Apparatus for degassing liquids

Rarefaction pulses are generated in a chamber containing a liquid to be degassed. The rarefaction pulses are generated by creating repeated water hammers in a conduit. The water hammers result in sudden high pressure pulses which deform a stiff springy, impermeable deflection cap. After the water hammer pulses pass, the deflection cap snaps back toward its equilibrium position. The snapping action of the deflection cap causes a rarefaction pressure pulse which enhances bubble formation in the chamber. The deflection cap may resonate for some time after each water hammer pulse passes. During the interval when the deflection cap resonates the deflection cap generates an attenuated acoustic wave which is transmitted into the liquid being degassed. The deflection cap may also be driven by a system in which a high pressure fluid, such as steam, is introduced into a sealed chamber behind the deflection cap and then suddenly vented.

FIELD OF THE INVENTION 
This invention relates to apparatus for generating intense rarefaction 
pressure waves in a liquid. Apparatus according to the invention may be 
used, for example, for degassing liquids, removing particles from liquids 
by flotation or treating fluids or slurties. 
BACKGROUND OF THE INVENTION 
Intense ultrasonic fields are used for treating materials in various ways 
including cleaning surfaces, promoting certain types of chemical 
reactions, and degassing liquids. Such fields are generally generated by 
electrically driven piezoelectric or magnetostrictive transducers. In 
general, these transducers produce acoustic waves which include intense 
compression pulses. For example, U.S. Pat. No. 5,164,094 Stuckart; U.S. 
Pat. No. 4,673,512 Schram; U.S. Pat. No. 4,983,189 Peterson et al.; and 
U.S. Pat. No. 5,192,450 Heyman disclose prior art acoustic liquid 
processing devices. Other prior art acoustic liquid processing devices 
include U.S. Pat. No. 2,578,505 Carlin; U.S. Pat. No. 3,056,589 Daniel; 
U.S. Pat. No. 3,021,120 Van der Burgt; U.S. Pat. No. 3,464,672 Massa; U.S. 
Pat. No. 4,369,100 Sawyer; U.S. Pat. No. 4,433,916 Hall; U.S. Pat. No. 
4,352,570 Firth; U.S. Pat. No. 3,946,829 Mori et al.; European Patent 
specification 0 449 008 Desborough; and Japanese patent 3-151084 Murata. 
McCord, U.S. Pat. No. 4,618,263 discloses an acoustic cleaner which 
incorporates a cavitation generator for agitating liquid in an enclosure. 
The enclosure is provided with a wave reflecting surface for reflecting 
acoustic waves from the margin of the liquid back into the body of the 
liquid to reinforce cavitation in the chamber. 
Kanazawa, U.S. Pat. No. 4,727,734 discloses an ultrasonic clothes washer. 
The washer has a metal tub for receiving clothes. Bubbles are introduced 
into the tub to promote cavitation and to reflect the ultrasound so that 
all articles in the tub are irradiated with ultrasound. 
A disadvantage of prior art cavitation chambers is that the 
electromechanical equipment for generating high powered acoustic signals 
with a piezoelectric or magnetostrictive transducer is inherently 
expensive and inefficient. Another disadvantage of such apparatus for 
liquid degassing purposes is that the intense high pressure pulses can 
interfere with the degassing process. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a robust inexpensive apparatus 
for degassing liquids. 
The invention provides a diquid degassing apparatus comprising: a driving 
system and a chamber coupled to the driving system by a coupler. The 
driving system comprises: means for causing a first liquid to flow through 
a first conduit from an upstream end to a downstream end; a valve in the 
first conduit for selectively substantially blocking the flow of the first 
liquid, the valve having an open position wherein the flow is 
substantially unimpeded and a closed position wherein the flow is at least 
substantially blocked; an actuator for repeatedly: opening the valve; 
keeping the valve open for a period sufficient to allow the first liquid 
to commence flowing through the first conduit and the valve with 
sufficient velocity to produce a water hammer within the first conduit 
when the valve closes; and closing the valve --to produce a continuous 
series of water hammer acoustic pulses within the first conduit. The 
container holds a second liquid to be degassed . . . the coupler comprises 
a fluid-filled passage having a first end connected to the first conduit 
upstream from the valve and a second end connected to an interior region 
of the chamber and a stiff, resiliently deformable, impermeable, 
deflection cap blocking said fluid-filled passage. 
A second aspect of the invention provides a method for treating a material. 
The method comprises the steps of: providing a liquid-filled conduit 
coupled to a chamber by a coupler comprising a stiff springy deflection 
cap; placing a material to be treated in the chamber; causing a liquid to 
flow through the conduit; suddenly blocking the conduit a distance D 
downstream from the coupler to cause a high pressure water hammer pulse in 
the liquid within the conduit; allowing the high pressure water hammer 
pulse to deform the deflection cap; allowing the deflection cap to snap 
back to an equilibrium position to transmit a rarefaction pressure pulse 
into the chamber; and repeating these steps until the material has been 
sufficiently treated by the rarefaction pulses. 
A third aspect of the invention provides liquid degassing apparatus 
comprising: a vessel to contain a liquid to be degassed; a stiff, 
resiliently deformable, fluid impermeable, deflection cap having a first 
side in contact with the liquid to be degassed the deflection cap having a 
second side closing a sealed chamber; a source of high pressure fluid 
coupled to a volume inside the sealed chamber through an inlet valve; an 
exhaust valve in fluid communication with the volume inside the sealed 
chamber; and control means for repeatedly opening the inlet valve, 
retaining the inlet valve open until the deflection cap is deformed by 
pressure of the high pressure fluid in the volume, dosing the inlet valve 
and suddenly opening the exhaust valve to allow the deflection cap to 
suddenly snap back toward an equilibrium position. 
A fourth aspect of the invention comprises a method for creating a series 
of rarefaction pulses in a liquid. The method comprises the steps of: 
providing a chamber having one side closed by a stiff, elastically 
deformable deflection cap, the deflection cap having an outer side in 
contact with a liquid; deforming the deflection cap by introducing a fluid 
into the chamber under high pressure and allowing the high pressure fluid 
to deform the deflection cap; allowing the deflection cap to snap back to 
an equilibrium position to transmit a rarefaction pressure pulse into the 
liquid; and repeating the last two steps.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
As shown in FIG. 1, liquid processing system 20 comprises a hydraulic 
driving system 22, a coupling 24, and a chamber 26. Hydraulic driving 
system 22 generates high intensity acoustic pulses. Coupling 24 conveys 
those acoustic pulses to chamber 26, alters the characteristics of the 
pulses, as described below, and prevents fluid 27 in chamber 26 from 
commingling with working fluid 32 in driving system 22. 
Hydraulic driving system 22 comprises a reservoir 30 containing a working 
fluid 32. Working fluid 32 may be any suitably inert and non-compressible 
fluid, such as water, hydraulic fluid, or the like. Working fluid 32 is 
preferably characterized by a high cavitation threshold. The creation of 
acoustic pulses for doing work by the generation of water hammer in a 
conduit is discussed in some detail in co-pending U.S. patent application 
Ser. Nos. 07/936,032 and 08/316,915 which are incorporated herein by 
reference. 
Working fluid 32 is drawn into a conduit 34 by a pump 36 which is driven by 
a motor 38. Pump 36 may be, for example, a centrifugal pump. The outlet of 
pump 36 is connected to a conduit 40 which carries working fluid 32 back 
to reservoir 30. A valve 42 is located in conduit 40. A valve actuator 44 
is provided to open and shut valve 42. Coupler 24 is connected to conduit 
40 by a venturi unit 90 or a T-junction at a point a distance D upstream 
from valve 42 and a conduit 52. Conduits 34, 40 and 52 are preferably 
thick-wall pipe. 
Driving system 22 operates as follows. Pump 36 pumps working fluid 32 
continuously through conduit 40. With valve 42 open, working fluid 32 
flows with a velocity V through conduit 40. Valve actuator 44 periodically 
suddenly doses valve 42 to substantially or completely block the flow of 
working fluid 32 through conduit 40. The sudden blockage of working fluid 
32 in conduit 40 creates a water hammer pressure pulse which propagates 
upstream in conduit 40 from valve 42. The generation of water hammer 
pulses is discussed in many texts on fluid mechanics including, for 
example, R. L. Daugherty and J. B. Franzini, Fluid Mechanics With 
Engineering Applications, pages 425-431 McGraw Hill Book Company, 1977. 
The magnitude of the water hammer pressure pulse is determined by the 
velocity V, the compressibility of the working fluid 32, the speed at 
which valve 42 is closed, the degree of closure of valve 42 and the speed 
of sound in working fluid 32, among other factors. Under ideal 
circumstances, when valve 42 closes fully, the magnitude of the water 
hammer pressure pulse is given by: 
EQU p.sub.h =QC.sub.p V (1) 
where P.sub.h is the pressure of the water hammer pulse, .rho. is the 
density of working fluid 32, and c.sub.p is the velocity at which the 
water hammer pulse travels in conduit 40. By increasing the velocity V of 
working fluid 32 in conduit 40, making conduit 40 rigid, selecting a 
working fluid 32 which is highly incompressible, and closing valve 42 
completely and very quickly the intensity of high pressure acoustic pulses 
generated by driving system 22 may be maximized. 
The high pressure pulse created by the water hammer propagates upstream 
from valve 42 until it reaches venturi unit 90. The high pressure pulse 
propagates into coupler 24 through conduit 52. To generate pressure pulses 
which carry the same amount energy with an electromechanical transducer, 
such as a magnetostrictive transducer, would require an impractically 
large transducer having an impractically long travel. 
Venturi unit 90 comprises a nozzle 92 which is connected to conduit 40 at 
the upstream end of venturi unit 90. Nozzle 92 is directed into a narrow 
portion 94 of conduit 40 which acts as a mixing area within venturi unit 
90. Conduit 52 is connected to an annular chamber 96 surrounding nozzle 
92. Chamber 96 is in fluid communication with conduit 40 through an 
annular orifice 97 around the tip of nozzle 92. 
Venturi unit 90 functions as an aspirator or "jet pump" to reduce the 
pressure inside conduit 52 while working fluid 32 is flowing with a 
significant velocity through venturi unit 90. The flow of working fluid 32 
reduces the pressure in annular chamber 96. This, in turn, reduces the 
pressure in conduit 52. When valve 42 is suddenly closed, a pressure pulse 
propagates upstream into chamber 96 and along conduit 52, through coupler 
24 and into chamber 26 as described above. Venturi unit 90 is not 
necessary to the practice of the invention and may be replaced with a 
simple T-junction. However, venturi unit 90 can increase the range of 
variation of pressure inside conduit 52. 
The average pressure within conduit 52 may be reduced by adjusting valve 
actuator 44 to leave valve 42 open for longer periods so that venturi unit 
90 spends a higher proportion of each cycle operating as an aspirator. 
Hydraulic driving system 22 has been described so far as a closed circuit. 
Hydraulic system 22 could equally well comprise an open circuit wherein 
working fluid 32 is simply discharged, or diverted to some other use, 
after exiting valve 42. A closed circuit is generally preferable because 
it avoids wasting working fluid 32. The purpose of pump 36 and motor 38 is 
to feed fluid 32 into conduit 40 under pressure. Pump 36 and motor 38 may 
be replaced with any means for driving working fluid 32 into conduit 40 
with sufficient velocity to create water hammer pulses as described above. 
The purpose of coupler 24 is to change the characteristics of the pressure 
pulses which are transmitted into chamber 26, as described below, and to 
prevent working fluid 32 from commingling with fluid 27 inside chamber 26. 
Coupler 24 comprises a body 60 within which is a channel 61 which extends 
from an end of conduit 52 into chamber 26. Conduit 52 and channel 61 
together form a fluid-filled passage extending between conduit 40 and 
chamber 26. A stiff, springy, fluid impervious deflection cap 62 blocks 
channel 61. Deflection cap 62 and channel 61 form a sealed chamber 161 
which is connected to conduit 40 through conduit 52. Water hammer pressure 
pulses generated in driving system 22 propagate into coupler 24 along 
conduit 52. The water hammer pressure pulses are intense enough to deform 
deflection cap 62, as indicated in dashed outline in FIG. 2. The inventor 
considers that the deformation of deflection cap 62 happens relatively 
slowly, in acoustic terms, because working fluid 32 must flow through 
conduit 52 into chamber 161 and do work to deflect deflection cap 62. 
During the deflection of deflection cap 62 energy is stored in deflection 
cap 62. The relatively slow deflection of deflection cap 62 toward chamber 
26 causes a relatively low intensity pressure pulse to propagate into 
fluid 27, this pressure pulse travels through channel 61 into chamber 26. 
Therefore, the inventor considers that deflection cap 62 initially 
attenuates somewhat the water hammer pulses as they propagate through 
coupler 24. 
After a water hammer pulse passes then the pressure within conduit 52 and 
chamber 161 decreases. When this happens the pressure of working fluid 32 
is no longer sufficient to hold deflection cap 62 in its deformed position 
and deflection cap 62 begins to snap back toward its equilibrium position. 
This snapping action is very sudden because deflection cap 62 is stiff. 
The snapping of deflection cap 62 forces excess working fluid 32 out of 
chamber 161. The sudden snapping of deflection cap 62 away from chamber 26 
causes an intense rarefaction pulse to propagate into chamber 26 from 
deflection cap 62 each time the pressure pulse generated by driving system 
22 passes. Such rarefaction pulses are useful in promoting the onset of 
cavitation and in creating bubbles in chamber 26. If a venturi unit 90 is 
used, the low pressures which result when venturi unit 90 is functioning 
as an aspirator help to draw deflection cap 62 more rapidly toward its 
equilibrium position. 
After each pulse from hydraulic driving system 22 deflection cap 62 will 
continue to oscillate back and forth for some time. This high frequency 
"ringing" is attenuated as energy, in the form of acoustic waves, is 
broadcast into fluid 27 and working fluid 32 by the vibrating deflection 
cap 62. Deflection cap 62 is preferably mounted so that it has a resonant 
mode of oscillation that is excited when a pressure pulse from hydraulic 
driving system 22 is applied to it. 
The inventor considers that the "ringing" of deflection cap 62 is 
advantageous for two reasons. Firstly, it provides acoustic pressure 
pulses to treat fluid 27 in chamber 26 during the intervals between pulses 
generated by hydraulic driving system 22. Secondly, the acoustic signal 
produced by the ringing deflection cap 62 comprises a series of 
rarefaction pulses alternating with compression pulses which steadily 
decreases in amplitude. Thus, each rarefaction pulse is followed by a 
compression pulse of lower amplitude. It is considered that this waveform 
promotes the formation of bubbles in fluid 27 because the rarefaction 
pulses tend to cause bubbles to grow and the compression pulses, because 
they are reduced in amplitude, are not sufficient to cause the bubbles to 
collapse. 
Deflection cap 62 is preferably formed from a stiff springy metal such as 
hardened steel. Deflection cap 62 is preferably round, as shown in FIG. 3, 
or an elongated oval, as shown in FIG. 4, but may have various shapes. 
Deflection cap 62 may be flat, but for more efficiency deflection cap 62 
should be contoured. There are many possible shapes for the contours of 
deflection cap 62. For example, deflection cap 62 may have a central area 
63 which is indented toward chamber 161. Deflection cap 62 may also have a 
region 64 which is indented away from chamber 161 surrounding central area 
63. Preferably the radius of central area 63 is approximately the same as 
the width of region 64. Most preferably the shape of deflection cap 62 is 
such that it can be held in a deformed position by a fluid pressure which 
is lower than the fluid pressure required to initially deform deflection 
cap 62 from its equilibrium position. This provides an enhanced "snap" 
action. 
Deflection cap 62 may be, for example, made from 4340 steel hardened to a 
Rockwell hardness (HRc) of 43-45. Deflection cap 62 may also be made of a 
suitable composite material, such as a fibre reinforced plastic (FRP) 
material having the required mechanical properties. Deflection cap 62 may 
also be coated with a thin layer of rubber to prevent cavitation damage to 
deflection cap 62. 
Channel 61 preferably gently tapers from the end of conduit 52 to a larger 
diameter area where deflection cap 62 is mounted. The total volume of 
conduit 52 and the portion of channel 61 in fluid communication with 
conduit 52 is preferably significantly less than the volume of fluid in 
conduit 40 which is arrested by the closure of valve 42. The end of 
channel 61 in fluid communication with chamber 26 may taper gradually to 
an aperture 67. 
Aperture 67 tends to prolong the most intense rarefaction pulses produced 
by the motion of deflection cap 62 by limiting the rate at which fluid 27 
can flow into the portion of channel 61 adjacent pressure cap 62. The 
inventor considers that prolonging such rarefaction pulses tends to 
increase the rate of bubble formation in liquid 27. Aperture 67 does not 
substantially effect the amplitude of acoustic pulses produced by smaller 
motions of deflection cap because small amplitude motions of deflection 
cap 62 are accompanied by very little flow in fluid 27. 
Deflection cap 62 is sealingly mounted in channel 61. For example, 
deflection cap 62 may be clamped between two parts of body 60, and sealed 
with O-rings 68, as shown in FIG. 2. 
Chamber 26 may be formed from a segment of pipe 70. Fluids to be treated 
may be introduced into chamber 26. The embodiment shown in FIGS. 1 and 2 
is adapted for degassing fluid 27. Chamber 26 is a tall vertical tube with 
an inlet 76 equipped with a valve 78 and an outlet 77 equipped with a 
valve 79. With valve 79 closed a batch of liquid 27 is introduced into 
chamber 26 by opening valve 78. A sensor 80 detects when liquid 27 reaches 
a level 100 and automatically closes valve 78. Hydraulic driving system 22 
can then be actuated to treat fluid 27 for a time sufficient to achieve 
the desired results. A vacuum pump 110 is provided to draw off gases 
released from fluid 27. Outlet valve 79 is then opened to alow the 
degassed fluid to be drawn off through outlet 77. 
In operation, water hammer pulses are developed in hydraulic driving system 
22, as described above. The high pressure water hammer pulses are 
generated periodically at first frequency f.sub.1 by valve actuator 44. 
The high pressure pulses pass into coupler 24, and deflect deflection cap 
62. Motion of deflection cap 62 causes some spherical acoustic wave 
fronts, which are indicated schematically in FIG. 1, to propagate into 
chamber 26 from aperture 67. 
Valve actuator 44 may be an electronically operated solenoid or any other 
known mechanism for rapidly opening and closing valve 42. A preferred form 
of valve actuator is shown in FIGS. 3 and 4 of my co-pending application 
Ser. No. 08/316,915 entitled Water Hammer Driven Cavitation Chamber. 
From the foregoing, it will be readily apparent to those skilled in the art 
that Hydraulic driving system 22 may be used together with a coupler 24 
incorporating a springy deflection cap 62 in other applications than 
degassing fluids. For example, FIG. 4 shows apparatus 120 according to the 
invention for removing suspended particles from a fluid 27 by flotation. 
Apparatus 120 comprises a hydraulic driving system 22 as described above. 
Fluid 27 is introduced into a tank 130 through an inlet 132. A coupler 24A 
is located in tank 130 below inlet 132. Hydraulic driving system creates 
pressure pulses which are delivered to coupler 24A through conduit 52 as 
described above. Coupler 24A is preferably elongated, as shown. An array 
of two or more smaller couplers may be used in place of the single coupler 
24A which is illustrated. 
The rarefaction pulses generated by hydraulic driving system 22 and coupler 
24A cause cavitation bubbles to form in fluid 27. The bubbles float upward 
in fluid 27 and carry suspended particles which are entrained in fluid 27 
with them. The bubbles and entrained particles form a froth 134 on the 
surface of fluid 27. Froth 134 may be skimmed off by any suitable means, 
such as a conveyor 138. Cleaned fluid 27 may be withdrawn through an 
outlet 140. Dissolved gases and/or frothing agents may be added to fluid 
27 upstream from tank 130 to enhance bubble formation in tank 130. The 
method and apparatus described herein are capable of producing a great 
many very small bubbles. 
FIG. 6 shows apparatus 24A which is similar to the apparatus 24 of FIG. 4 
but is adapted for continuous degassing of a liquid 27. Liquid 27 flows 
slowly through a tank 130A. Liquid 27 enters tank 130A through inlet 132. 
Degassed liquid is drawn off through outlet 140. Tank 130A is closed and 
equipped with a vacuum pump 110 which lowers the ambient pressure at the 
surface of liquid 27 inside tank 130 A and draws off gases which are 
released from liquid 27. 
As described above, with reference to FIG. 5, rarefaction pulses generated 
by hydraulic driving system 22 and coupler 24A cause dissolved gases in 
fluid 27 to be released in the form of small bubbles. These bubbles float 
to the surface of liquid 27 where they ultimately break, and release their 
gaseous contents to be drawn off by pump 110. 
FIG. 7 shows an alternative embodiment of the invention in which the motion 
of deflection cap 62 is driven by a high pressure liquid or gas instead of 
by high pressure pulses generated by water-hammer. In the apparatus of 
FIG. 7, a source of a high pressure fluid, which may be a gas or a liquid, 
is connected through a valve 153 and a section of conduit 40 to channel 
61. The high pressure fluid may be, for example, high pressure steam which 
is available in many industrial settings. An exhaust valve is provided to 
allow high pressure liquid or gas to escape from channel 61. Valves 153 
and 155 may be operated by a controller 158, such as an electronic 
controller. 
In operation, valve 153 is opened with valve 155 closed to allow high 
pressure liquid or gas to pass into channel 61 where it pushes on, and 
deforms, deflection cap 62. This deformation can be caused to occur 
relatively slowly by limiting the opening of valve 153. Valve 153 is then 
closed and valve 155 is suddenly opened. When valve 155 is opened then the 
pressure in channel 61 suddenly drops and deflection cap 62 begins to snap 
toward its equilibrium position, as described above. The cycle is 
completed by closing valve 155 and re-opening valve 153. Deflection cap 62 
may be allowed to "ring" for an interval before closing valve 155 and/or 
before re-opening valve 153. 
EXAMPLE 
A hydraulic driving system substantially as shown in FIG. 1 was used in 
which a 2 horsepower motor operating at approximately one eighth load 
drove a centrifugal pump, the centrifugal pump pumped hydraulic fluid 
through a loop of 3 meters of 1/2 inch internal diameter reinforced 
hydraulic hose. The flow of hydraulic fluid in the hydraulic hose was 
interrupted at a frequency of approximately 35 Hz. by a cam operated 
valve. A section of 1/2 inch internal diameter reinforced hydraulic hose 
was connected between a tee in the first hydraulic hose and a coupler, as 
described below. The tee was located 1 meter upstream from the valve. The 
coupler comprised a metal body having a 3 inch diameter deflection cap 
made of 1/32 inch thick 4340 steel hardened to 45 HRc mounted in it with 
O-rings substantially as shown in FIG. 1. The deflection cap had a profile 
substantially as shown in FIG. 1. The depth of indentation 63 was 
approximately 1/4 inch. The diameter of aperture 67 was approximately 1/4 
inch. A 2 inch diameter vertical plexiglass tube filled with water to a 
height of approximately 2 meters was attached to the coupler. Each time 
the hydraulic driving system created a pressure pulse, the interior of the 
plexiglass tube became filled with small bubbles. 
As will be apparent to those skilled in the art in the light of the 
foregoing disclosure, many alterations and modifications are possible in 
the practice of this invention without departing from the spirit or scope 
thereof. Accordingly, the scope of the invention is to be construed in 
accordance with the substance defined by the following claims.