Patent Publication Number: US-6990829-B2

Title: Air cycle HVAC system having secondary air stream

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to air cooling systems, and more particularly relates to open loop air cycle systems having a secondary air stream. 
     BACKGROUND OF THE INVENTION 
     An air cycle HVAC system typically employs a compressor, a heat exchanger, and an expander in an open loop system to generate cold air. These air cooling systems are currently commonly found in aircrafts. The compressor receives ambient air and pressurizes the same causing the air to become hot. The heat exchanger dissipates some of the heat in the air exiting the compressor. The air then flows through the expander which removes work and brings the air back to atmospheric pressure, resulting in cold air which can be supplied to the passenger cabin. 
     In such an air cycle system, there may be times when additional air is needed to increase the total air flow of the system. Generally, prior solutions have been to provide a secondary air flow of ambient air that is immediately mixed with the cold air from the air cycle to meet the demands on the system. Unfortunately, the secondary flow of ambient air is relatively humid, and may condense on the interior of the cockpit, such as on the inside surface of the windows. Further, the two separate air streams will result in hot and cold stratification in the air distribution system. Accordingly, there exists a need to provide an air cycle system that can provide an increased total air flow of the system while preventing unwanted condensation and hot and cold stratification. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides an air cooling system for cooling ambient air. The system includes a compressor receiving ambient air, and a first heat exchanger receiving pressurized air from the compressor. An expander receives warm air from the first heat exchanger. A second heat exchanger receives cold air from the expander. The second heat exchanger also receives supplemental ambient air, and is structured to utilize the cold air to cool the supplemental air and provide mixed cool air. 
     According to more detailed aspects, the second heat exchanger generally includes a first plurality of passageways receiving the cold air and a second plurality of passageways receiving the supplemental ambient air. The first and second plurality of passageways are proximate each other to effectuate heat transfer. The second plurality of passageways preferably include corrugations or fins to provide turbulent flow to the supplemental ambient air. The second heat exchanger may further include a manifold receiving the cold air and distributing the cold air to the first plurality of passageways. The manifold is elongated and includes an inlet end, and tapers as the manifold extends away from the inlet. Stated another way, the volume of the manifold decreases in relation to the distance from the inlet for equal flow distribution. 
     The second heat exchanger preferably defines a discharge surface, and the cold air and supplemental ambient air exit the second heat exchanger proximate the discharge surface. The heat exchanger is preferably structured to promote mixing of the cold air with the supplemental ambient air. This also allows dehumidification of the supplemental ambient air and the moisture runs down the discharge surface, and more particularly the face of the fins in the second plurality of passageways. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a schematic depicting an air cooling system constructed in accordance with the teachings of the present invention; 
         FIG. 2  is perspective view of a heat exchanger forming a portion of the air cooling system depicted in  FIG. 1 ; and 
         FIG. 3  is a perspective view of a portion of the heat exchanger depicted in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to the figures,  FIG. 1  depicts a schematic of the air cycle defined by the air cooling system  20  constructed in accordance with the teachings of the present invention. The cooling system  20  has been constructed for use in an automotive vehicle, although other environments which require air cooling may also employ the present invention. The system  20  generally utilizes ambient air indicated by arrow  22 , which is typically taken from the exterior of the vehicle. However, it will be recognized by those skilled in the art that the ambient air  22  may also be replaced by recirculated air from within the vehicle, and hence as used herein ambient air is also intended to include recirculated air. 
     The ambient air  22  is routed to a compressor  26  as indicated by arrow  24 . The compressor pressurizes the ambient air  22 , and in turn heats the same. The pressurized air  28  is provided to a first heat exchanger  30  as indicated by the arrow in  FIG. 1 . The heat exchanger  30  dissipates some of the heat, and provides high pressure warm air  32  to the expander  34 . The compressor  26 , heat exchanger  30  and expander  34  are all of general construction as is well understood in the art. 
     Upon passing through the expander  34 , cold air  36  emerges and would normally be used by the system  20  within the passenger compartment of a vehicle. However, according to the present invention the cold air  36  is sent to a second heat exchanger  40 . The second heat exchanger  40  is of a novel construction as will be discussed in further detail below. Suffice it to say at this point that the heat exchanger  40  utilizes secondary or supplemental ambient air  38  in order to increase the total air flow of cooled dehumidified air  42  to the passenger cabin. The heat exchanger  40  is also structured to remove moisture  44  from the supplemental ambient air  38  as will be further discussed herein. 
     Turning now to  FIG. 2 , the second heat exchanger  40  has been depicted in perspective view. As previously indicated, the heat exchanger  40  receives cold air  36  from the expander  34  via a manifold  46  having an inlet  48 . The cold air  36  is typically dehumidified through the normal air cycle (i.e. via compressor  26 , heat exchanger  30  and expander  34 ). The heat exchanger  40  also receives supplemental ambient air  38  as indicated by the arrows. The additional ambient air  38  simply blows through a rear side face (not shown) of the heat exchanger  40 . 
     The heat exchanger  40  generally includes a first plurality of passageways  52  for receiving and distributing the cold air  36  received and the manifold  46 . Further, the heat exchanger  40  includes a second plurality of passageways  56  for receiving and distributing the supplemental ambient air  38 . The first plurality of passageways  52  are located proximate the second plurality of passageways  56  such that the cold air  36  is utilized to remove heat from the ambient air  38 . By way of this operation, two important objects are achieved. First, the ambient air  38  is cooled, to limit stratification of the air supply to the passenger cabin. Furthermore, humidity in the ambient air  38  is removed, thereby minimizing the potential for condensation within the passenger compartment, and especially on the windows of the vehicle. 
       FIG. 3  provides a more detailed view of the inner construction of the heat exchanger  40 . As shown, the manifold  46  is elongated and includes an inlet  48  at one end. The opposing end  50  of the manifold  46  is closed, and the manifold  46  tapers as it flows from the inlet end  48  to the opposing end  50 . Stated another way, the volume within the manifold  46  decreases as the manifold extends away from the inlet  48 . In this way, uniform distribution of the cold air  36  is provided. 
     The plurality of first passageways  52  are defined by a plurality of tubes  54 . The tubes  54  are shown as generally flat in shape, although they may comprise any shape depending upon the particular application. Each tube  54  has at least one exit opening  55  for directing the cold air  36 ′ ( FIG. 2 ) outward from a discharge face  60  defined on one side of the heat exchanger  40 . Turning back to  FIG. 2 , the second plurality of passageways  56  are located in between each of the tubes  54  defining the first plurality of passageways. The second plurality of passageways  56  are generally comprised by a corrugated or finned surface  58 . The corrugations or fins  58  define a torturous pathway which imparts turbulent flow to the supplemental ambient air  38  flowing through the heat exchanger  40  for improved heat transfer. 
     As is known in the art, by positioning the first plurality of passageways  52  proximate the second plurality of passageways  56 , the relatively warm and humid supplemental ambient air  38  is cooled by the cold air  36  flowing through the tubes  54 . As indicated by arrow  36 ′, the cold air exits the outlets  55  of tubes  54  proximate the partially cooled air  38 ′ exiting the fins  58 . The heat exchanger  40  is structured such that the cold air  36 ′ and partially cooled air  38 ′ mix to form cool air  42  to be used within the passenger compartment. That is, the supplemental ambient air  38  is first cooled within the second heat exchanger  40 , and then is further cooled by being mixed with cold air  36 ′. Both the cold air and the supplement ambient air exit the second heat exchanger  40  proximate the discharge surface  60 . 
     Furthermore, it will be recognized that by virtue of passing the ambient air  38  proximate the cold dry air  36 , moisture will be removed from the ambient air  38 . The moisture will be forced to the discharge surface  60  and will flow down the face of the fins  58  as indicated by arrow  44 . That is, the force of gravity will direct the moisture  44  down the discharge face  60  at the fins  58 , and the moisture  44  will flow and fall from the bottom of the heat exchanger  40 . 
     The foregoing description of various embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Numerous modifications or variations are possible in light of the above teachings. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.