Air-liquid separator assembly and system

A system for separating an air-liquid mixture in a low gravity environment is disclosed having a high speed separator to initially process the air-liquid mixture. A second, low-speed separator has its inlet connected to the liquid discharge outlet of the high speed separator in order to remove the entrained air bubbles from the liquid discharge of the high speed separator. The low speed separator has a stationary housing enclosing a rotating, paddle-type separator. The housing defines a liquid collector portion which communicates directly with a liquid discharge outlet. Air removed by the low speed separator may be vented to the ambient atmosphere, or may be returned to the air-liquid mixture inlet of the high speed separator.

BACKGROUND OF THE INVENTION 
The present invention relates to a system for separating an air-liquid 
mixture, as well as a separator assembly to be used in this system. The 
assembly and the system finds particular use in separating air-liquid 
mixtures in low gravity environments. 
In zero gravity or low gravity environments, such as those found in 
spacecraft and space stations, airflow is used to entrain free floating 
liquid. The mixture is then processed through phase separators which 
return the air to the ambient atmosphere and transfer the separated liquid 
to other processing equipment. The known separators operate at high 
speeds, on the order of several thousand rpm, which results in the 
entrainment of air bubbles in the liquid output. This is particularly 
troublesome when the liquid contains any soaps or foaming agents 
The known high speed separators provide excellent separation of air (or any 
gas) from the liquid. The separation of air from liquid is coarse and 
partially controlled only by applying very high back pressure on the 
liquid discharge line. Low speed or non-rotating separators (such as 
cyclone or vortex separators) do not provide the level of air separation 
as the high speed separators, nor are they as dependable. 
SUMMARY OF THE INVENTION 
A system for separating an air-liquid mixture in a low gravity environment 
is disclosed having a high speed separator to initially process the 
air-liquid mixture. A second, low-speed separator has its inlet connected 
to the liquid discharge outlet of the high speed separator in order to 
remove the entrained air bubbles from the liquid discharge of the high 
speed separator. The low speed separator has a stationary housing 
enclosing a rotating, paddle-type separator. The housing defines a liquid 
collector portion which communicates directly with a liquid discharge 
outlet. Air removed by the low speed separator may be vented to the 
ambient atmosphere, or may be returned to the air-liquid mixture inlet of 
the high speed separator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The system according to the invention, as illustrated in FIG. 1, comprises 
an air-liquid mixture inlet line 10 to direct the air-liquid mixture into 
a mixture inlet 12 of a high speed separator 14. Separator 14 may be any 
type of known, high-speed separator and has an air outlet line 16 and a 
liquid outlet 18. A conduit 20 interconnects the liquid outlet 18 of the 
high speed separator 14 to a mixture inlet 22 of a low-speed separator 24. 
A check valve 26 is located in conduit 20 to allow fluid flow only in the 
direction from the high speed separator toward the low speed separator and 
to prevent any return flow. 
Low speed separator 24 has an air outlet 28 to which is connected an air 
outlet conduit 30. Conduit 30 may direct the removed air back into the 
air-liquid inlet 10 of the high speed separator 14 or, alternatively, may 
vent the air to the ambient atmosphere after passing through filter 32, 
illustrated in dashed lines in FIG. 1. 
A liquid discharge outlet 34 is also defined by low speed separator 24 to 
which is connected liquid discharge conduit 36. Control valve 38 is 
operatively interposed in liquid conduit 36 to control the flow of the 
liquid through the conduit. Control valve 38 is controlled by differential 
pressure transducer 40 which has means to sense the pressure of the liquid 
collected in the low speed separator 24, through line 42, and a static 
pressure reference line 44 connected to the air-liquid inlet conduit 20. 
A positive pressure is maintained within the interior of the low speed 
separator 24 by establishing pressure opening settings for check valve 26 
and bleed valve 46, which is operatively interposed in the air bleed line 
30. Bleed valve 46 should be set to a higher opening pressure than check 
valve 26 to generate a positive pressure within low speed separator 24 
which pumps the collected liquid out of the separator. Typical pressure 
settings are an opening pressure of 1 psi for check valve 26 and an 
opening pressure of 20 psi for bleed valve 46. Quite obviously, other 
settings may be utilized depending upon the specific application of the 
system. The function of valve 26 is solely to prevent back flow from 
separators 24 when the separators are not operating. 
As the liquid accumulates in the low speed separator 24 it generates an 
increased pressure on differential pressure transducer 40. If the 
separator is rotated at a given speed, the pressure will be a function of 
the mass of the liquid being accumulated in the separator. Once the 
pressure of the liquid reaches a predetermined value, differential 
pressure transducer 40 will open valve 38, thereby allowing the liquid to 
flow out of the separator through outlet 34 and conduit 36. The positive 
pressure within the low speed separator 24 will act as a pump to urge the 
liquid out of the separator. 
The low speed separator 24 is shown in detail in FIG. 2. As can be seen, 
the separator 24 has a stationary housing comprised of upper and lower 
walls 48 and 50 spaced apart and interconnected by a sidewall 52 having a 
generally "V" shaped cross-sectional configuration. The area between the 
legs of the "V" define a liquid collector portion of the low speed 
separator 24. 
Rotatably enclosed within the housing is a paddle-type separator member 54 
that is rotated by motor 56 mounted exteriorly of the housing. The 
connection between the motor 56 and the separator member 54 may be via a 
shaft 58 having a dynamic seal 60 interposed between it and wall 50. 
Alternatively, a known magnetic coupling may be utilized between these 
elements such that the motor 56 may rotate the separator 54. 
Separator 54 has a generally hollow, cylindrical configuration such that 
the interior of the separator member 54 communicates directly with the 
mixture inlet 22 as well as the air outlet 28. The separator member 54 has 
vanes 54a extending internally and externally of its cylindrical walls and 
may also comprise a disposable filter basket providing filtration of 
solids from the processed liquid. Typical filtration requirements for the 
space station or 100 microns. The filter material also enhances the 
debubbling function of the separator, in addition to providing a large 
capacity filter. Motor 56 rotates the separator member 54 at a speed of 
less than 300 rpm for a typical 6-8 inches diameter separator. 
The air-liquid mixture enters the interior of the separator member 54 
indicated by arrows 62. The rotation of the separator member 54 causes the 
air bubbles to separate from the liquid and pass out through the air 
opening 28 in air bleed conduit 30. The air opening 28 is offset from the 
axis of rotation 20 that the inlet opening may be wiped by the internal 
vanes of member 54 thus removing any liquid droplets that may contact the 
tube. The liquid component of the mixture passes radially outwardly 
through the separator member 54, as illustrated by arrow 64 and collects 
in the radially outermost portions of the "V" shaped sidewalls 52. The 
rotation of the separator member 54 imparts a similar rotation to the 
liquid, thereby causing it to collect at the sidewall 52, as illustrated 
at 66. As noted previously, continued accumulation of the liquid at 66 
will increase the pressure on differential pressure transducer 40 in order 
to control the operation of valve 38. 
The low speed separator according to this invention is completely enclosed 
and may be attached to the remaining elements of the system by 
quick-disconnect couplings illustrated schematically at 68 and 70. Motor 
56 may also be attached to the liquid separator 54 via a quick-disconnect 
coupling. 
The present invention uses a high speed separator for air separation and a 
low speed separator for further liquid separation or debubbling. It takes 
advantage of the high pressure potential of the high speed separator to 
pressurize the low speed separator, thereby eliminating the need for pumps 
to remove the liquid from the low speed separator. The pressure 
differential maintained in the interior of the low speed separator 
effectively "pumps" the liquid out of the separator. Because of the 
relatively large volume available in the low speed separator, as well as 
the low liquid velocities, the low speed separator also functions as a 
large capacity dynamic filter for filtering the liquid. 
The foregoing description is provided for illustrative purposes only and 
should not be construed as in any way limiting this invention, the scope 
of which is defined solely by the appended claims.