Patent Document

BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to a process for making a heat exchanger. 
     (2) Description of Related Art 
     Heat exchangers are generally known in the art and one common type consists of a number of parallel tubes, fin-like elements being provided between each part of neighbouring tubes. An example of such a heat exchanger has been described in U.S. Pat. No. 5,780,825. Such heat exchangers can be either a so-called parallel flow heat exchanger, or a single flow heat exchanger such as a serpentine like heat exchanger. 
     Normally such heat exchangers are produced by extruding a number of tubes, making a set of fins to be placed between each pair of neighbouring tubes, and providing end connectors or collectors to the end portion of the tubes, where upon the whole assembly is brased together. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a process for making a heat exchanger, which is less complicated to make, and in which less components need to be handled in order to obtain the final assembly of the heat exchanger. 
     This and other objects are achieved in that a profile is extruded which is composed of a number of parallel tubes and web-like portions interconnecting said tubes, in that part of the connection made by the web-like portions is removed and the extruded product is expanded in a direction perpendicular to the longitudinal direction of the tubes, and in that connecting means are provided allowing a fluid to flow through the tubes. 
     In this way, a single extrusion can provide a heat exchanger which is as efficient as the standard heat exchanger, and which can be obtained with less effort. 
     It should be noted that it is well known that extruded aluminium profiles can be shaped and manipulated in order to produce mesh-shaped products. Such products have been described in GB-A-2 101176 and GB-A-1 588 197. In all these examples the ribs forming the mesh have been considered as being solid and the product is only envisaged in a mesh functionality. 
     In the present invention, the aluminium extrusions comprising solid ribs lined by the webs is converted by cutting slots a specific length in the webs and thereafter stretching the profile laterally. 
     By using tubular elements instead of solid elements and fin like protrusions it is possible to modify the heat transfer characteristics. By varying the length of the slots cut into the web part of the extruded profiles before stretching in a lateral manner, it is possible to affect the air flow patterns and induce turbulence which will further improve heat transfers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and characteristics of the invention will become clear from the following description reference being made to the annexed drawings, in which: 
         FIG. 1  is a perspective view of an extruded profile as seen in the direction of the tubes, which can be used in the process according to the invention, 
         FIG. 2  is a perspective view of the profile of  FIG. 1 , 
         FIG. 3  is a perspective view of the product obtained after expanding the profile according to  FIGS. 1 and 2 , 
         FIG. 4  is a perspective view corresponding to  FIG. 1  of a modified profile, 
         FIG. 5  is a perspective view corresponding to  FIG. 2  of the modified profile of  FIG. 4 , 
         FIG. 6  is a perspective view of the product obtained after expanding the profile according to  FIGS. 4 and 5 , and 
         FIG. 7  is a perspective view of a completed heat exchanger obtained by means of the profile according to  FIGS. 1 and 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIGS. 1 and 2  there is shown a first profile  1  which can be used in the process according to the invention. The profile  1  consists of a number of parallel tubes  2  and a number of webs  3  interconnecting each pair of neighbouring tubes  2 . As shown all tubes are located in the same plane and have a ring shaped cross-section, but it will be obvious that it is not required to have all tubes  2  in the same plane and that any suitable cross-section can be used, such as flat tubes, hexagonal tubes, or the like. 
     After extrusion of the profile, each web  3  is provided with a number of slots  4 , extending parallel to the tubes  2 . In the embodiment shown the slots  4  have a length which is substantially longer than the remaining web portion between two adjacent slots in the same web. Moreover the slots  4  in the different webs are all positioned in the same way with respect to the end face of the extruded profile. 
     After expansion of the profile in a direction perpendicular to the longitudinal direction of the tubes  2  a product as shown in  FIG. 3  will be obtained. The tubes  2  have been deformed so as to form curved tubes and between each part of adjacent tubes air gaps  8  originating from the slots  4  have been formed. 
     By providing suitable connecting means to the end portions of the tubes, so as to form an input and an output for a fluid and interconnecting the different tubes a fluid heat exchanger can be obtained. 
     In  FIG. 7  there is shown such a heat exchanger which in this case is a single flow heat exchanger. However, it will be obvious that by simply replacing the U-shape end connectors by a manifold type, a parallel flow heat exchanger can be obtained. 
     In the  FIGS. 4-6  there is shown a modified embodiment of an extruded profile  11 . The profile  11  as extruded comprises a number of parallel tubes  12 , each pair of neighbouring tubes  12  being connected by means of a web  13 . As shown all tubes  12  are in the same plane and have a ring shaped cross-section, but as explained with respect to the first embodiment, other shapes are possible as well. 
     Each web  13  is provided with a number of protruding portions extending from both faces of the web  13 . In the embodiment shown there are four protruding portions  14 ,  15 ,  16 ,  17  having a planar shape, and the extrusions  14  and  15  are located in the same plane as the extrusions  16  and  17  respectively. 
     It will be obvious that other types or shapes of protruding portions and different numbers than four are possible. 
     After extrusions of the profiles  11 , a number of slots is made in each web, as shown in  FIG. 5 . A first set of slots  18  is made in the web  13  between each tube  11  and the protruding portions  14 ,  16  and  15 ,  17  respectively. All the slots  18  have the same length and the same position with respect to the end of the tube  12 . Between the protruding portions  14 ,  16  and  15 ,  17  another set of slots  19  is made. Basically each slot  19  has the same length as the slot  18 . Their position however is such that as seen along the longitudinal direction of the tubes  12  each slot  19  is extending halfway between two successive slots  18  in the neighbouring part of the same web  13 . 
     In this way each web  13  is provided with a number of slots  18 ,  19  whereby the slots  19  are offset with respect to the slots  18 . 
     After expansion of the extruded profile in the direction perpendicular to the axis of the tubes  12 , a product as shown in  FIG. 6  will be obtained, in which a fin-like construction  20  is present between each pair of neighbouring tubes. Based upon the product as shown in  FIG. 6  it is possible to make a heat exchanger as explained with respect to the  FIG. 3 . 
     In order to test the performance of a heat exchanger obtained by means of the extruded and expanded products a test made with a heat exchanger of the type shown in  FIG. 7 . 
     EXAMPLE 
     A profile consisting of 8 tubular members 8 mm outside diameter with a 1.0 mm wall thickness and an interconnecting web of 2 mm width similar to the profile shown in  FIG. 1  was produced. Slots were made in the web, 64 mm long and the profile was sideways stretched from an initial dimension of 78 mm wide to 128 mm wide. (i.e. 64% extension) 
     Individual expanded profiles were assembled to make a panel with an overall width of 360 mm and a height of 300 mm. Tubes were interconnected by means of ‘U’ bends so that flow paths within each set of panels could be controlled. The size of the panels was matched to the available opening on a wind tunnel that was used to assess the heat transfer efficiency of the system. 
     A conventional tube and fin brazed radiator, designed for automotive use, was used in the trials to provide comparative data to existing state of art heat exchangers. 
     Oil, preheated to 100° C., was passed through the tubular profiles at rates of either 150 or 300 liters per hour and the wind speed was varied from 4 meters per second up to 11 meters per second. The temperature of the out-going oil was measured after an operating time of 5 minutes. 
     Efficiency was calculated using the formula
 
(T oil inlet −T oil outlet )/(T oil inlet −T Air )
 
     Where oil inlet is 100° C. and the air temperature is 20° C. 
     Thus, for a panel consisting of 3 layer with each layer being a separate oil circuit and where oil flow rate is 150 liters/hr and the wind speed is 11 m/sec, the temperature drop for oil is (100-49.6)° C. and the difference between oil inlet and ambient air temperature is 80° C., an efficiency of 0.64 is calculated. 
     The results from the testing are detailed in table 1-6. 
     The best heat transfer results were obtained with oil flow of 150 liters per hour in the test panels as well as in the conventional radiator. Surprisingly, the extruded panel heat exchanger performed up to over 70% of the efficiency of the state of the art heat exchanger. This is despite the fact that the air-side flow path had not been optimised and the shape of the tubular elements was not optimised. Ideally the tube profile would preferably be oval or tear-drop shaped and could incorporate internal fin to enhance heat transfer. 
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                   
                 3 layer 
                   
               
               
                   
                 3 flow paths 
                   
               
             
          
           
               
                   
                 Oilflow 150 l/hr 
                 Oilflow 300 l/hr 
                   
               
             
          
           
               
                 Wind speed 
                 4 
                 8 
                 11 
                 4 
                 8 
                 11 
                 m/s 
               
               
                   
               
             
          
           
               
                 OilTempOut 
                 65.4 
                 54.2 
                 49.6 
                 79.2 
                 69.9 
                 61.8 
                 ° C. 
               
               
                 Performance 
                 2521 
                 3336 
                 3681 
                 3017 
                 4094 
                 4284 
                 Watt 
               
               
                 Efficiency 
                 0.44 
                 0.57 
                 0.64 
                 0.26 
                 0.37 
                 0.43 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                   
                 3 layer 
                   
               
               
                   
                 6 flow paths 
                   
               
             
          
           
               
                   
                 Oilflow 150 l/hr 
                 Oilflow 300 l/hr 
                   
               
             
          
           
               
                 Wind speed 
                 4 
                 8 
                 11 
                 4 
                 8 
                 11 
                 m/s 
               
               
                   
               
             
          
           
               
                 OilTempOut 
                 67.5 
                 58.2 
                 53.9 
                 80 
                 72.8 
                 68.3 
                 ° C. 
               
               
                 Performance 
                 2389 
                 3051 
                 3342 
                 2909 
                 3942 
                 4337 
                 Watt 
               
               
                 Efficiency 
                 0.42 
                 0.53 
                 0.59 
                 0.25 
                 0.35 
                 0.39 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                   
                 2 layer 
                   
               
               
                   
                 2 flow paths 
                   
               
             
          
           
               
                   
                   
                 Oilflow 300 l/hr 
                   
               
               
                   
                   
                 Oil Pressure 
                   
               
               
                   
                 Oilflow 150 l/hr 
                 drop too high 
                   
               
             
          
           
               
                 Wind speed 
                 4 
                 8 
                 11 
                 4 
                 8 
                 11 
                 m/s 
               
               
                   
               
             
          
           
               
                 OilTempOut 
                 72.7 
                 62.8 
                 58.5 
                   
                   
                   
                 ° C. 
               
               
                 Performance 
                 2030 
                 2742 
                 3038 
                   
                   
                   
                 Watt 
               
               
                 Efficiency 
                 0.35 
                 0.48 
                 0.53 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                   
                 2 layer 
                   
               
               
                   
                 4 flow paths 
                   
               
             
          
           
               
                   
                 Oilflow 150 l/hr 
                 Oilflow 300 l/hr 
                   
               
             
          
           
               
                 Wind speed 
                 4 
                 8 
                 11 
                 4 
                 8 
                 11 
                 m/s 
               
               
                   
               
             
          
           
               
                 OilTempOut 
                 73.2 
                 65 
                 60.9 
                 84.2 
                 77.7 
                 75.1 
                 ° C. 
               
               
                 Performance 
                 1965 
                 2576 
                 2850 
                 2267 
                 3137 
                 3582 
                 Watt 
               
               
                 Efficiency 
                 0.34 
                 0.45 
                 0.5 
                 0.2 
                 0.28 
                 0.32 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                   
                 1 layer 
                   
               
               
                   
                 6 flow paths 
                   
               
             
          
           
               
                   
                 Oilflow 150 l/hr 
                 Oilflow 300 l/hr 
                   
               
             
          
           
               
                 Wind speed 
                 4 
                 8 
                 11 
                 4 
                 8 
                 11 
                 m/s 
               
               
                   
               
             
          
           
               
                 OilTempOut 
                 84.7 
                 80 
                 77.4 
                 91 
                 88.2 
                 86.3 
                 ° C. 
               
               
                 Performance 
                 1104 
                 1456 
                 1624 
                 1199 
                 1691 
                 1926 
                 Watt 
               
               
                 Efficiency 
                 0.19 
                 0.25 
                 0.28 
                 0.11 
                 0.15 
                 0.17 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                   
                 Radiator - Benchmark 
               
             
          
           
               
                   
                 Oilflow 150 l/hr 
                 Oilflow 300 l/hr 
                   
               
             
          
           
               
                 Wind speed 
                 4 
                 8 
                 11 
                 4 
                 8 
                 11 
                 m/s 
               
               
                   
               
             
          
           
               
                 OilTempOut 
                 39.9 
                 32.0 
                 31.0 
                 59.2 
                 52.8 
                 50.4 
                 ° C. 
               
               
                 Performance 
                 4266 
                 4566 
                 5060 
                 6134 
                 6851 
                 7183 
                 Watt 
               
               
                 Efficiency 
                 0.77 
                 0.85 
                 0.85 
                 0.51 
                 0.59 
                 0.62

Technology Category: 2