KURENAI : Kyoto University Research Information Repository

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BI. 2 DROPLET GENERATION MECHANISMS
Droplets can be generated by a number of different ways such as the liq-
uid jet breakup, droplet disintegration and droplet entrainment from a body
of liquid [1,12-14]. The former two mechanisms have been reviewed in detail
by Brodkey [12]. A liquid jet or sheet disintegrates into small droplets due
to interfacial instabilities [15,16].
Disintegration of droplets in gas stream has been studied by a number of
researchers [12,13,17-23]. Several different mechanisms of droplet break-up
have been recognized. The mode by which the disintegration occurs depends on
the initial droplet size and the flow condition. A large free-falling drop
initially becomes unstable due to the Taylor instability and then it is blown
in by gas and disintegrates into fine droplets.
A criterion for droplet disintegration can be expressed in terms of the
Weber number defined by
p v2D
We = g 6g(1)
where D is the droplet size. Then the criterion is given by a critical Weber
number beyond which droplets disintegrate into smaller droplets.
In case of a falling drop, the critical Weber number is given [13,17,20]
We c= 22(falling drop) .(2)
However, direct observations of droplet sizes indicate that the critical di-
ameter is approximately given [22,24] by
D c - (4 6) a /gap .(3)
This value can be also obtained from the consideration of the Taylor Instabil-
ity [22]. On the other hand, the terminal velocity of a large drop [24,25]
is about
v = (1.4 ti 1.7)
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cig6,P\
Pg
1/4
157
(4)