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

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The (total) mass flux G(kg/m 2 s) is defined by the ratio:
« * 5 • (2.4)
The mean velocity of the gas u (m/s) is related to G through
g
u - - mx _ Gx
9 ' °g A g " p g A g " V
where p (kg/m ) is the density of the gas.
The relationship between the mass flux and the mean velocity
of the liquid (film and entrainment) u,(m/s) is developed in a
similar way:
u = mi = nd-x) _ G(l-x) ._ ,,
U l PlA x Pl A x " pjd-o)
U ' 6)
where p^(kg/m ) is the density of the liquid.
The ratio between u and u, is denominated the mean slip
ratio S(-):
u , p,
S = -2 = -*_ il« _i ,2 71
" u,
X " x a p g *
( ' J
2.3. Previous Experimental Work
2.3.1. Measurements of Film Flow Rates
Measurements of the liquid film flow rate by extraction of
the film through a permeable section of the channel have been
carried out through several years.
In some of the earliest investigations (Bennet and Thornton
(1961)i Collier and Hewitt (1961)j Gill, Hewitt and Lacey (1965))
a slit in the wall was used to divert the liquid film. These
measurements were carried out with air-water in a perspex tube
with an inner diameter of 31.8 mm. However, a disadvantage of
the slit is that the large roll waves are likely to overshoot
the rather narrow gap. Therefore poreous sinters or perforated
wall sections with a length of app. 5 cm were used in the later
studies.
The film flow rate is measured by an estimation of the
liquid and the gas flow rate in the extracted mixture. In a
two-component system (e.g. air-water) this is done by means of
a cyclone separator (cf. e.g. Bennet and Thornton (1961)). For