Patent Publication Number: US-6907919-B2

Title: Heat exchanger louver fin

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates generally to heat exchangers. More specifically, the present invention relates to heat exchanger fins. 
     2. Background Information 
     Heat exchangers are used in many types of industries. For example, heat exchangers with louvered fins are in common usage in the automobile industry, in particular, in many air-liquid, air-refrigerant, and air—air heat exchangers. To provide the required heat transfer capability in these applications, the heat exchangers are typically large and therefore do not lend themselves to compact packaging. Moreover, their large size makes them expensive to fabricate. 
     While these large heat exchangers work sufficiently well for their intended purposes, for cost cutting and compact packaging reasons, original equipment manufacturers are now demanding miniaturized heat exchangers. Unfortunately, the smaller heat exchangers are less efficient than their larger counterparts and therefore do not meet the heat transfer requirements. 
     From the above, it is seen that there exists a need for an improved heat exchanger with enhanced heat transfer capabilities that can be provided in a compact package. 
     BRIEF SUMMARY 
     In overcoming the above mentioned and other drawbacks, the present invention provides a heat exchanger fin that incorporates one or more vortex generator louvers. The fin provides enhanced heat transfer performance with the use the vortex generator louvers, such that the performance of these efficient fins is comparable or exceeds that of conventional fins that do not include vortex generator louvers. 
     In general, each vortex generator louver is provided with mini-vortex generators along an outer edge of the louver. These louvers are placed towards the front of the fin so that the mini-vortex generators trigger vortices which effectively thins the thermal boundary layer across the louver, thereby enhancing the heat transfer performance of the heat exchanger. 
     The heat exchanger fin may include a plurality of louvers spaced apart, such that there is a gap between adjacent louvers through which a fluid, such as air, flows. The mini-vortex generators may be protuberances extending from respective outer edges of the vortex generator louvers. The fin may also include a plurality of non-vortex generator louvers. 
     Depending on the application of the fin, the proportion of vortex generator louvers to non-vortex generator louvers may be between about 20% and 50%. The protuberance may be inclined at an angle relative to a planar portion of the vortex generator louver. For example, the angle of inclination may be between about 30° and 45°. Each protuberance may have a triangular shape that generates a pair of counter-rotating vortices as the fluid encounters the tip of the protuberance. 
     The foregoing discussion has been provided only by way of introduction. Nothing in this section should be taken as a limitation on the following claims, which define the scope of the invention. 
    
    
     
       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. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the views. In the drawings: 
         FIG. 1  illustrates the fluid dynamics of fluid flow over a mini-vortex generator; 
         FIG. 2  is a cross-sectional view of a louver fin with mini-vortex generator louvers in accordance with the invention; 
         FIG. 3A  depicts a louver fin viewed along the line  3 A of  FIG. 4  featuring vortex generator louvers in accordance with the invention; 
         FIG. 3B  is a view of a portion of a vortex generator louver with mini-vortex generators in accordance with the invention; 
         FIG. 4  illustrates a heat exchanger with a pair of louver fins in accordance with the invention; and 
         FIG. 5  is a bar graph of the test results of the heat transfer enhancements of louver fin with min-vortex generators as compared to a conventional louver fin without mini-vortex generators. 
     
    
    
     DETAILED DESCRIPTION 
     As an overview of the vortex generation principles employed in the present invention,  FIG. 1  depicts a mini-vortex generator  10  attached to a flat plate  12  and positioned at an angle (α) from the plane of the plate  12 . The mini-vortex generator  10  is, for example, a triangular shaped protuberance having a length (c) and a base with a width (b). As air flows in the direction of arrow  14  over the mini-vortex generator  10 , the tip  20  of the mini-vortex generator  10  triggers a pair of counter-rotating vortices  16  and  18  which flow from the trailing edge of the mini-vortex generator  10  (or the leading edge  22  of the plate  12 ) across the plate  12 . 
     Looking downstream from the tip  20  (i.e. in the direction of arrow  14 ), the vortex  16  rotates clockwise as it moves across the plate  12 , while the vortex  18  rotates counterclockwise. The rotation of the vortices  16 ,  18  enhances the mixing of the fluid, such as air, as it flows across the plate  12 . Hence, if the fluid is hotter than the plate  12 , the vortex mixing brings the hotter fluid towards the plate. And as heat is rejected from the fluid to the plate, the vortex mixing takes the cooler fluid away from the plate. Such mixing enhances the heat exchange capability of the plate  12  over that which would occur without vortex mixing. 
     Typically, without the mini-vortex generator  10 , the boundary layer over the plate  12  is laminar, increasing in thickness from the leading edge  22  of the plate  12  towards its trailing edge. With the use of the mini-vortex generator  10 , the vortices  16 , 18  effectively thins the boundary layer, which resists heat transfer less than a thicker boundary layer, thereby increasing the heat exchange capabilities of the plate  12 . 
     Referring now to  FIG. 2 , there is shown a heat exchanger fin  30  that employs mini-vortex generators for enhanced heat exchange capabilities in accordance with the invention. The fin  30  includes a set of entrance louvers  32 , a set of vortex generator louvers  34 , a set of forward regular louvers  36 , a set of turnaround louvers  50 , a rear set of regular louvers  40 , and a set of exit louvers  42 . Each mini-vortex generator louver  34  is provided with a set of mini-vortex generators  10 , such as those described with reference to  FIG. 1 , extending from a planar portion of the louver. As shown, the mini-vortex generators  10  are angled downwards from the planar portion of the louvers  34 . Alternatively, the mini-vortex generators can be angled upwards. 
     For this illustrated embodiment, there is one column of entrance louvers  32 , two columns of vortex generator louvers  34 , two columns of forward regular louvers  36 , one column of turnaround louvers  50 , four columns of rear regular louvers  40 , and one column of exit louvers  42 . Each column has six of the respective louvers, so that in this example there are twelve vortex generator louvers  34  (i.e. two columns of louvers, each column having six louvers). However, depending on the particular application, there may be as many as 200 or more louvers in each column. Moreover, there can be three to six or more columns of the vortex generator louvers  34 . Typically, the proportion of the columns of the vortex generator louvers  34  to the columns of the forward regular louvers  36  is between about 20% to 50%. 
     The entrance louvers  32  have a horizontal portion  44  and an angled portion  46 . The angle of inclination of the angled portion  46  matches the angle of inclination of the vortex generator louvers  34 , the forward set of the regular louvers  36 , as well as a front portion  48  of the turnaround louvers  50 , as indicated by the angle (β), which is about 45° in this example. The turnaround louvers  50  are also provided with a reverse angled portion  52  that matches the angle of inclination of the rear set of regular louvers  40  and an angled portion  54  of the exit louvers  42 , which are also provided with a horizontal portion  56 . 
     The louver pitch (d 1 ) between the mini-vortex generator louvers  34  is between about 0.8 mm to 1.5 mm, and the fin pitch (d 2 ) is between about 0.8 mm to 1.8 mm. Although the louver pitch (d 1 ) and the fin pitch (d 2 ) between respective louvers are shown to be the same, either or both of the pitches may be different depending on the application requirements of the fin  30 . 
     When the fin  30  is in use, air enters the fin  30  as indicated by the arrow  58 . The entrance louvers  32  divert the air upwards over the vortex generator louvers  34 , as indicated by the upward angled arrow. The mini-vortex generators  10  of the vortex generator louvers  34  trigger vortices in the airflow, thereby thinning the thermal boundary layer, as discussed earlier, and hence enhancing the heat transfer capabilities of the heat exchanger fin  30 . The air flows past the forward set of regular louvers  36  and is diverted downwards by the turnaround louvers  50 , past the rear set of regular louvers  40 , as indicated by the downward angled arrow, and exits through the exit louvers  42  in the direction of the arrow  60 . 
     Illustrated in  FIG. 4  is an example of a heat exchanger fin generally identified by the reference numeral  70 . A portion of the fin  70  is shown in  FIG. 3A  with vortex generator louvers  34 , forward regular louvers  36 , and rear regular louvers  40 . In this embodiment, the louvers  34 ,  36 ,  38  have a length (L) of about 6 mm to 10 mm and a width (w) of about 0.8 mm to 1.5 mm. Note that depending upon the application of the fin  70 , the length and width of the louvers can be smaller or greater than the aforementioned dimensions. 
     Referring in particular to  FIG. 3B , each vortex generator louver  34  includes a set mini-vortex generators  10  along the outer edge of the louver. Each louver  34  can have as few as one mini-vortex generator  10  or as many as eight to nine or more mini-vortex generators. In some embodiments, the mini-vortex generators  10  are spaced apart by about 1 mm, and each mini-vortex generator  10  has a length (c) of less than about 1 mm and a base width (b) of less than about 1 mm. In a particular embodiment, the length (c) and base width (b) are each about 0.4 mm. The mini-vortex generators  10  can have an angle of inclination (α), as shown for example in  FIG. 1 , in the range of about 30° to 45°. Again, depending upon the application of the fin  70 , these dimensions can be smaller or greater than those just mentioned. 
       FIG. 5  illustrates the enhanced performance provided by a fin with vortex generator louvers in accordance with the invention. As shown, the fin with vortex generator louvers, provided with mini-vortex generators  10 , has a heat rejection capability of about 100% to 110%, as indicated by the bar  90 , while a fin that is not provided with such vortex generator louvers has a base performance of 100%, as indicated by the bar  80 . 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.