Abstract:
A regenerative heat exchanger includes an inlet and an outlet in communication with the inlet. The heat exchanger is configured to operate in two modes. A first mode uses only an ambient flow to cool a hot flow and a second mode uses both the ambient flow and a regenerative flow to cool the hot flow.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention generally relates to heat exchangers and, more particularly, to apparatus and methods of using regenerative and ambient flows into heat exchangers. 
         [0002]    Many environmental control systems (ECS) utilize “regenerative” flow to cool the cycle operating fluid. Regenerative flow is conditioned air or liquid flow that has been cooled, and then used to perform high-quality (i.e., low temperature) cooling of system heat loads. After the flow has performed this cooling, it is warm, but still cooler than the fluid temperature at the hot portions of the cycle. Because of this, the flow can be used to “self-cool” the cycle hot fluid. After it is thus used, it is then very hot and no longer useful for cooling, and is typically rejected to ambient as waste heat. 
         [0003]    To perform this regenerative cooling, heat exchangers are needed. These heat exchangers are often used to supplement other heat exchangers that directly use external ambient fluid (e.g., air, water) to cool the working cycle fluid. By supplementing the main, ambient fluid heat exchangers with the regenerative heater exchangers, it is possible to reduce the size of the main ambient heat exchangers, and the amount of ambient fluid that is used. This offers benefits in terms of system weight and outside power or aerodynamic drag. 
         [0004]    At some design conditions, it is common for the regenerative flow to be limited due to the scarcity of working fluid (for example, during low engine settings for cycles using bleed air from jet engines.) At these design conditions, the benefit from the regenerative heat exchangers will be significantly reduced or completely eliminated, which reduces the sizing benefit that can be granted to the other main heat exchangers. 
         [0005]    As can be seen, there is a need for improved apparatus and methods for regenerative heat exchange. 
       SUMMARY OF THE INVENTION 
       [0006]    In one aspect of the present invention, a heat exchanger comprises an inlet; and an outlet in communication with the inlet, wherein the heat exchanger is configured to operate in two modes: wherein a first mode uses only an ambient flow to cool a hot flow; and wherein a second mode uses both the ambient flow and a regenerative flow to cool the hot flow. 
         [0007]    In another aspect of the present invention, a cross flow heat exchanger comprises an inlet; an outlet in communication with the inlet; wherein the heat exchanger is configured to enable heat exchange between a hot flow and a mixture of ambient flow and regenerative flow; and wherein the heat exchanger is configured to vary the amount of regenerative flow from zero flow to full flow. 
         [0008]    In yet another aspect of the present invention, an environmental control system comprises a regenerative heat exchanger configured to put an ambient flow in cross-flow communication with a hot flow; and wherein the regenerative heat exchanger is configured to provide varying mixtures of ambient flow and regenerative flow in heat exchange relationship with the hot flow. 
         [0009]    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 
         [0010]      FIG. 1  is a schematic view of an environmental control system according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a schematic view of a regenerative heat exchanger in a closed mode according to an embodiment of the present invention; 
           [0012]      FIG. 3  is a schematic view of a regenerative heat exchanger in an operating mode according to an embodiment of the present invention; 
           [0013]      FIG. 4  is a schematic view of a regenerative heat exchanger in another operating mode according to an embodiment of the present 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. However, any single inventive feature may not address any of the problems discussed above or may only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below. 
         [0016]    Generally, the present invention provides a simple means to use regenerative heat exchangers even during conditions with limited or no regenerative flow by making them dual-use regenerative/ambient heat exchangers. The present invention eliminates the need for multiple flow control devices (e.g., valves) and ducting to control both the regenerative flow and the ambient fluid flow, and thus removes undesirable pressure losses within the ambient fluid circuit that restricts flow. The present invention makes use of a single regenerative flow control device to effect the same control, without restriction of ambient flow during conditions when no regenerative flow is available. 
         [0017]    Moreover, the present invention can replace separate ambient-cooled and regeneratively-cooled heat exchangers with one or more heat exchangers placed in the ambient fluid circuit. When there is no regenerative flow, the full extent of the heat exchangers can be used to cool the working fluid with ambient air being forced through the circuit. 
         [0018]    When regenerative air is available, the regenerative air can be injected into the ambient fluid circuit. This injection can be done in a way to optimize the flow pattern so that the temperature and flow profile within the ambient fluid circuit matches the thermodynamic optimum cycle. Specifically, for cross-flow heat exchangers, an optimum distribution of cooling fluid places the colder fluid on the side nearest the hot fluid side outlet. 
         [0019]    Thus, for regenerative flows that are typically colder than the ambient fluid at the heat exchanger inlet, the regenerative flow will be injected to flow along the side of the ambient air circuit on the hot-fluid outlet side. For regenerative flows that are typically hotter than the ambient fluid, the regenerative flow would be injected to flow along the side of the ambient air circuit on the hot-fluid inlet side. This flow and temperature stratification within the ambient fluid circuit can effectively achieve the cooling performance of separate regenerative/ambient air circuits without introducing extra equipment or circuit obstructions. 
         [0020]      FIG. 1  is a schematic depiction of an exemplary environmental control system (ECS)  10  that can be used, for example, in vehicles such as aircraft. The ECS  10  can include a first regenerative heat exchanger  11  and/or a second regenerative heat exchanger  12  that is downstream of the first regenerative heat exchanger  11 . In embodiments, the first regenerative heat exchanger  11  can be a primary heat exchanger. 
         [0021]    In embodiments, the ECS  10  may further include a reheater  21  downstream of the second regenerative heat exchanger  12 , a condenser  22  downstream of the heat exchanger  12 , and a water extractor  23  downstream of the condenser  22 . An air cycle machine  24  may be downstream of the primary heat exchanger  11  and the reheater  21 . However, the present invention contemplates that one or more regenerative heat exchangers of the present invention can be used in other configurations of an ECS. 
         [0022]    In  FIG. 2 , according to various embodiments, the regenerative heat exchangers  11  and/or  12  may be of a cross-flow type. Accordingly, and only for purposes of illustrating both heat exchangers, the heat exchanger  11  may receive one flow  15 , such as ambient air flow, at an inlet  19  of the heat exchanger  11  and exit at an outlet  20  thereof. The heat exchanger  11  may also receive a second flow  16 , such as a hot flow, wherein the first and second flows  15 ,  16  pass through the heat exchanger  11  in a generally perpendicular orientation to one another. 
         [0023]    In embodiments, the ambient flow  15  may originate from a ram scoop or fan circuit, as an example. The ambient flow  15  may exit the heat exchanger  11  and flow directly overboard or be used to ventilate other areas of the aircraft, as an example. 
         [0024]    In embodiments, the hot flow  16  may originate from an aircraft bleed system or ECS air cycle machine, as an example. The hot flow  16  may exit the heat exchanger and flow directly into an ECS air cycle machine or water separate equipment, as an example. 
         [0025]    In embodiments, the regenerative heat exchanger  11  may further include a flow control device  18 , such as a valve, that can adjust the cross sectional area or amount of the hot flow  16  that is cooled by a regenerative flow  14  which may originate from a load such as the cabin of an aircraft and/or electronics of an aircraft. 
         [0026]    The cooled amount of the hot flow  16  can be anywhere from zero to a majority thereof. This can be achieved by adjusting the control device  18  which, in turn, can adjust a size of an opening  18   a,  for the regenerative flow,  14  into the heat exchanger  11 . The control device  18  can also adjust a direction of the regenerative flow  14  so that a cross sectional area or amount of the hot flow  16  that is cooled by the regenerative flow  14  can be adjusted. In embodiments, the control device  18  may be manually controlled or automatically controlled. 
         [0027]    In  FIG. 2 , the control device  18  is depicted in a closed position or mode. In other words, the opening  18   a  is completely closed and the heat exchanger  11  is operating in a closed mode. In such instance, absolutely no or essentially no regenerative flow  14  is entering the heat exchanger  11 , and only the ambient flow  15  is cooling the hot flow  16 . Thus, a cross-sectional area  17  of the hot flow  16  is being entirely cooled by the ambient flow  15 . 
         [0028]    In embodiments, the ECS  10  may be configured so that the regenerative flow  14  may be hotter than the ambient flow  15 . In such instance, the ECS  10  may be configured so that the hot flow  16  may flow in a first direction  16   a.  On the other hand, the ECS  10  may be configured so that the regenerative flow  14  may be colder than the ambient flow  15 . In such instance, the ECS  10  may be configured so that the hot flow  16  may flow in a second direction  16   b.    
         [0029]    In  FIG. 3 , the control device is depicted in a partially open position or mode. In other words, the opening  18   a  is partially open and the heat exchanger  11  is operating in a partially open mode. In that instance, a full regenerative flow  14  is entering the heat exchanger  11 , but less than a majority of the cross sectional area of the hot flow  16  is being cooled. Accordingly, in the partially open mode, a mixture of ambient flow  15  and regenerative flow  14  is cooling the hot flow  16 . Thus, a first cross sectional area  17   a  of the hot flow  16  is being all or mostly cooled by the ambient flow  15 . At the same time, a second cross sectional area  17   b  of the hot flow is being all or mostly cooled by the regenerative flow  14 . In an embodiment, the first cross sectional area  17   a  is larger than the second cross sectional area  17   b.    
         [0030]    Still referring to  FIG. 3 , in embodiments and as described above, the regenerative flow  14  may be hotter than the ambient flow  15 . In such instance, the ECS  10  may be configured so that the hot flow  16  may flow in first direction  16   a,  and the regenerative flow  14  may pass through and adjacent a side of the heat exchanger  11  that is adjacent an outflow of the hot flow  16 . On the other hand, when the regenerative flow  14  may be colder than the ambient flow  15 , the ECS  10  may be configured so that the hot flow  16  may flow in a second direction  16   b,  and the regenerative flow  14  may pass through and adjacent a side of the heat exchanger  11  that is adjacent an inflow of the hot flow  16 . 
         [0031]    In  FIG. 4 , the control device is depicted in a fully open position or mode. In other words, the opening  18   a  is fully open and the heat exchanger  11  is operating in a fully open mode. In that instance, a full flow of the regenerative flow  14  is entering the heat exchanger  11 , as in the partially open mode. Accordingly, in the fully open mode, a mixture of ambient flow  15  and regenerative flow  14  is cooling the hot flow  16 . However, in contrast to the partially open mode, the regenerative flow  14  is cooling a majority of the cross-sectional area of the hot flow  16 . 
         [0032]    Thus, a first cross sectional area  17   a  of the hot flow  16  is being all or mostly cooled by the ambient flow  15 . At the same time, a second cross sectional area  17   b  of the hot flow is being all or mostly cooled by the regenerative flow  14 . In an embodiment, the second cross sectional area  17   b  is larger than the first cross sectional area  17   a.    
         [0033]    Still referring to  FIG. 4 , in embodiments as described above, the regenerative flow  14  may be hotter than the ambient flow  15 . In such instance, the ECS  10  may be configured so that the hot flow  16  may flow in direction  16   a,  and the regenerative flow  14  may pass through and at a side of the heat exchanger  11  adjacent an outflow of the hot flow  16 . On the other hand, when the regenerative flow  14  may be colder than the ambient flow  15 , the ECS  10  may be configured so that the hot flow  16  may flow in a direction  16   b,  and the regenerative flow  14  may pass through and adjacent a side of the heat exchanger  11  that is adjacent an inflow of the hot flow  16 . 
         [0034]    As can be appreciated, as the control device  18  moves from a closed position to a fully open position, the cross sectional area of the hot flow being cooled by the regenerative flow  14  increases. Similarly, as the control device  18  moves from a fully open position to a closed position, the cross sectional area of the hot flow being cooled by the regenerative flow  14  decreases. 
         [0035]    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.