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

- 24 -
3.2.5. Measurements of Wave Frequency and Velocity
Besides being used for the determination of the film thickness,
the needle contact probes were also used to measure the
frequency and velocity of the roll waves on the film. (Cf
Whalley, Hewitt, Hutchinson (1973)).
By means of the Hewlett Packard 3721A correlator, an autocorrelation
of the signal from one needle was recorded. The
correlation was then processed by a Hewlett Packard 3720A
spectrum display to obtain the power spectrum of the signal.
The signals from two needles, mounted 0.5 m apart, were then
cross-coirrelated using the 3721A correlator.
Typical examples of correlations and power spectra are
shown on figs. 3.35 and 3.36.
3.3. Experimental Data
A summary of the experiments is given in table 3.2. This
lists the test sections, the main system parameters and the
measurements carried out in the experimental periods.
In the table, the diabatic length L- refers to the distance
between the inner sides of the power clamps. The adiabatic length
L is the distance between the inner side of the upper power
cl
clamp and the lower end of the suction area. In the adiabatic
experiments this length is identical to the total length of the
test section.
The majority of the data obtained are reported graphically
in this section. A complete list or the data is given in tabular
form in Appendix.
3.3.1. Film Flow Rates
The film flow rates are estimated from suction curves, which
are obtained as described in sect. 3.2.2. In fig. 3.9 an example
of a suction curve is shown. Two straight lines are drawn through
the measuring points. The line with the slope s is assumed to
represent the situation where droplets are sucked off the core.
The intersection of this line with the line in • 0 (x^ -m /m =
g out g
x Qut ) is assumed to represent the film flow rate m f . In this
figure and in the tables the film flow rate is designated m f .
The line with the slope s
is assumed to represent the case
where waves on the film are sucked off. Thus the intersection