Patent Publication Number: US-4317484-A

Title: Heat exchanger core

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a heat exchanger core comprising a fluid passage member within which a fluid flows and outside of which another fluid flows and fin members formed thereon for promoting heat exchange between the two fluids, and more particularly to a heat exchanger core whose fluid passage member is made of an aluminum base alloy and whose fin members also serve as sacrificial anodes for protecting the fluid passage member from corrosion, when the heat exchanger core is used in the heat exchangers for condensers of car coolers or for radiators of cars. 
     A conventional heat exchanger for use in air-cooled heat exchangers, which is made of an aluminum base alloy and is assembled by brazing, comprises a fluid passage member for allowing a heat exchange medium, such as cooling medium or cooling water, to pass therethrough, and fin members disposed on the air-cooled side. In the heat exchanger, either the fluid passage member or the cooling fin members or both are prepared from brazing sheets comprising a layered member consisting of a core metal layer made of aluminum or a corrosion-resistant aluminum alloy, and a cleaning metal layer made of an Al-Si base alloy or an Al-Si-Mg base alloy, and these members are joined to each other by brazing. 
     However, when the heat exchanger is exposed to a severe corrosive atmosphere, considerable corrosion takes place in the air-cooled side of the heat exchanger and the fluid may leak from the fluid passage member. Therefore, the applications of such an air-cooled heat exchanger are severely limited. More specifically, in the conventional heat exchanger as shown in FIG. 1, a soldered fillet portion 2 between a fin member 1 and a fluid passage member 3 becomes a cathode, while the fluid passage member 3 itself becomes an anode, and a corrosion-current flows in the direction of the arrow from the fluid passage member 3 to the soldered fillet portion 2, so that pitting corrosion 4 occurs in the fluid passage member 3. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a corrosion-resistant heat exchanger core. 
     According to the present invention, fin members which are attached to the outer surface of the fluid passage member for increasing heat exchange efficiency serve as sacrificial anodes by an appropriate combination of the materials for use in the heat exchanger core and the fin members, so that the fluid passage member is protected from corrosion, while the corrosion of the fin members is minimized. 
     The heat exchanger core according to the present invention can find wide application since corrosion of the fluid passage member is prevented by the fin members. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
     FIG. 1 illustrates a corrosion state of part of a conventional heat exchanger core. 
     FIG. 2 illustrates the function of a sacrificial anode according to the present invention. 
     FIG. 3 illustrates the fin pitch of a corrugated type fin member according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 2, there is schematically shown part of an embodiment of a heat exchanger core according to the present invention. In this embodiment, a fin member 11 made of a brazing sheet consisting of a core metal layer 15 and cladding metal layers 14 becomes an anode, while a fluid passage member 13 becomes a cathode, so that the corrosion-current flows in the direction of the arrow from the fin member 11 to the fluid passage member 13 and to a brazed fillet portion 12 and therefore pitting corrosion 5 occurs in the fin member 11, whereby the fluid passage member 13 is protected from corrosion. 
     In order that the fluid passage member 13 is protected from corrosion in the above-mentioned manner, it is required that the corrosion-current flow through the whole outer surface of the fluid passage member 13 and, at the same time, it is required that the rate of corrosion of the fin member 11 be minimized. 
     In order to satisfy the above-mentioned requirements, the heat exchanger cores according to the present invention comprise fin members made of a brazing sheet consisting of a core metal layer and a cladding metal layer, and a fluid passage member. More specifically, in a first embodiment of a heat exchanger core according to the present invention, the core metal layer is made of an aluminum base alloy containing Sn in the range of 0.01 to 0.09 wt.%, and the cladding metal layer is made of a brazing material comprising an Al-Si base alloy or an Al-Si-Mg base alloy, and the fluid passage member is made of a corrosion-resistant aluminum base alloy containing Mn in the range of 0.2 to 2 wt%. 
     In a second embodiment of a heat exchanger core according to the present invention, the core metal layer is made of an aluminum-base alloy, which contains Sn in the range of 0.01 to 0.09 wt.% and at least one substance selected from the group consisting of Mg in the range of 0.1 to 2 wt.%, Mn in the range of 0.1 to 2 wt.%, Zn in the range of 0.1 to 5 wt.%, Cu in the range of 0.01 to 2 wt.%, Cr in the range of 0.01 to 0.05 wt.%, Zr in the range of 0.01 to 0.5 wt.%, Fe in the range of 0.01 to 2 wt.%, and Si in the range of 0.01 to 1 wt.%, and the cladding metal layer is made of a soldering material comprising an Al-Si base alloy or an Al-Si-Mg base alloy, and the fluid passage member is made of a corrosion-resistant aluminum base alloy containing Mn in the range of 0.2  to 2 wt.%. 
     In a third embodiment of a heat exchanger core according to the present invention, the core metal layer is made of an aluminum base alloy containing Sn in the range of 0.01 to 0.09 wt.%, and the cladding metal layer is made of a soldering material comprising an Al-Si base alloy or an Al-Si-Mg base alloy, and the fluid passage member is made of a corrosion-resistant aluminum base alloy containing Mn in the range of 0.2 to 2 wt.% and at least one substance selected from the group consisting of Mg in the range of 0.1 to 2 wt.%, Cr in the range of 0.01 to 5 wt.%, Ti in the range of 0.01 to 0.5 wt.%, Zr in the range of 0.01 to 0.5 wt.%, Cu in the range of 0.01 to 1 wt.%, Fe in the range of 0.01 to 1 wt.% and Si in the range of 0.01 to 2 wt.%. 
     In a fourth embodiment of a heat exchange core according to the present invention, the core metal layer is made of an aluminum-base alloy containing Sn in the range of 0.01 to 0.09 wt.% and at least one substance selected from the group consisting of Mg in the range of 0.1 to 2 wt.%, Mn in the range of 0.1 to 2 wt.%, Zn in the range of 0.1 to 5 wt.%, Cu in the range of 0.01 to 2 wt.%, Cr in the range of 0.01 to 0.5 wt.%, Zr in the range of 0.01 to 0.5 wt.%, Fe in the range of 0.01 to 2 wt.%, and Si in the range of 0.01 to 1 wt.%, and the cladding metal layer is made of a soldering material comprising an Al-Si base alloy or an Al-Si-Mg base alloy, and the fluid passage member is made of a corrosion-resistant aluminum-base alloy containing Mn in the range of 0.2 to 2 wt.% and at least one substance selected from the group consisting of Mg in the range of 0.1 to 2 wt.%, Cr in the range of 0.01 to 5 wt.%, Ti in the range of 0.01 to 0.5 wt.%, Zr in the range of 0.01 to 0.5 wt.%, Cu in the range of 0.01 to 1 wt.%, Fe in the range of 0.01 to 1% and Si in the range of 0.01 to 2 wt.%. 
     In the brazing sheet which constitutes the fin members in the present invention, the aluminum base alloy of the core metal layer contains Sn in the range of 0.01 to 0.09 wt.%. The Sn contained serves to make the fin members anodic, so that each of the fin members serves as a sacrificial anode for preventing the fluid passage member from being corroded. When the content of Sn exceeds the above-mentioned range, the plasticity of the aluminum base alloy decreases so that it becomes difficult to form the brazing sheet into the desired shape to make the fin members and, at the same time, considerable self-corrosion tends to take place in the fin members. On the other hand, when the content of Sn is less than the lower limit, the desired corrosion prevention effect is not obtained. 
     The other substances, such as Mg, Mn, Cu, Cr, Zr, Fe and Si, which can be contained in the fin members, serve to improve strength, sag-resistance, and moldability of the fin members. When the contents of those substances exceed their respective upper limits which have been previously mentioned, the plasticity for molding is lowered. On the other hand, when the contents of those substances are less than their previously mentioned respective lower limits, they do not contribute to improvement of strength, sag-resistance, and moldability of the fin members. 
     Zn provides the fin members with the sacrificial anode effect and promotes the effect of Sn. When the content of Zn exceeds its upper limit, brazing capability of the fin members is lowered and when the content of Zn is less than its lower limit, the corrosion prevention effect is decreased. 
     The fluid passage member according to the present invention is characterized by containing Mn in the range of 0.2 to 2 wt.%. The Mn makes the fluid passage member cathodic so as to increase the difference of potential between the fluid passage member and the fin members. Consequently, the sacrificial anode effect of the fin members is increased. Therefore, the fluid passage member is protected from corrosion. When the content of Mn exceeds its upper limit, the workability of the aluminum alloy for the fluid member is reduced. On the other hand, when the content of Mn is less than its lower limit, the corrosion prevention effect is reduced. 
     The other substances that can be added to the fluid passage member, such as Mg, Cr, Ti, Zr, Cu, Fe and Si, serve to increase strength of the fluid passage member and to make the surface of the fluid passage member smooth by rendering the size of alloy crystals minute, without changing the potential of the fluid passage member greatly. When the contents of these substances exceed their respective upper limits, the workability of the aluminum alloy for the fluid passage member is reduced. On the other hand, when the contents of those substances are less than their respective lower limits, the effects of improving the strength and of refining the alloy crystals cannot be obtained. 
     In the cladding metal layer of the fin members, an Al-6-14%-Si alloy and an Al-6-14%-Si-0.3-2.0%-Mg alloy can be used equally. Furthermore, an Al-6-14%-Si alloy containing a small amount of Bi, Sr, Ba, Sb and/or Be can be used in the cladding metal layer. 
     As the brazing method for use in the present invention for making the heat exchange core, a flux method, a vacuum method, a low pressure atmosphere method and an inert gas atmosphere method can be used equally. 
     By defining the composition of the aluminum alloy for use in the fin members and the fluid passage member as mentioned above, an excellent sacrificial anode effect can be obtained in the present invention. As mentioned previously, in order to obtain the sacrificial anode effect, it is required that corrosion-current for preventing corrosion be supplied to the whole outer surface of the fluid passage member. In order to attain this, in the case of a corrugated type fin members as shown in FIG. 3, it is required that the surface area of the fin members be 2.5 or more times the outer surface of the fluid passage member and that the fin pitch l be not more than 10 mm. When the above-mentioned area ratio is less than 2.5 and the fin pitch is greater than 10 mm, corrosion current becomes insufficient and corrosion takes place in part of the fluid passage member. 
     Table 1 through Table 4 summarize the embodiments of heat exchanger cores according to the present invention together with their test results. 
     Table 1 shows the chemical composition of a variety of fluid passge members tested in the present invention. In the table, A11 and A12 represent comparative examples. The main component of each fluid passage member is Al. 
     
                       TABLE 1                                                     
______________________________________                                    
Chemical Composition of Tested                                            
Aluminum Alloys for Fluid Passage                                         
Members                                                                   
Chemical Composition (%)                                                  
No.    Mn      Mg      Cr   Ti   Zr   Cu   Fe   Si                        
______________________________________                                    
A1     0.3     0.3                                                        
A2     0.3     0.5     0.1                                                
A3     0.6                  0.1                                           
A4     0.6                       0.1                                      
A5     1.2                            0.2                                 
A6     1.2                                 0.5                            
A7     1.5     0.3                              0.2                       
A8     1.8                       0.1  0.1  0.3                            
A9     0.2                                                                
 A10   2                                                                  
 A11                                       0.2  0.1                       
 A12   0.1     0.1                    0.1                                 
______________________________________                                    
 
    
     Table 2 shows the chemical composition of the core metal layers of a variety of brazing sheets for making fin members. In the cladding layer in each brazing sheet, Al-10% Si-1.5% Mg alloy was employed. In the table, B11 and B12 represent comparative examples. The main component of the core metal layer of each brazing sheet is Al. 
     
                       TABLE 2                                                     
______________________________________                                    
Chemical Composition of Core Metal                                        
Layers of Brazing Sheets                                                  
Chemical Compositions (%)                                                 
No.  Sn      Mn     Mg   Zn   Cu   Cr   Zr   Fe   Si                      
______________________________________                                    
B1   0.03                1.0                                              
B2   0.04                     0.1                                         
B3   0.04                          0.1                                    
B4   0.05                               0.1                               
B5   0.05                                    0.5                          
B6   0.06           0.6                           0.4                     
B7   0.06    1.2                                                          
B8   0.08    1.0    0.5       0.1                                         
B9   0.01                                                                 
 B10 0.09                                                                 
 B11                                         0.5  0.2                     
 B12  0.005  1.2              0.1            0.5  0.2                     
______________________________________                                    
 
    
     Table 3 summarizes the results of measurement of potentials of the aluminum alloys listed in Table 1 and the brazing sheets of Table 2. 
     
                       TABLE 3                                                     
______________________________________                                    
Measurement of Potentials of Aluminum                                     
Alloys Listed in Table 1 and Table 2                                      
Fluid Passage Member                                                      
                   Brazing Sheet                                          
No.       Potential (V)                                                   
                       No.      Potential (V)                             
______________________________________                                    
A1        -0.69        B1       -0.79                                     
A2        -0.69        B2       -0.76                                     
A3        -0.68        B3       -0.78                                     
A4        -0.68        B4       -0.78                                     
A5        -0.66        B5       -0.77                                     
A6        -0.67        B6       -0.76                                     
A7        -0.67        B7       -0.77                                     
A8        -0.66        B8       -0.78                                     
A9        -0.69        B9       -0.75                                     
 A10      -0.67         B10     -0.79                                     
 A11      -0.74         B11     -0.73                                     
 A12      -0.73         B12     -0.72                                     
______________________________________                                    
 (note) The potential in a 3% NaCl aqueous solution, using a saturated    
 calomel reference electrode.                                             
 
    
     Table 4 summarizes the construction of each embodiment of a heat exchanger core according to the present invention and the results of corrosion testing with respect to each embodiment. In the table, No. 22 through No. 26 are comparative examples. 
     
                                           TABLE 4                                 
__________________________________________________________________________
Construction of Heat Exchanger Cores                                      
and Their Corrosion Tests                                                 
Materials                                                                 
         Core                                                             
         Metal  Construction                                              
                          Maximum Depth of                                
Fluid    Layer of                                                         
                of Heat   Pitting Corrosion (mm)                          
passage  Brazing                                                          
                Exchanger        Alternate-.sup.3                         
   member                                                                 
         Sheet       Fin  Cass.sup.2                                      
                                 Wet and                                  
   (pipe (Fin   Area.sup.1                                                
                     Pitch                                                
                          Test   Dry Test                                 
No.                                                                       
   material)                                                              
         Members)                                                         
                Ratio                                                     
                     (mm) (1 month)                                       
                                 (3 months)                               
__________________________________________________________________________
1  A1    B1     5    4    0.07   0.03                                     
2  A2    B2     5    4    0.16   0.07                                     
3  A3    B3     3    6    0.14   0.06                                     
4  A4    B4     3    6    0.13   0.06                                     
5  A5    B5     6    8    0.11   0.05                                     
6  A6    B6     6    8    0.18   0.09                                     
7  A7    B7     6    6    0.14   0.06                                     
8  A8    B8     6    6    0.09   0.04                                     
9  A1    B6     7    4    0.16   0.07                                     
10 A2    B4     7    4    0.18   0.09                                     
11 A3    B2     7    6    0.17   0.08                                     
12 A4    B8     6    6    0.13   0.06                                     
13 A5    B5     6    6    0.11   0.05                                     
14 A6    B7     5    5    0.13   0.06                                     
15 A7    B3     5    5    0.12   0.05                                     
16 A9    B9     6    6    0.19   0.09                                     
17  A10   B10   5    4    0.11   0.05                                     
18 A9    B1     5    4    0.14   0.07                                     
19  A10  B2     4    6    0.15   0.08                                     
20 A2    B9     6    6    0.15   0.08                                     
21 A3     B10   5    4    0.11   0.06                                     
22  A11  B4     6    5    0.67   0.41                                     
23 A4     B11   6    5    0.54   0.33                                     
24  A12   B12   6    5    0.91   0.62                                     
25 A5    B5     24   12   0.36   0.20                                     
26  A11   B11   4    12   0.95   0.64                                     
__________________________________________________________________________
 .sup.1 Area Ratio = Area of Fin Member/Area of Fluid Passage Member      
 (pipe).                                                                  
 .sup.2 In accordance with Japanese Industrial Standard (JIS) H8681, a cas
 test was conducted for each sample for one month. When the maximum       
 corroded depth was not more than 0.2 mm, the sample was judged good, and 
 when the maximum corroded depth was 0.3 mm or more, the sample was judged
 defective.                                                               
 .sup.3 Alternate Wet and Dry Test: Each brased sample was immersed in a 3
 NaCl aqueous solution (pH = 3) at 40° C. for 30 minutes, and was  
 then dried at 50° C. for 30 minutes. This cycle was repeated for  
 one month. After this test, when the maximum corroded depth was not more 
 than 0.1 mm, the sample was judged good, and when the maximum corroded   
 depth was 0.2 mm or more, the sample was judged defective.               
 
    
     In the above-mentioned embodiments and comparative examples, the thickness of the fluid passage member was 1.0 mm, and the thickness of the brazing sheet for the fin members was 0.16 mm, which was cladded on both sides with each cladding ratio being 12%. 
     The brazing was conducted at temperatures in the range of 590° C. to 610° C. at 10 -5  torr over the period of 3 to 5 minutes. 
     As above mentioned, according to the present invention, heat exchanger core having highly improved corrosion resistance can be attained by the combination of the sacrificial fin member and the more noble fluid passage member whose potential is widely different from that of the fine member. Consequently, the heat exchanger core according to the present invention can be used for many purposes and is very useful in various applications.