Patent Publication Number: US-11660557-B2

Title: Low-gravity water capture device with water stabilization

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. National Entry and claims priority to PCT International Patent Application No. PCT/US2019/046918, filed Aug. 16, 2019, and entitled “LOW-GRAVITY WATER CAPTURE DEVICE WITH WATER STABILIZATION”, which claims priority to U.S. Provisional Patent Application No. 62/723,087, filed Aug. 27, 2018, the entire disclosures of which are incorporated herein by this reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to water capturing devices, and more particularly to water capturing devices in low-gravity environments. 
     BACKGROUND 
     Water is not readily available in space. Since the beginning of space travel, there has been a need for smart consumption and recycling and reusing of water. In addition, space environments offer unique challenges of power usage and the space available for these recycling systems. Power must be smartly consumed to power the space environments and ensure power consumption for those environments. Systems and electronics on those space environments may necessitate efficient power consumption and engineering specific to conserve power and consume very little space. Therefore, there is a need for a low-power, low-mass liquid collection apparatus. 
     An example of collecting water in space is disclosed in U.S. Pat. No. 9,416,026 to Eurica, Calif. The &#39;026 patent discloses coating a surface of a spaceship with a drying agent to capture ambient water moisture from space as it impinges on the spaceship. The &#39;026 patent focuses on the external collection of water in space versus the recycling and reusing of water internal to a space vehicle. 
     SUMMARY 
     In one embodiment, a method of separating water droplets from a stream of water laden air is described. The water laden air stream may be collected into a semi-closed environment. The water laden air stream is forced into a helical-shaped channel to create a turbulent, rapid circumferential flow of air. The helical-shaped channel has a variable pitch along its length. The water droplets are separated from the air stream within the helical-shaped channel. A rivulet is formed with the separated water droplets. A speed of the air stream is reduced after the water droplets have been separated. The turbulent, rapid circumferential flow of air is transitioned into a less rapid axial flow. The water droplets from the rivulet flow are collected into a reservoir. 
     In some embodiments, separating water droplets from the air stream may include contacting the air stream against one or more surfaces of the helical-shaped channel. In alternative embodiments, forming the rivulet may include collecting the separated water droplets from the one or more surfaces of the helical-shaped channel. In some instances, the water droplets within the single rivulet flow may be stabilized using the flow of the air stream. The separated water droplets may be guided towards the rivulet with one or more secondary vanes. In some embodiments, forming the rivulet may further include forming a wind-driven cross-axial air stream. In some embodiments, the wind-driven cross-axial rivulet flow may be converted into a streamwise flow aligned with the rivulet. Collecting the water droplets from the rivulet flow into a reservoir may include guiding a flow of the rivulet into the reservoir. 
     In another embodiment, an apparatus to separate water droplets from an air stream is described. The apparatus includes an elongated tube having a first end and a second end. The elongated tube includes an opening at a first end of the elongated tube, the opening is positioned to accept the air stream. A reservoir is positioned at a second end of the elongated tube. A helix structure is positioned within the elongated tube. The helix structure includes an upper surface, a lower surface arranged opposite the upper surface, an outer edge, and a variable pitch along a length of the elongated tube. The variable pitch provides a variable interior angle between an inner wall of the elongated tube and the upper surface of the helix structure. 
     In further embodiments, the helix structure may include an initial helical pitch at the first end of the elongated tube. The initial helical pitch may initiate turbulence in an air stream entering the opening. The helix structure may include a transitional pitch that may initiate water droplets in the air stream to separate from the air stream and a final pitch that may induce a lower velocity flow in the air stream from which the water droplets have been separated. In some embodiments, the apparatus may include an initial interior angle between the inner wall of the elongated tube and the upper surface of the helix structure at a first location which may force water droplets into a single rivulet using capillary forces. A transitional interior angle may be between the inner wall of the elongated tube and the upper surface of the helix structure at a second location providing a decreasing potential in the water droplets in a direction of the reservoir. A final interior angle may be between the inner wall of the elongated tube and the upper surface of the helix structure at a third location to transition from the single rivulet flow into the reservoir. 
     In some embodiments, an air exit may be positioned at the second end of the elongated tube. The air exit may be formed as a hollow cylinder. A vane may bisect the reservoir. The vane may be positioned to retain water droplets in the reservoir while allowing the air stream to exit the apparatus through the air exit. In some embodiments, the apparatus may include a drain access to the reservoir. In some embodiments, the upper surface of the helix structure is smooth and continuous. In some instances, one or more secondary vanes may be positioned on the inner wall of the elongated tube. The one or more secondary vanes may mimic a pitch angle of the helix structure. 
     In some instances, one or more vanes may be positioned on the upper surface of the helix structure. The one or more vanes may begin near a center point of the helix and may extend towards the outer edge of the helix structure. The helix structure may include a length over diameter ratio of less than four. In some embodiments, the pitch angle may continuously increase along the length of the helix structure. In some embodiments, the interior angle between an inner wall of the elongated tube and the upper surface of the helix structure may continuously decrease along the length of the helix structure. 
     In a further embodiment, an apparatus to separate water droplets from an air stream is disclosed. The apparatus includes an elongated housing having a first end and a second end, an inlet opening at a first end of the housing, the inlet opening positioned to accept the air stream, a reservoir positioned at a second end of the elongated tube, and a helix structure positioned within the elongated tube. The helix structure includes an upper surface, a variable pitch along a length of the housing, the variable pitch providing a variable interior angle between an inner wall of the elongated tube and the upper surface of the helix structure, an initial helical pitch at the first end of the elongated tube, the initial helical pitch initiating turbulence in the air stream entering the opening, and a transitional pitch that initiates water droplets in the air stream to separate from the air stream. 
     In some embodiments, the helix structure further includes a final pitch that slows the air stream from which the water droplets have been separated. 
     Another embodiment is directed to an apparatus to separate water droplets from an air stream. The apparatus includes an elongated tube, a reservoir, and a helix structure. The elongated tube has a first end, a second end, a longitudinal axis, an inner surface, an inlet opening at the first end of the elongated tube, the inlet opening arranged to accept the air stream tangentially relative to the longitudinal axis, and an outlet opening at the second end of the elongated tube. The reservoir is positioned at a second end of the elongated tube. The helix structure is positioned within the elongated tube and includes an upper surface, a lower surface arranged opposite the upper surface, an outer edge, and a variable pitch along a length of the elongated tube, the variable pitch providing a variable interior angle between an inner wall of the elongated tube and the upper surface of the helix structure. 
     The apparatus may also include an inner hollow cylinder positioned at the second end of the elongated tube and arranged coaxially with the longitudinal axis, the inner hollow cylinder defining a first air flow path, the reservoir being defined at least in part between an exterior surface of the hollow inner tube and the inner surface of the elongated tube, and the reservoir defining a second air flow path. The reservoir may include a reservoir chamber positioned external the elongated tube. The helix structure may terminate in the reservoir chamber. The apparatus may include a plurality of vanes positioned in the reservoir to direct water droplets collected on surfaces of the helix structure and inner wall of the elongated tube into a base of the reservoir chamber. The apparatus may include a water outlet opening formed in the base of the reservoir chamber. The apparatus may include at least one via formed in each of the plurality of vanes and the helix structure along the base of the reservoir, and the vias in adjacent vanes and the helix structure may be offset from each other. 
     The reservoir chamber may include an inlet portion having a first cross-sectional area, and a collection portion having a second cross-sectional area that is greater than the first cross-sectional area. The inlet portion of the reservoir chamber may provide a tangential flow path out of the elongated tube. The second air flow path may include an air flow orifice, the airflow orifice being sized to control a volume of air flow through the second air flow path. The first and second air flow paths may combine downstream of the inner hollow cylinder and before exiting the outlet opening of the elongated tube. The inner hollow cylinder may include an inlet opening, an outlet opening, an exterior surface, and a lip extending radially outward from the exterior surface. The apparatus may include an inner cylinder support configured to support the inner hollow cylinder within the elongated tube spaced away from the inner surface of the elongated tube, and the inner cylinder support may have a helical shape and define a surface of the reservoir. The elongated tube may include an inlet structure defining the inlet opening, an outlet structure defining the outlet opening, and a mid-section extending between the inlet and outlet structures, and interfaces between the inlet structure and the mid-section and between the outlet structure and the mid-section may include contoured surfaces. The contoured surfaces may include at least one of concave surfaces and convex surfaces that define spherical joints. The second air flow path may include a return tube positioned external of the elongated tube, the return tube including at least first and second tube segments, and the first and second tube segments may be connected with a slip joint. At least one of the first and second tube segments may have an elbow shape. 
     Another embodiment relates to an apparatus to separate water droplets from an air stream. The apparatus includes an elongated housing having a first end, a second end and in inner surface, an inlet structure positioned at the first end and defining an inlet opening configured to accept the air stream, an outlet structure positioned at the second end and defining an outlet opening, a reservoir positioned at a second end of the elongated housing, the reservoir configured to collect water, a helix structure positioned within the elongated housing, a first air flow path coupled in flow communication with the outlet opening, and a second air flow path separate from the first flow path and coupled in flow communication with the outlet opening, the second air flow path defined in part by the reservoir. 
     The reservoir may include a reservoir chamber, the reservoir chamber may be positioned outside of the elongated tube, and the reservoir chamber may define a portion of the second air flow path. The helix structure may include an upper surface, a variable pitch along a length of the housing, the variable pitch providing a variable interior angle between an inner wall of the housing and the upper surface of the helix structure, an initial helical pitch at the first end of the housing, the initial helical pitch initiating turbulence in the air stream entering the inlet opening, and a transitional pitch that initiates water droplets in the air stream to separate from the air stream. 
     A further embodiment is directed to a method of assembling a water capture device. The method includes providing a water capture device having an elongated tube, an inlet structure positioned at a first end of the elongated tube and defining an inlet opening configured to receive a stream of water laden air into the water capture device, an outlet structure positioned at a second end of the elongated tube and defining an outlet opening, a helical structure positioned internal the elongated tube, and a reservoir configured to collect water that has been separated from the stream of water laden air within the elongated tube. The method also includes securing the inlet structure to the elongated tube at a first joint, and securing the outlet structure to the elongated tube at a second joint, the first and second joints each having at least one contoured surface. 
     The method may further include forming the elongated tube, the inlet structure and the outlet structure using 3D printing. At least one contoured surface may be formed as a spherical, a hemispherical, or an arch shaped surface. The water capture device may further include first and second air flow paths coupled in flow communication with the outlet opening, the second air flow path being defined at least in part by first and second tube segments, the method may include securing the first and second tube segments together with a slip joint. The water capture device may further include at least one vane positioned in the reservoir, and the first and second tube segments are adjustable relative to each other and relative to the elongated tube to align the at least one vane with the helical structure. The water capture device may further include first and second air flow paths coupled in flow communication with the outlet opening, the second air flow path including an orifice, and the method may include adjusting a size of the orifice to control a rate of air flow through the second air flow path. The first and second joints may be formed in part by applying uncured base material resin to the contoured surfaces, and then curing the resin. 
     A method of separating water from a stream of water laden air is also disclosed. The method includes delivering the stream of water laden air into a helical-shaped channel of a water capture device, the helical-shaped channel having a variable pitch along its length, separating water from the air flow within the helical-shaped channel, collecting the water into a reservoir, the reservoir including a plurality of vanes, dividing the air flow into a first air stream and a second air stream, the second air stream passing through the reservoir, combining the first and second air streams after the second air stream has passed through the reservoir, passing the combined air stream out of the water capture device, and removing the water from the reservoir. 
     Separating water droplets from the air flow may include contacting the air flow against one or more surfaces of the helical-shaped channel, and the method may further include collecting the separated water droplets from the one or more surfaces of the helical-shaped channel in the reservoir. The method may include stabilizing the water within the reservoir using the second air stream. The water capture device may include a helical structure that defines in part the helical-shaped channel, and the helical structure may extend continuously into the reservoir. The water capture device may include an elongated tube housing the helical-shaped channel, and a portion of the reservoir may extend outside of the elongated tube, the portion of the reservoir defining an air channel through which the second air stream passes out of the elongated tube at a tangential angle. Delivering the stream of water laden air into the helical-shaped channel may include delivering the stream of water laden air at a tangential angle relative to a longitudinal axis of the water capture device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings and figures illustrate a number of exemplary embodiments and are part of the specification. Together with the present description, these drawings demonstrate and explain various principles of this disclosure. A further understanding of the nature and advantages of the present invention may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. 
         FIG.  1    illustrates an example of an environment of a low-gravity water capture device in accordance with the present disclosure; 
         FIG.  2    is a perspective view of an exemplary low-gravity water capture device; 
         FIG.  3    is a perspective view of an exemplary low-gravity water capture device showing internal features in broken line; 
         FIG.  4    is a perspective view of the low-gravity water capture device of  FIG.  3   ; 
         FIG.  5 A  is a cutaway view of the low-gravity water capture device of  FIG.  4    taken along lines  5 A- 5 A; 
         FIG.  5 B  is a cutaway view of the low-gravity water capture device of  FIG.  4    taken along lines  5 B- 5 B; 
         FIG.  5 C  is a cutaway view of the low-gravity water capture device of  FIG.  3    taken along lines  5 C- 5 C; 
         FIG.  5 D  is a cutaway view of the low-gravity water capture device of  FIG.  4    taken along lines  5 D- 5 D; 
         FIG.  5 E  is an exemplary view of a helix structure of the low-gravity water capture device of  FIG.  4   ; 
         FIG.  6    is a top perspective view of another exemplary low-gravity water capture device in accordance with the present disclosure; 
         FIG.  7    is a top perspective view of the low-gravity water capture device of  FIG.  6    showing internal features in broken line; 
         FIG.  8    is a bottom perspective view of the low-gravity water capture device of  FIG.  6   ; 
         FIG.  9 A  is a cut-away view of the low-gravity water capture device of  FIG.  8    taken along lines  9 A- 9 A; 
         FIG.  9 B  is a cut-away view of the low-gravity water capture device of  FIG.  6    taken along lines  9 B- 9 B; 
         FIG.  9 C  is an exemplary view of a helix structure of the low-gravity water capture device of  FIG.  6   ; 
         FIG.  10    is a truncated cutaway view of an exemplary low-gravity water capture device showing secondary vanes; 
         FIG.  11    is a schematic side view of an exemplary low-gravity water capture device; 
         FIG.  12    is a flow diagram illustrating steps of an example method relating to low-gravity water capture devices; 
         FIG.  13    is a flow diagram illustrating steps of an example method relating to low-gravity water capture devices; 
         FIG.  14    is a top perspective view of another exemplary low-gravity water capture device in accordance with the present disclosure; 
         FIG.  15    is another top perspective view of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  16    is a bottom perspective view of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  17    is a front view of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  18    is a side view of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  19    is an exploded perspective view of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  20    is a cross-sectional view of the low-gravity water capture device of  FIG.  17    taken along lines  20 - 20 ; 
         FIG.  21    is a cross-sectional view of the exemplary low-gravity water capture device of  FIG.  18    taken along lines  21 - 21 ; 
         FIG.  22    is a cross-sectional view of the exemplary low-gravity water capture device of  FIG.  18    taken along lines  22 - 22 ; 
         FIG.  23    is a close-up view of a joint between an inlet structure and elongated tube portion of the low-gravity water capture device of  FIG.  14   ; 
         FIGS.  24 A- 24 C  are perspective views showing assembly of reservoir return segments of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  25    is a partial cross-sectional view of the low-gravity water capture device of  FIG.  15    showing a return orifice plate; 
         FIG.  26    shows fluid flow within a reservoir component of the low-gravity water capture device of  FIG.  14   ; 
         FIGS.  27 A- 27 D  illustrate vias formed internal the reservoir component of the low-gravity water capture device of  FIG.  26   ; 
         FIG.  28    is a cross-sectional perspective view of a portion of the low-gravity water capture device of  FIG.  14   ; 
         FIG.  29    is a close-up view of the cross section of the exemplary low-gravity water capture device shown in  FIG.  28   ; 
         FIG.  30    is a perspective view of a portion of the exemplary low-gravity water capture device shown in  FIG.  14   ; 
         FIG.  31    is a perspective view of another exemplary low-gravity water capture device in accordance with the present disclosure; 
         FIG.  32    is another top perspective view of the low-gravity water capture device of  FIG.  31   ; 
         FIG.  33    is a bottom perspective view of the low-gravity water capture device of  FIG.  31   ; 
         FIG.  34    is a front view of the low-gravity water capture device of  FIG.  31   ; 
         FIG.  35    is a side view of the low-gravity water capture device of  FIG.  31   ; 
         FIG.  36    is a cross-sectional view of the exemplary low-gravity water capture device of  FIG.  35    taken along lines  36 - 36 ; 
         FIG.  37    is a cross-sectional view of the exemplary low-gravity water capture device of  FIG.  35    taken along lines  37 - 37 ; 
         FIG.  38    is a flow diagram illustrating an example method relating to low-gravity water capture devices; and 
         FIG.  39    is a flow diagram illustrating another example method relating to low-gravity water capture devices. 
     
    
    
     While the embodiments described herein are susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, the exemplary embodiments described herein are not intended to be limited to the particular forms disclosed. Rather, the instant disclosure covers all modifications, equivalents, and alternatives falling within the scope of the appended claims. 
     DETAILED DESCRIPTION 
     Water is a scarce resource in outer space. It is not readily available and must be mined from extraterrestrial resources if it is to be collected at all in outer space, which is a currently developing technology. Therefore, all water used in spacecraft is carried from earth. As such, the preservation, recycling, and reusing of water in extraterrestrial living systems may reduce the amount of water initially needed at the onset of an extraterrestrial mission. Water may be harvested and recycled from unlikely sources. However, power is also a scarce resource in space and must be used wisely. Therefore, a solution is needed to harvest water from on board resources using as little power as possible. The solution though, must also be lightweight and relatively small as to not encumber the mission or add unnecessary extra weight to the space vessel. 
       FIG.  1    illustrates an example of a potential system  100  which may utilize a low-gravity water separator  102 . The system  100  may include the low-gravity water separator  102 , an air intake  104 , and an air output system  106 . The air intake  104  may be cabin air intake. The air intake  104  may pass air through a filter  108 , such as a HEPA filter or the like. After air passes through the filter  108 , air may enter a temperature and humidity control device  110 . The temperature and humidity control device  110  may include a multitude of devices including a heat exchanger. The temperature and humidity control device  110  may emit an air stream laden with water droplets along path  112 . In some embodiments, the temperature and humidity control device  110  may output water laden air using a fan or other device to generate a force on the air. In some embodiments, gravity may alternatively and/or additionally act on the water laden air. The water laden air may enter the low-gravity water separator  102 . The low-gravity water separator  102  may separate the water droplets from the air stream. The low-gravity water separator  102  may then discharge air free of water droplets into the air output system  106 . In some embodiments, the air output system  106  may include an evaporator  114  and one or more fans  116  to circulate the air and/or pull the air from the water separator  102 . In some embodiments, the air output system  106  may output air to a ducting and ventilation system (not shown) along path  118 . 
     The low-gravity water separator  102  may additionally incorporate a water-output device  120  which may enable water to be discharged from the low-gravity water separator  102 . The water-output device  120  may incorporate and/or communicate with one or more sensors  122  which may enable the water-output device  120  to automatically pull water from the low-gravity water separator  102 . The water-output device  120  may discharge water to a liquid-output system  124 . The liquid-output system  124  may include one or more pumps and one or more filters. The liquid-output system  124  may discharge water to a liquid processing system (not shown) along path  130 . 
       FIG.  2    is a perspective view of an exemplary low-gravity water separator  200 . The low-gravity water separator  200  may be an example of the low-gravity water separator  102  described with reference to  FIG.  1   . The low-gravity water separator  200  may include an air inlet  202 , an air outlet  204 , and a water discharge  206 . In some embodiments, the air outlet  204  may be cylindrical-shaped and create a sort of chimney for air free of water droplets to be discharged. The air outlet  204  may enable air to be discharged from the low-gravity water separator  200 . The air outlet  204  may be oriented in any desired direction. 
       FIG.  3    is a perspective view of the low-gravity water separator  200  showing internal features, such as the helix structure  218 , shown in broken lines without the chimney air outlet component.  FIG.  4    is another perspective view of the low-gravity water separator  200  without the chimney air outlet component.  FIG.  5 A  is a cutaway view of the low-gravity water separator  200  along lines  5 A- 5 A in  FIG.  4   .  FIG.  5 B  is another cutaway view of the low-gravity water separator  200  along lines  5 B- 5 B in  FIG.  4   .  FIG.  5 C  is a further cutaway view of the low-gravity water separator  200  along lines  5 C- 5 C in  FIG.  3   .  FIG.  5 D  is a still further cutaway view of the low-gravity water separator  200  along lines  5 D- 5 D in  FIG.  4   .  FIG.  5 E  is a view of the helix structure  218  of the low-gravity water separator  200  of  FIG.  4   . 
     The low-gravity water separator  200  may include an air inlet  202 , an air outlet  204 , and a water discharge  206 . The low-gravity water separator  200  may comprise an elongated tube  208  (also referred to as a housing or an elongated housing) with an inner wall  210  and an outer wall  212 . An opening  214  to the low-gravity water separator  200  may be on a first end  216  of the elongated tube  208 . The opening  214  may be positioned to accept an air stream. For example, the opening  214  of the low-gravity water separator  200  may be positioned proximate an outlet of a heat exchanger or another device which may output water laden air that includes a plurality of water droplets—also referred to as droplet laden air (see e.g.,  FIG.  1   ). 
     A helix structure  218  may be positioned within the elongated tube  208 . The helix structure  218  may guide the droplet laden air from the opening  214  at the first end of the elongated tube  208  to a second end  220  of the elongated tube  208 . When the droplet laden air reaches the second end  220 , at least some of the water droplets may be separated from the air stream and the water droplets may be captured in a reservoir  222  proximate the second end  220  of the elongated tube  208 . The air stream may continue past the reservoir  222  and release into an air output system (e.g., air output system  106  shown in  FIG.  1   ). 
     The geometry of the helix structure  218  may cause water droplets to separate from the air stream as the air travels through the helix structure  218  to the second end  220  of the low-gravity water separator  200 . In some embodiments, the flow path and velocity of the air stream may cause water droplets to separate from the air stream. Contact between the water laden air and a surface (e.g., helix structure  218  or inner wall  210 ) may create separation of the water droplets from the air as well. The helix structure  218  may have an upper surface  224  and a lower surface  226  arranged opposite the upper surface  224 . The helix structure  218  may additionally include an outer edge  228 . The outer edge  228  of the helix structure  218  may continuously contact the inner wall  210  of the elongated tube  208 . 
     The helix structure  218  may have a varying helical pitch as the helix structure  218  traverses from the first end  216  of the elongated tube  208  toward the second end  220  of the length of the elongated tube  208 . For example, the helix structure  218  may have an initial helical pitch p 1 , a transitional helical pitch p 2 , and a final helical pitch p 3 . The pitch of a helix may be defined as the height of a complete turn of a single helix structure, measured parallel to the axis of the helix structure or as the distance between revolutions of the helix. The varying helical pitch of the helix structure  218  may increase as the helix structure  218  traverses the elongated tube  208 . The initial helical pitch p 1  may be smaller and/or shorter than the transitional helical pitch p 2 , which may in turn be smaller and/or shorter than the final helical pitch p 3 . 
     The initial helix pitch p 1  may be governed by an effective flow area of the cross-axial circumferential air stream as it enters the helix structure  218 . The pitch p 1  may allow an acceptable restriction on the air stream which may cause a desired pressure drop and air speed. If the pitch p 1  is too small, the air stream may face an unnecessary restriction which may cause excessive air flow acceleration which may lead to an unnecessary pressure drop and an associated unnecessary increase in fan power. The level of necessary air flow acceleration or peak velocity may be a factor of the size of the water droplets dispersed within the gas stream along with gas viscosity, and a density difference between the liquid and gas phases. In some embodiments, smaller water droplets may require higher peak gas velocities to be spun out of the air stream in the same amount of time that larger water droplets would spin out in lower air flow velocities. 
     The initial p 1  may be a factor of a ratio of gas flow residence time-to-water droplet drift time. The water droplet drift time may be a maximum average time for a water droplet of a specific size to travel from the axis of the device to the inner wall  210  of the elongated tube  208 . The gas flow residence time may be an average time for the entire gas volume to be completely changed in the low-gravity water separator  200 . Another way to describe gas flow residence time is the length of time for air entering the low-gravity water separator  200  to exit the low-gravity water separator  200 . This may be determined by a volume to volumetric flow rate ratio. The volume to volumetric flow rate ratio may be a ratio of internal air volume to volumetric air flow rate, for example, the amount of volume contained within the low-gravity water separator  200  divided by the rate at which the volume of air is exchanged within the low-gravity water separator  200  as follows: 
     
       
         
           
             
               
                 Device 
                 ⁢ 
                     
                 Air 
                 ⁢ 
                     
                 
                   volume 
                   ( 
                   
                     ft 
                     3 
                   
                   ) 
                 
               
               
                 Air 
                 ⁢ 
                     
                 volume 
                 ⁢ 
                     
                 per 
                 ⁢ 
                     
                 
                   Time 
                   ( 
                   
                     
                       ft 
                       3 
                     
                     sec 
                   
                   ) 
                 
               
             
             = 
             
               Average 
               ⁢ 
                   
               time 
               ⁢ 
                   
               to 
               ⁢ 
                   
               exchange 
               ⁢ 
                   
               all 
               ⁢ 
                   
               air 
               ⁢ 
                   
               in 
               ⁢ 
                   
               the 
               ⁢ 
                   
               device 
               ⁢ 
                   
               with 
               ⁢ 
                   
               new 
               ⁢ 
                   
               air 
               ⁢ 
                   
               
                 ( 
                 sec 
                 ) 
               
             
           
         
       
     
     The volume to volumetric flow rate ratio may be greater than the water droplet drift time. A ratio as such may enable a water droplet to drift towards and collide with the inner wall  210  and/or the upper surface  224  before flowing out the air outlet  204 . A residence time to drift time ratio may be in a range of the volume to volumetric flow rate ratio of approximately 5000 based on an initial water droplet size. In some embodiments, an initial helical pitch p 1  may be sized approximately between ½ and 1½ times a diameter of the elongated tube  208  to achieve this ratio. 
     The transitional helical pitch p 2  may be a portion of the overall length L of the helix structure  218  to enable a transition between the initial helical pitch p 1  to the final helical pitch p 3 . The final helical pitch p 3  may transition the gas velocity field at the air outlet  204  to a mostly axial air stream. For example, the final helical pitch p 3  may reduce and/or remove the tangential air flow velocity component from an initial tangential air flow velocity. The tangential air flow velocity may also include a measure of the air flow rate of revolution about the helix structure  218 . In some embodiments, the final helical pitch p 3  may comprise most of the length L of the elongated tube  208  while maintaining an acceptable initial helical pitch p 1 . The final helical pitch p 3  may also produce a smooth transition from the initial helical pitch p 1  to the reservoir  222  and air outlet  204 . 
     The changing helical pitch may also cause an interior angle between the upper surface  224  of the helix structure  218  and the inner wall  210  of the elongated tube  208  to change. For example, an initial interior angle α 1  between the upper surface  224  and the inner wall  210  may be less than 90°. In some embodiments, the initial interior angle α 1  may be approximately 50° to 80°. The initial angle α 1  may change as the initial helical pitch p 1  transitions to the transitional helical pitch p 2 . 
     The initial angle α 1  may transition to a transitional interior angle α 2  between the upper surface  224  and the inner wall  210 . The transitional interior angle α 2  may be sized such that it smoothly and relatively constantly (i.e. linearly) changes the interior angle formed by the upper surface  224  and the inner wall  210  between reservoir  222  and inlet. 
     The final interior angle α 3  may begin at the end range of the transitional interior angle α 2  with a range of approximately 2° to 10°. The continuously diminishing interior angles α 1 , α 2 , α 3  may aid in water flow from the air inlet  202  of the low-gravity water separator  200  to the reservoir  222 . 
     The reservoir  222  may collect water droplets as water flows down the helix structure  218 . The water droplets, as will be discussed with reference to  FIG.  11   , may be separated from the air stream as the air stream travels through the helix structure  218 . The helix structure  218  and elongated tube  208  may gradually transition into the reservoir  222 . For example, the reservoir  222  may be located in the second end  220  of the low-gravity water separator  200  and the transition between the elongated tube  208  and the reservoir  222  may be a smooth and continuous curved geometry  240 . 
     The reservoir  222  may comprise a bulbous cavity  242 . The bulbous cavity  242  may have an entry point  244  which may enable the flow of water from the final interior angle p 3  to the water reservoir  222 . The water reservoir  222  may be bisected by a stabilizing vane  246 . The stabilizing vane  246  may maintain water within the reservoir  222  and may prevent water laden air from being dispersed into the atmosphere. The stabilizing vane  246  may additionally guide water droplets towards one or more reservoir vanes  248 . The one or more reservoir vanes  248  may use capillary action to maintain the water in the reservoir  222 . Capillary action, which may arise due to the interaction of surface tension of a liquid and adhesive forces acting between the liquid and adjacent surfaces, may cause the water to minimize its surface area exposed to the air. For example, the water may naturally seek minimum interfacial energy. In the reservoir  222 , the water may pull itself into the series of reservoir vanes  248  where the vanes  248  are closest together to minimize an exposed water surface. The reservoir vanes  248  may be spaced apart such that water, or another liquid, may use surface tension or cohesion and adhesive forces between the liquid and the reservoir vanes  248  to maintain the liquid in the reservoir  222 . 
     For example, with reference to  FIG.  5 E , the reservoir vanes  248  may be arranged at various angles α 4 , α 5 , α 6 , and α 7  relative to each other. The angles α 4 , α 5 , α 6 , and α 7  may all protrude from a common area or point  264 . This point  264  is typically contained within the reservoir  222  (as shown in the Figures) or may be a point or area located outside the confines of the low-gravity water separator  200 . In some embodiments, the various angles α 4 , α 5 , α 6 , and α 7  may all comprise the same angle separating each vane  248 . In other embodiments, each angle α 4 , α 5 , α 6 , and α 7  may be distinct from the others. In some embodiments, the angles α 4 , α 5 , α 6 , and α 7  may be continuous as the vanes  248  extend outward from the point  264 . For example, the angle α 4 , α 5 , α 6 , and α 7  separating adjacent vanes may be constant along a length of each vane  248 . In other embodiments, the angles α 4 , α 5 , α 6 , and α 7  may be variable as the vanes  248  extend away from the point  264 . For example, the vanes  248  may have a curvature or variable geometry that causes the angles α 4 , α 5 , α 6 , and α 7  to change along the length of each vane  248 . The angles α 4 , α 5 , α 6 , and α 7  may be constant or variable angles in the range of about 10 degrees to about 45 degrees, and more particularly in the range of about 10 degrees to about 20 degrees. 
     The spacing between, the shape and size, and the position within reservoir  222  of stabilizing vanes  248  may be determined based on a target Weber number. A Weber number is a dimensionless number for analyzing fluid flows at an interface between two different fluids. The Weber number is calculated as a ratio between a dynamic pressure of air and a capillary pressure of the water. A final calculation of the Weber number is indicative of whether the kinetic energy of the air or interfacial energy of the water is dominant. In the current situation, the Weber number should indicate a dominant interfacial energy of the water to indicate the water will remain in a coalesced state in the reservoir  222  and not disperse into droplets. The Weber number may also be calculated by either of the following equations: 
               We   =       D   ⁢   y   ⁢   namic   ⁢         pressure   ⁢         of   ⁢         air       Capillary   ⁢         pressure   ⁢         of   ⁢         water         ⁢   
     We   =       Kinetic   ⁢         energy   ⁢         of   ⁢         air       I   ⁢   nterfacial   ⁢         energy   ⁢         of   ⁢         water               
To achieve water stability, the Weber number may be in the range of about 8 to about 12.
 
     In further embodiments, a stability rule may be used to determine a distance between the stabilizing vanes  248 . For example, to achieve water stability, a stabilizing calculation may be performed. The calculation may be performed using the following equation for air/water separation: 
     
       
         
           
             
               
                 V 
                 
                   a 
                   ⁢ 
                   i 
                   ⁢ 
                   r 
                 
                 2 
               
               * 
               D 
             
             &lt; 
             ∼ 
             
               20 
               ⁢ 
                   
               
                 
                   ft 
                   3 
                 
                 
                   s 
                   2 
                 
               
             
           
         
       
     
     V air  may be air velocity. D may be distance between the stabilizing vanes  248  at the interface between the water and the air. In some embodiments, the reservoir vanes  248  may additionally be of sufficient height to maintain an adequate amount of liquid within the reservoir  222 . The water discharge  206  may be positioned proximate a bottom end  250  reservoir  222 . 
     In some embodiments, the water discharge  206  may enable water to be drawn from the stabilizing vanes  248  within the reservoir  222 . In some embodiments, the low-gravity water separator  200  may incorporate an automated drain cycle which may utilize liquid level sensing. The water discharge  206  may be controlled by sensing an amount of water present in the reservoir  222  (e.g., water-output device  120  shown in  FIG.  1   ). When the reservoir  222  is full, a pump (not shown) may be started. The pump may cease operation when the reservoir  222  is empty. In some embodiments, capacitive level sensors (e.g., sensors  122 ,  FIG.  1   ) may be used. Capacitive level sensors may be capable of sensing through a wall and may be positioned on an outside of the reservoir  222  to determine when the reservoir is ‘full’ and when it is ‘empty.’ 
     In some embodiments, the low-gravity water separator  200  may include a lip  252  proximate the opening  214  of the elongated tube  208 . The lip  252  may mate with another piece of equipment such as a heat exchanger, tube, or other device and/or apparatus which may transfer droplet laden air from a source to the opening  214 . The opening  214  may additionally and/or alternatively incorporate a multitude of other attachment features such as a male or female threaded end, an interference fit device, or the like. 
     Likewise, the air outlet  204  may comprise an opening  254  with a lip  256 . The lip  256  may provide a clamping surface to attach an apparatus to the air outlet  204 . An apparatus may include, for example, a tube or other transfer structure to move and/or guide air to an air output system (e.g., air output system  106  shown in  FIG.  1   ). The opening  254  may additionally and/or alternatively incorporate other connection mechanisms such as threaded ends, interference fits, or the like. The air outlet  204  may form a sort of chimney shaped structure with an interior wall  259 . The wall  259  protrudes into the reservoir  222  and may create an interior corner. The interior corner  261  may capture any stray wall-bound water droplets and highly wetted liquid films from migrating out of the air outlet  204 . 
       FIG.  5 E  is a view of the helix structure  218  of the low-gravity water separator  200  of  FIG.  4   . In some embodiments, the helix structure  218  may have various features on the upper surface  224  of the helix structure  218 . For example, the helix structure  218  may have a groove in the upper surface  224  of the first helix turn  258 . The second helix turn  260  and the third helix turn  262  may also have a groove in the upper surface  224 . The groove may use surface tension and/or capillary forces to guide the water towards the edge  228  of the helix structure  218 . This may stabilize the water flow as it transitions towards the reservoir  222 . In other embodiments, a tertiary vane may be provided as a protruding feature on the upper surface  224  of the helix structure  218  to provide a stabilizing force for a water rivulet and/or water droplets. In some embodiments, a water rivulet may be a small stream of coalesced or gather water particles or water droplets. Either feature, a groove or a tertiary vane, may direct water droplets to the outer edge  228  of the helix structure  218  towards a rivulet. The groove or tertiary vane may provide stability to water rivulets. 
       FIG.  6    is a perspective view of an alternative configuration for a low-gravity water separator  600 . The low-gravity water separator  600  may incorporate similar features as the low-gravity water separator  102 ,  200  discussed with reference to  FIGS.  1 - 5 D . The low-gravity water separator  600  may include an elongated tube  608 . The elongated tube  608  may have a cylindrical shape or may be tapered and/or conical-shaped. The elongated tube  608  may include an air inlet  602 , an air outlet  604 , and one or more water discharges  606 .  FIG.  7    is a perspective view of the low-gravity water separator  600  with internal features, such as the helix structure  618 , shown in broken lines.  FIG.  8    shows a plan view of the low-gravity water separator  600 . 
       FIG.  9 A  and  FIG.  9 B  show cutaway views of the low-gravity water separator  600  along lines  9 A- 9 A and  9 B- 9 B as shown in  FIGS.  8  and  6   , respectively.  FIG.  9 C  is an exemplary view of a helix structure of the low-gravity water capture device of  FIG.  6   . The low-gravity water separator  600  includes the helix structure  618 . The elongated tube  608  may include with an inner wall  610  and an outer wall  612 . An opening  614  to the low-gravity water separator  600  may be on a first end  616  of the elongated tube  608 . The opening  614  may be positioned to accept the air stream. 
     A helix structure  618  may be positioned within the elongated tube  608 . The helix structure  618  may guide an air stream from the opening  614  at the first end of the elongated tube  608  to a second end  620  of the elongated tube  608 . By the time the air reaches the second end  620 , at least some of the water droplets may be separated from the air stream and captured in a reservoir  622  proximate the second end  620  of the elongated tube  608 . The air stream may continue past the reservoir  622  and release into an air output system (e.g., air output system  106  shown in  FIG.  1   ). 
     The geometry of the helix structure  618  may cause water droplets to separate from the airflow as the air stream travels through the helix structure  618  toward the second end  620  of the low-gravity water separator  600 . In some embodiments, the flow path and velocity of the air may cause water droplets to separate from the air streams. The helix structure  618  may have an upper surface  624  and a lower surface  626  arranged opposite the upper surface  624 . The helix structure  618  may additionally include an outer edge  628 . The outer edge  628  of the helix structure  618  may continuously contact the inner wall  610  of the elongated tube  608 . 
     The helix structure  618  may have a varying helical pitch as the helix structure  618  traverses from the first end  616  of the elongated tube  608  to the second end  620  of the elongated tube  608 . For example, the helix structure  618  may have an initial helical pitch p 1 , a transitional helical pitch p 2 , and a final helical pitch p 3 . The initial helical pitch p 1 , transitional helical pitch p 2 , and final helical pitch p 3  may be similar to the initial helical pitch p 1  as described with reference to  FIGS.  5 A- 5 D . As the helical pitch changes, the upper surface  624  of the helix structure  618  may maintain a smooth and continuous surface. 
     The changing helical pitch may also cause an interior angle between the upper surface  624  of the helix structure  618  and the inner wall  610  of the elongated tube  608 . For example, an initial interior angle α 1 , transitional interior angle α 2 , and final interior angle α 3  may be sized similarly to the initial interior angle α 1 , transitional interior angle α 2 , and final interior angle α 3  described with reference to  FIGS.  5 A- 5 D . The interior angles α 1 , α 2 , α 3  may aid in water flow from the air inlet  602  of the low-gravity water separator  600  to the reservoir  622 . 
     The reservoir  622  in the low-gravity water separator  600  may be formed between the inner wall  610  of the elongated tube  608  and an exterior wall  644  of an interior cylinder  646  located within the elongated tube  608 . The height of the interior cylinder  646  may be high enough to hold the water separated from the air entering the opening  614 . A connecting wall  648  may form a bottom  650  of the reservoir  622 . The connecting wall  648  may connect a bottom of the elongated tube  608  to approximately a midpoint of the interior cylinder  646 . Dry air may pass through an opening  652  formed in the interior cylinder  646 . Water collected in the reservoir  622  may be extracted from the reservoir via one or more water discharges  606 . 
     In some embodiments, an inlet cap  654  may be positioned proximate the air inlet  602  (see  FIG.  9 A ). The inlet cap  654  may prevent the formation of a rivulet on an inside edge of the helix structure  618 . The inlet cap  654  may set a predetermined distance between the inside edge of the helix structure  618  and a center axis  656  of the low-gravity water separator  600 . The inlet cap  654  may prevent the air stream from entering the helix structure  618  at a trajectory directly down the center axis  656 . 
     In some embodiments, air may enter the reservoir  622  at a rapid velocity. The velocity of the air flow entering the reservoir  622  may continue to increase after the air has entered the reservoir  622  and may turn into turbulent air flow. Turbulent air flow in the reservoir may disrupt a water rivulet or pool of water that may be gather in the reservoir  622 . 
     In some embodiments, air flow to the reservoir  622  may be restricted. For example, a baffle (not shown) may sit atop the exterior wall  644  of the interior cylinder  646 . The baffle may have a donut-like shape or toroidal shape. For example, the baffle may have an interior hole which may allow air to flow out of the low-gravity water separator  600  through interior cylinder  646 . An outer diameter of the baffle may be smaller than an inner diameter of the inner wall  610  of the low-gravity water separator  600 . For example, there may be gap or predetermined distance between the inner wall  610  and a perimeter edge the baffle. The gap, or space, between the inner wall  610  and the baffle may enable the rivulet and water laden air to enter the reservoir  622  while reducing the velocity and volume of air flow to the reservoir. 
     In some embodiments, the exterior wall  644  of the interior cylinder  646  may incorporate one or more holes along its surface at locations between its open distal and proximal end. The one or more holes may allow turbulent air to exit the reservoir  622  while water remains in the reservoir. For example, capillary forces may retain the water inside the reservoir while turbulent air may exit the reservoir  622  through the one or more holes. 
     In another embodiment, one or more fins (not shown) may be incorporated into the reservoir  622 . For example, after the helix structure  618  enters the reservoir  622 , the helix structure  618  may terminate near the second end  620  of the low-gravity water separator  600 . One or more stabilizing fins may wrap around interior cylinder  646  and/or connecting wall  648 ,  650 . The stabilizing fins may transition the turbulent, fast airflow entering and swirling in the reservoir  622  into smooth and slower laminar air flow. Laminar airflow in the reservoir may reduce or lessen interruptions to the water rivulet formed within the reservoir. Fewer disruptions to the rivulet may enable to the water to stay within the reservoir. Furthermore, the fins may provide the same or similar benefits related to stabilizing the water collected in the reservoir  622  as the vanes  248  described above with reference to the low-gravity water separator  200 . 
       FIG.  9 C  is a side view of the helix structure  618  of the low-gravity water separator  600  of  FIG.  6   . The helix structure  618  may incorporate similar features of the helix structure  218  discussed previously. For example, in some embodiments, the helix structure  618  may have various features on the upper surface  624  of the helix structure  618 . For example, the helix structure  618  may have a groove in the upper surface  624 . The groove may use surface tension and capillary forces to guide or direct the water towards the outer edge  628  of the helix structure  618 . The groove may help stabilize the water flow as it transitions towards the reservoir  622 . In other embodiments, a tertiary vane may protrude from and extend along the upper surface  624  of the helix structure  618  to provide a stabilizing force for a water rivulet and water droplets. Either feature, a groove or a tertiary vane, may direct water droplets to the outer edge  628  of the helix structure  618  towards a rivulet. The groove or tertiary vane may provide stability to water rivulets. 
       FIG.  10    is a perspective view of a cutaway of an internal portion of a low-gravity water separator  1000 . The low-gravity water separator  1000  may include an inner wall  1002 , an outer wall  1004  positioned opposite the inner wall  1002 , and a helix structure  1006  positioned within the inner wall  1002 . The low-gravity water separator  1000  may include one or more secondary vanes  1008 . The secondary vanes  1008  may protrude from the inner wall  1002  towards a centerline of the low-gravity water separator  1000 . The secondary vanes  1008  may be of sufficient size to guide water droplets which may be stuck on the inner wall  1002 . The secondary vanes  1008  may be formed on the inner wall  1002 , may be integrally formed as a single piece with the inner wall  1002 , or may be formed separately and mounted to the inner wall  1002  in a separate assembly step. 
     The secondary vane  1008  may begin at a first location  1012  at an initial predetermined distance from an upper surface  1014  of the helix structure  1006 . A pitch of the secondary vane  1008  may then be greater than a pitch of the corresponding portion of the helix structure  1006  such that an end location  1016  is proximate the upper surface  1014  of the helix structure  1006 . In some embodiments, the end location  1016  may merge into the upper surface  1014  of the helix structure  1006 . In another embodiment, the end location  1016  may not touch or come into contact with the upper surface  1014 , but rather may be a distance away from the upper surface  1014 . The secondary vane  1008  may enable water droplets clinging to the edge of the inner wall  1002  to be guided down into a rivulet flow as will be discussed with reference to  FIG.  11   . 
       FIG.  11    is an example of a low-gravity water separator  1100 . The low-gravity water separator  1100  may be an example of one or more aspects of a low-gravity water separator  102 ,  200 ,  600 ,  1000  described with reference to  FIGS.  1 - 10   . The low-gravity water separator  1100  may include an elongated tube  1102  with a helix structure  1104 . The low-gravity water separator  1100  may include an air inlet  1106 , air outlet  1108 , and one or more water discharges  1110 . 
     The helix structure  1104  may have a changing helical pitch along its length L. The helix structure  1104  may have an initial helical pitch p 1 , a transitional pitch p 2 , and a final pitch p 3 , as discussed previously. The helix structure  1104  may additionally include an initial angle α 1 , a transitional angle α 2 , and a final angle α 3 , as discussed previously. 
     Air  1112  laden with water droplets may enter the low-gravity water separator  1100  through an air inlet  1106 . The water laden air  1112  may be forced into an air stream as it enters the low-gravity water separator  1100  through gravity or an external forcing device such as a fan or the like. 
     The initial angle α 1  combined with the initial helical pitch p 1  at the air inlet  1106  may create an overall angle of an upper surface  1116  of the helix structure  1104 . The initial range of the initial angle α 1  may drive wall-bound water laden air  1112  towards an interior corner  1118  where the upper surface  1116  of the helix structure  1104  meets with an inner wall  1120  of the elongated tube  1102 . The initial angle α 1  may induce a radial velocity of the water laden air  1112 . The radial velocity may be within a range of 700 to 2000 RPM. The rapid circumferential flow may create a radial acceleration of the water laden air  1112 , or entrained drops. The radial acceleration may be within a range of 30 g and 150 g. The radial acceleration may cause water droplets  1122  to separate from the air  1112 . 
     For example, the helix structure  1104  may cause a centrifugal, or cyclonic, liquid separation of the water droplets from the air stream. The centrifugal liquid separation may exploit the density difference between the liquid and gas in the air flow to concentrate the water droplets  1122  on the inner wall  1120  and upper surface  1116 . Air  1112  entering the low-gravity water separator  1100 , with entrained water droplets, may rapidly change flow direction from an even axial flow to a rapid cross-axial rotating flow. The axial airflow may be airflow mostly perpendicular to an axis of the helix structure  1104 . This axial airflow may change to cross-axial airflow, or airflow that is aligned with the direction of the helix structure  1104 . The relatively ‘lighter’ air  1112  may change direction more easily than the ‘heavier’ water droplets  1122  forcing the water droplets  1122  to drift toward, and eventually collide with, the inner wall  1120  and upper surface  1116 . 
     As the water droplets  1122  separate from the air  1112 , the remaining radial velocity of the air  1112  may drive the water droplets  1122  into the interior corner  1118 . The water droplets  1122  may form a rivulet  1124 , or a very small stream, of the water droplets  1122 . For example, a centripetal force acting on the air  1112  may cause the water droplets  1122  to drive toward the rivulet  1124 . Centripetal force may be a force that acts on the air  1112  as it moves in a circular path down the helix structure  1104 . The centripetal force acting on the air  1112  may be directed toward a center of the helix structure. The centripetal force acting on the air  1112  may be, for example, approximately 6×10 −7  lbf to 1×10 −3  lbf. As described previously, the speed is dependent on the ratio of air residence time to droplet drift time. The physical parameters that influence this are the size of the droplets, gas viscosity, and the density difference between the liquid and gas. Therefore, the centripetal force may change as the mass and acceleration of the droplets change. 
     As more water droplets  1122  coalesce with the rivulet  1124 , the rivulet  1124  may swell until it fills a gas boundary layer. A gas boundary layer may be a region of air flow near a surface of the inner wall  1120  or upper surface  1116  of the helix structure  1104  over which the gas is flowing, which may move at a lower velocity than the bulk of the freestream air flow. The thickness of the gas, or air, boundary layer may increase as the air flows through the helix structure  1104 . The size of the gas boundary layer may determine how large the rivulet  1124  may swell while still maintaining stability of the rivulet. The boundary layer may be defined as the layer of air that is moving at less than 99% of the velocity of the main bulk air stream. In the low-gravity water separator  1100 , the boundary layer may be approximately 0.5 inches. In some embodiments, the boundary layer may vary along the length of the helix structure  1104 . The boundary layer may be thinner at the leading edge of the helix structure  1104  near the air inlet  1106 . The boundary layer may increase until it exits the low-gravity water separator  1100 . This natural viscous nature may provide a low velocity zone proximate the inner wall  1120  and may prevent the rivulet  1124  from being destabilized even when the bulk of the air is moving rapidly. 
     For example, the rivulet  1124  may continue to swell and the rivulet  1124  may press into a gas velocity stream and the air stream may force the coalesced water droplets  1122  in the rivulet  1124  down the interface between helix structure  1104  and inner wall  1120 . This may cause a cross-section of the rivulet  1124  to shrink as the rivulet  1124  is elongated by the air stream. As more water droplets  1122  coalesce within the rivulet  1124 , the rivulet  1124  may once again swell and repeat the process. The process may repeat as water droplets coalesce within the rivulet  1124  which may cause the rivulet  1124  to migrate toward the reservoir  1126 . 
     Some water droplets  1122  may be driven efficiently to the rivulet  1124 . Other water droplets  1122  may glide or move along the inner wall  1120  of the elongated tube  1102  or the upper surface  1116  of the helix structure  1104 . In some embodiments, the water droplets  1122  may work their way into the rivulet  1124 . In other embodiments, secondary vanes (e.g., secondary vanes  1008 ,  FIG.  10   ) may also guide the water droplets  1122  to the rivulet  1124 . In additional and/or alternative embodiments, helical vanes (not shown) may also guide water droplets  1122  to the rivulet  1124 . Helical vanes may be similar to the secondary vanes but rather than being located on the inner wall  1120  of the elongated tube  1102 , may be located on the upper surface  1116  of the helix structure  1104 . 
     The rivulet  1124  may be a stable two-phase flow regime. For example, the rivulet  1224  may form a long connected ‘string’ of water along the interior corner of the intersection between the upper surface  1116  and the inner wall  1120  and may remain in that interior corner  1118 . The flow of the air  1112  may help stabilize the rivulet  1124 , but if the air flow exceeds, for example, about 36 feet per second, the speed of the air  1112  may disrupt the rivulet  1124 . For example, the rivulet  1124  may experience stable two-phase flow when velocity of the air is not fast enough to pull water out of the rivulet  1124 . 
     The decreasing interior angles α 1 , α 2 , α 3  may also stabilize the rivulet  1124 . The decreasing interior angles α 1 , α 2 , α 3  may induce capillary forces in the water droplets  1122 . The capillary forces may maintain stability of the rivulet  1124 . The decreasing interior angles α 1 , α 2 , α 3  also may provide a decreasing potential in the direction of a reservoir  1126  where the water droplets  1122  form a collective pool of water  1128 . 
     The decreasing interior angles α 1 , α 2 , α 3  may correlate to an increasing pitch of the helix structure  1104 . As the rivulet  1124  is formed, the flow of the air  1112  may be slowed as the transitional pitch p 2  increases. The initial helical pitch p 1  may initiate a high air flow  1112  and the transitional pitch p 2  may slow down the air flow to, for example, about 18 feet per second for the size, shape, and range of flow rates typical for the embodiment shown in  FIG.  7   . The slower air speed in the transitional pitch p 2  may stabilize the rivulet  1124 . The slower air speed may be less rapid axial flow. The less rapid axial air flow may drive the water droplets  1122  down the rivulet  1124  and into the reservoir  1126 . The less rapid axial flow of the air  1112  may also allow droplet free air to escape the low-gravity water separator  1100 . A gradual transition between the final pitch p 3  and the air outlet  1108  may maintain the air flow and may enable the droplet free air to be emitted. 
       FIG.  12    is a flow chart illustrating an example of a method relating to air and water separation, in accordance with various aspects of this disclosure. The method may include collecting droplet laden air  1202 . The droplet laden air may enter a water separator  1204 . The water separator may be a low-gravity water separator. Water droplets may be separated from air stream  1206 . For example, a variable helix structure within the low-gravity water separator may use air flow and inertial forces to separate water droplets and air stream. The water droplets may be collected in a reservoir for harvesting  1208 . The droplet free air may be emitted back into the environment or other system  1210 . 
       FIG.  13    is another flow chart illustrating an example of a method  1300  relating to air and water separation, in accordance with various aspects of this disclosure. The method  1300  may be performed using any one of the low-gravity water separators  102 ,  200 ,  600 ,  1000 ,  1100  discussed herein. 
     The method  1300  may collect water laden air into a semi-closed environment  1302 . The water laden air may be forced into the semi-closed environment using a forcing function such as fan and/or gravity. The semi-closed environment may consist of a low-gravity water separator. 
     The method  1300  may force the water laden air into a helical-shaped channel  1304 . The forcing function may cause a turbulent, rapid circumferential flow of the air. The helical-shaped channel may include a variable pitch along its length. The variable pitch of the helical shaped-channel may separate water droplets from the air stream  1306 . For example, the air stream may contact one or more surfaces of the helical-shaped channel. 
     A rivulet may be formed with the separated water droplets  1308 . The water droplets may be stabilized in the rivulet using the air stream. In some embodiments, one or more secondary vanes may guide separated water droplets towards the rivulet. The speed of the air stream may be reduced after the water droplets have been separated  1310 . For example, the variable pitch of the helical-shaped channel may cause the air speed to decrease. This may cause the turbulent, rapid circumferential air stream transition into less rapid axial flow  1312 . As the air flow slows, the flow may change from a cross-axial flow perpendicular to the axis of the low-gravity water separator  1100  into a streamwise flow parallel to the axis of the low-gravity water separator  1100 . The water droplet from the rivulet flow may then be collected into a reservoir  1314 . This may include guiding the streamwise driven rivulet flow into the water reservoir. The method  1300  may then discharge droplet free air  1316  and may harvest the water  1318  as necessary. 
       FIGS.  14 - 30    illustrate another example low-gravity water separator  1400 . The low-gravity water separator  1400  may incorporate similar features as the low-gravity water separators  102 ,  200 ,  600  discussed above with reference to  FIGS.  1 - 13   . The low-gravity water separator  1400  may include various features to help stabilize the collected water within a reservoir portion of the device so that the amount of water that is drawn out of the device with the exiting air flow is minimized. For example, the low-gravity water separator  1400  may include unique water reservoir features (e.g., shape, size, and location), a helix structure shape and orientation, and air flow paths that provide stabilizing forces for the collected water. Other unique aspects of the low-gravity water separator  1400  relate to, for example, how various components of the device are assembled together during manufacturing, how airflow is controlled internal the device, and how collected water is directed into and stabilized within the water reservoir. 
     Referring to  FIGS.  14 - 19   , the low-gravity water separator  1400  includes an inlet structure  1402 , an outlet structure  1404 , an elongated tube  1406 , a reservoir assembly  1408 , and a helix structure  1410  (see  FIG.  20   ). The inlet structure  1402  is mounted at one end of the elongated tube  1406 , and the outlet structure  1404  is mounted to an opposite end of the elongated tube  1406 . 
     The inlet structure  1402  includes an inlet opening  1412  surrounded by a flange  1416 . The inlet structure  1402  also includes a seat  1414  that provides an interface with the elongated tube  1406 . The outlet structure  1404  includes an outlet opening  1418  surrounded by a flange  1422 . The outlet structure  1404  also includes a seat  1420  to interface with the elongated tube  1406 . The inlet opening  1412  is arranged along a side surface and at a radially inward directed orientation relative to a longitudinal axis L. The inlet opening  1412  is also arranged offset from the longitudinal axis L. This offset radially inward directed arrangement for the inlet opening  1412  provides a tangential flow of air into the low-gravity water separator  1400 . This tangential flow facilitates movement of the flow of air into the helical channel defined between the helix structure  1410  and an inner surface of the inlet structure  1402  and elongated tube  1406 . The tangential arrangement for the inlet opening  1412  also allows the air to begin swirling droplets of water out of the air flow ahead of the entrance into the helical channel defined in part by the helix structure  1410 . The swirling of the water droplets out of the air ahead of the helix structure causes the droplets to preferentially collide with the walls rather than the helix. Water droplets on the walls are more easily driven to the vertex and into the rivulet. 
     The outlet opening  1418  also extends radially relative to the longitudinal axis L. The inlet opening  1412  and outlet opening  1418  are arranged in the same direction, which may facilitate easier mounting to other features of the water separator system (e.g., system  100  described with reference to  FIG.  1   ). In other embodiments, the inlet opening  1412  and outlet opening  1418  may be arranged facing in different radial directions, or in longitudinal direction, such as to accommodate the orientation of features to which the low-gravity water separator  1400  are mounted to. 
     The elongated tube  1406  includes first and second ends  1424 ,  1426 , first and second seats  1428 ,  1430 , an inner surface  1432 , an outer surface  1434 , and an internal cavity  1436  (see  FIG.  20   ). The inlet structure  1402  is mounted to the first seat  1428  at the first end  1424 . The outlet structure  1404  is mounted to the second seat  1430  at the second end  1426 . The seats  1414 ,  1428  and  1420 ,  1430  may be formed as spherical structures or having a spherical portion and/or a contoured surface. For example, the seats may form segments of a sphere to allow slight misalignments of the axis of the inlet and outlet structures  1402 ,  1404  relative to the longitudinal axis L of the elongated tube  1406  to allow the inlet and outlet structures  1402 ,  1404  to align with the elongated tube  1406  even if the components  1402 ,  1404 ,  1406  have significant dimensional errors. Thus, the joints between the components  1402 ,  1404 ,  1406  may be able to accommodate relatively large dimensional errors inherent in some types of manufacturing (e.g., additive manufacturing). The spherical shape of the seats  1414 ,  1418 ,  1428 ,  1430  may provide three rotational degrees of freedom at the joints between the components  1402 ,  1404 ,  1406 . This allows the flanges  1416 ,  1422  at the inlet and outlet to be relatively co-planer surfaces so that the interfaces when fastened to a main structure do not experience significant strains and may be able to provide a sufficient air- and water-tight seal. The presence of extra strain at the interface of the flanges to a mating structure resulting from a non-planer inlet and outlet orientation could result in damage to the final assembled low-gravity water separator  1400 . 
     Other types of joint structures may be possible for assembling the components  1402 ,  1404 ,  1406 ,  1408  together. In some embodiments, at least some of the components  1402 ,  1404 ,  1406 ,  1408  may be integrally formed as single pieces rather than as separate pieces that are later assembled together. Some types of additive manufacturing (e.g., 3D printing) may facilitate creation of the components or combination of components of the low-gravity water separator  1400  as integral pieces in spite of the relatively complex interior geometries of the various features (e.g., the helical shape of helix structure  1410 ). 
     In another example, at least some of the components  1402 ,  1404 ,  1406 ,  1408  may be secured together with a bonding agent such as an adhesive. The components may be bonded by applying uncured resin or other adhesive material to the seats of the joint, following by curing the material using, for example, a suitable ultraviolet (UV) curing light. This method may be particularly useful for the present application because it can eliminate the need to certify additional materials and processes, which may be resourced intensive for items intended for certain applications (e.g., space flight). 
     The reservoir assembly  1408  may include an inner reservoir  1440  (see  FIG.  20   ), a reservoir outlet segment  1442  having a seat  1444  (see  FIG.  19   ), a reservoir chamber  1446  (see  FIG.  19   ), a chamber bottom  1448  (see  FIG.  26   ), a chamber cavity  1450  (see  FIG.  22   ), a water outlet  1452  (see  FIG.  22   ), reservoir return segments  1454 ,  1456 ,  1458  (see  FIG.  19   ), and a plurality of vanes  1460 ,  1462  (see  FIG.  22   ). The return segment  1454  includes seats  1466 ,  1468 . The return segment  1456  includes seats  1470 ,  1472 . The return segment  1458  includes seats  1474 . The seats  1466 - 1474  mate with each other and other components (e.g., the sidewall of elongated tube  1406  and the reservoir chamber  1446 , etc.). 
     The inner reservoir  1440  is defined between the inner surface  1432  of the elongated tube  1406  and an interior cylinder  1486  that defines an outlet from the elongated tube  1406  into the outlet structure  1404 . Water collected within the elongated tube  1406  gathers in the inner reservoir  1440  where it is directed through the reservoir outlet segment  1442  into the reservoir chamber  1446 . A bottom surface of the inner reservoir  1440  is defined by a connecting helix  1492  that extends from the inner surface  1432  of the elongated tube  1406  to an outer surface of the interior cylinder  1486 . The reservoir outlet segment  1442  opens directly into the inner reservoir  1440  through an opening defined in the wall of the elongated tube  1406 . The helix structure  1410  may extend continuously from internal the elongated tube  1406 , into the inner reservoir  1440 , through the reservoir outlet segment  1442 , and into the reservoir chamber  1446  (see  FIGS.  21  and  22   ). 
     A plurality of additional vanes  1460 ,  1462  may also be positioned within the reservoir chamber  1446  as shown in  FIG.  22   . The position, size, and angle between vanes  1460 ,  1462  may be designed to stabilize the water based on Weber number, as described above related to separator  200 ,  600 . Furthermore, the angle β between the vanes (˜10 degrees, shown in  FIG.  27 B ) helps to promote passive bubble separation, in the event that bubbles appear, as a result of a disturbance. The position, size and angle of the vanes  1460 ,  1462  can also be used to remove bubbles form liquid output system  124  (i.e., if bubbles are present, liquid can be pumped back into the reservoir, and the capillary forces with these vane angles will cause the bubbles to leave the liquid). The bubbleless liquid can then be recovered from the reservoir back to the liquid output system  124  shown in  FIG.  1   . These features and functionality may be applicable for all the reservoir designs disclosed herein. 
     Vias  1464  may be formed in the vanes  1460 ,  1462  and the portion of the helix structure  1410  positioned within the reservoir chamber  1446  as shown in  FIGS.  27 A and  27 B . The vias  1464  may be offset relative to each other along the length of the vanes  1460 ,  1462  and helix structure  1410 . The offset vias may also be spaced apart from the water outlet  1452 . This arrangement for the vias may improve stability of the water through the water outlet  1452  and between the vanes  1460 ,  1462  and helix structure  1410  within the reservoir chamber  1446  along the chamber bottom  1448  by preventing water from pulling away from the via due to the larger vertex angle if the via were to overlap or coincide on adjacent vanes. 
       FIG.  27 B  shows the edges of the vias  1464  being radiused or contoured. The radii R 1 , R 2  of the vias  1464  may help eliminate pinning edges, which could prevent liquid (e.g., water) from entering the vias  1464 . The radii R 1 , R 2  may provide a smoother and/or open path through the respective vane  1460 ,  1462  and helix structure  1410  through in which the vias  1464  are formed. Further, an angle θ from a center of each via  1464  may be provided to assist with directing air bubbles from the vias  1464  into spaces between the vanes  1460 ,  1462 , helix structure  1410 , and internal walls of the reservoir chamber  1446 . 
       FIG.  27 D  shows a side view of one of the vias  1464 . The vias  1464  may have a length L 1  and a height H 1 , and have an acute angle α. The length L 1  may, in some embodiments, be in the range of about 0.5 in. to about 2 in., and more particularly about 1 in. The height H 1  may, in some embodiments, be in the range of about 0.1 in. to about 0.5 in., and more particularly about 0.125 in. The angle α may, in some embodiments, be in the range of about 10 degrees to about 30 degrees, and more particularly about 15 degrees. 
     The connecting helix  1492  may have a helical shape as shown in  FIG.  28   . This helical shape may assist with capturing and directing wall-bound water droplets that are not captured by the main helix structure  1410  toward the reservoir outlet segment  1442 . Like the main helix structure  1410 , the connecting helix  1492  may form an acute angle between the inner surface  1432  of the elongated tube  1406 . The size of the acute angle may change as the connecting helix  1492  approaches the reservoir outlet segment  1442 . 
     The reservoir return segments  1454 ,  1456 ,  1458  may provide an air flow path from the reservoir chamber  1446  back into the main body of the low-gravity water separator  1400  in the outlet structure  1404 . The seats  1466 - 1474  of the return segments  1454 ,  1456 ,  1458  may provide a slip joint or other connection that provides some translational flexibility required in the reservoir return tube between the slip joint and the spherical cut ends defined by the seats  1466 - 1474  to help maintain an improved alignment between the helix structure  1410  that passes from the inner reservoir  1440 , through the reservoir outlet segment  1442 , and into the reservoir chamber  1446 . The size and shape of the seats  1466 - 1474  may be designed specifically to allow adjustability in both axial and radial placement of the reservoir assembly  1408  relative to the elongated tube  1406  and helix structure  1410 , as well as the outlet structure  1404  relative to the elongated tube  1406  and the reservoir assembly  1408 . The construction of the seats  1466 - 1474  may help preserve the ability to more ideally align the helix structure while still securing the components of the reservoir assembly  1408 .  FIGS.  24 A- 24 C  illustrate assembly of reservoir return segments  1456 ,  1458  with a slip joint. Other types of joints and connection features are possible to provide the desired adjustability for the assembly of various components of low-gravity water separator  1400 . 
     The reservoir chamber  1446  may include an enlarged portion along the bottom end thereof that provides for re-circulated flow  1504 . The re-circulated flow  1504  is outside of a first flow path  1500  for air flow passing from the reservoir outlet segment  1442  to the reservoir return segments  1454 ,  1456 ,  1458 . The re-circulated flow  1504  may involve a sudden drop off area that causes an air velocity profile to separate from the vertex, thereby leaving a calm zone immediately above the water outlet  1452 . The recirculation flow pattern may be set up by drop off and air exit placement. The recirculation sweeps downstream water back towards the water outlet  1452  to a stagnation zone formed by the opposing stream lines  1500 ,  1504 . Generally, the dramatic change in depth of the reservoir chamber  1446  may be referred to as a reservoir boundary layer separator and may cause an air boundary layer in the vertex to largely separate from the vertex as the air passes over the sudden drop off area. This causes a low velocity zone immediately downstream of the drop off where the liquid is especially stable. Additionally, the boundary layer separation promotes a re-circulated flow  1504  that causes air flow streamlines to collide from opposite directions, which forms a stagnation zone. This creates an air flow pattern that sweeps water into this dead zone from upstream and downstream, which makes it a more ideal location for the water outlet  1452 . 
     The reservoir assembly  1408  may include features that assist in controlling air flow through the air reservoir assembly  1408 . For example, an orifice plate  1498  may be positioned in one or more of the reservoir return segments  1454 ,  1456 ,  1458 . The orifice plate  1498  may be used to control proper reservoir air flow for a given overall design flow rate. For example, the orifice may be sized such that the air flow velocity in the reservoir is slow enough to maintain a stable reservoir (i.e., the water collected in the reservoir remains stable), even when the overall device volumetric flow is at its design point. The orifice plate  1498  may be replaceable with orifice plates having different sized orifices to provide the size adjustability. In other embodiments, a single orifice plate may have an adjustable sized opening that is adjustable from exterior of the reservoir assembly  1408 . Some of the reservoir assembly  1408  may include multiple orifice plates  1498  at locations before or after the reservoir chamber  1446 , or multiple orifice plates within the return channel defined by the reservoir return segments  1454 ,  1456 ,  1458 . 
     Water collected in the inner reservoir  1440  may be inhibited from moving out through the interior cylinder  1486  and out through the outlet structure  1404  by features provided on the interior cylinder  1486 . Any water that ends up inside the interior cylinder  1486  is lost and represents failure of primary function for the low-gravity water separator  1400 . Water droplets positioned on the outer wall of the interior cylinder  1486  may be prevented from traveling up the wall and over the top edge at the proximal end of the interior cylinder  1486  by a lip  1489 , as shown in  FIG.  29   . The lip  1489  may protrude radially outward from the exterior surface of the interior cylinder  1486 . The lip  1489  may include an interior angle on the outside of the interior cylinder  1486  near the top proximal edge. Alternatively, the lip  1489  may be positioned further along the length of the interior cylinder  1486  in a distal direction spaced away from the proximal edge and inlet opening  1488 . Water being driven up the outside surface of the interior cylinder  1486  will encounter this lip  1489  to be prevented from migrating over the top edge and through the opening  1488  where it can escape through the outlet opening  1490 . 
     The helix structure  1410  may include an upper surface  1480 , a lower surface  1482 , and an outer edge  1484 , as shown in  FIG.  20   . An inlet cap  1494  may be positioned at the upper end of helix structure  1410  near the inlet opening  1412  (see  FIG.  20   ). The helix structure  1410  may have a variable pitch along its length as described above with reference to low-gravity water separators  102 ,  200 ,  600 . Generally, the helix structure  1410  may have many of the same or similar features and functionality of the other helix structures described with reference to  FIGS.  1 - 13   . 
     The helix structure  1410  may extend continuously through the inner reservoir  1440 , through the reservoir outlet segment  1442 , and into the reservoir chamber  1446 , as shown in  FIGS.  20 - 22   . The helix structure  1410  may define a reservoir vane and provide a single connective capillary path between the inlet of the helical channel open to the inlet opening  1412  where the swirl and separation of water droplets happens, and the bottom of the reservoir chamber  1446 . Additionally, the helix surface and surface of the reservoir vane may be completely enveloped into the secondary annular water pick-up area between the interior cylinder  1486  and the interior wall or inner surface  1432  of the elongated tube  1406  at an entrance to the reservoir component positioned external to the elongated tube  1406 . 
     The helix structure  1410  may be divided into different segments along its length. For example, the low-gravity water separator  1400  may be divided into different components (e.g., components  1402 ,  1404 ,  1406 ,  1408 ), and the helix structure  1410  may be divided into segments  1410 A,  1410 B at the interface between the elongated tube  1406  and the reservoir assembly  1408 , as shown in  FIG.  30   . This interface may be an angled interface  1506 . The angled surface joint at interface  1506  may provide a pinning edge that stray droplets on the surface of the helix structure  1410  will encounter. The stray water droplets on the helix surface will typically migrate along the helix surface without moving towards the vertex. The interface  1506  (also referred to as a joint) in the helix surface may be angled such that when droplets encounter the interface  1506  and pin to its edge, the air flow will drive the droplets along the pinning edge toward the vertex where it will be carried into the main rivulet in the chamber bottom  1448 . Thus, the interface  1506  may provide both an interface or connection point between segments  1410 A,  1410 B of the helix structure, as well as provide a feature to help direct the water droplets to the primary rivulet for collection within the reservoir chamber  1446 . 
     In other embodiments, the helix structure  1410  may be formed as a single unitary piece along its entire length, such as when the entire low-gravity water separator  1400  is formed from an additive manufacturing method, or at least the elongated tube  1406 , reservoir assembly  1408  and helix structure  1410  are formed integrally as a single piece. A pinning feature, groove, vane or similar feature may be formed in the helix structure  1410  to mimic the interface  1506 . Other types of joints may be used in other embodiments for connecting various segments of the helix structure  1410  to each other. In one example, UV curable material may be used to provide a positive connection between the helix segments  1410 A,  1410 B, or other segments or portion of the helix structure. 
     The water outlet  1452  may join the spaces between the vanes  1460 ,  1462  together to draw water evenly from each channel within the reservoir chamber  1446 , as shown in the cross-sectional view of  FIG.  27 C . The channels within reservoir chamber  1446  (e.g., those channels defined between the vanes  1460 ,  1462 , the helix structure  1410 , and walls of the reservoir chamber  1446 ) are joined together in a manner such that only two flow paths are joined together at a time. Flow path bifurcation promotes even distribution of flow, whereas joining three or more paths together simultaneously can cause uneven flow distribution.  FIG.  27 C  shows flow paths C 1 , C 2  joining to form flow path B 1 , flow paths C 3 , C 4  joining to form flow path B 2 , and flow paths B 1 , B 2  joining to form flow path A, which then exits out of the water outlet  1452 . 
     The water outlet  1452  may have different shapes, sizes and connecting features based on a number of criteria, such as the device to which the water outlet  1452  is to be connected. While any number of fitting choices were available to connect to the water outlet  1452 , such as numerous standard tapped thread styles or an integrally printed barb fitting, a fitting geometry for water outlet  1452  consisting of a flanged double o-ring face seal may be selected that is compatible with a commercial KF style vacuum fitting clamp. A KF style vacuum clamp may help eliminate the need to do any post machining of threads required for other types of connection. the KF style clamp may also provide a quick and secure connection that does not involve transfer of any appreciable torque or force to the rest of the low-gravity water separator  1400 , for example, during installation or removal of a liquid drain line from the water outlet  1452 . This means there is a reduced risk of damaging the hardware by, for example, over tightening a threaded connection, or snapping off a barb fitting while trying to install or remove tubing. Additionally, use of a KF style clamp may have advantages over embodiments that include machined threads in an additive manufacturing application (e.g., the 3D printed material of the remaining portions of the low-gravity water separator  1400 ), in which threads could create micro cracks that may propagate to complete failure under the vibrations present in some types of environments (e.g., launch of a spacecraft). 
     Referring to  FIG.  20   , air flowing into the low-gravity water separator  1400  through the inlet opening  1412  may pass into the helical channel between surfaces  1480 ,  1482  of the helix structure  1410  and the inner surface  1432  of the elongated tube  1406  along the length of the elongated tube  1406 . At the bottom or distal end of the helix structure  1410 , the air flow in the helical channel is divided into first and second air flows that are directed along first and second flow paths  1500 ,  1502 . The first flow path  1500  passes from the helical channel into the inlet opening  1488  of the interior cylinder  1486 . A significant portion of the air flow that enters into the inlet opening  1412  is typically directed into the first flow path  1500  due to the size, shape and orientation of the inlet opening  1488  provided by the interior cylinder  1486 . The remainder of the air flow passes into the second flow path  1502 : first into the inner reservoir  1440  and then through the reservoir outlet segment  1442  into the reservoir chamber  1446  and through the reservoir return segments  1454 ,  1456 ,  1458  back into the outlet structure  1404  downstream of the interior cylinder  1486 . The air flows through first and second flow paths  1500 ,  1502  recombine at the outlet opening  1418  provided by the outlet structure  1404 . 
     The splitting of the air flow passing through the helical channel into the first and second flow paths  1500 ,  1502  may be referred to as a split air flow path or the creation of parallel air flow paths. The splitting or providing of parallel air flow paths may allow air velocity over the collected water within the reservoir chamber  1446  to be locally reduced without the need to expand the flow area of the entire low-gravity water separator  1400 . Expanding the flow area of the entire device may not be feasible in some scenarios due to volume constraints for the size of the entire low-gravity water separator  1400 . 
       FIGS.  31 - 37    illustrate another example low-gravity water separator  3100 . The low-gravity water separator  3100  may incorporate similar features as the low-gravity water separators  102 ,  200 ,  600 ,  1400  discussed above with reference to  FIGS.  1 - 30   . The low-gravity water separator  3100  may include various features to help stabilize the collected water within a reservoir portion of the device so that the amount of water that is drawn out of the device with the exiting air flow is minimized. For example, the low-gravity water separator  3100  may include unique water reservoir features (e.g., shape, size, and location), a helix structure shape and orientation, and air flow paths that provide stabilizing forces for the collected water. Other unique aspects of the low-gravity water separator  3100  relate to, for example, how various components of the device are assembled together during manufacturing, how airflow is controlled internal the device, and how collected water is directed into and stabilized within the water reservoir. 
     Referring to  FIGS.  31 - 37   , the low-gravity water separator  3100  includes an inlet structure  3102 , an outlet structure  3104 , an elongated tube  3106 , a reservoir assembly  3108 , and a helix structure  3110  (see  FIG.  36   ). The inlet structure  3102  is mounted at one end of the elongated tube  3106 , and the outlet structure  3104  is mounted to an opposite end of the elongated tube  3106 . 
     A plurality of additional vanes  3160 ,  3162  may be positioned within the reservoir chamber  3146  as shown in  FIGS.  36  and  37   . Vias may be formed in the vanes  3160 ,  3162  and the portion of the helix structure  3110  positioned within the reservoir chamber  3146  (e.g., the vias  1464  shown in  FIGS.  27 A and  27 B ). The offset vias may be spaced apart from a water outlet  3152 . The water outlet  3152  may be positioned at an opposite end of the reservoir chamber  3146  as compared to the location of the water outlet  1452  of the separator  1400  shown in  FIGS.  14 - 30   . The size, shape and orientation of the vanes  3160 ,  3162  and helix structure  3110  within the reservoir assembly  3108  are comparable to the vanes  1460 ,  1462  and helix structure  1410  shown in, for example,  FIGS.  21  and  22   . 
     The low-gravity water separator  3100  may have only two revolutions of helix surface for the helix structure  3110 . The two revolutions may be distinct from other designs such as the low-gravity water separators  102 ,  200 ,  600 ,  1400  discussed above with reference to  FIGS.  1 - 30    for at least the reason that they have three full revolutions of helix surface for their respective helix structures. 
     The low-gravity water separator  3100  may also have a configuration for the reservoir chamber  3146  that is different from reservoir  1446  described above, specifically related to the size, shape and orientation of vanes  3160 ,  3162 . low-gravity water separator  1400  may have a single vane that provides a continuation of the helix structure  1410  with a pair of vanes  1460 ,  1462  positioned to a side of the continuous helix structure  1410 . With the design of low-gravity water separator  1400 , the only way for water to access the areas between the two side vanes  1460 ,  1462  is through the vias  1464 . In the low-gravity water separator  3100 , a vane in the reservoir  3164  is also a continuation of the helix structure  1410 , but the other two vanes  3160 ,  3162  extend upward from a vertex formed on either side of the continuous helix structure  1410  within the reservoir chamber  3146 . 
     The vanes  3160 ,  3162  may grow from the vertex formed on either side of the helix  3110 , thereby bifurcating the rivulet in each vertex to evenly divide the flow across the separate channels between the vanes  3160 ,  3162  and helix structure  3110 . Furthermore, the vanes extending out from the vertex provides a sudden decrease in the interior angle of the capillary corner. This design helps pin water within the reservoir where the angle is smallest, and prevent water from wicking from the reservoir back up toward the elongated tube  3106 , particularly in the event that airflow is interrupted. 
     Additionally, the reservoir chamber  3146  does not employ a significant depth change that creates boundary layer separation as in the reservoir chamber  1446  described above, and thus the water outlet  3152  is positioned as far downstream as practical. 
     Referring to  FIG.  38   , an example method  3800  related to assembly or manufacture of a low-gravity water separator is shown and described. The method  3800  may include, at block  3805 , the step of providing a water capture device having an elongated tube, an inlet structure position of the first end of the elongated tube and defining an inlet opening configured to receive a stream of water-laden air into the water capture device, an outlet structure positioned at the second end of the elongated tube and defining an outlet opening, a helical structure positioned internal the elongated tube, and a reservoir configured to collect water that has been separated from the stream of water-laden air within the elongated tube. 
     At block  3810 , the method  3800  may include securing the inlet structure to the elongated tube at a first joint, and securing the outlet structure to the elongated tube at a second joint, wherein in the first and second joints each have at least one contoured surface. The contoured surface may include a spherical portion, a hemispherical portion or an arc portion. The method may include forming the elongated tube, inlet structure and/or the outlet structure using 3D printing or other additive manufacturing process. The water capture device may further include first and second air flow paths coupled inflow communication with the outlet opening, the second air flow path being defined at least in part by the first and second tube segments, the method including securing the first and second tube segments together with a slip joint. The water-capture device may further include at least one vane positioned in the reservoir, and the first and second tube segments may be adjustable relative to each other and relative to the elongated tube to align at least one vane with the helical structure. The water-capture device may further include first and second air flow paths coupled in flow communication with the outlet opening, the second air flow path including an orifice, the method including adjusting the size of the orifice to control a rate of air flow through the second air flow path. The first and second joints may be formed in part by applying uncured base material resin to the contoured surfaces, and then curing the resin, such as by using ultraviolet (UV) light. 
       FIG.  39    illustrates an example method  3900  of separating water from a stream of water-laden air. The method  3900  may include, at block  3905 , a step of delivering the stream of water-laden air into a helical-shaped channel of a water capture device, the helical-shaped channel having a variable pitch along its length. Block  3910  may include separating water from the air flow within the helical-shape channel. Block  3915  may include collecting the water into a reservoir, the reservoir including a plurality of vanes. Block  3920  includes dividing the air flow into a first air stream and a second air stream, the second air stream passing through the reservoir. Block  3925  includes combing the first and second air streams after the second air stream has passed through the reservoir. The method  3900  includes, at block  3930 , passing the combined air streams out of the water-capture device. Block  3935  includes removing the water from the reservoir. 
     The method  3900  may also include separating water droplets from the air flow by contacting the air flow against one or more surfaces of the helical-shaped channel, and collecting the separated water droplets from the one or more surfaces of the helical-shaped channel in the reservoir. The method may include stabilizing the water within the reservoir using the second air stream. The water capture device may include a helical structure that defines in part the helical-shaped channel, the helical structure extending continuously into the reservoir. The water capture device may include an elongated tube housing the helical-shaped channel, and a portion of the reservoir extends outside of the elongated tube, the portion of the reservoir defining an air channel through which the second air stream passes out of the elongated tube at a tangential angle. Delivering the stream of water laden air into the helical-shaped channel may include delivering the stream of water laden air at a tangential angle relative to a longitudinal axis of the water capture device 
     Any other methods related to manufacturing, assembly, operating and adjusting a low-gravity water separator may be carried out using the various embodiments and functionality disclosed herein. The example methods of  FIGS.  38  and  39    are exemplary only and may include more or fewer steps in other embodiments. 
     Various inventions have been described herein with reference to certain specific embodiments and examples. However, they will be recognized by those skilled in the art that many variations are possible without departing from the scope and spirit of the inventions disclosed herein, in that those inventions set forth in the claims below are intended to cover all variations and modifications of the inventions disclosed without departing from the spirit of the inventions. The terms “including:” and “having” come as used in the specification and claims shall have the same meaning as the term “comprising.”