Abstract:
A gas-liquid separator uses a helical passageway to impart a spiral motion to a fluid passing therethrough. The centrifugal fore generated by the spiraling motion urges the liquid component of the fluid radially outward which forces the gas component radially inward. The gas component is then filtered through a gas-permeable, liquid-impervious membrane and discharged through a central passageway.

Description:
ORIGIN OF THE INVENTION 
   The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
   BACKGROUND OF THE INVENTION 
   The invention relates generally to the separation of gas and liquids, and more particularly, to a gas-liquid separator that uses centrifugal force to separate the gas component from the liquid component. 
   The formation of gas bubbles in the fluid of any equipment or hardware system designed to contain such fluids can significantly degrade the performance of the equipment or system. This problem is particularly acute in low or zero-gravity environments such as in space where there is no gravitational force to pull the denser liquid components down and consequently force the less dense gas components up. Thus, the gas bubbles remain suspended within the fluid instead of rising to the top as would be the case in normal (1-g) gravity. For example, formation of gas bubbles have been consistently observed in space bioreactors which are cell culture vessels used to cultivate cells in space. The gas bubbles displace nutrient-rich fluids that provide nutrients for the cells and severely disrupt the flow dynamics of the fluid within the vessel. Accordingly, it is desirable to be able to remove or eliminate gas bubbles from the fluid in such bioreactor vessels. 
   One prior art method of removing gas bubbles from the bioreactor vessels involves subjecting the vessel to high-speed rotation. However, the high rotation speed may degrade the low-shear fluid dynamics of the environment in the vessel (necessary for cultivation of mammalian cells) and compromise the experiment. 
   Another prior art methods of separating gas and liquid apply centrifugal force to the fluid to separate the heavier liquid components from the lighter gas components. Such methods typically employ a helical passageway to impart a spiraling motion to the fluid passing therethrough. The centrifugal force generated by the spiraling motion drives the heavier liquid components radially outward, separating them from the lighter gas components, which are forced toward the center of the passageway. The liquid and gas components are then discharged through different outlets. However, the fluid at the center of the passageway may still have some gas mixed therein because there is no barrier in the passageway physically separating the liquid from the gas. 
   Therefore, there exists a need for an apparatus and method of removing gas from a fluid which will preserve the low-shear environment and prevent the gas from mixing with the fluid at the boundary therebetween. 
   SUMMARY OF THE INVENTION 
   The invention provides a low-shear method and apparatus for removing gas from a fluid mixture wherein the gas components are physically separated from the liquid components. 
   In one aspect, the invention relates to a method of removing gas from a fluid mixture, comprising receiving the fluid mixture within a cylindrical chamber, advancing the fluid mixture in a helical path through the chamber such that the liquid component is urged radially outward while the gas component is urged radially inward, filtering the gas component from the liquid component, and discharging the gas component from the chamber. 
   In another aspect, the invention relates to an apparatus for removing gas from a fluid mixture, comprising a cylindrical housing, first and second inner flanges attached to a proximal end and a distal end, respectively, of the cylindrical housing, and first and second outer flanges connectable to the first and second inner flanges, respectively. Each of the first and second outer flanges has a port therein for providing fluid communication with the cylindrical housing. The apparatus further comprises a spiral core mounted on a hollow, perforated spiral core support member and housed within the cylindrical housing and a membrane layer coaxially adjacent to the hollow, perforated spiral core support member. 
   In yet another aspect, the invention relates to apparatus for removing gas from a fluid mixture containing a gas component and a liquid component. The apparatus comprises means for receiving the fluid mixture in a cylindrical chamber, means for advancing the fluid mixture in a helical path through the chamber such that the liquid component is urged radially outward while the gas component is urged radially inward, means for filtering the gas component from the liquid component, and means for discharging the gas component from the chamber. 
   In still another aspect, the invention relates to an apparatus for removing gas from a fluid mixture containing a gas component and a liquid component. The apparatus comprises a cylindrical housing, a first inner flange and a second inner flange coaxially attached to a proximal end and a distal end, respectively, of the cylindrical housing, and first and second outer flanges connectable to the first and second inner flanges, respectively. Each of the first and second outer flanges has a port therein for providing fluid communication with the cylindrical housing. The apparatus further comprises a spiral core mounted on a hollow, perforated spiral core support member and housed in the cylindrical housing, a membrane layer adjacent to an inner surface of the hollow, perforated spiral core support member and supported by a hollow, perforated membrane support member, and an annular seal between the first inner flange and the first outer flange and between the second inner flange and a second outer flange, the annular seal disposed in an annular groove formed in each of the first and second outer flanges. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a perspective view of the invention. 
       FIG. 2  illustrates an exploded view of the invention. 
       FIG. 3  illustrates a partially-longitudinal-sectional view of one embodiment of the invention wherein the spiral discs, such as representative disc  34 ( e ), have not been sectioned in order to enhance the clarity of the drawing. 
       FIG. 4  illustrates a partially-longitudinal-sectional view of another embodiment similar to the embodiment of  FIG. 3 , but without a membrane support support member, and wherein the spiral discs, as represented by disc  34 ( e ), have not been sectioned in order to enhance the clarity of the drawing. 
       FIG. 5  illustrates a partially-longitudinal-sectional view of yet another embodiment, similar to the embodiment of  FIGS. 3 and 4 , wherein the membrane is in between the spiral disc, as represented by disc  34 ( e ), again remain unsectioned for enhanced clarity. 
       FIG. 6  illustrates the effect of centrifugal force on the gas bubbles. 
       FIGS. 7A-7B  show parallel and series configurations of the invention. 
       FIGS. 8A-8F  show different spacings of the spiral discs. 
       FIG. 9  illustrates the change in the amount of centrifugal force generated for different spiral disc spacings. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Following is a detailed description of the various embodiments of the invention. Throughout the description, the term “fluid” is used to mean a mixture which may contain both a liquid component and a gas component. 
   Referring now to  FIG. 1 , a fully assembled fluid bubble eliminator  10  has a cylindrical housing  12  which is connected at its proximal and distal ends to a first inner flange  16  and a second inner flange  18 , respectively, as shown. The cylindrical housing  12  and the first inner and outer flanges  16 ,  18  together define a fluid passageway  14  (shown in  FIG. 2 ) through the cylindrical housing  12 . The first inner flange  16  is in turn connected to a first outer flange  22  and the second inner flange  18  is connected to a second outer flange  24 . In some embodiments, the cylindrical housing  12  and the first and second inner flanges  16 ,  18  are formed from a single piece, while in other embodiments they may be made of separate pieces which are then connected together during assembly of the fluid bubble eliminator  10 . A set of holes  20  (shown in  FIG. 2 ) are formed in the first and second inner flanges  16 ,  18 , and a corresponding set of holes  26  are formed in the first and second outer flanges  22 ,  24 . The holes  20  and  26  are adapted to receive one or more screws  28  for connecting the first inner flange  16  to the first outer flange  22  and the second inner flange  18  to the second outer flange  24 , as shown. Although screws  28  are used in this embodiment, alternative means for connecting or otherwise attaching the inner flanges  16 ,  18  to the outer flanges  22 ,  24  together may certainly be used. 
   Referring now to  FIG. 2 , in addition to the components previously described, the fluid bubble eliminator  10  further includes a spiral assembly  30  having a spiral core  32  made of a plurality of spiral disks  34   a - 34   k . The spiral disks  34   a - 34   k  are evenly spaced relative to one another and are mounted on a hollow, perforated tubular spiral core support member  36 . The perforations  38  in the spiral core support member  36  are shown as holes in this embodiment, but may be in the form of slits or other types of openings. Also, although eleven spiral disks  34   a - 34   k  are shown here, other embodiments may have fewer or more spiral disks that may be evenly or unevenly spaced within a given area, depending on the particular need of the application. 
   The fluid bubble eliminator  10  further includes a membrane  40  which is attached to, or mounted on a hollow, perforated tubular membrane support member  42 . The perforations  44  in the membrane support member  42  may be holes as shown here, or may be slits, or any other type of suitable openings. The membrane  40  and membrane support member  42  are of such dimensions so as to coaxially fit inside the spiral core support member  36 . Similarly, the entire spiral assembly  30  is of such dimensions as to coaxially fit inside the cylindrical housing  12 . 
   It is important the membrane  40  be made of a material that is gas-permeable, but liquid-impervious so only gas may pass therethrough. The other components of the fluid bubble eliminator  10 , however, may be made of any material suitable for the particular application. For example, in an application involving corrosive fluids, the cylindrical housing  12 , spiral disks  34   a - 34   k , spiral core support member  36 , etc., should be made of steel or other types of corrosive-resistant materials. 
   Referring now to  FIG. 3  (with continued reference to FIG.  2 ), the first outer flange  22  has a port  46  formed therein for allowing fluid to flow into or out of the fluid passageway  14  in the cylindrical housing  12 . Likewise, the second outer flange  24  has a port  48  for allowing fluid to enter and exit the cylindrical housing  12 . The first and second outer flanges  22 ,  24  also have annular grooves  50 ,  52  formed therein for receiving annular, elastomeric rings or seals  54 ,  56 . The seals  54 ,  56  form a fluid-tight contact between the inner flanges  16 ,  18  and the first and second outer flanges  22 ,  24 . Each of the first and second outer flanges  22 ,  24  also has an annular shoulder  60 ,  62  formed therein which defines an annular recess  64 ,  66  for receiving the ends of the spiral core support member  36 . The first and second outer flanges  22 ,  24  further include openings  68 ,  70  which, in conjunction with the membrane support member  42 , forms a gas passageway  58  in which gas may be collected and discharged from the fluid bubble eliminator  10 . Cap screws  72   a , and  72   b  may be inserted into either or both of the openings  68 ,  70  to prevent or control the exit of the gas from the fluid bubble eliminator  10 . 
   In operation, fluid is pumped or otherwise introduced into the fluid bubble eliminator  10  through one of the ports  46 ,  48 . Once the fluid enters the cylindrical housing  12 , it follows a helical path defined by the spiral disks  34   a - 34   k  that make up the spiral core  32 . As the fluid flows along the helical path, the centrifugal force generated therefrom drives the heavier liquid component radially outward, which forces the lighter gas component radially inward. The inwardly moving gas component passes through the perforations  38  in the spiral core support member  36 , is filtered through the membrane  40 , passes through perforations  44  in the membrane support member  42 , and into the gas passageway  58 . The fluid, which is now substantially free of the gas component, exits the fluid bubble eliminator  10  through one of the previously described ports  46 ,  48  formed in the outer flanges  22 ,  24 . 
   The gas component in the gas passageway  58  is discharged from the fluid bubble eliminator  10  through one of the previously described openings  68 ,  70  formed in the outer flanges  22 ,  24 . In some embodiments, the gas component is discharged directly into an external environment by simply exposing the gas to the environment such that the gas naturally diffuses into the external environment. In other embodiments, the gas component is discharged by reducing the air pressure in the vicinity of one of the openings  68 ,  70 . 
   By virtue of the symmetrical shape and even spacing of the spiral disks  34   a - 34   k , the fluid bubble eliminator  10  is bi-directional, i.e., the direction of the fluid flow does not affect the utility or efficiency of the fluid bubble eliminator  10 . However, in other embodiments, the spacing and shapes of the spiral disks  34   a - 34   k  may be customized to maximize the fluid flow rate in a particular direction or in a particular section (e.g., the middle) of the cylindrical housing  12 . 
   Referring to  FIG. 4 , in another embodiment, the membrane  40  is not mounted on the membrane support member  42 , but is instead attached to the inner surface of the spiral core support member  36  and supported thereby. 
   Referring to  FIG. 5 , in yet another embodiment, the membrane  40  is attached to the outer surface of the spiral core support member  36 . In this embodiment, the membrane  40  may be in the form of a strip that is wound around the spiral core support member  36  in between the spiral disks  34   a - 34   k.    
     FIG. 6  is a graphical representation of the effects of centrifugal force on gas bubbles in a fluid flowing through the fluid bubble eliminator  10 . As the fluid flows through the helical path, gas bubbles are forced toward the middle due to the centrifugal force acting on the heavier liquid components. Although the invention was or originally designed for low or zero-gravity applications, it should be clear to one of ordinary skill in the art the principles and concepts disclosed herein are equally applicable to normal gravity environments. 
   The quality of the fluid from which gas is removed may be improved by connecting multiple fluid bubble eliminators in series as shown in FIG.  7 B. Each additional fluid bubble eliminator removes any gas not previously removed by the upstream fluid bubble eliminators. Alternatively, the quantity of the fluid from which gas is removed may be increased by connecting multiple fluids in parallel as shown in FIG.  7 A. Each additional fluid bubble eliminator allows that much more fluid to be processed at the same time. 
   As shown in  FIGS. 8A through 8F , different configurations of the spiral core are possible. As shown in  FIGS. 8A and 8B , the core may have a relatively tight spacing, or as shown in  FIGS. 8C and 8D , a relatively loose spacing; or as shown in  FIGS. 8E and 8F , spacing of an intermediate pitch. As will be understood by those in the art, with the tight spacing as shown in  FIGS. 8A and 8B , the spiral disks define a relatively longer helical path; in the case of the relatively loose spacing as shown in  FIGS. 8E and 8F , they define a relatively shorter helical path, and in the case of the intermediate configuration shown in  FIGS. 8C and 8D , they define a helical flow path of intermediate length. 
   As shown in  FIG. 9 , the amount of centrifugal force generated for the tight, medium, and loose spacing of the spiral disc varies, and it also varies with increasing fluid flow rates. As can be seen from  FIG. 9 , the degree of centrifugal force generated increases more rapidly for tightly spaced spiral disc than for the loosely spaced spiral disc. 
   Advantages of the invention include a passive (i.e., no external power needed), low-shear method and apparatus for removing gas from a fluid that also physically separates the gas components from the liquid components. Furthermore, the invention may be easily scaled larger or smaller to suit the size requirement of a particular application without affecting the utility thereof. 
   It is to be understood that the various embodiments described herein are illustrative only, and that other embodiments may be derived without departing from the scope and spirit of the invention. Accordingly, the invention should be limited only by the following claims.