Patent Publication Number: US-2007113589-A1

Title: Gas Control Device and Corresponding Method for Recovering Coolant Gases in a Fiber Coolant System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority from U.S. Provisional Patent Application Ser. No. 60/738,365, entitled “System for Recovery of Helium”, and filed Nov. 18, 2005. The disclosure of this provisional patent application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND  
      1. Field  
      The disclosure pertains to gas control devices to control gas flow within cooling tubes or chambers during processing of fibers, particularly optical fibers.  
      2. Related Art  
      Optical fibers are typically formed by a process in which hot fibers are drawn from the end of a massive silica or glass preform that has been heated up to its softening point in a drawing furnace. This drawing process is followed by cooling the fibers within a heat exchanger or cooling tube utilizing a coolant gas that flows through the cooling tube in a co-current or countercurrent direction with respect to the velocity vector of the fiber traveling through the exchanger. The drawn fibers must be cooled to a sufficient temperature within the cooling tube prior to further processing (e.g., cladding the fiber with a heat sensitive protective coating).  
      Utilizing a relatively inert coolant gas such as helium provides a safe and efficient gaseous heat exchange agent for cooling the hot drawn fibers at the desired rate and to the desired temperatures within the cooling tube. However, one problem with utilizing helium is the excessive loss of this gas through the inlet and outlet ends of the cooling tube into the surrounding atmosphere during cooling of the fiber. Keeping the loss of helium and/or other coolant gases from the cooling tube to a minimum during operation is highly desirable to maximize cooling efficiencies within the cooling tube and minimize operating costs.  
      Another problem relates to minimization of the amount of air that may be drawn into the cooling tube from the surrounding atmosphere and thus mix with the flowing helium and/or other coolant gases within the heat exchanger. For example, the entry of air into the cooling tube can significantly alter the cooling rate of the fiber moving through the cooling tube due to the poor heat transfer characteristics of helium/air mixtures versus substantially pure helium.  
     SUMMARY  
      A gas control device is provided for a fiber cooling system that effectively recovers coolant gases utilized within the cooling system and also minimizes or prevents the flow of air into the cooling system as well as turbulent gas flow conditions from occurring within the cooling system.  
      In particular, a gas control device for a fiber cooling system comprises an inner fiber flow passage extending in a longitudinal direction of the device to facilitate travel of a fiber through the device. The device further comprises a chamber that is separated from and at least partially surrounds the inner fiber flow passage, a flow stabilizer region that facilitates and controls gas flow between the inner fiber flow passage and the chamber, and a gas flow port in fluid communication with the chamber to facilitate withdrawal of gas from the inner fiber flow passage into the chamber and removal of the withdrawn gas from the chamber and the device during travel of the fiber through the device.  
      A method is also provided for cooling a fiber and controlling gas flows around the fiber in a fiber cooling system. The method comprises moving the fiber through a fiber flow passage of a cooling tube, flowing a coolant gas into the fiber flow passage of the cooling tube to facilitate cooling of the fiber within the cooling tube, and selectively withdrawing gas proximate the moving fiber with a gas control device. The gas control device includes an inner fiber flow passage that communicates with the fiber flow passage of the cooling tube and that receives the moving fiber, a chamber that is separated from and at least partially surrounds the inner fiber flow passage of the device, a flow stabilizer region that facilitates and controls gas flow between the inner fiber flow passage and the chamber of the device, and a gas flow port in fluid communication with the chamber, wherein gas is withdrawn from the inner flow passage of the device and into the chamber of the device via the flow stabilizer region, and the withdrawn gas is removed from the chamber into the gas flow port.  
      The gas control device facilitates withdrawal of gas from the inner fiber flow passage in a substantially uniform and circumferentially expanding direction so as to minimize or eliminate turbulent gaseous currents from forming around the fiber during such gas withdrawal.  
      The above and still further features and advantages will become apparent upon consideration of the following detailed description of specific embodiments thereof, particularly when taken in conjunction with the accompanying drawings wherein like reference numerals in the figures are utilized to designate like components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional side view in elevation of a first embodiment of a gas recovery cap secured to a cooling tube of a fiber cooling system.  
       FIG. 2  is a top view in plan of the gas recovery cap that is secured to the cooling tube of the fiber cooling system of  FIG. 1 .  
       FIG. 3  is a cross-sectional side view in elevation of a second embodiment of a gas recovery cap secured to a cooling tube of a fiber cooling system.  
       FIG. 4  is a cross-sectional side view in elevation of a third embodiment of a gas recovery cap secured to a cooling tube of a fiber cooling system.  
       FIG. 5  is a top view in plan of the gas recovery cap that is secured to the cooling tube of the fiber cooling system of  FIG. 4 .  
       FIG. 6  is a cross-sectional side view in elevation of a fourth embodiment of a gas recovery cap secured to a cooling tube of a fiber cooling system. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
      The gas control and recovery device described herein is configured for engagement with a cooling tube for a fiber cooling system, such as an optical fiber cooling system. As noted above, an optical fiber is formed by drawing a hot fiber from the end of a silica or glass preform that has been heated up to its softening point in a drawing furnace. The hot fiber is then cooled in a suitable elongated heat exchanger that includes a cooling tube through which the fiber is directed. The cooling tube can have any suitable cross-sectional geometry (e.g., circular, square, rectangular, etc.) and has suitable cross-sectional and longitudinal dimensions that facilitate sufficient cooling of the fiber traveling through the cooling tube. The components of the gas recovery devices described herein and the cooling tube can be constructed of any suitable materials including, without limitation, metals (e.g., stainless steel), metal alloys, suitable plastic or polymer materials, and combinations of such materials.  
      A coolant gas is also injected into the cooling tube to facilitate heat exchange with the hot fiber so as to cool the fiber within the tube. The coolant gas can be injected in a co-current or countercurrent direction in relation to the direction of travel of the fiber through the cooling tube. The coolant gas may be any one or a combination of suitable cooling gases including, without limitation, helium, neon, argon, krypton, xenon, hydrogen, nitrogen, and carbon dioxide. Helium is a preferred coolant gas for cooling optical fibers. However, in certain embodiments, a combination of different coolant gases may be desirable to optimize heat exchange for a particular fiber cooling application.  
      The gas recovery device facilitates recovery of at least some or a substantial portion of coolant gas from the cooling tube, while preventing or minimizing the potential for turbulence that may occur around the fiber within the cooling tube as the gas is being withdrawn. The gas recovery device further minimizes or prevents air from entering at the inlet or outlet of the cooling tube as the fiber travels through the tube and is cooled.  
      In exemplary embodiments, such as the embodiments described below, the gas recovery device is provided as an enclosure or cap that surrounds the inlet and/or outlet of the cooling tube and is configured to monitor and control the flow of gases flowing within the cooling tube. In other embodiments, the gas recovery device can be provided at one or more selected locations within the cooling tube rather than as a cap disposed at an inlet end or an outlet end of the cooling tube.  
      The gas recovery device includes a hollow interior or inner fiber flow path or channel that preferably extends axially through the device to facilitate an inner flow path for a fiber traveling into and through the cooling tube. In addition, the gas recovery device preferably includes a pressure port to measure and monitor the pressure within the inner fiber flow passage of the gas recovery device, and a gas withdrawal port that selectively withdraws gases from the flow passage.  
      The gas recovery device is further preferably designed such that gas is withdrawn radially and in a substantially uniform and circumferentially expanding manner from the inner fiber flow passage into an annular plenum or chamber that is separated from and surrounds at least a portion of the inner fiber flow passage within the device. A flow stabilizer orifice is provided that surrounds or is circumferentially oriented with respect to a portion of the inner fiber flow passage and facilitates fluid communication between the flow passage and the annular chamber. The design of the annular chamber and flow stabilizer orifice with respect to the inner fiber flow passage within the device facilitates a substantially uniform pressure drop between the flow passage and the annular chamber during such gas withdrawal. Withdrawal of the gas from the device in this manner significantly reduces or eliminates the potential for turbulence around the fiber, thus minimizing or preventing the potential for vibration, disturbance or damage to the fiber. Thus, the gas recovery device facilitates the collection and recovery of coolant gases, such as helium, from the cooling tube for recycling or reuse of the coolant gases. The gas recovery device further withdraws any ambient air that may enter the device, thus preventing or minimizing the presence of air in the cooling tube during cooling of the fiber.  
      An exemplary embodiment of a gas recovery device is depicted in  FIGS. 1 and 2 . The gas recovery device is configured as a cap including a hollow housing  2  that fits around an inlet or outlet end of a hollow cooling tube  4 , where the cooling tube is disposed within a fiber production system at a suitable location downstream from a preform furnace. The hollow cooling tube  4  can have any suitable length (e.g., a length in the range of about 1 meter to about 3 meters) to facilitate sufficient residence time of the fiber within the cooling tube during cooling of the fiber. A coolant gas is injected within the cooling tube at a selected location along the length of the cooling tube. Alternatively, the coolant gas can be injected at a suitable location upstream from the cooling tube, where the fiber travels with the coolant gas into the cooling tube.  
      Both the gas recovery cap and the cooling tube can include an axially split or “clam-shell” configuration, where the components of the cap and tube are separated along their axial dimensions into two or more sections (e.g., with hinged sections). As can be seen in  FIG. 2 , one or more sealing members  3  (e.g., gaskets) are preferably provided between the split sections of the gas recovery cap housing and the cooling tube to maintain a gas-tight seal when the sections are secured together. The split configuration allows a fiber to be initially drawn from a preform furnace to a take-up spindle at the outset of the fiber forming process, where the fiber can be easily guided through the open or split gas recovery cap and cooling tube. The cap and cooling tube can then be closed once the fiber has been wound onto the spindle.  
      A first end  6  of cap housing  2  includes an opening or recess defined by interior side walls  8  that extend from the first end to an end wall  9  of the recess. The recess is suitably dimensioned to receive and engage with an end (e.g., an inlet or outlet end) of cooling tube  4 . The first end of the cap housing is secured to the cooling tube with one or more suitable fasteners  7  (e.g., mounting screws) that extend transversely through the cap housing at the recess to secure the cooling tube end to recess side walls  8 . The cap housing is secured to the cooling tube in a suitable manner to facilitate a gas tight seal at such connection. Optionally, gaskets or other suitable sealing members can also be provided at the first end of the cap housing to ensure a gas tight seal is maintained between the cap and the cooling tube during operation.  
      The recess of cap housing  2  extends from the first end  4  to a cavity  10  that has a smaller cross-sectional dimension (e.g., diameter) than the cross-sectional dimension of the recess. The cavity  10  is defined by sidewalls  12  that extend from the recess end wall  9  toward a second end  14  of the housing. The second end  14  of housing  2  includes an opening or fiber orifice  15  that communicates with cavity  10 . The fiber orifice  15  is much smaller in dimension (e.g., diameter) than the transverse cross-sectional dimension of the cavity  10 . In addition, the fiber orifice  15 , cavity  10  and recess of the cap housing are all suitably dimensioned and aligned with each other to provide a central or axial and substantially linear pathway that extends through the cap and corresponds with a fiber flow passage  16  defined within and extending through cooling tube  4 .  
      An annular member or ring  20  is provided within the cavity  10  of housing  2 . The ring  20  is suitably dimensioned with outer peripheral wall portions that engage with cavity walls  12 . The passage through the ring  20 , which is formed by the ring inner diameter, defines an inner fiber flow path or channel (indicated by dashed line  17  in  FIG. 1 ) that is aligned and in fluid communication with fiber flow passage  16  of the cooling tube.  
      The ring is located along the cavity walls  12  with a first end surface that is generally coplanar with end wall  9 . As can be seen in  FIG. 1 , ring  20  can be secured within housing  2  such that its first end surface is adjacent the end of cooling tube  4  when the cooling tube is secured to the first end of the cap. Optionally, sealing members (e.g., gaskets) can be provided at the interface between the first end surface of the ring and the cooling tube end to ensure a gas tight seal is established at this engagement. The ring  20  is secured within the cap housing  2  with suitable fasteners  21  (e.g., screws) that extend transversely through portions of the housing and the ring.  
      The ring  20  extends toward and terminates at a second end surface that is proximate an interior wall surface of the cap housing second end  14 , such that a slight gap is defined between the second end surface of the ring and the interior wall surface of the second end  14 . The ring  20  further includes a removed annular portion or reduced thickness section that extends from the ring second end surface to the ring outer peripheral wall portions that engage cavity walls  12 , such that the wall thickness of the ring at the second end is reduced and considerably less than the wall thickness of the ring at the first end. An annular chamber  22  is thus defined between portions of the housing cavity walls  12  and reduced wall thickness portions of ring  20 .  
      The gap between the second end of ring  20  and the interior wall surface of the housing first end is in fluid communication with annular chamber  22  and defines an annular shaped flow stabilizer orifice  24 . The flow stabilizer orifice  24  surrounds or is circumferentially oriented around a portion of the inner fiber flow path or channel  17  extending axially within the housing  2  and facilitates flow of gas from the fiber flow passage to the annular chamber defined between the ring and cap housing.  
      The gas recovery cap further includes a gas withdrawal channel or port  25  that extends transversely through housing  2  at a suitable location so as to be in fluid communication with annular chamber  22 . Port  25  connects with a suitable flow line  26  to facilitate withdrawal of gas from cavity  10  and annular chamber  22  during system operation. One or more valves can be provided within port  25  and/or flow line  26  to facilitate selective control of gas flow through the port. In addition, a suitable pressure control device (e.g., a pump or blower) can be provided within flow line  26  as an alternative to or in combination with a valve to selectively control withdrawal of gas from the cap by establishing a vacuum within the flow line. Further, one or more pressure, flow rate and/or concentration sensors can be provided within port  25  and/or line  26  to monitor the flow of gases (and amount of air in such gases) being removed from the cap during operation.  
      A pressure sensor port  28  is also provided in the gas recovery cap to monitor pressure within cavity  10  and the fiber flow passage during operation. Port  28  extends transversely through cap housing  2  and ring  20  so as to be in fluid communication with the inner fiber flow passage  17  within the cap housing. A suitable pressure sensor is provided within port  28  (or a fluid flow line connected with the port) to measure and monitor at least one of a pressure within the fiber flow passage and a differential pressure between the fiber flow passage and the ambient environment external to the gas recovery cap during operation. For example, the pressure sensor port can be configured to monitor a differential pressure at the fiber orifice  15 . Any change in pressure can be communicated to an operator or, optionally, a controller, to facilitate manual or automatic control of the gas withdrawal port  24  (e.g., via control of one or more valves and/or operation of a vacuum source) to control the amount of gas extracted from the fiber flow passage.  
      Each of the fiber orifice  15 , flow stabilizer orifice  24 , annular chamber  22 , fiber flow passage within the cap  2  and fiber flow passage  16  within the cooling tube  4  are suitably dimensioned to facilitate a generally laminar flow of coolant gases through the fiber flow passage as well as a radial and generally uniform withdrawal of gas from the inner fiber flow passage  17  to annular chamber  22  within the cap housing. The dimension of the fiber orifice  15  in the cap is selected based upon the transverse cross-sectional dimension of the flow path  16  within the cooling tube  4 . Preferably, the maximum transverse cross-sectional dimension (e.g., diameter) of the fiber orifice  15  is no greater than the transverse cross-sectional dimension of the fiber flow passage  16  within the cooling tube  4 . In addition, the flow stabilizer orifice  24  is preferably suitably dimensioned to ensure that, during operation, the pressure drop or differential pressure across orifice  24  is less than the differential pressure across fiber orifice  15 . This in turn ensures a uniform radial withdrawal of gases from the flow passage  17  into annular chamber  22  (e.g., for recovery by gas withdrawal port  25 ).  
      The transverse cross-sectional dimension of the inner fiber flow passage  17  within the gas recovery cap  2  (which is defined by the inner diameter dimension of ring  20 ) is selected to maintain a laminar flow of gas within this region. In particular, it is preferable to provide the inner fiber flow passage of the gas recovery cap with a transverse cross-sectional dimension (i.e., provide an inner diameter of ring  20 ) that is greater than the transverse cross-sectional dimensions of each of the fiber orifice for the cap and the fiber flow passage of the cooling tube.  
      Preferably, the dimensions of the ring, fiber orifice and cooling tube fiber flow passage can be selected such that the transverse cross-sectional dimension of the inner fiber flow passage of the cap (i.e., the inner diameter of the cap housing ring) is at least twice as large as the dimension of the fiber orifice and the transverse cross-sectional dimension of the cooling tube fiber flow passage. In an exemplary embodiment, the components of the gas recovery cap and the cooling tube are suitably dimensioned such that the fiber orifice of the cap has a diameter of about 6 millimeters, the cap housing ring has an inner diameter of about 15 millimeters, and the cooling tube fiber flow passage has a diameter of about 7 millimeters.  
      In operation, gas recovery cap housing  2  is secured to an end of a fiber cooling tube  4 . The gas recovery cap can be secured to an inlet or an outlet end of the cooling tube. Optionally, a gas recovery cap can be secured to both inlet and outlet ends of the cooling tube. For example, a gas recovery cap may be secured to an inlet end of the cooling tube to control and remove the flow of air that may enter the housing with a fiber moving through the housing and into the cooling tube. A gas recovery cap may also be secured to an outlet end of the cooling tube to remove and recover coolant gases that have been used to cool the fiber within the cooling tube. At the outlet end of the cooling tube, the gas recovery cap can further be used to withdraw any air that may enter through the outlet end.  
      The pressure sensor port  28  facilitates the monitoring of the pressure within the inner fiber flow passage and/or a differential pressure at the fiber orifice  15 . This pressure or pressure differential is monitored manually (e.g., by an operator) or automatically (via controller), and the amount of gas that is withdrawn into the gas withdrawal port  25  and flow line  26  is controlled accordingly (manually or automatically) by controlling operation of valves and/or the pressure control device as noted above. Gas within the inner flow path of housing  2  is withdrawn through flow stabilizer orifice  24 , into annular chamber  22  and port  25 , and through flow line  26 .  
      When the gas recovery cap is operated without the need for recovering coolant gases (e.g., at the inlet and/or outlet ends of the cooling tube), the pressure within the inner fiber flow passage of the cap can be slightly larger than the ambient pressure surrounding the cooling tube (e.g., atmospheric pressure). This will minimize or substantially prevent air from entering the cooling tube. However, when recovery of the coolant gases is desired (e.g., at the outlet end of the cooling tube), it is preferable to maintain the pressure within the inner fiber flow passage of the gas recovery cap at about the same pressure or slightly less than the ambient pressure surrounding the cap and cooling tube. Preferably, the pressure within the recovery cap and cooling tube is adjusted during operation, via the one or more valves and/or pressure control device disposed in the gas withdrawal port or flow line, such that a slight negative pressure or vacuum exists within the cap housing (i.e., a difference in pressure between the ambient pressure and the pressure at the interior of the cap housing) of no more than about 0.025 kPa.  
      The design of annular chamber  22 , in combination with the selection of suitable dimensions for the fiber flow passage, the flow stabilizer orifice and the fiber orifice of the gas recovery cap, facilitates a generally uniform withdrawal of gas in a radial and generally circumferentially expanding manner from inner fiber flow passage  17 , through flow stabilizer orifice  24  and into the annular chamber. The gas within annular chamber  22  is then withdrawn through port  25  and into flow line  26 . Such uniform withdrawal of gas away from the fiber disposed in the inner fiber flow passage reduces or eliminates any potential turbulent effect of gaseous currents that might otherwise be generated, thus minimizing the potential for generating undesirable vibrations and damage to the fiber.  
      The design of the gas recovery cap can be modified in any number of different ways and is thus not limited to the embodiment described above and depicted in  FIGS. 1 and 2 . For example, the orientation of ring  20  within cap housing  2  can be rotated by 180° as shown in another embodiment of the cap depicted in  FIG. 3 . In other words, the gas recovery cap of  FIG. 3  is configured such that the annular chamber  22  and flow stabilizer orifice  24  are located closer to the housing first end  6  than housing second end  14 . In this embodiment, gas withdrawal port  25  is also suitably positioned along housing  2 ′ so as to be aligned with and in fluid communication with annular chamber  22 . The annular shaped flow stabilizer orifice  24  is also disposed proximate the cooling tube end so as to be in fluid communication with the annular chamber. The gas recovery cap of  FIG. 3  operates in a similar manner as the cap described above and depicted in  FIGS. 1 and 2 , with gas being withdrawn in a generally uniform and radial manner away from a central portion of the inner fiber flow passage along which a fiber travels within the cap.  
      Another embodiment of a gas recovery cap is depicted in  FIGS. 4 and 5 . In this embodiment, cap housing  30  is substantially similar in design as the cap housing of  FIGS. 1 and 2 , including a first end  6  with a recess that engages with an inlet or outlet end of a cooling tube  4  and a second end  14  that includes a fiber orifice  15 . A ring  40  is disposed within housing cavity  10  and is suitably dimensioned such that outer peripheral wall portions of the ring engage with the housing cavity walls. The ring includes a first end that is disposed near recess end wall  9  so as to engage with the cooling tube end in a similar manner as described above for the previous embodiment. Fasteners  21  extending transversely through housing  30  into ring  40  retain the ring in its position within the housing. The inner diameter of ring  40  further defines the inner fiber flow passage  17  through which a fiber travels during operation. The dimensions of the fiber flow passage within the cap, the fiber orifice of the cap and the cooling tube fiber flow passage are similar to those described above for the previous embodiment.  
      A second end of the ring  40  terminates a selected distance from the housing second end  14 , thus leaving a gap between the second end of the ring and an interior surface of housing second end  14 . Pressure sensor port  28  extends transversely through housing  40  at a location corresponding with the gap between the ring and the housing second end so as to be in fluid communication with the cavity  10  and the inner fiber flow passage  17  within the cap housing. As with the previous embodiment, a suitable pressure sensor is provided within port  28  to measure and monitor at least one of the pressure within the fiber flow passage and the differential pressure at the fiber orifice during operation.  
      The ring  40  includes a removed annular portion or reduced thickness section that is formed between but does not completely extend to each of the first and second end surfaces of the ring. Annular chamber  42  is thus defined between portions of the housing cavity walls  12  and reduced wall thickness portions located between the first and second ends of the ring  20 . In addition, the second end of the ring has an outer diameter that is slightly smaller than the outer diameter of the first end of the ring, such that a slight space or gap exists between the ring second end and the cavity walls  12  in the housing  30 . This gap defines an annular flow stabilizer orifice  44  at the ring second end that provides fluid communication between annular chamber  42  and the inner fiber flow passage  17 .  
      Gas withdrawal port  25  extends transversely through housing  30  at a location that corresponds with annular chamber  42 , such that port  25  is in fluid communication with the annular chamber. The gas withdrawal port is substantially similar to the gas withdrawal port described above and depicted in  FIGS. 1 and 2 , and the port connects with a suitable flow line  26  to facilitate withdrawal of gas from cavity  10  and annular chamber  22  during system operation. As in the previous embodiment, one or more valves can be provided within port  25  and/or flow line  26  to facilitate selective control of gas flow through the port. In addition, a suitable pressure control device (e.g., a pump or blower) can be provided within flow line  26  as an alternative to or in combination with a valve to selectively control withdrawal of gas from the cap by establishing a vacuum within the flow line. Optionally, one or more pressure, flow rate and/or concentration sensors can be provided within port  25  and/or line  26  to monitor the flow of gases (and amount of air in such gases) being removed from the cap during operation.  
      The gas recovery cap of  FIGS. 4 and 5  operates in a similar manner as the previous embodiments, where gas is withdrawn in a radial, circumferentially expanding and generally uniform manner from the inner fiber flow passage within housing  30 , through flow stabilizer orifice  44  and into gas withdrawal port  25  and flow line  26 . In addition, the pressure differential at the fiber orifice  15  (i.e., the difference in pressure between the inner fiber flow passage  17  within housing  30  and the ambient environment surrounding the housing) can be selectively adjusted and controlled to generate a vacuum or slight negative pressure within the housing so as to draw coolant gas and/or air into gas withdrawal port  25  during system operation.  
      The ring of the gas recovery cap of  FIGS. 4 and 5  can be modified to replace the flow stabilizer orifice with a membrane through which gaseous fluids can flow from the inner fiber flow passage to the annular chamber. Referring to  FIG. 6 , housing  30  includes a ring  40 ′ that is similar in design to the ring described in the previous embodiment, with the exception that the second end of the ring has an outer diameter that is the same as the outer diameter of the first end of the ring (thus eliminating the gap or flow stabilizer orifice between the ring second end and the cavity walls of the housing).  
      In addition, the thin wall thickness section that extends between the first and second ends and defines a major portion of the inner diameter of ring  40 ′ is formed from a porous membrane material  45 . The porous membrane material is annular in configuration and surrounds or is circumferentially oriented around a portion of the inner fiber flow passage disposed within the housing. The porous membrane material  45  has a suitable porosity that permits coolant gases and air to flow from the inner fiber flow passage within housing  30 , through membrane material  45  and into annular chamber  42 . The porous membrane material can be a metal mesh material or any other suitably porous material (e.g., a porous polymer) that facilitates gas flow through the material.  
      Operation of the gas recovery cap of  FIG. 6  is similar to that of the previous embodiments, where gas flows in a radial, circumferentially expanding and generally uniform manner from the fiber inner flow path  17  within the housing  30 , through membrane  45  and into gas withdrawal port  25  and flow line  26 . Thus, the annular shaped membrane stabilizes the flow of gas between the inner fiber flow passage and the annular chamber in a similar manner as the previous embodiments to minimize or prevent undesirable turbulence and potential damage to the fiber during withdrawal of gases from the cap.  
      While the previous embodiments describe a cap or member that is secured or securable to an inlet or outlet end of a cooling tube, the gas recovery device is not limited to such cap embodiments. Rather, the gas recovery device can be disposed within the cooling tube (e.g., at a selected location between the inlet and outlet ends of the cooling tube).  
      In addition, in certain applications, the gas withdrawal port can be configured to generate a positive pressure rather than a negative pressure or suction. For example, for applications in which one or more gas recovery devices are implemented near the inlet and/or outlet ends of the cooling tube (e.g., as gas recovery cap devices), it may be desirable to provide a slightly higher pressure within the device than the ambient pressure so as to prevent any air from entering the cooling tube. The uniform and circumferential manner in which the pressure is applied within the inner fiber flow passage, via the flow stabilizer orifice (or annular porous membrane section) substantially minimizes or prevents turbulence around and disturbance to the fiber traveling through the device.  
      Further, the device is not limited to an annular shaped flow stabilizer orifice (or porous membrane) and annular chamber. Rather, any one or more orifices (or membranes) that provide fluid communication between the inner fiber flow passage and one or more chambers at least partially surrounding the flow passage can be provided within the device that facilitates generally uniform and radial withdrawal of gases from the flow passage to the chamber. For example, a plurality of separate and distinct chambers can be defined within the device that at least partially surround and communicate with the inner fiber flow passage via a plurality of orifices (or porous membranes) which also are aligned to at least partially surround the flow passage.  
      Having described novel gas recovery devices and corresponding methods for recovering coolant gases in a fiber coolant system, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope as defined by the appended claims.