 24 avril 2001 demande:
On cold nights Florida farmers spray oranges with water which quickly freezes into ice on the oranges. How would this protect the oranges from freezing?
vu 11147 fois
La réponse
Barry Shell
répondu le 25 avril 2001
This has to do with the latent heat of phase change between ice and water. The most common method of active frost protection is the use of overhead sprinklers while the frost risk is present. When water is applied to crops under zero or sub zero temperature conditions, it freezes. On freezing the water releases heat, which offsets the heat lost by the crop to its cooler surroundings. To achieve successful frost control a film of continuously freezing water must be maintained on the surface of the formed ice. When the ice begins to melt, usually after dawn when the air temperature begins to rise, heat must be applied to the ice or this heat will be drawn from the crop. This heat is supplied by water applied to the crop via the irrigation system. Generally an application rate of 3.5 mm/hr is adequate for frosts down to 4.0C.
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