Heat exchanger having variable thickness tie rods and method of fabrication thereof

Abstract

In at least one embodiment, the apparatus of the present invention is a heat exchanger which includes a core having a thermally variable size and a support structure. To minimize, or eliminate, differential thermal expansion, the support structure is connected to the core and thermally deforms to accommodate variations in the size of the core. The support structure employs a thermally deformable member which can be a tie rod with a planar center section. In other embodiments, the support structure includes a first strongback, a second strongback, and at least one variable thickness tie rod mounted between the strongbacks. The variable thickness tie rod can be a broadened end tie rod having an end or ends which are thicker (wider) than a center section. The present invention also includes methods of fabrication. One embodiment includes the steps of obtaining a tie rod having a substantially uniform thickness and forging the tie rod to define a planar center section. Another embodiment includes obtaining a tie rod of uniform thickness, forging a first end of the tie rod to broaden the thickness of the first end, and applying threads to the first end of the tie rod.

What is claimed is:  
     
         1 . A heat exchanger comprising: 
 a. a core having a thermally variable size; and    b. a support structure connected to the core, wherein the support structure thermally deforms to accommodate variations in the size of the core.    
     
     
         2 . The heat exchanger of  claim 1 , wherein the support structure thermally deforms at a rate at least similar to a rate of change in the size of the core.  
     
     
         3 . The heat exchanger of  claim 1 , wherein the support structure thermally deforms substantially the same amount as the thermal variation in the core size.  
     
     
         4 . The heat exchanger of  claim 3 , wherein the support structure further comprises a thermally deformable member.  
     
     
         5 . The heat exchanger of  claim 4 , wherein the thermally deformable member comprises a tie rod having a planar section.  
     
     
         6 . The heat exchanger of  claim 5 , wherein the planar section of the tie rod thermally deforms at a rate so that the deformation of the support structure is substantially the same as the thermal variation in the core size.  
     
     
         7 . The heat exchanger of  claim 4 , wherein the thermally deformable member comprises a plurality of tie rods, wherein each tie rod has a planar section.  
     
     
         8 . The heat exchanger of  claim 6 , wherein the planar section is substantially aligned with a flow passing the planar section.  
     
     
         9 . The heat exchanger of  claim 8 , wherein the support structure further comprises a first strongback and a second strongback positioned about the core, wherein the tie rod is connected between the first and second strongbacks.  
     
     
         10 . A heat exchanger comprising: 
 a. a core having a first end and an opposing second end; and    b. a support structure, wherein the core is received by the support structure, wherein the support structure comprises: 
 i. a first strongback adjacent to the first end of the core;  
 ii. a second strongback adjacent the second end of the core; and  
 iii. a variable thickness tie rod mounted between the first strongback 
 and the second strongback.  
 
   
     
     
         11 . The heat exchanger of  claim 10 , wherein the variable thickness tie rod has a planar center section.  
     
     
         12 . The heat exchanger of  claim 10 , wherein the variable thickness tie rod further comprises a center section and a first end, wherein the center section has a center section thickness, wherein the first end has a first end thickness, and wherein the first end thickness is greater than the center section thickness.  
     
     
         13 . The heat exchanger of  claim 12 , wherein the tie rod further comprises a set of threads at the first end.  
     
     
         14 . The heat exchanger of  claim 13 , wherein the threads have an inner thread diameter and an outer thread diameter, wherein the inner thread diameter is greater than the center section thickness.  
     
     
         15 . The heat exchanger of  claim 13 , wherein the threads have an inner thread diameter and an outer thread diameter, wherein the inner thread diameter is at least substantially equal to the center section thickness.  
     
     
         16 . The heat exchanger of  claim 14 , wherein the support structure further 
 comprises fasteners for securing the tie rod to the first strongback and the second strongback, wherein the fasteners are mounted between the tie rod and the first strongback and the second strongback.    
     
     
         17 . The heat exchanger of  claim 12 , wherein the tie rod has a rounded cross-section.  
     
     
         18 . The heat exchanger of  claim 12 , wherein the variable thickness tie rod further comprises a second end opposing the first end, wherein the second end has a second end thickness, and wherein the second end thickness is greater than the center section thickness.  
     
     
         19 . The heat exchanger of  claim 18 , wherein the tie rod further comprises a set of first threads at the first end and a set of second threads at the second end.  
     
     
         20 . The heat exchanger of  claim 19 , wherein the first threads have an inner first thread diameter and an outer first thread diameter, wherein the second threads have an inner second thread diameter and an outer second thread diameter, wherein the first inner thread diameter and the second inner thread diameter are greater than the center section thickness.  
     
     
         21 . The heat exchanger of  claim 19 , wherein the first threads have an inner first thread diameter and an outer first thread diameter, wherein the second threads have an inner second thread diameter and an outer second thread diameter, wherein the first inner thread diameter and the second inner thread diameter are at least substantially equal to the center section thickness.  
     
     
         22 . A method of fabricating a tie rod comprising: 
 a. obtaining a tie rod having a substantially uniform thickness; and    b. forging the tie rod to define a planar center section.    
     
     
         23 . The method of  claim 22 , wherein the tie rod having substantially uniform thickness has a rounded cross section.  
     
     
         24 . The method of  claim 22 , wherein the forging comprises heating the tie rod and applying pressure to the uniform thickness tie rod to form the planar center section.  
     
     
         25 . The method of  claim 24 , wherein the method further comprises defining threads in an end of the tie rod.  
     
     
         26 . A method of fabricating a tie rod comprising: 
 a. obtaining a tie rod of uniform thickness;    b. forging a first end of the tie rod to broaden the thickness of the first end; and    c. applying threads to the first end of the tie rod.    
     
     
         27 . The method of  claim 26 , wherein applying the threads to the first end comprises rolling a die over the first end to define the threads in the first end of the tie rod.  
     
     
         28 . The method of  claim 27 , wherein the method further comprises: 
 a. forging a second end of the tie rod to broaden the thickness of the second end; and    b. applying threads to the second end of the tie rod.    
     
     
         29 . The method of  claim 26 , wherein the tie rod having substantially uniform thickness has a rounded cross section.  
     
     
         30 . The method of  claim 27 , wherein the forging comprises heating the first end of the tie rod and applying pressure to the tie rod to broaden the thickness of the first end.