Note: Descriptions are shown in the official language in which they were submitted.
10~7~70
e present invention relates to submersible gas-
evolvlng devices such as sea water batteries, and has for
its object the reduction of acoustic noise associated with
bubbles formed by the escape of gases ~rom the submerged
device.
An example of such devices is a sea water battery
used for powering underwater electrical equipment suc'n as
sonar buoys.
Conventionally employed undersea batteries of this
type, such as but not limited to those employing silver
chloride and magnesium electrodes, employ sea water as the
electrolyte, the battery being activated on submersion by the
entry of sea water by means of one or more inlet ports located
near the base of the battery, and an outlet port located
adjacent the top of the battery. During operation of the
battery, hydrogen gas is evolved, which collects at the top
of the battery and escapes through the outlet port. When such
a battery is employed in a sonar listening device, the noise
of the escaping hydrogen bubbles can seriously reduce the
available useful listening time of the device.
The present invention is directed to an arrangement
which reduces this noise, and is particularly applicable to
such devices, although it will be appreciated from the
description which follows, that the invention is applicable
to the reduction of acoustic noise generally, in any case ~
where bubbles are formed by the escape of gas from a submerged
device.
10C~75~0
nvestigations have shown that a major contribution
to the noise generated by evolving bubbles in such a situation
arises rom the actual formation of each discrete bubble. A
discrete bubble, by virtue of surface tension, atternpts to
minimise its surface area and hence occupies a smaller volume
than does the volume of gas partly bounded by a gas/water
interface and partly bounded by a gas/orifice interface from
which it forms.
Upon formation of the discrete bubble, water collapses
around the gas as it contracts to the smaller volume with
subsequent damped resonant vlbration of the gas/water inter-
face surface There is also collapse of water onto the
orifice where a new gas/water interface is formed and collapse
of water against water in the vicinity of the orifice where
previously two water surfaces were held apart by a volume of gas
In accordance with the present invention, noise
generated in this way upon bubble formation is reduced by the
provision, immediately above and adjacent to the gas escape
orifice, of a surface against which the bubble may be formed.
~y allowing the bubble to form against a surface rather than
freely in the water adjacent the outlet port, the noise is
reduced, and furthermore by suitable choice of the material
by which this surface is provided, damping of the resonant
vibration of the bubble can be increased, thereby reducing
the period of transient noise.
Preferably, but not necessarily, the surface which is
provided immediately above the outlet port is provided with a
smooth curve in the -
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757~
vertical ~]alle so that b~lbbles formed against the surface maygently move outwardly and upwar~ly and pass ~rom the surface
into ~ree water wi-thout disturbance which could create noise.
~ny material surface so shaped, positioned above and adjacent
to the orifice will reduce the noise because the initial
distention of the bubble is decreased. Preferably, the
material surface immediately adjacent to the port should
exhibit a finite wetting angle with sea water.
~ccording to one aspect of the present invention,
a method for reducing noise generated by a gas eminating
from a device submerged in a liquid having an upper gas
interface comprises the steps of issuing yas from said device
through an orifice disposed on the device, and allowing issued
gases immediately to form discrete bubbles on a surface
disposed closely adjacent said orifice externally of the
device and facing away from the upper gas interface.
According to a second embodiment of the invention,
an apparatus for carrying out this method comprises an
orifice through which the gas is allowed to issue from the
device into the liquid, and a surface facing away from the
upper gas interface and disposed externally of the device
and closely adjacent said orifice, the surface being adapted
to permit issued gases to form discrete bubbles thereon
immediately upon issuance fro~ the orifice.
One embodiment of the invention will now be described
with reference to the accompanying drawings. In the present
example the apparatus is a submersible battery.
Figure 1 is a schematic isometric view of a battery
modified in accordance with the present invention,
_ 4 ~
'7S~
Figure 2 sho~s a schematic front elevation of the
battery in Figure 1, and
Figure 3 shows the battery in sc~ematic side
...~..........................................................
- 4a -
elevation
I'igure 4 shows in detail that part of the battery
which possesses a surface against which bubbles form.
Figures 5 and 6 are a side elevation and an end
elevati.on respectively of the part sho~n in Figure 4.
The battery 10 illustrated, which is of a kno~in
type employing electrodes of silver chloride and magnesium
is provided with an inlet port 11 and an outlet port 12.
The outlet port 12 is an orifice having dimensions 3.5 mm
by 3.0 mm in one e~ample and 7.0 mm by 3,0 mm in a second
example. Mounted on the top of the battery is a flat piece
of polyurethane 13 which is provided with an outwardly
extending lip 14 the lower surface 15 of which forms ~he
surface against which bubble formation will occur. The
surface 15 is curved upwardly and outwardly from the outlet
port 12, and it will be noted that this surface 15 is formed
so as to be located immediately at the upper edge of the
outlet port 12.
Gas evolved from the outlet port 12 forms into
bubbles against the adjacent surface 15, and these bubbles
then pass outwardly and upwardly against the surface 15 before
they escape into the free water.
In the present embodiment the piece of polyurethane
13 and lip 14 have the dimensions as shown in Figures 4, 5
and 6, and surface 15 has the shape shown in those figures,
where dimension A is 32 mm; B is 13 mm; C is 20 mm;
D is 26 mm; E is 58 mm; F is 32 mmj G is 25 mm; H is 5 mm;
~ ~,7 5
I is 6 mm; J is 72 mm.
The~se dimensions have proved effective ~ith bubble
evolutiQn rates of 0.5 cc to 3 cc per second at standard
temperature and pressure,
As mentioned above, the material employed for the
lip 14 is in this case polyurethane, This has been found
to have suitable surface and bulk characteristics. The
particular polyurethane material employed in the illustrated
embodiment is available from Dupont under the trade mark
ADIPRENE, although any polyurethane material should be
suitable. Other suitable materials include silicones, and
synthetic and natural rubbers.
In conjunction with the present invention, it is
preferred in order further to reduce the noise associated
with bubble formation, to use an outlet port of greater
dimension than that conventionally employed in devices of
this type.
It will be appreciated that the manner in which
the surface against which bubble formation occurs is provided,
is not restricted to the example illustrated. The surface
may be provided in a lip or shelf formed integrally with the
battery housing or provided in any other suitable way, and
the shape and size of the surface and its distance from an
edge of the orifice will be a matter for design choice for
particular applications.
