Abstract:
A heat exchange rib through which a gaseous medium flows to be in heat exchange with another medium. The rib is a strip adapted to receive flow of the gaseous medium along the surfaces thereof, wherein the strip has a first thickness and an edge portion of the strip has a second thickness greater than the first thickness. The edge portion extends in the flow direction of the gaseous medium a width sufficient to increase the average temperature difference between the media.

Description:
CROSS REFERENCE TO RELATED APPLICATION(S)  
       [0001]     Not applicable.  
       Statement Regarding Federally Sponsored Research or Development  
       [0002]     Not applicable.  
       Reference to a Microfiche Appendix  
       [0003]     Not applicable.  
       Technical Field  
       [0004]     The present invention is directed toward heat exchanger ribs, and more particularly toward ribs through which a gaseous medium flows in order to exchange heat with another medium.  
       BACKGROUND OF THE INVENTION AND TECHNICAL PROBLEMS POSED BY THE PRIOR ART  
       [0005]     Heat exchangers having ribs through which gas flows to exchange heat with another medium are old. Commonly the ribs contact tubes or the like through which the other medium flows, wherein heat is passed from one medium to the other via flow of the media over the tube walls and the ribs.  
         [0006]     JP-A-60-018240, and also the more recent EP 1 028 303 B1, have provided heat exchanger ribs (e.g., flat, plate or corrugated ribs) in which both opposite edge strips are reinforced by turning in the edges over the narrowest possible section. Such reinforcement has increased the stability of the ribs and the heat exchanger since the thickness of the ribs is generally is well below 0.5 mm. That is, while the main function of the ribs is to facilitate efficient heat exchange, they also importantly function to retain the stability of the heat exchanger. Further, it is known that the heat exchange performance is better in thicker ribs than in thinner ones, perhaps due to the fact that the amount of heat transported per unit time is smaller in thinner ribs, since resistance to heat conduction rises. At the same time, however, thick ribs may block more surface area, leaving less area for gas flow therethrough. In short, the wall thickness of the heat exchange ribs cannot be arbitrarily reduced.  
         [0007]     The geometry of the heat exchange ribs, for example corrugated ribs, cannot be arbitrarily altered either. For example, the wavelength could be reduced, but the pressure loss, for example, of the cooling air would be undesirably increased on this account. A longer sheet material would naturally also be required, which could result in additional weight which is undesirable in many applications such as vehicle cooling systems.  
         [0008]     Consequently, conflicting design requirements exist, with some requirements pointing toward lighter and even more compact heat exchangers, while at the same time desiring higher (or at least not distinctly lower) heat exchange performance. Ideally in many applications such as vehicle cooling systems, design improvements will provide lighter and more compact heat exchangers while maintaining or improving performance characteristics.  
         [0009]     Proposals have been advanced such as disclosed in GB-B-2 133 525, which provide heat exchanger tubes, especially flat tubes, having wall thicknesses larger in sections. This structure is intended to improve corrosion resistance.  
         [0010]     The present invention is directed toward overcoming one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0011]     In one aspect of the present invention, a heat exchange rib is provided through which a gaseous medium flows to be in heat exchange with another medium. The rib is a strip adapted to receive flow of the gaseous medium along the surfaces thereof, wherein the strip has a first thickness and an edge portion of the strip has a second thickness greater than the first thickness, with the edge portion extending in the flow direction of the gaseous medium a width sufficient to increase the average temperature difference between the media.  
         [0012]     In one form of this aspect of the present invention, the gaseous medium flows from front to back of the rib, and the edge portion is the front portion of the rib.  
         [0013]     In another form of this aspect of the present invention, the first thickness of the sheet material is generally in the range from 0.04-0.15 mm, and the second thickness is generally double the first thickness.  
         [0014]     In a further form of this aspect of the present invention, the second thickness is substantially a multiple of the first thickness, and the edge portion is formed by one or more folds of the rib strip.  
         [0015]     In still another form of this aspect of the present invention, the edge portion comprises combined strips having at least two different wall thicknesses.  
         [0016]     In a still further form of this aspect of the present invention, cuts in the ribs are adapted to cause turbulence in the gaseous medium flowing along the rib surfaces. In a further form, the cuts are in the edge portion.  
         [0017]     In yet another form of this aspect of the present invention, the width of the edge portion in the flow direction is about 5-60% of the total width of the rib. In a further form, the width of the edge portion in the flow direction is about 10-30% of the total width of the rib.  
         [0018]     In another form of this aspect of the present invention, the rib is flat. In another form, the rib is corrugated and the height of the corrugations is about 3-10 mm.  
         [0019]     In another aspect of the present invention, a heat exchanger is provided with ribs disposed between flat tubes adapted to carry the other medium. Gaseous medium flows through the ribs to be in heat exchange with the other medium. The rib is a strip adapted to receive flow of the gaseous medium along the surfaces thereof, wherein the strip has a first thickness and an edge portion of the strip has a second thickness greater than the first thickness, with the edge portion extending in the flow direction of the gaseous medium a width sufficient to increase the average temperature difference between the media. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a diagram of the temperature trend over the block depth of heat exchangers equipped with three different corrugated ribs, with an edge view of the different ribs graphically illustrated at the top of the Figure;  
         [0021]      FIG. 2  is a progressive perspective illustration of a metal sheet worked into a corrugated rib according to the present invention with a turned-in edge and cuts over the entire width;  
         [0022]      FIG. 3  is similar to  FIG. 2 , but illustrating a corrugated rib according to the present invention having cuts only in the region not turned in.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]      FIG. 1  illustrates the result of extensive studies conducted by the Applicant, with the temperature trend over the entire width W of three corrugated ribs  10  is plotted (wherein the width W corresponds to the block depth of the heat exchanger): 
    1. Study results for a first corrugated rib  10  having a 0.12 mm sheet thickness and without a reinforced edge are illustrated by the solid curve.     2. Study results for a second corrugated rib  10  having a 0.06 mm sheet thickness, and also without a reinforced edge, are illustrated by the dashed line. As contrasted with the first rib design, the second rib design has a weight reduction of 50% and a performance loss of 2.64% occurs. Moreover, the two curves make it clear that the different thicknesses T of the corrugated ribs  10  with increasing block depth and increasing temperature ensure that the temperature difference becomes greater, in which case a performance loss will manifest itself.     3. Study results for a third corrugated rib  10 , this one according to the present invention, are illustrated in  FIG. 1  by the solid curved line with stars. The third corrugated rib  10  includes an edge strip  20  of greater wall thickness resulting from the metal sheet being turned in once. The thicker edge strip  20  may advantageously run over the entire length of corrugated rib  10  and have a substantially uniform width W E  over the entire length of the rib  10  which is about 30% of the total width W of the corrugated rib  10  (or the block depth of the heat exchanger). Like the second rib, the third corrugated rib  10  also has a sheet thickness of 0.06 mm, but because of the turned-in (thicker) edge strip  20 , with the same total width W the weight reduction is only 35% but the performance loss is also less pronounced, namely only 1.11%.      
         [0027]     It should be appreciated that the curve for the third corrugated rib  10  (i.e., the curve with stars) in the region of the edge strip  20  (through width W E ) is almost congruent with the solid curve representing the corrugated rib  10  with 0.12 mm sheet thickness without the wall or edge reinforcement. The curve for the third corrugated rib  10  is therefore well about the dashed curve for the second corrugated rib in that region as well.  
         [0028]     Behind the edge strip  20  (i.e., to the right of the  FIG. 1  chart), with increasing total width W (e.g., block depth of the heat exchanger), the solid curves and the curves provided with stars (for the first and third corrugated ribs, respectively) separate somewhat from each other, since the poorer heat transfer of the thinner corrugated rib  10  in that region (0.06 mm for the third rib vs. 0.12 mm for the first rib) comes into play and a lower average temperature is obtained over the entire corrugated rib  10 , which leads to an increased average temperature difference between the media.  
         [0029]     As a result, the inventor hereof has established that the entry region into the heat exchange rib  10  for cooling air, for example, has a relatively low temperature and that the temperature has a comparatively higher value roughly from the center of the width of the heat exchange rib  10 , since the cooling air on its path through the heat exchanger has already absorbed heat. Moreover, this finding means that the temperature difference between air flowing past the ribs  10  and the other medium flowing in the tubes, for example, which influences heat exchange performance, is also different. By increasing the wall thickness, most advantageously in the entry region for cooling air flow (see arrow  24  in  FIGS. 2-3 ) past the ribs  10 , the temperature difference between the entry region and the region of the heat exchange rib lying far along in the air flow direction is somewhat reduced, but overall this means that, over the entire width of the heat exchange rib, the average temperature difference between the two media is increased, so that the improved heat exchange performance relative to a heat exchange rib without wall thickening can be explained. Such improved heat exchange performance can also be explained by the fact that the increase in temperature in the inlet area caused by the increase in wall thickness comes out smaller than the reduction in temperature in the region distant from it. For example, in the front, at the entry region, if the temperature is 5° C. higher and, at the rear, in the exit region, 10° C. lower, then the average temperature on the air side is 5° C. lower. Therefore, the temperature difference between the air and the coolant in the tubes is increased.  
         [0030]     It should thus be appreciated that use of the present invention, with a thicker edge portion  20  extending sufficiently along the width of the rib  10  to increase the average temperature differential between the media (with the third rib when compared to the second rib, each having a general [first] thickness of 0.06 mm), may provide a noticeable weight reduction with only slight performance losses that lie within the acceptable range, which slight performance losses can easily be compensated by other expedients, or even tolerated.  
         [0031]     As illustrated in  FIGS. 2 and 3 , corrugated ribs  10  according to the present invention may be formed from a flat metal sheet  30   a  having the selected minimum thickness. The sheet  30   b  may be folded over along the front edge to form the thickened edge strip  20 , where the edge strip thickness is therefore twice the thickness of the sheet with a single fold. It should be understood, however, that it would be within the scope of the present invention to form the edge strip  20  with multiple folds whereby the edge strip  20  may be several times the sheet thickness in which case correspondingly more favorable values with respect to performance may be achieved. It should also be understood that it would be within the scope of the present invention to form the ribs  10  of sheets which are rolled with different sheet thicknesses (i.e., having at least one gradation of wall thickness) along their length, in which case an identical curve trend could also be obtained. The sheet  30   b  may then be suitably bent so as to be serpentine or corrugated as shown at  30   c.    
         [0032]     The width W E  of the edge strip  20  according to the present invention should be selected so that the average temperature between the media may be increased. In this regard, it has been found that the edge strip width W E  may advantageously be about 5% to 60% of the width W of the rib  20 , and most advantageously 10 to 30% of the total width W of the heat exchange rib.  
         [0033]     Further, the wall thickness of the heat exchange rib according to the present invention may advantageously lie in the range from about 0.04 to 0.12 mm, with a particularly advantageous range being between 0.04 and 0.08 mm. In heat exchange ribs  10  formed wave-like as previously described (i.e., serpentine or corrugated ribs), particularly advantageous results may be achieved with a rib height  34  (see  FIG. 3 ) between about 3 and 10 mm.  
         [0034]     Thus, it should be appreciated that by using an extremely thin sheet material, particularly lightweight construction may be advantageously achieved, while at the same time achieving acceptable heat exchange performance. Moreover, the wall thickening at the edge strip  20  also contributes to the stability of the heat exchange rib and the heat exchanger.  
         [0035]     Cuts  40  which advantageously add turbulence to the flow of air over the ribs  10  may also be provided in the flanks of the ribs  10 . For example,  FIG. 2  shows a corrugated rib  10  which includes cuts  40  over the entire width W of the rib  10  which may be formed, for example, by use of a corresponding design in the rib die (not shown). The cuts  40  facilitate the production of deliberate deflection and multiplication of flow paths. The ribs  10  may also be formed with cuts  40  omitted from the edge strip  20  as shown in  FIG. 3 .  
         [0036]     Further, although the depicted variants refer only to corrugated ribs  10 , it should be appreciated that the advantages of the present invention may also be naturally achieved with flat ribs. It will be appreciated by those skilled in this art that flat ribs usually have openings through which the heat exchanger tubes are inserted. Additional details concerning flat ribs can, however, be taken from EP 1 028 303 B1, the full disclosure of which is hereby incorporated by reference. Moreover, it should be appreciated that corrugated ribs  10  as used herein refer to all heat exchange ribs having any wave-like trend, for example rectangular, or as shown in  FIG. 2 .  
         [0037]     Heat exchangers incorporating ribs  10  according to the present invention as described above may be advantageously manufactured, wherein the ribs  10  are disposed between tubes for the other medium. Headers or collecting tanks may be secured to the tube ends such as is known in the art, whereby controlled flow of the medium through the tubes may be achieved, with heat transfer occurring through the tube walls and ribs  10  between the air passing over the ribs and outside the tubes and the medium inside the tubes. Both the tubes and ribs  10  may advantageously be formed of metal, and suitably connected to each other.  
         [0038]     Still other aspects, objects, and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims. It should be understood, however, that the present invention could be used in alternate forms where less than all of the objects and advantages of the present invention and preferred embodiment as described above would be obtained.