Foul-resistant heat exhanger

Abstract

A heat exchanger is disclosed for use with an air handling system. The heat exchanger may have an inlet, an outlet, and at least one passage fluidly connecting the inlet and the outlet. The at least one passage may include a wall configured to transfer heat between a first fluid inside the at least one passage and a second fluid outside the at least one passage. The heat exchanger may also have a plurality of heat conducting features disposed along a length of the at least one passage, and a foul-resistant coating applied to only a subset of the plurality of heat conducting features.

What is claimed is: 
     
         1 . A heat exchanger, comprising:
 an inlet;   an outlet;   at least one passage fluidly connecting the inlet and the outlet and having a wall configured to transfer heat between a first fluid inside the at least one passage and a second fluid outside the at least one passage;   a plurality of heat conducting features disposed along a length of the at least one passage; and   a foul-resistant coating applied to only a subset of the plurality of heat conducting features.   
     
     
         2 . The heat exchanger of  claim 1 , wherein the plurality of heat conducting features are fabricated from stainless steel. 
     
     
         3 . The heat exchanger of  claim 1 , wherein the foul-resistant coating has a surface finish that is smoother than a surface finish of the plurality of heat conducting features. 
     
     
         4 . The heat exchanger of  claim 1 , wherein the foul-resistant coating is fabricated from a ceramic material. 
     
     
         5 . The heat exchanger of  claim 4 , wherein the ceramic material is one of a boron-nitride super-enhanced graphite or a silicon carbide.  6 , The heat exchanger of  claim 1 , wherein the subset includes only a downstream half or less of the plurality of heat conducting features. 
     
     
         7 . The heat exchanger of claim  6 , wherein the subset includes only a 20-50% of the plurality of heat conducting features located closest to the outlet. 
     
     
         8 . The heat exchanger of  claim 1 , wherein a thickness of the foul-resistant coating is about 1/50- 1/100 th  of a thickness of each of the plurality of heat conducting features. 
     
     
         9 . The heat exchanger of  claim 1 , wherein the foul-resistant coating results in a loss of thermal conductivity through the subset of the plurality of heat conducting features by an amount less than about 0-10%. 
     
     
         10 . The heat exchanger of  claim 1 , wherein a coefficient of thermal expansion of the foul-resistant coating is about the same as a coefficient of thermal expansion of the plurality of heat conducting features when fluid exposed to the plurality of heat conducting features has a temperature of about 100-180° C. 
     
     
         11 . The heat exchanger of  claim 1 , wherein the plurality of heat conducting features includes fins. 
     
     
         12 . The heat exchanger of  claim 1 , wherein:
 one of the first and second fluids is recirculated exhaust gas; and   the other of the first and second fluids is a coolant.   
     
     
         13 . The heat exchanger of  claim 12 , wherein the plurality of heat conducting features extend into the recirculated exhaust gas. 
     
     
         14 . The heat exchanger of  claim 13 , wherein:
 the plurality of heat conducting features includes a first plurality of heat conducting features; and   the heat exchanger further includes a second plurality of heat conducting features that extend into the coolant.   
     
     
         15 . The heat exchanger of  claim 14 , wherein the second plurality of heat conducting features are uncoated. 
     
     
         16 . A heat exchanger, comprising:
 an inlet;   an outlet;   at least one passage fluidly connecting the inlet and the outlet and having a wall configured to transfer heat between a recirculated exhaust gas located at one side of the wall and a coolant located at an opposing side of the wall;   a plurality of stainless steel fins disposed along a length of the at least one passage; and   a foul-resistant ceramic coating applied to only one-half or less of the plurality of stainless steel fins located closest to the outlet,   wherein:
 the foul-resistant ceramic coating is fabricated from one of a boron-nitride super-enhanced graphite or a silicon carbide; and 
 the foul-resistant ceramic coating has a surface finish that is smoother than a surface finish of the plurality of stainless steel fins. 
   
     
     
         17 . The heat exchanger of  claim 16 , wherein the foul-resistant ceramic coating is applied to only 20-50% of the plurality of stainless steel fins located closest to the outlet. 
     
     
         18 . The heat exchanger of  claim 16 , wherein a thickness of the foul-resistant ceramic coating is about 1/50- 1/100 th  of a thickness of each of the plurality of stainless steel fins. 
     
     
         19 . The heat exchanger of  claim 16 , wherein:
 the foul-resistant ceramic coating results in a loss of thermal conductivity through a downstream half or less of the plurality of stainless steel fins by an amount less than about 0-10%; and   a coefficient of thermal expansion of the foul-resistant ceramic coating is about the same as a coefficient of thermal expansion of the plurality of stainless steel fins when the recirculated exhaust gas has a temperature of about 100-180° C.   
     
     
         20 . A fluid handling system for an engine, comprising:
 a supply of air;   a supply of recirculated exhaust gas;   an inlet manifold configured to communicate with the engine; and   a heat exchanger configured to cool the recirculated exhaust gas and to direct the cooled recirculated exhaust gas to mix with the air entering the inlet manifold, the heat exchanger including:
 an inlet in communication with the supply of recirculated exhaust gas; 
 an outlet in communication with the inlet manifold; 
 at least one passage fluidly connecting the inlet and the outlet and having a wall configured to transfer heat between a recirculated exhaust gas located at one side of the wall and a coolant located at an opposing side of the wall; 
 a plurality of stainless steel fins disposed along a length of the at least one passage; and 
 a foul-resistant ceramic coating applied to only a portion of the plurality of stainless steel fins located closest to the outlet, 
 wherein:
 the foul-resistant ceramic coating is fabricated from one of a boron-nitride super-enhanced graphite or a silicon carbide; and 
 the foul-resistant ceramic coating has a surface finish that is smoother than a surface finish of the plurality of stainless steel fins.