Agriculture Reference
In-Depth Information
play an important role in splash formation (Fig. 16.4b). The power law relationship
between drop diameter and mass of water splashed established experimentally for
horizontal dry glass plates with 2 <
D
< 5 mm appears to apply for incident drops
impacting on tobacco leaves when
D
> 3 mm (Huber
et al.
, 1997). The quantities of
water splashed from tobacco leaves were much smaller than from oilseed rape
leaves (by a factor of 6), probably because the hairy surface of the tobacco leaves
absorbed a much larger proportion of the drop momentum than the smooth waxy
surface of the oilseed rape leaves. Surface wetness must also be taken into account
because large differences exist between plant species (Brewer and Smith, 1997).
The physical analysis of drop impaction on a strawberry fruit surface provides
another example (Yang
et al.
, 1991b) in which the droplet trajectory vectors were
related to fruit surface inclination. The angle of reflection (measured from impact
surface normal) was close to the angle of impact (also measured from impact surface
normal) and the percentage of droplets moving in the same direction as that of
impact surface normal was a linear function of the sine of the impact angle (Fig.
16.5); this relationship was independent of both incident drop diameter and release
height (and thus velocity).
90
75
60
45
0
15
30
45
60
Angle of impact
Figure 16.5. Relation between impact angle of a falling drop (defined as the angle between
the surface normal and the trajectory direction) and the percentage of droplets moving in the
direction of the surface normal. Points are for four drop sizes (1, 2, 3, or 4 mm) and are
means of replicates for different heights of drop release (redrawn from Yang
et al
., 1991b).
