Mixed material tubular heat exchanger

Abstract

Apparatus for cooling bleed air on an aircraft may include a source of cooling fluid driven by an engine of the aircraft, a source of bleed air driven by the engine and a heat exchanger configured allow the cooling fluid to pass over tubes through which the bleed air flows. The heat exchanger may have a high-temperature zone constructed from material with a first density, and a low-temperature zone constructed from material with a second density lower than the first density.

We claim: 
     
         1 . Apparatus for cooling bleed air on an aircraft comprising:
 a source of cooling fluid driven by an engine of the aircraft;   a source of bleed air driven by the engine;   a heat exchanger configured to allow the cooling fluid to pass over tubes through which the bleed air flows;   the heat exchanger having,
 a) a high-temperature zone constructed from material with a first density, and 
 b) a low-temperature zone constructed from material with a second density lower than the first density. 
   
     
     
         2 . The apparatus of  claim 1 ;
 wherein the heat exchanger has a medium-temperature zone interposed between the high-temperature zone and the low-temperature zone; and   wherein the medium-temperature zone is constructed from material with a third density lower than the first density and higher than the second density.   
     
     
         3 . The apparatus of  claim 2  wherein the medium-temperature zone includes tube segments constructed from titanium or titanium alloy. 
     
     
         4 . The apparatus of  claim 1  wherein the high-temperature zone includes tube segments constructed from stainless steel, nickel or nickel-based alloy. 
     
     
         5 . The apparatus of  claim 1  wherein the low-temperature zone includes tube-segments constructed from aluminum or aluminum-based alloy. 
     
     
         6 . The apparatus of  claim 1  wherein the source of cooling fluid is a by-pass fan of the engine. 
     
     
         7 . The apparatus of  claim 1 :
 wherein the heat exchanger includes a hot-fluid inlet manifold constructed from the material with the first density; and   wherein the heat exchanger includes a hot-fluid outlet manifold constructed from the material with the second density.   
     
     
         8 . A heat exchanger comprising:
 a high-temperature zone constructed from material with a first density, and   a low-temperature zone constructed from material with a second density lower than the first density.   
     
     
         9 . The heat exchanger of  claim 8  further comprising a medium-temperature zone interposed between the high-temperature zone and the low-temperature zone, wherein the medium-temperature zone is constructed from material with a third density lower than the first density and higher than the second density. 
     
     
         10 . The heat exchanger of  claim 9  wherein the medium-temperature zone includes tube segments constructed from titanium or titanium-based alloy. 
     
     
         11 . The heat exchanger of  claim 9  comprising:
 a plurality of hot-fluid passage tubes, each of the tubes including, 
 a) a high-temperature tube segment constructed from the material with the first density, 
 b) a low-temperature tube segment constructed from the material with the second density and 
 c) a medium-temperature tube segment constructed from material with a third density, said third being lower than the first density and higher than the second density. 
 
     
     
         12 . The heat exchanger of  claim 8  wherein the high-temperature zone includes tube segments constructed from stainless steel, nickel or nickel-based alloy. 
     
     
         13 . The heat exchanger of  claim 8  wherein the high-temperature zone includes tube segments constructed from titanium or titanium-based alloy. 
     
     
         14 . The heat exchanger of  claim 8  wherein the low-temperature zone includes tube-segments constructed from aluminum, aluminum-based alloy, titanium or titanium alloy. 
     
     
         15 . The heat exchanger of  claim 8  further comprising:
 a hot-fluid inlet manifold constructed from the material with the first density; and 
 a hot-fluid outlet manifold constructed from the material with the second density. 
 
     
     
         16 . The heat exchanger of  claim 15 :
 wherein the medium-temperature tube segments are brazed to the high-temperature tube segment with a first brazing filler that remains solid at a temperature of at least 1000° F.; and   wherein the medium-temperature tube segments are brazed to the low-temperature tube segments with a second brazing filler that remains solid at a temperature of at least 600° F.   
     
     
         17 . The heat exchanger of  claim 15  wherein the high-temperature tube segments are brazed to a hot-fluid inlet manifold with brazing filler that remains solid at a temperature of at least 1200° F. 
     
     
         18 . A method for cooling hot fluid comprising the steps:
 passing the hot fluid through first tube segments of a heat exchanger;   passing the hot fluid through second tube segments of the heat exchanger directly from the first tube segments, the second tube segments having a lower temperature tolerance than the first tube segments;   passing cooling fluid over the first segments to cool the hot fluid to a temperature within a range of temperature tolerance of the second tube segments; and   passing the cooling fluid over the second segments to further cool the hot fluid.   
     
     
         19 . The method of  claim 18  further comprising the steps:
 passing the hot fluid through third tube segments of the heat exchanger, the third tube segments having a lower temperature tolerance than the second tube segments; 
 passing the cooling fluid over the second segments to cool the hot fluid to a temperature within a range of temperature tolerance of the third tube segments; and 
 passing the cooling fluid over the third segments to further cool the hot fluid. 
 
     
     
         20 . The method of  claim 18 :
 wherein the hot fluid is bleed air driven with an engine of the aircraft; and   wherein the cooling fluid is by-pass air driven by the engine.