. Effectiveness of orchard heaters. Fruit. 10 O 2 Curve applies to response in center portion of heated areas larger than 5 to 7 acres, without regard to border heating requirements. Fuel requirements at or near borders will be greater than indicated by this 2 4 6 8 10 12 Inversion, °F, in unheated plot (5-ft. tree-center to 60 ft. above ground) 14 16 Fig. 18. This shows the effect of temperature inversion on fuel requirements per degree of response, in the center portion of 7- to 28-acre heated areas. of one heater per tree, the drift entered from this direction during only about one-
. Effectiveness of orchard heaters. Fruit. 10 O 2 Curve applies to response in center portion of heated areas larger than 5 to 7 acres, without regard to border heating requirements. Fuel requirements at or near borders will be greater than indicated by this 2 4 6 8 10 12 Inversion, °F, in unheated plot (5-ft. tree-center to 60 ft. above ground) 14 16 Fig. 18. This shows the effect of temperature inversion on fuel requirements per degree of response, in the center portion of 7- to 28-acre heated areas. of one heater per tree, the drift entered from this direction during only about one-third of the time; usually the drift was more nearly parallel with this border. The three curves represent the three periods during which different numbers of heaters were burning. The heating effects indicated in figure 17 were measured in a row next to one in which heaters were burning during the entire time. These results indicate a nearly uniform response in this row when only every fourth row of heaters was burning. As the number of heaters was increased, the difference between the center response and that near the edge increased, perhaps because of additional indraft caused by the stronger orchard stack action with more heaters. The re- sponse in the outside row was greater, presumably because of the nearly parallel wind and the direct heating by radiation from the heavy row of border heaters, while the indraft of cold air flowed past these trees and prevented the next trees in from being warmed as much. Tree-center temperatures during both of the nights indicated that when only every fourth row of heaters was burning, trees in the three cold rows each had about 25 per cent less response (° F less) than trees in a row containing lighted heaters. Relation of response to size of heated area. The effect of temperature inversion upon fuel requirements per de- gree of response at the centers of the 7-acre, 15-acre, and 28-acre orchards is shown in figure 18. The fuel inpu
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