Abstract:
An environmental control system (ECS) for an aircraft may be employed to regulate temperature of air entering a cabin of the aircraft. During conditioning of the air, condensate may form in the air. A multiple-stage condensate extraction unit may be incorporated into the ECS to remove the condensate. The extraction unit may be provided with two fluid collection stages built into a cylindrical duct. The duct may have a bend therein. One of the collection stages may be positioned on an upstream side of the bend while the second one of the stages may be positioned on a downstream side thereof. The combination of the two stages and their positioning on either side of the bend may provide a particularly compact and efficient condensate extraction unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This invention is disclosed in United Kingdom Patent Application No. 0505572.8 filed on 18 Mar., 2005 and priority for United Kingdom filing date is being made under 35 U.S.C. 119. 
     BACKGROUND OF THE INVENTION 
     This invention generally relates to extraction of a fluid such as water from a gas stream. More particularly, the present invention relates to improvements in apparatus and methods for extracting condensate from a gas stream of an aircraft environmental control system (ECS). 
     In a typical aircraft, an ECS supplies air to the cabin or passenger compartment at a desired comfortable temperature. Generally, air for this purpose is obtained from the engines or the auxiliary power unit of the aircraft. In many operating conditions of an aircraft this air is humid. It is common practice to cool the humid air by passing it through a condenser. As humid air cools, water vapor in the air condenses into liquid droplets. It is highly desirable that the water droplets be removed from the air before it is routed to the cabin or passenger compartment. Failure to remove the water may result in various problems, such as reduction of efficiency of the ECS, icing problems, fogging in the cabin or passenger compartment, corrosion of ECS components and shorting or failure of electrical equipment. 
     It is well known in the prior art to deploy a fluid extraction unit in an aircraft ECS. However, as with any airborne device, there are design considerations that balance efficiency with size and weight. Fluid extraction units used in non-aircraft applications may be made more efficient by employing multiple staging. In other words a series of extractor stages may be placed in a gas stream, with each successive stage removing residual water that passes a previous stage. However, multiple-stage fluid extraction units are inherently large and heavy. Therefore, because of this design consideration, it has heretofore been common practice, in many aircraft applications, to forego some of the efficiency of a multiple-stage fluid extraction unit in favor of a single stage extractor which is inherently lighter and smaller. 
     Numerous attempts have been made in the prior art to provide improved efficiency of single stage fluid extraction units for aircraft applications. Also there have been prior art efforts directed to producing more efficient multiple-stage extractors which are small in size and weight. Typically such prior-art, multiple-stage fluid extraction units may combine a swirl-type fluid collection stage and a split-duct type fluid collection stage in a sequential configuration along a longitudinal axis of an air passage duct. The two stages may be closely spaced to one another and thus an overall size of unit may be kept relatively small. 
     Even though these prior-art multiple-stage fluid extraction units achieve an improved efficiency over single stage units, they are nevertheless less efficient than the larger and more complex multiple-stage units which are employed in typical ground level, non-aircraft applications. In applications where space and weight are not important, multiple fluid collection stages may be displaced a substantial distance from one another, thus promoting coalescing of the liquid and enhancing liquid collection. A fluid extraction unit with widely separated fluid collection stages is inherently more efficient than one in which the stages are closely spaced. 
     As can be seen, there is a need for an ECS fluid extraction unit that provides an inherent efficiency of a unit with widely separated multiple fluid collection stages while at the same time consuming only a small space on an aircraft and adding only a small weight to the aircraft. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a fluid extraction unit for separating fluid from a gas stream comprises a gas stream constraining passageway, a first fluid collection stage, and a second fluid collection stage. The gas stream constraining passageway comprises a deflection segment therein. The first fluid collection stage is located upstream from the deflection segment and the second fluid collection stage is located downstream from the deflection segment. 
     In another aspect of the present invention, an environmental control system for an aircraft comprises a heat exchanger unit, and a fluid extraction unit adapted to receive air from the heat exchanger unit and extract condensate from the air. The fluid extraction unit comprises an upstream end positioned to receive the air, a downstream end positioned to deliver the air to a transfer duct for delivery to the heat exchanger unit, a gas stream constraining passageway interconnecting the upstream end and the downstream end of the fluid extraction unit, a first fluid collection stage, and a second fluid collection stage. The gas stream constraining passage has a bend therein. The first fluid collection stage is located upstream from the bend and the second fluid collection stage is located downstream from the bend. 
     In yet another aspect of the present invention a method for extracting droplets of fluid from a gas comprises the steps of injecting the gas into a constraining passageway to form a gas stream with an overall longitudinal trajectory, imparting a swirling motion to the gas stream to produce a centrifugal force on droplets of the fluid which may be suspended in the gas stream so that the droplets are propelled to an inner surface of the constraining passageway, collecting the propelled droplets through first openings in the constraining passageway, deflecting the gas stream from its overall longitudinal trajectory to impinge the gas stream onto the inner surface of the constraining passageway, and collecting a fluid stream that coalesces on the constraining passageway during said deflecting step through an outlet opening in the constraining passageway. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevation view of an aircraft environmental control system (ECS), in an orientation consistent with level flight of an aircraft, in accordance with the present invention; 
         FIG. 2  is a bottom view of the ECS of  FIG. 1 , in accordance with the present invention; 
         FIG. 3  is an isometric view of the ECS of  FIG. 1 , in accordance with the present invention; 
         FIG. 4  is a partial sectional view of a fluid extraction unit in accordance with the present invention; 
         FIG. 5  is an elevation view of the ECS of  FIG. 1  shown in an orientation consistent with non-level flight of an aircraft, in accordance with the present invention; and 
         FIG. 6  is an illustration of a method of extracting fluid in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Broadly, the present invention may be useful in improving the efficiency and reducing size and weight of fluid extraction units on aircraft environmental control systems (ECS). In that regard, the invention may provide a multiple-stage fluid extraction unit which may be placed into a space that is large enough only for a prior-art single-stage fluid extraction unit. For illustrative purposes, the following description includes an example of inventive apparatus that may be employed to achieve these desired capabilities in a fluid extraction unit for an aircraft ECS. However, it is understood that other applications can be substituted for the inventive apparatus. 
     The present invention is an improvement over the prior art in that an inherent efficiency of widely separated multiple-stages is provided in the fluid extraction unit while maintaining a small size and weight of the unit. This improvement over the prior art may be achieved by combining a deflection or bend in the fluid extraction unit with a fluid collection stage on both an upstream side and a downstream side of the bend. 
     Referring now to  FIGS. 1 ,  2  and  3 , there is shown an aircraft environmental control system (ECS) according to the present invention, and designated by the numeral  10 . The ECS  10  may comprise a heat exchanger unit  11  which may comprise a reheater  12  and a condenser  13 . The condenser  13  may be connected by an air flow duct  14  to a fluid extraction unit  16 . The ECS  10  may be supplied processed air from a compressor of a turbine engine, shown schematically in  FIG. 2  and designated by the numeral  17 . As illustrated in  FIG. 2 , air may flow into a first inlet port  18 , through the reheater  12 , then to the condenser  13  and into the fluid extraction unit  16 . Thence air may flow into a transfer duct  20 . The air may then travel through the transfer duct  20 , across the reheater  12 , out through a first outlet port  21  and into a conventional expansion turbine, shown schematically in  FIG. 2  and designated by the numeral  22 . The air may then flow through a second inlet port  23  across the condenser  13 , through a second outlet port  24  into a conventional distribution network (not shown) and into an aircraft cabin, shown schematically in  FIG. 2  and designated by the numeral  25 . 
     In operation, the heat exchanger unit  11  and the expansion turbine  22  may function in a conventional manner to provide a desired temperature for air entering the cabin  25 . Condensate may form in the air as it initially passes through the reheater  12  and the condenser  13 . This condensate may produce operational problems if allowed to remain in the air that passes into the cabin  25 . Icing, cabin air fogging, material corrosion and electrical equipment shorting or failure are possible undesirable consequences of allowing excessive condensate to remain in air that flows through the ECS  10 . 
     It has been common practice, in the prior art, to place a fluid extraction unit into a flow path of air passing through an ECS. The ECS  10  which is the subject of the present invention may utilize the fluid extraction unit  16  for purposes of removing condensate from air passing through the ECS  10 . In  FIG. 1  the fluid extraction unit  16  can be seen to extend from an upstream end  26  thereof to a downstream end  27  thereof. The upstream end  26  of the fluid extraction unit  16  may be attached to the air flow duct  14  and the downstream end  27  of the fluid extraction unit  16  may be attached to the transfer duct  20 . A distance L designates a size of a space envelope of an aircraft in which the fluid extraction unit  16  is installed. 
     Referring now to  FIG. 4  there is shown a partial sectional view of the fluid extraction unit  16  constructed in accordance with the present invention. The extraction unit may comprise a gas-stream constraining passageway  30  which interconnects a first fluid collection stage  32  and a second fluid collection stage  34 . The gas-stream constraining passageway  30  may comprise a longitudinal segment  36  and a deflection segment  38 . The deflection segment  38  may comprise a bend  40  in the passageway  30 . In a non-limiting example, the passageway  30  may comprise a cylindrical duct  41 . 
     Referring still to  FIG. 4 , an exemplary operation of the fluid extraction unit  16  may be understood. A gas such as air may enter the fluid extraction unit  16  at the upstream end  26  thereof. At this point, the gas may become identifiable as a gas stream  42 , designated by multiple arrows in  FIG. 4 . The gas stream  42  may first flow into the longitudinal segment  36  of the passageway  30 . A swirl device  46  may be positioned near the upstream end  26  of the unit  16 . The swirl device  46  may be of a type described in U.S. Pat. No. 6,331,195 issued to Faust et al. which patent is incorporated herein by reference. However, many different swirl devices may be suitable for application in the present invention and may be positioned in differing locations. As the gas stream  42  passes the swirl device  46 , a rotational motion may be imparted to the gas stream  42 . Condensate which may be present in the gas stream  42  may be in the form of droplets  48 . These droplets  48  may be driven to an inner surface  50  of the longitudinal segment  36  of the passageway  30 . Upon reaching the inner surface  50 , the droplets may coalesce into a first fluid steam  51  which may flow out through the annular gap  52  between the first collector stage  32  and the duct  41  of the unit  16 . The first fluid stream  51  may flow into a first fluid collector  54 . From the first fluid collector  54 , the first fluid stream  51  may flow through a first exit port  56  and into conventional discharge tubing  57 , shown in  FIGS. 1 through 3 . As shown in  FIGS. 1 through 3 , the discharge tubing  57  may convey the first fluid stream  51  to other locations in the aircraft to provide additional evaporative cooling. 
     A major portion of the fluid in the gas stream  42  may be removed in the first fluid collection stage  32 . But, some droplets, designated  48   a  in  FIG. 4 , may continue traveling with an overall longitudinal trajectory through the passageway  30 . In particular, droplets which are furthest from the inner surface  50  of the passageway  30  may continue traveling in the gas stream  42  without coalescing onto the inner surface  50  of the passageway  30 . In  FIG. 4 , these uncoalseced droplets  48 a are shown entering the deflection segment  38  of the passageway  30 . 
     The gas stream  42  may be deflected from an overall longitudinal trajectory when it enters the deflection segment  38 . The droplets  48   a  may be denser than the gas stream  42 . Consequently, the droplets  48   a  may maintain their overall longitudinal trajectory, even though the gas stream  42  may not. This may cause the droplets  48   a  to impinge on the inner surface  50  of the passageway  30  within the deflection segment  38 . As the droplets  48   a  impinge on the inner surface  50 , the droplets may coalesce into a second fluid stream  58 . The second fluid stream  58  may flow along the inner surface  50  in a downstream direction. 
     In a non-limiting example, the constraining passageway  30  may be the cylindrical duct  41  which may have a diameter of about 2 inches to about 6 inches. The deflection segment  38  of the passageway  30  may produce a change in trajectory of the gas stream  42  of about 30° to 120° and the deflection segment  38  may comprise the bend  40  with a bend angle A of about 30° to about 120°. 
     A discontinuity or gap  62  may be located between the constraining passageway  30  and the transfer duct  20  at the downstream end  27  of the fluid extraction unit  16 . The gap  62  may be surrounded by a second fluid collector  68 . Adjacent the gap  62 , a bell-shaped lip  64  may be formed at an outlet end of the passageway  30 . The second fluid stream  58  may travel along the inner surface  50  of the passageway  30  and around the lip  64 . The second fluid stream  58  may then flow into the second fluid collector  68 , through second exit ports  70  and into the discharge tubing  57 , shown in  FIGS. 1 through 3 . 
     The second exit ports  70  may be canted downwardly with respect to a “level-flight” orientation of the longitudinal segment  36  of the fluid extraction unit  16  as illustrated in  FIG. 1 . In other words, when the longitudinal segment  36  of the unit  16  is perpendicular to gravitational force, the second fluid stream  58  may flow under the force of gravity through the second exit ports  70 . In a non-limiting example, the downward canting of the second exit ports  70  may be at an angle of between about 20° and 90°. 
     A plurality of the second exit ports  70  may be distributed around a circumference of the second fluid collector  58 . The usefulness of this arrangement may be understood by referring to  FIG. 5 .  FIG. 5  illustrates the ECS  10  in an orientation that may be associated with a vertically-climbing, high performance aircraft. It can be seen that at least one of the second ports  70  may be oriented to accommodate gravitationally induced flow of fluid therefrom. In particular, in  FIG. 5 , a port  70   a  may permit such fluid flow. It may readily be seen that irrespective of the orientation of the ECS  10  with respect to gravity, at least one of the second exit ports  70  may be positioned to permit gravitationally induced fluid flow therethrough. 
     It can therefore be seen that a useful aspect of the present invention is that each of the fluid collectors  54  and  68  may be positioned in different planes. Consequently, irrespective of orientation of the aircraft, there may always be a “low side” of at least one of the collectors into which fluid may readily flow. This desirable opportunity for fluid flow is an inherent product of a shape of the fluid extraction unit  16 , in particular, the bend  40  thereof. There may be no need to add additional moving parts or added weight to the fluid extraction unit  16  in order for it to operate successfully in non-level flight of high-performance aircraft. 
     After the gas stream  42  enters the transfer duct  20  it may be substantially free of condensate. The gas stream  42  may have between about 83% and about 96% of its initial water content removed at this stage of its traverse through the ECS  10 . This is noteworthy because this water removal rate is consistent with that which is normally found in non-aircraft, multiple-stage fluid extraction units which may be constructed with wide spacing between their successive extraction stages. In prior-art aircraft ECS water extraction units, water extraction rates of only about 65% and 72% may be typical. 
     In the present invention, this desirable extraction efficiency of about 83% to about 96% may be developed in a compact configuration in which the upstream end  26  and the downstream end  27  of the fluid extraction unit  16  may be close enough together so that unit  16  may fit within the space envelope L, which envelope may be, as a non-limiting example, only about 15 to about 30 inches. This compact size of the fluid extraction unit  16  may be a desirable feature of the present invention. 
     An additional advantage of the present invention is its ability to provide high fluid extraction efficiencies while producing only minor pressure drops in the gas stream  42  passing through the ECS  10 . In the prior-art, ECS fluid extraction units were constructed as single stage extractors. In order to provide improved efficiency, these prior-art single stage extractors were constructed with swirl devices that produced high pressure drops in a passing gas stream. An inherent feature of swirl devices is that, as their effectiveness increases, their associated pressure drop increases. In the fluid extraction unit  16  of the present invention, the swirl device  46  may be constructed to produce a relatively low pressure drop in the gas stream  42 . Reduced effectiveness of the swirl device  46  may be offset by the unique extraction capability of the present invention. 
     By way of non-limiting example, the fluid extraction unit  16  of the present invention may produce an overall pressure drop of only about 1 to about 2 psid when the gas stream  42  is introduced to the unit  16  at an inlet pressure of about 35 to about 100 psia. In other words, there may be an overall pressure drop of only about 2% to about 4% of the inlet pressure. As stated above, this low pressure drop is attainable even though the fluid extraction unit  16  may provide an extraction efficiency of about 83% to about 96%. Such a desirably low pressure drop associated with such a desirably high efficiency has heretofore only been achieved in multiple-stage fluid extraction units with widely spaced collection stages, i.e. spacing in excess of about 60 inches. 
     In designing an aircraft ECS, it is desirable to maintain a small size for any component. The fluid extraction unit  16  may achieve this design goal by providing high extraction efficiency with low pressure drop in the space envelope L that may be as short as about 15 to about 30 inches. 
     The present invention can also be understood to relate to a novel method for extracting fluid from a gas stream in an aircraft ECS. This inventive method designated by the numeral  100  is illustrated in  FIG. 6 . The method may comprise a step  102  of injecting gas into a constraining passageway to produce a gas stream. In a subsequent step  104 , a swirl may be imparted to the gas stream to radially propel fluid droplets to an inner surface of the constraining passageway to coalesce the droplets into a fluid stream. In a step  106 , the fluid stream may be collected from the inner surface of the constraining passageway through first openings in the passageway. In a subsequent step  108 , the gas stream may be deflected from an overall longitudinal trajectory so that remaining fluid droplets coalesce onto the inner surface of the constraining passageway. In a step  110  a fluid stream formed from the droplets coalesced in step  108  may be collected through an outlet end of the passageway and thus removed from the gas stream. 
     In a non-limiting, exemplary operation, the present invention may be practiced by injecting the gas into the constraining passageway  30  at a pressure of about 35 psia to about 100 psia. The gas stream  42  may have a velocity of about 35 ft/sec to about 80 ft/sec. 
     It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.