KURENAI : Kyoto University Research Information Repository

The experimental data show that the entrainment Efg is a strong
function of the gas superficial velocity jgand the distance from the
surface of a pool h. When the entrainment is plotted against the gas
superficial velocity at a fixed distance h-, at least three entrainment
regimes can be observed [33,38,49]. In a low gas flux regime, the
entrainment is small and entrained liquid consists of very fine
droplets. In this regime, Efg is approximately proportional to the gas
flux. In an intermediate gas flux regime, larger drops are ejected from the
pool and Efg increases with 4"4. At a higher gas flux, large gas slugs
are formed and a pool is highly agitated. Then a considerable amount of
liquid can be entrained by splashing. In this high gas flux regime, Efg
increases very rapidly with the gas flux, i.e., Efg4-20.
As for the effect of the distance from the surface of a pool, there
are at least two distinct regions. In the first region (momentum
controlled region), entrainment consists of larger droplets which rise due
to their initial momentum at the surface and smaller droplets which are
carried away by streaming gas. In this region, Efg decreases rapidly with
increasing distance, i.e., Efg h-3. In the second region (deposition
controlled region), entrainment consists only of small droplets whose
terminal velocity is smaller than the gas velocity. Entrainment in this
region decreases gradually due to the droplet depositions. This trend can
be expressed as an exponential decay function of the height.
Although there have been no theoretical methods of predicting
entrainment, several semi-empirical correlations [37,40,46] based on
various data [35,38,39,41,44,49] and dimensional analyses have been
proposed.
Kruzhilin [37] proposed a dimensionless correlation for the
intermediate gas flux regime and momentum controlled region based on a
dimensional analysis. With an assumption that the initial velocity of
droplets at the interface is determined by the kinetic energy of vapor
Pgj9/2,he obtained
Efg = CK 3g4ppAID
f
Here ,j9 is the dimensionless gas flux defined by
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