An Experimental and Theoretical £ Investigation of Annular Steam ...

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The measurements presented by Gill. Hewitt and Lacey (1963)
and Kirillov et al. (1973) confirm that a logarithmic law describes
the gas velocity profile in annular two-phase flow adequately
well. The measurements indicate, however, that < does
not (as in single-phase flow) remain constant. This is illustrated
in fig. 4.3 where the measurements of K made by Kirillov
et al. are plotted versus the experimental film thickness. The
correlation shown indicates that the roll waves on the film
(not the droplets in the core) are responsible for the decrement
of the turbulence constant. This was also suggested to be the
most likely explanation by Gill, Hewitt and Lacey. Their airwater
measurements also showed that < lies in the interval 0.2-
0.4. It was, however, impossible to correlate their values to
the film thickness. Because of this lack of a consistent way
to correlate the two sets of data, it was decided to apply the
classical constant value of < in eq. (4.18):
< = 0.4. (4.21)
The mean gas velocity is obtained by -
2
f r i2
u_ 9 =
i2 2
0
u g (r)r dr . (4.22)
On the other hand, we have (cf. eq. (2.5)):
»g = fjjj ' (4.23)
If no slip is assumed between the gas and the droplets, the
mean void can be calculated from
a / r 2
i2\
m q /p q
* \JT)