Frost protection in orchards using air from the temperature inversion layer

Abstract

A new type of wind machine comprising a 21-ft. diameter, low-speed, vertical-axis fan is described, and its efficacy in raising the air temperature in orchards and in protecting citrus and deciduous trees from frost damage is discussed. The fan was shown to be effective in raising the temperature in the orchard, the amount being governed by the strength of temperature inversion. The actual range of effect of the fan was found to be inversely related to the rise in temperature at the centre of the fan's zone of influence. The extent of a rise in temperature equivalent to 25 per cent. of that under the fan varied from 1 to 1½ acres in citrus and from 2 to 8 acres in almonds, depending on the strength of the inversion. The range in citrus was considerably increased by skirting the trees. It was shown that under exceptionally severe frost conditions the area in which actual frost damage to the fruit and trees was reduced by the fan was very small, and because of this the fan in its present form is not considered an economic means of frost protection. The theoretical basis for the formation of temperature inversion is considered and data showing the types of temperature inversion recorded at Griffith, N.S.W., are presented and discussed.