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

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ary to use an empirical relationship to estimate the mean void
fraction.
In this case we chose the Bankoff-Jones void formula, where
the mean slip ratio S is calculated from:
S = — (3.24)
k s -a+U-k s )a
with the following constants
k s " ^U-WP'Pcr
(3 ' 25)
R = 3.33 + 0.0026 bar" 1 -? + 0.000097 bar~ 2 -p 2 (3.26)
kgj = 0.9086 G/(G+123 kg/m 2 s) (3.27)
where p is the critical pressure 221.2 bar.
The mean void fraction is related to the mean steam quality
through the continuity equation (cf. eq. (2.7)):
1-x 1-a p'
The mean steam quality at the axial position _ is calculated
from (cf. eqs. (3.1) and (3.2)):
U) = w L j ("nT " (h(T .«t> " W) (»a^atic; (3.29)
&v sat
X(Z) = r ev (T sat )( mL^ " (h(T sat>- h i)) «»iabatic) (3.30)
where t aat refers to the saturation temperature at z.
It is seen that this void correlation depends neither on
the geometry nor on the heat flux. To give an impression of the
error this simplification gives, values calculated from eqs.
(3.24) - (3.30) are compared with void fractions estimated from
eq. (4.24). The latter equation relates the measured film flow
rate to the mean void fraction under the assumption of no slip
between the gas and droplets in the core. The comparison is
illustrated in figs. 3.21.a-b, where the diabatic film flow data
from tables Al and A3 are used to calculate a from eq. (4.24) .
The observed good agreement indicates that eqs. (3.24) *