Abstract:
An apparatus for providing air at a given temperature to an air separation module has a first path for delivering air having a temperature to the air separation module, a second path for delivering air having a temperature to the air separation module, a heat exchanger through which the second path flows, the heat exchanger modulating the temperature of the air from the given temperature to a second temperature, and a valve for controlling an amount of air flowing through the second path whereby if the air delivered to the air separation module by the first path and the second path is below a temperature desired to run the air separation module essentially all of the air may flow through the first path.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application 61/203,081, which was filed Dec. 18, 2008. 
     
    
     BACKGROUND 
       [0002]    Aircraft may use on board inert gas generating system (“OBIGGS”) to minimize fuel tank accidents. Potentially dangerous fuel and air mixtures (such mixtures known as “ullage”) in the air space in fuel tanks are diluted and minimized by reducing the oxygen content of ullage. The OBIGGS accomplishes this by adding nitrogen enriched air (NEA) to the ullage. The OBIGGS separates oxygen from ambient air and pumps relatively inert, oxygen impoverished NEA to the fuel tanks. 
         [0003]    The OBBIGS may produce NEA by using permeable membranes in an air separation module (“ASM”). The ASM typically has a bundle of hollow, permeable fiber members packaged in a cylindrical shell with an inlet, an outlet at the ends of the shell and a side vent port. Pressurized air enters the ASM inlet and, as it passes through the hollow fibers, oxygen is separated from the air stream due to diffusion through the fiber walls. Oxygen exits through the side vent port and can be captured, but often the oxygen is considered a waste gas and is exhausted overboard. 
         [0004]    The remaining air is deemed to be nitrogen enriched because, due to normal levels of gas in the air, if all the oxygen is removed from air, about 97% of the remaining air is nitrogen. Normal concentrations of oxygen in the NEA are usually above zero. 
         [0005]    The remaining NEA flows out of the ASM via the outlet port and is distributed to the ullage space of the fuel tank or tanks for the purpose of inerting the fuel tanks and reducing a possibility of flammability. The ASM operates most efficiently, in terms of permeability of oxygen through the tubes at an elevated temperature, usually between 180° and 200° F. 
         [0006]    Pressurized air used for NEA generation will usually originate from either an engine bleed or from another pressure source within the aircraft. With an engine bleed system, compressed hot air is usually cooled by a heat exchanger to an optimal temperature before being vented to an ASM. 
       SUMMARY 
       [0007]    According to a non-limiting embodiment of the invention, an apparatus for providing air at a given temperature to an air separation module has a first path for delivering air having a temperature to the air separation module, a second path for delivering air having a temperature to the air separation module, a heat exchanger through which the second path flows, the heat exchanger modulating the temperature of the air from the given temperature to a second temperature, and a valve for controlling an amount of air flowing through the second path whereby if the air delivered to the air separation module by the first path and the second path is below a temperature desired to run the air separation module essentially all of the air may flow through the first path. 
         [0008]    According to another non-limiting embodiment shown herein, a method for providing air at a given temperature to an air separation module that operates at a desired temperature range and encounters cooler temperatures includes providing a first flow of air to an air separation module, selectively providing a second flow of air to a heat exchanger, and mixing the first flow of air with the second flow of air if mixing delivers the air at or within the desired temperature range. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    These and other features of the present embodiment may be shown and best understood from the following specification and drawings. 
           [0010]      FIG. 1A  is a first schematic, prior art depiction of an OBIGGS delivering air to an ASM. 
           [0011]      FIG. 1B  is a second schematic, prior art depiction of an OBIGGS delivering air to an ASM. 
           [0012]      FIG. 2  is a schematic view of a non-limiting embodiment of an OBIGGS delivering air to an ASM. 
           [0013]      FIG. 3  is a schematic view of a non-limiting embodiment of an OBIGGS delivering air to an ASM. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring now to  FIG. 1A , a prior art depiction of an OBIGGS  10  delivering compressed air to an ASM  15  is shown. A compressed air source  20 , such as an aircraft engine (not shown), delivers compressed air to the ASM  15  through ducting  60  and two separate paths. The first path  25  delivers a first portion of the heated, compressed air, without any gating thereof, through a heat exchanger  30 . The heat exchanger takes the heated compressed air and cools it with air from ambient or another cooled air source  35  within an aircraft (not shown). The second path  40  delivers a second portion of the heated, compressed air through a valve  45  to be mixed with air in the first path  25  downstream of the air provided through the heat exchanger  30 . 
         [0015]    Typically, an ASM  15  requires air at or about 180-200° F. to operate efficiently. Air from the compressed air source  20  is typically supplied at temperatures ranging from 300-500° F. A sensor  50  determines the temperature of the air entering the ASM and a controller  55  receives feedback from the sensor  50  and controls a position of the valve  45  so that a mixture of different temperature air from the first path  25  and the second path  40  is provided to the ASM at a proper temperature. 
         [0016]    Referring now to  FIG. 1B , a second prior art system of an OBIGGS  65  delivering compressed air to an ASM  115  is shown. According to this system, all air intended for the ASM  115  is sent through a heat exchanger  130  that cools the air intended for ASM. This system modulates the temperature of the air intended for the ASM by controlling an amount of air provided to the heat exchanger  135  by valve  145 . A sensor  150  determines the temperature of the air entering the ASM  115  and a controller  155  receives feedback from the sensor  150  and controls a position of the valve  145  ducting cooling air to the heat exchanger  130  so that the air intended for the ASM  115  is cooled to the proper temperature range to run the ASM  115  efficiently. 
         [0017]    There are problems with the prior art systems shown in  FIGS. 1A and 1B . There are large heat losses during cruise in the ducting  60 ,  160  and the paths  40 ,  140 ,  25 ,  125  between the compressed air source  20 , 120  and the heat exchanger  30 ,  130  and the ASM  15 ,  115 . Temperatures at 30,000 feet, for instance may be −30° F. or lower. Such low temperatures can cause great heat losses in the system. These heat losses can cause the maximum temperature of air delivered to the ASM to be below the optimal temperature range to run the ASM efficiently. Further complicating the issue of heat loss in the ducts, aircraft engines (not shown) require less power at altitude and engine bleed air temperature may at the lower end of the bleed air temperature range. 
         [0018]    For instance, in  FIG. 1A , air passing through the heat exchanger  30  is not modulated so that the very cool air at altitude passing through the heat exchanger  30  and the cool air affecting the ducting  60  and paths  25 ,  45  may combine to lower the temperature below 180° F. even if the valve  45  allowing air at higher temperature to pass through the second path  40  is fully open. Compressed air in the first path  25  passing through the heat exchanger  30  may lower the temperature too much to allow the amount of higher temperature compressed air passing through the valve  45  in the second path  40  to raise the air temperature enough to heat the air between 180-200° F. 
         [0019]    Similarly, in  FIG. 1B , the higher temperature compressed air always passes through the heat exchanger  130 . Even though cooling air from cooling air source  135  passing through the heat exchanger  130  can be modulated, temperature losses in the ducting  160  and the paths  125 ,  140  and a radiator effect of the heat exchanger  135  may cause the temperature of the air delivered to the ASM to be below 180° F. This may be true even if the valve  145  allowing cooler air from the cooling air source  135  to pass through the heat exchanger is fully closed. 
         [0020]    Referring to  FIG. 2 , a non-limiting embodiment of an OBIGGS  70  delivering compressed air to an ASM  215  is shown. In this embodiment, a compressed air source  220  communicates compressed air having an elevated temperature via duct  260  and a first path  240  in which the compressed air passes directly to the ASM  215 . The compressed air source also communicates compressed air having an elevated temperature via a second path  225  through a heat exchanger  230 . The second path  225  through the heat exchanger is modulated by a valve  245  located downstream of the heat exchanger  230 . A sensor  250  determines the temperature of the air entering the ASM  215  and a controller  255  receives feedback from the sensor and controls a position of the valve  245  so that a mixture of different temperature air from the first path and the second path is provided to the ASM at a proper temperature. 
         [0021]    Referring still to  FIG. 2 , if the valve  245  controlling cooling air flow through the heat exchanger  230  is shut, the higher temperature compressed air travels through the first path  240  to the ASM directly. In other words, contrary to the prior art, the output of the higher temperature compressed air may be delivered directly to the ASM without passing through a heat exchanger  230  first (see also  FIGS. 1A and 1B ) so that heat loss in the ducting  260 , the second path  225  and the heat exchanger  230  does not drop the temperature of air entering the ASM  215  below the required temperatures. Cooling may not be necessary if heating losses in the compressed air passing through the heat exchanger  230  and the paths  225 ,  240  and ducting  260  is too great. 
         [0022]    Referring to  FIG. 3 , a further non-limiting embodiment of an OBIGGS  70  delivering compressed air to an ASM  315  is shown. In this embodiment, a compressed air source  320  communicates compressed air having an elevated temperature via duct  360  and a first path  340  in which the compressed air passes directly to the ASM  315 . The compressed air source also communicates compressed air having an elevated temperature via a second path  325  through a heat exchanger  330 . The ratio of air passing through the first path  340  and the second path  325  through the heat exchanger is modulated by a valve  345  that is located upstream of the heat exchanger  330 . A sensor  350  determines the temperature of the air entering the ASM  315  and a controller  355  receives feedback from the sensor  350  and controls a position of the valve  345  so that a mixture of different temperature air from the first path and the second path is provided to the ASM at a proper temperature. 
         [0023]    Referring still to  FIG. 3 , if the valve  345  controlling cooling air flow through the heat exchanger  330  is shut, the higher temperature compressed air travels through the first path  340  to the ASM directly. In other words, contrary to the prior art, the output of the higher temperature compressed air may be delivered directly to the ASM without passing through a heat exchanger  330  first (see also  FIGS. 1A and 1B ) so that heat loss in the ducting  360 , the second path  325  and the heat exchanger  330  does not drop the temperature of air entering the ASM  315  below the required temperatures. Cooling may not be necessary or desirable if heating losses in the compressed air passing through the heat exchanger  330  and the paths  325 ,  340  and ducting  360  is too great. 
         [0024]    The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.