EVAPORATION RATES OF AGRICULTURAL SPRAY MATERIAL AT LOW RELATIVE WINDSPEEDS

The evaporation rates of several agricultural spray materials are inve stigated as relative wind speed (between the droplet and ambient air) approaches zero. Laboratory studies show that application of the class ical approach to interpreting these results overestimates the evaporat ion rate lambda by more than a factor of 2 in this speed regime, and c all into question the functional forms of Sherwood number used previou sly to connect forced convection with free convection. In particular, a bounding curve may be developed as lambda/lambda(infinity) = 0.4 + 0 .116 Re for Reynolds numbers Re < 5.16 (lambda(infinity) is the evapor ation rate at Re = 5.16 and higher), This result suggests that Sherwoo d number approaches 0.8 (rather than 2) as relative wind speed (and Re ) approach zero. Implications of this finding, particularly in agricul tural spraying and peripherally in spray applications of complex mixtu res, are examined.