The behaviour and characteristics of a vortex diode in steam flows.
The forward and reverse flow characteristics have been measured for
Zobel type vortex diode with 19 mm throat diameter using superheated stea
with inlet pressures up to 12 bar absolute, and exhausting into a subatmospheric
condenser to achieve inlet to outlet pressure ratios up to 30
A discharge factor, Cf, which relates the measured mass flow rate to the
theoretical mass flow rate of a critical flow through a comparable
isentropic nozzle, has been used to describe the resistance of the diode.
In the choked region of the forward and reverse flow, Cf has a constant
value of 0.95 and 0.38 respectively. The critical pressure ratios in the
forward and reverse flow are approximately 2 and 4.
Repeating the tests using wet steam with known dryness fractions, ha
shown separately the effects of wetness on the diode performance. The
forward flow discharge factor in the choked condition is seen to be
independent of dryness fraction, and found to lie between 0.9 and 1.0,
which is similar to that found with superheated steam. The reverse flow
discharge factor in the choked condition varied from about 0.4 for a
dryness fraction of, 0.98, to 0.48 for a dryness fraction of 0.92.
Excessive steam wetness (quality less than 0.93) in the reverse flow
direction led to a build-up of water and when this was eventually swept
through to the diode, the resistance was seen to fall substantially as th
strong internal vortex was destroyed. This problem can be overcome in
practice, however, by installing a water separator before the diode.
Reverse flow characteristics of four 10 mm throat diameter Zobel typ
vortex diodes have been measured using air with inlet pressure up to 31
bar absolute, and exhausting into atmosphere. The characteristics are
seen to be similar to those found with superheated steam, with a value of
Cf of 0.38. The effect of installing the four diodes in series was
investigated. It was shown that by sharing the pressure drop between the
diodes and moving the operating point into the incompressible regime, som
of the high resistance performance could be recovered.
A detailed study of vortex flow was carried out using a large vortex
throttle with superheated steam as the working fluid. The static pressur
distribution has been determined experimentally both across the vortex an
along the axis of the chamber exit duct. The chamber internal wall
temperatures have been obtained using insulated, flush-mounted
thermocouples. The measurements enabled the velocity field to be
calculated. The bulk of the internal vortex was found to have an exponer.
of 0.69. It was found that the vortex throttle choked at an upstream to
downstream pressure ratio of about 6 with corresponding Cf value of 0.28.
The resistance of vortex chambers is known to be strongly influenced
by the presence of reversed flow in the exit, due to vortex breakdown.
Schlieren photography of the swirling exhaust flow was used to show that
whilst vortex breakdown does occur, it can only do so after the flow has
become subsonic downstream of the exit and cannot therefore influence the
vortex chamber resistance.