Abstract:
An environmental control system (ECS) for an aircraft may include a mixing diffuser configured to admit a stream of cold air and a stream of hot air and a reheater-condenser fluidly coupled with an output end of the mixing diffuser. The mixing diffuser may include a diffuser cone with a plurality of holes configured to allow passage of hot air into the stream of cold air so that the cold air and the hot air are combined to produce a mixed airstream. The reheater-condenser may include mixing tabs configured to produce further mixing of the mixed airstream.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to gas mixing and, more particularly, to mixing a hot stream of air with a cold stream of air to attain a single thermally mixed airstream with a uniform temperature. 
         [0002]    In a typical aircraft employing an environmental control system (ECS), a cold air stream may be mixed with a hot air stream to produce a temperate air stream that may be introduced into a cabin of the aircraft. Many aircraft employ two or more air conditioning packs which may collectively provide conditioned air to the cabin. Accurate measurement of temperature of individual outputs of the packs may be required so that the packs may be operated in an efficient and well-coordinated manner. 
         [0003]    At an output of each pack, cold air may be mixed with hot air to achieve a desired output air temperature. In many instances, thermal stratification of the cold and hot air may occur during mixing. Determination of average temperature of output air may be difficult when the output air is thermally stratified. A failure to accurately determine output air temperature may result in a failure to achieve well coordinated operation of the multiple packs. 
         [0004]    As can be seen, there is a need for a system of mixing cold air and hot air in an ECS to produce a mixed air output with a uniform average temperature that may be accurately measured. More particularly there is a need for such a system that may produce output air that is free of thermal stratification. 
       SUMMARY OF THE INVENTION 
       [0005]    In one aspect of the present invention, an environmental control system (ECS) for an aircraft may comprise: a mixing diffuser configured to admit a stream of cold air and a stream of hot air; and a reheater-condenser fluidly coupled with an output end of the mixing diffuser, wherein the mixing diffuser includes a diffuser cone with a plurality of holes configured to allow passage of hot air into the stream of cold air so that the cold air and the hot air are combined to produce a mixed airstream, and wherein the reheater-condenser includes mixing tabs configured produce further mixing of the mixed air stream. 
         [0006]    In another aspect of the present invention, an environmental control system (ECS) for an aircraft may comprise a mixing diffuser configured to admit a stream of cold air and a stream of hot air, the mixing diffuser including a diffuser cone with a plurality of holes configured to allow passage of hot air into the stream of cold air so that the cold air and the hot air are combined to produce a mixed airstream. 
         [0007]    In still another aspect of the present invention, an environmental control system (ECS) for an aircraft may comprise a reheater-condenser fluidly coupled with an output end of a mixing diffuser to receive a mixed air stream from said output end, the reheater-condenser including mixing tabs configured to produce further mixing of a mixed air stream emerging from the mixing diffuser. 
         [0008]    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 
         [0009]      FIG. 1  is a perspective view of a portion of an environmental control system in accordance with an exemplary embodiment of the invention; 
           [0010]      FIG. 2  is a cut-away elevation view of a mixing diffuser in accordance with an exemplary embodiment of the invention; 
           [0011]      FIG. 3  is a cut-away perspective view of a reheater-condenser in accordance with an exemplary embodiment of the invention; 
           [0012]      FIG. 4  is a schematic side view of the reheater-condenser of  FIG. 3  in accordance with an exemplary embodiment of the invention; and 
           [0013]      FIG. 5  is a schematic end view of the reheater-condenser of  FIG. 3  in accordance with an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    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. 
         [0015]    Various inventive features are described below that can each be used independently of one another or in combination with other features. 
         [0016]    The present invention generally provides an air mixing system that employs mixing chambers with internal devices that promote mixing of streams of air that are introduced into the mixing chambers. More particularly, the present invention provides for an aircraft environmental control system (ECS) in which hot and cold airstreams may be mixed to produce an output air stream free of thermal stratification. 
         [0017]    Turning now to the description,  FIG. 1  illustrates a portion of an environmental control system (ECS)  100  of an aircraft (not shown). More particularly,  FIG. 1  shows a portion of a pack  102  of the ECS  100 . The pack  102  may include an air cycle machine  104 , an expansion turbine  106 , a mixing diffuser  108 , a reheater-condenser  110  and a pack discharge sensor (PDS)  112 . In operation, a flow of hot air  114  may enter the mixing diffuser  108  from a compressor discharge duct  116 . A flow of cold air  118  may enter the mixing diffuser  108  from the expansion turbine  106 . A flow of thermally mixed airstream  120  may emerge from the mixing diffuser  108  and pass through the reheater-condenser  110  and the PDS  112  as it progresses to an aircraft cabin (not shown). 
         [0018]    Referring now to  FIG. 2 , a cut-away view of the mixing diffuser  108  shows that an outer shell  122  may surround a portion of a diffusing cone  124 . The cold air  114  may enter the diffusing cone  124  at an inlet end  126  and the mixed airstream  120  may emerge from an output end  127  of the mixing diffuser  108 . The hot air  118  may enter the shell  122  at an inlet  128 . The hot air  118  may pass through holes  130  formed in the diffusing cone  124 . The holes  130  may be arranged in a first set positioned on a centerline  132  and a second set positioned on a centerline  134 . The centerlines  132  and  134  may be oriented on a plane that is orthogonal to an axis  135  of the diffusing cone  124 . Flow of the hot air  118  may be blocked by a flange  136  of the diffuser cone  124  and an annular end cap  138  of the shell  122  thus assuring that the hot air  118  may flow only through the holes  130 . 
         [0019]    Locations of the holes  130  may be selected so that the presence of the holes  130  in the diffuser cone  124  have only a minimal impact on the diffusing capability of the diffuser cone  124 . Hot air  118  entering the shell  122  may produce a relatively high air pressure near the annular end cap  138 . Consequently, high-pressure hot air  118  may also be present at the holes  130 , which may be located only short distances from the annular end cap  138 . When high-pressure hot air  118  is present at the holes  130 , the diffuser cone  124  may behave as if its diffusing capability is virtually undiminished by the presence of the holes  130 . 
         [0020]    In an exemplary embodiment, all of the holes may have the same diameter. A distance between the centerline  132  and the annular end cap  138  may be no greater than a diameter of one of the holes  130 . Also, a distance between the centerlines  132  and  134  may be no greater than a diameter of one of the holes  130 . Such a hole-spacing arrangement may result in each hole  130  being close to the annular end cap  138  while being surrounded with only enough of the material of the diffuser cone  124  so that structural integrity of the diffusing cone  124  is preserved. In the exemplary embodiment described above the hole-surrounding material may be at least as wide as a radius of one of the holes  130 . 
         [0021]    As described above, the hot air  118  may experience a pressure increase near the annular end cap  138 . This increased pressure may develop around the entire circumference of the diffuser cone  124 . Consequently, the hot air  118  may enter all of the holes  130  at substantially equal flow rates. Thus there may be a low likelihood that the mixed airstream  120  will experience thermal stratification. 
         [0022]    Referring now to  FIGS. 3 ,  4  and  5 , there are shown various aspects of the reheater-condenser  110  which contribute to further mixing of the mixed airstream  120 . In an exemplary embodiment, the mixed airstream  120  may flow through two heat exchangers  140  and through a by-pass gap  142  between the heat exchangers  140 . Mixing tabs  144  and  146  may be positioned at an output end  148  of the by-pass gap  142 . As the mixed airstream  120  passes over the mixing tabs  144  and  146 , the mixed airstream  120  may be further mixed and transformed into airstream  150 . 
         [0023]    Referring more particularly to  FIGS. 4 and 5 , it may be seen that the tabs  144  and  146  may be oriented at an angle A relative to a plane that is parallel to an axis  152  of the by-pass gap. In an exemplary embodiment, the angle A may be about 40° to about 60°. Additionally, the tabs  144  and  146  may each have a width that is only about ⅙ of the width W of the by-pass gap  142 . Also, the tabs  144  and  146  may have a height that is about ⅓ of a height H of the by-pass gap  142 . Each of these dimensional features of the tabs  144  and  146  may, individually and/or collectively, provide that the tabs  144  and  146  may produce only minimal pressure drop in the mixed airstream  120  as the mixed airstream  120  passes over the tabs  144  and  146 . 
         [0024]    It may be noted in  FIG. 5 , that the tabs  144  and  146  may be laterally offset from one another. When considering the view of  FIG. 5 , the tab  144  may be positioned to the right of the tab  146  by a distance of about the width of the tab  146 . The offset arrangement of the tabs  144  and  146  may produce an advantageous swirling effect on the mixed airstream  120  as it passes over the tabs  144  and  146 . As shown in  FIG. 5 , clockwise swirling may be produced. The tabs  144  and  146  may be offset from one another to produce either clockwise or counterclockwise swirling. In an exemplary embodiment, it may be beneficial to provide offsetting that produces swirling in the same direction that the expansion turbine  106  of  FIG. 1  produces swirling. In that construct, swirling produced by the tabs  144  and  146  may reinforce swirling produced by the expansion turbine  106 . Swirling of the mixed airstream  120  may further reduce the likelihood that thermal stratification will be present in the airstream  150 . 
         [0025]    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.