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The Physics of Humidification

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Frost Protection with Fog

or to formulate it exactly -

Prevention of frost damage in fruit orchards by means of Icing.

At the first moment it seems crazy to prevent frost damage by ice, however if we look at basic physics it is totally sensible.

Water turns to ice at 0°C. A sheet of ice on an object can provide  insulation against even deeper temperatures outside. Each mountaineer will dig into deep snow and take shelter in a snow hollow in case of danger like an eskimo in his snow and ice igloo. If we look at this comparable situation we can assume that the blossoms of a fruit tree can also be protected against hoar frost by means of an amour of ice.

Actually temperatures down to –3°C are not dangerous for a blossom, lower values however destroy usually the blossoms and any fruit as a consequence. This means that the trees are never in danger, the expected harvest however can be partly or totally destroyed.

Late frosts occurs usually during very early morning hours as hoar-frosts during spring when weather conditions usually do not favour frost anymore. Damages of this type can be covered by insurances, the later consequences - when fruit growers are not able to deliver their goods may worsen their position in the marketplace.

Late frost occur always during the night with cloudless sky and calm air !

Such late frost often is called "radiation frost" because the warmth remaining from the previous day is given off into the cold and black sky in the form of infrared radiation. This means that it is NOT the cold surrounding air which does suck off energy, the plant tissue itself is giving it off.
Sometimes temperatures of plant tissue can be as low as - 7°C, which means a total loss of the harvest.

With a cloud cover this situation cannot occur, because the infrared radiation would be much lower. Therefore we can deduct that an insulating layer which prevents radiation could protect the fruit cultures.

In earlier times farmers created such insulating layer by lighting smoky fires with moist straw and other nasty things; the resulting smoke cloud did insulate very effectively. However such methods are not possible anymore, if only for environmental regulations.

In established fruit growing areas (South Tyrol) mostly Sprinkler-Systems are used.
This does not create an insulating layer, however a protecting ice-coating is deposited on the blooms. As effective this process seems it has several setbacks :

o    large amounts of water are needed
the amounts of clean drinking water used for sprinkling are not provided for easily...

o    a large fraction of the distributed water simply does not reach the twigs of the trees and wets the soil between the trees. This leads to a compactification of the soil which needs later reworking

o    part of the blooms are lost by broken twigs which cannot bear the additional weight of the ice coating

Application of Water-Fog

If a hovering fog is created and distributed across the orchard an artificial insulating layer and a coating with water-ice can be achieved ( refer to remark)

This method provides serveral advantages -

o    the thickness of the insulating layer can be easily regulated.

o    water consumption is considerably lower than with sprinklers

o    consumption of electrical energy is considerably lower

o    soil compactification cannot occur because no water will fall down directly

o    broken twigs will occur only sparingly because the ice coating is much thinner however more regular

Fogging as a successful method of prevention of hoar frost is known for many years and is used regularly in fruit growing areas in North America; why European fruit growers do not acknowledge this simple method is not known.

remark )
it is important to remark that topographic issues are to be observed. Sloping plantations are not suited because the fog will "run off". If public road cross the area an additional fact has to be observed - dense fog creates accident-prone conditions.
Ideal locations are flat areas or flat valleys. Fencing in the fog with hedges is only partly possible...




The Physics of Humidification

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last modified JAN 2020
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