High density corrosive resistant gas to air heat exchanger

Abstract

A gas to air heat exchanger includes corrosive resistant tubes made from one material, and high thermal conductivity air fins made from another material. This construction allows for meeting heat transfer requirements in a spatially constrained application, such as over the road trucks, where a compressed mixture of recirculated exhaust gas and incoming air are compressed and then cooled before being supplied to the engine intake. In one example, the heat exchanger includes tubes made from stainless steel brazed to relatively thin copper air fins in a low temperature brazing process, and the tubes are brazed on respective ends to heads of stainless steel via a high temperature brazing process. This core is then joined to an aluminum inlet tank and possible non-metallic outlet tank via a mechanical crimping process that positions a seal between the tanks and the respective heads.

1 . A gas to air heat exchanger comprising: 
 a core with a plurality of tubes fluidly isolated from, but being in heat transfer contact with, a plurality of air fins;    the tubes comprising a tube material, and the air fins comprising an air fin material;    the tube material having high corrosive resistance relative to the air fin material; and    the air fin material having high thermal conductivity relative to the tube material.    
   
   
       2 . The heat exchanger of  claim 1  including first and second heads brazed to opposite ends of the tubes, respectively; 
 first and second tanks mechanically attached to the first and second heads, respectively; and    first and second seals operably positioned between the first head and the first tank, and between the second head and the second tank, respectively.    
   
   
       3 . The heat exchanger of  claim 1  wherein the air fin material is predominantly copper; 
 the tube material is predominantly stainless steel; and    at least one of the first and second tanks comprise a tank material that is predominantly aluminum.    
   
   
       4 . The heat exchanger of  claim 2  wherein at least one of the first tank and the second tank has a minimum wetted wall thickness that is greater than a minimum wetted wall thickness of the tubes, which is greater than a minimum wetted wall thickness of the air fins.  
   
   
       5 . The heat exchanger of  claim 2  wherein the heads are attached to the tubes with a high temperature brazing material; and 
 the air fins are attached to the tubes with a low temperature brazing material.    
   
   
       6 . The heat exchanger of  claim 2  including a turbulator positioned in at least one of the tubes.  
   
   
       7 . The heat exchanger of  claim 4  wherein the tube material is predominantly at least one of stainless steel, titanium, NI-plated aluminum and Ni-plated steel; 
 the air fin material is predominantly at least one of copper, cuprobraze copper, and stainless steel;    the heads are attached to the tubes with a high temperature brazing material that is predominantly at least one of Ni-based, Ni-plating and a Bnix alloy;    the air fins are attached to the tubes with a low temperature brazing material that is predominantly at least one of OKC600, Ni-plating and Copper based.    
   
   
       8 . The heat exchanger of  claim 2  wherein the air fin material is predominantly copper; 
 the tube material is predominantly stainless steel;    at least one of the first and second tanks comprise a tank material that is predominantly aluminum;    at least one of the first tank and the second tank has a minimum wetted wall thickness that is greater than a minimum wetted wall thickness of the tubes, which is greater than a minimum wetted wall thickness of the air fins;    the heads are attached to the tubes with a high temperature brazing material; and    the air fins are attached to the tubes with a low temperature brazing material.    
   
   
       9 . An engine system comprising: 
 a gas to air heat exchanger fluidly positioned between a compressor outlet and an engine intake;    an exhaust gas recirculation system fluidly connected between an engine exhaust and a compressor inlet;    the heat exchanger including an inlet tank with a first minimum wetted wall thickness, a plurality of tubes with a second minimum wetted wall thickness, and a plurality of air fins with a third minimum wetted wall thickness; and    the first minimum wetted wall thickness is greater than the second minimum wetted wall thickness, which is greater than the third minimum wetted wall thickness.    
   
   
       10 . The engine system of  claim 9  wherein the gas to air heat exchanger includes first and second heads brazed to opposite ends of the tubes, respectively; 
 the inlet tank and an outlet tank being mechanically attached to the first and second heads, respectively; and    first and second seals operably positioned between the first head and the inlet tank, and between the second head and the outlet tank, respectively.    
   
   
       11 . The engine system of  claim 10  wherein the tubes comprise a tube material, the air fins comprise an air fin material, and the inlet tank comprises a tank material; and 
 the tube material is more corrosive resistant than the tank material, which is more corrosive resistant than the air fin material.    
   
   
       12 . The engine system of  claim 11  wherein the air fin material has higher thermal conductivity than the tank material, which has higher thermal conductivity than the tube material.  
   
   
       13 . The engine system of  claim 12  wherein the first and second heads are brazed to opposite ends of the tubes with a high temperature brazing material; and 
 the air fins are attached to the tubes with a low temperature brazing material.    
   
   
       14 . The engine system of  claim 13  wherein at least one of the tubes includes a turbulator therein.  
   
   
       15 . The engine system of  claim 14  wherein the air fin material is predominantly copper; 
 the tube material is predominantly stainless steel; and    the tank material is predominantly aluminum.    
   
   
       16 . A method of making a gas to air heat exchanger, comprising the steps of: 
 assembling a core out of at least two different materials in a two step brazing process at high and low temperatures, respectively; and    mechanically attaching a tank to the core with a seal positioned therebetween.    
   
   
       17 . The method of  claim 16  wherein the assembling step includes the steps of: 
 brazing high thermal conductivity air fins to low thermal conductivity tubes at the low temperature; and    brazing a head to the tubes at the high temperature.    
   
   
       18 . The method of  claim 17  wherein the mechanically attaching step includes a crimping process.  
   
   
       19 . The method of  claim 17  wherein the high temperature brazing step includes brazing a turbulator inside at least one tube.