[0001] The term "jet pump" describes a pump in which motive power is provided by a high-pressure
stream of fluid which is directed through a nozzle designed to impart a high velocity
to the fluid so that the fluid issues in a high velocity jet into a mixing chamber
and creates a low-pressure area in the mixing chamber which causes a suction fluid
to flow into this chamber. At this point there is an exchange of velocities producing
a uniformly mixed stream travelling at a velocity intermediate to the motive and suction
velocity. In a diffuser which is shaped to reduce velocity gradually, the energy of
the moving stream is converted to pressure at the discharge end.
[0002] A ring jet pump is a jet pump with an annular nozzle, the suction fluid being induced
axially through the centre of the jet or nozzle. In order that a nozzle should emit
a jet of fluid having the greatest possible energy related to the energy input, the
expansion ratio from the throat of the nozzle to the exit of the nozzle will vary
depending on whether the fluid is a gas or a liquid. The expansion ratio is the ratio
of the cross-sectional area at the exit to that of the throat. In the case where the
fluid is a gas, if the pressure for given density of the incoming gas is sufficient,
a divergent discharge portion is required to prevent a shock wave, and the energy
loss it entails, from forming across the exit. If the pressure is insufficient, no
shock wave will form and the discharge portion may be parallel or non- existent depending
upon the application. It so happens that a high pressure gas is usually required at
small volumetric flow and therefore needs to discharge through a nozzle having a small
throat and having a high divergence ratio, while a low pressure gas or a liquid is
normally associated with a high flow rate in order to possess a substantial energy
level, and therefore needs to discharge through a nozzle having a large throat and
having a divergence ratio of unity.
[0003] Jet pumps are known in which the nozzle can be proportioned to control the motive
flow, but as far as the present applicants are aware there is no ring jet pump with
a variable geometry, nor has it been possible to provide a ring jet nozzle the divergence
ratio of which is variable to accommodate both high and low pressure motive fluids.
[0004] It is an object of this invention to provide such a jet.
[0005] According to the invention there is provided a nozzle for a ring jet pump including
inner and outer boundaries defining an annular throat, the outer boundary being formed
on a female element and the inner boundary being formed on a male element which is
located within the female element and is axially adjustable with respect thereto from
a first to a second position to increase the cross-sectional area of the throat progressively,
the boundaries being shaped to diverge from the throat to the exit when the male element
is in the first position and to be parallel when the male element is in the second
position.
[0006] With the male element in the first position, the expansion ratio will desirably have
a high value, while the expansion ratio preferably will not significantly exceed a
value of unity in the second position of the male element.
[0007] In the preferred form of the invention the male element is movable beyond the second
position to further increase the cross sectional area of the throat and the boundaries
are shaped to maintain the expansion ratio substantially at unity notwithstanding
the movement of the male element beyond the second position.
[0008] The boundaries may be in the shape of two cones of differing angles, the boundary
on the female element merging, at one end thereof, with the bore of a mixing chamber
and terminating at the other end in a convex radius in a manifold or plenum, and the
conical boundary on the male element being truncated where the element projects into
the mixing chamber and merging into a convex radius where it enters the manifold.
[0009] An embodiment of the invention is described below with reference to the accompanying
drawings in which:
FIGURE 1 is a partial view in axial section through a ring jet pump having a variable
geometry nozzle embodying the invention; and
FIGURES 2, 3 and 4 are partial sectional views showing the nozzle at various stages
of axial displacement of the male element relatively to the female element.
[0010] In Figure 1 a ring jet pump 10 with an annular, variable geometry nozzle is shown.
The motive fluid enters the pump 10 by means of a connection 20 and a manifold 14,
which acts as a plenum. From the manifold 14 the fluid discharges through the nozzle
and induces a suction fluid to flow axially along the bore of the jet into a mixing
chamber 16.
[0011] The manifold 14 with the motive fluid connection 20 thereon is rigidly mounted on
a male element 22 of the nozzle and is sealed with respect to element 22 by means
of an O-ring 24. Entrainment takes place at the surface of a cone 18 extending downstream
from the tip of the male element 22 and forming the interface between the motive fluid
and the induced fluid. A female element 26 of the nozzle is formed at the end of a
diffuser tube 28. The tube 28 extends into the end of the manifold and is in screw-threaded
arrangement therewith via interengaging complementary screw threads 30 on the tube
28 and the manifold. The tube 28 is sealed with respect to the manifold by means of
an O-ring 32. By rotating the male element 22 and manifold 14 relatively to the diffuser
tube 28, the male element 22 of the nozzle may be axially displaced with respect to
the female element 26.
[0012] The male element 22 is generally tubular and has an approximately frusto conical
outer surface at one end, which end, in the position shown in Figure, 1 extends into
an approximately frusto conical recess formed internally in female element 26, the
internal and external surfaces being substantially coaxial in relation to the tube
28, tapering in the same axial direction relative to the pump axis, and defining respective
boundaries of an annular-section passage connecting the interior of manifold 14 with
the mixing chamber. The boundaries are, more particularly, in the shape of two cones
of differing angles, the boundary of the female element merging, at the end thereof
further from member 22, with the bore of the mixing chamber 16 and terminating at
the free end of the female element in a convex radius (as viewed in axial section),
and the conical boundary afforded by the male element being truncated at the free
end of the male element where the male element projects into the mixing chamber and
merging into a convex radius (as viewed in axial section), further from the free end
of the male element.
[0013] In operation of the pump a fluid jet, of annular cross section, is formed by fluid
passing under pressure from the manifold 14 through through said annular section passage.
[0014] In Figure 2 the tube 28 is shown to be screwed in to an extreme position in which
the conical boundary formed on the female element 26 is closely adjacent to the conical
boundary formed on the male element 22. The nozzle aperture is therefore of a small
cross-sectional area, while at the same time, the divergence ratio of the two boundaries
is high, e.g. over 2:1. This is a situation appropriate for a high pressure gaseous
motive fluid.
[0015] In Figure 3 the diffuser tube 28 has been unscrewed to a central position and the
male and female boundaries define between them a large aperture for moderate pressure
gaseous motive fluid with a moderate divergence ratio e.g. 1,5 to 2:1.
[0016] In Figure 4 the diffuser tube 28 has been unscrewed even further so that the male
and female boundaries define between them an aperture with a large cross sectional
area which is suitable for liquid or low pressure gaseous motive fluid. The divergence
ratio in this position is unity. Any further unscrewing of the diffuser tube 28 with
a consequent axial displacement of the female element 26 of the nozzle relatively
to the male element 22, will merely result in an aperture with an enlarged cross-sectional
area while the divergence ratio maintains a value of unity.
[0017] It will be appreciated that, for any set of conditions, a ring jet can be designed
having a fixed geometry to suit the conditions but the variable geometry nozzle proposed
confers the advantage that one jet pump may be used and adjusted to suit a large variety
of conditions.
1. A nozzle for a ring jet pump including inner and outer boundaries defining an annular
throat, the outer boundary being formed on a female element and the inner boundary
being formed on a male element which is located within the female element and is axially
adjustable with respect thereto from a first to a second position to increase the
cross-sectional area . of the throat progressively, the boundaries being shaped to
diverge from the throat to the exit when the male element is in the first position
and to be parallel when the male element is in the second position.
2. The nozzle of claim 1 in which, with the male element in the first position, the
expansion ratio has a high value while the expansion ratio does not exceed a value
of unity in the second position of the male element.
3. The nozzle of claim 2 in which the male element is movable beyond the second position
to further increase the cross sectional area of the throat and the boundaries are
shaped to maintain the expansion ratio at unity notwithstanding the movement of the
male element beyond the second position.
4. The nozzle of claim 1 in which the boundaries are in the shape of two cones of
differing angles, the boundary of the female element merging, at one end thereof,
with the bore of a mixing chamber and terminating at the other end in a convex radius
on a manifold, and the conical boundary on the male element being truncated where
the element projects into the mixing chamber and merging into a convex radius where
it enters the manifold.
5. A nozzle substantially as hereinbefore described with reference to, and as shown
in, the accompanying drawings.