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A method of establishing a leak tight and structural connection between a core tube and an accommodating header plate in a tubular heat exchanger, including the steps of positioning the core tube into bores of the header plate and a braze foil, installing a ferrule inside the core tube end, radially

A method of establishing a leak tight and structural connection between a core tube and an accommodating header plate in a tubular heat exchanger, including the steps of positioning the core tube into bores of the header plate and a braze foil, installing a ferrule inside the core tube end, radially expanding the ferrule in the core tube end, thus expanding the core tube end into intimate contact with the header plate in which it is received, deforming a ferrule into pinching contact with the braze foil plate, directing the flow of the braze material towards the contact surface area, and brazing the tubular heat exchanger in order to form a seal at the intimate contact area. A leak tight connection and a tubular heat exchanger having a leak tight connection produced via the noted method are also set forth.

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1. A method of providing a leak tight and structural connection between a core tube and an accommodating header plate in a tube and shell type heat exchanger, including the steps of:a. providing a header plate of a deformable metallic material with a core tube-accommodating through bore therein; b.

1. A method of providing a leak tight and structural connection between a core tube and an accommodating header plate in a tube and shell type heat exchanger, including the steps of:a. providing a header plate of a deformable metallic material with a core tube-accommodating through bore therein; b. providing a metallic material braze foil with a core tube accommodating through bore therein; c. providing a core tube of a deformable metallic material with an end having an outside diameter approximately the same as said header plate bore diameter; d. positioning said braze foil on top of said header plate so that said accommodating bore in said braze foil is aligned with said accommodating bore in said header plate; e. inserting said core tube end into the bore in said header plate so that it is received therein and said core tube end is substantially coplanar with said braze foil; f. installing a ferrule of a deformable metallic material into said inserted core tube end, said ferrule including a first cylindrical body portion having an outside diameter approximately the same as the inside diameter of said core tube and a second annular portion extending axially outwardly of said core tube end and having a radial extent greater than the wall thickness of said core tube; g. radially expanding said ferrule first cylindrical body portion so that cylindrical body portion is pressed against said core tube, thus in turn deforming said core tube into an area of intimate contact with said accommodating bore of the header plate; h. deforming said ferrule second annular portion into an area of deformation contact with an adjacent portion of said braze foil at said intimate contact area of said header plate and core tube; and i. brazing said core tube and header plate in a brazing furnace at a temperature and for a time sufficient for said braze foil to melt and flow from said deformation contact area towards and into said intimate contact area of said header plate and core tube, thus forming a leak tight seal in said intimate contact area. 2. The method of claim 1, further including:a. effecting the expansion of said ferrule by movement of a mandrel with an expander portion longitudinally through said ferrule from said cylindrical shank portion to and through said head portion, said expander portion having an outside diameter greater than the inside diameter of said ferrule; and b. simultaneously applying an opposing force to said ferrule in a direction opposite to said movement. 3. The method of claim 1, wherein said brazing step takes place in a vacuum furnace.4. The method of claim 2, wherein said expander portion is a tear-drop shaped portion, flexibly affixed to said mandrel.5. The method of claim 1, wherein the axial extent of said intimate contact area corresponds to the length of said ferrule first cylindrical body portion.6. The method of claim 1, wherein the axial extent of said seal substantially corresponds to the length of said ferrule first cylindrical body portion.7. The method of claim 1, wherein the surface extent of the braze foil substantially corresponds to a bottom surface area of said deformed ferrule second annular portion.8. The method of claim 1, wherein said deformed ferrule second annular portion directs said melted braze foil material into said intimate contact area.9. The method of claim 1, wherein the deformable metallic material of at least said core tube is comprised of one of aluminum and an aluminum alloy.10. The method of claim 1, wherein said metallic material braze foil is comprised of an aluminum braze alloy.11. The method of claim 1, wherein in the installing step, the ferrule takes the form of a rivet and the first cylindrical body portion of said ferrule is a cylindrical shank portion of said rivet and wherein the second annular portion of said ferrule is a head portion of said rivet.12. The method of claim 11, wherein the head portion of said rivet is dome shaped.13. The method of claim 11, wherein the head portion of said rivet is flat.14. The method of claim 1, wherein in the installing step, the ferrule first cylindrical body portion takes the form of a cylindrical sleeve of a predetermined length having an outside diameter selected so as to permit a slip fit thereof into the inside diameter of said core tube, and the ferrule second annular portion forms an integral top portion of said cylindrical sleeve that extends axially outwardly from said core tube end at least past a top surface of said braze foil.15. The method of claim 1, wherein in the brazing step, said braze foil melts and flows into said intimate contact area of said header plate and core tube via capillary action.16. A leak tight connection between a core tube and an accommodating header plate in a tube and shell type heat exchanger prepared according to the method of claim 1.17. A tube and shell type heat exchanger including a plurality of core tubes interposed between spaced accommodating header plates, wherein leak tight connections are provided between said core tubes and said header plates according to the method of claim 1.18. A tube and shell type heat exchanger, comprising:a. a header plate of a deformable metallic material with a core tube accommodating through bore therein; b. a metallic material braze foil with a core tube accommodating through bore therein positioned on the outer surface of said header plate so that said accommodating bore in said braze foil is aligned with said accommodating bore in said header plate; c. a core tube of a deformable metallic material with an end having an outside diameter approximately the same as said header plate bore diameter received within said accommodating through bores of said header plate and said braze foil; d. a ferrule of a predetermined length and a deformable metallic material, said ferrule including a first cylindrical portion of a predetermined length having an outside diameter approximately the same as the inside diameter of said core tube inserted within said core tube end such that an expansion of said first cylindrical portion presses said core tube into intimate contact with said header plate and said ferrule having a second annular portion extending axially outwardly of said core tube end for a distance greater than a wall thickness of said core tube whereby deformation of said ferrule second annular portion directs said braze foil into said intimate contact area; and e. a fillet formed by heating said core tube and said accommodating header plate in a brazing furnace at a temperature and for a time sufficient for said braze foil to melt and flow from said deformation contact area towards and into said intimate contact area of said header plate and core tube and forming a seal therebetween via capillary action. 19. The tube and shell type heat exchanger of claim 18, wherein the ferrule comprises a rivet and the first cylindrical portion of said ferrule is a cylindrical shank portion of said rivet and wherein the second annular portion of said ferrule is a head portion of said rivet.20. The tube and shell type heat exchanger of claim 18 wherein the ferrule first cylindrical portion comprises a cylindrical sleeve of a predetermined length having an outside diameter selected so as to permit a slip fit thereof into an inside diameter of said core tube, and the ferrule second annular portion forms an integral top portion of said cylindrical sleeve that extends axially outwardly from said core tube end at least past a top surface of said braze foil.21. The tube and shell type heat exchanger of claim 18, wherein the deformable metallic material of at least said core tube is comprised of one of aluminum and an aluminum alloy.22. The tube and shell type heat exchanger of claim 18, wherein said metallic material braze foil is comprised of an aluminum braze alloy.23. The tube and shell type heat exchanger of claim 18, wherein the fillet is formed by heating said core tube and said accommodating header plate in a vacuum brazing furnace.24. The tube and shell type heat exchanger of claim 18, wherein the fillet is formed by heating said core tube and said accommodating header plate in an inert atmosphere furnace.25. The tube and shell type heat exchanger of claim 18, wherein the axial extent of said intimate contact area substantially corresponds to the length of said ferrule first cylindrical portion.26. The tube and shell type heat exchanger of claim 18, wherein the axial extent of said seal substantially corresponds to the length of said ferrule first cylindrical portion.27. The tube and shell type heat exchanger of claim 18, wherein the surface extent of the braze foil substantially corresponds to the bottom surface area of said ferrule second annular portion.28. The tube and shell type heat exchanger of claim 18, wherein said deformed ferrule second annular portion directs said melted braze foil into said intimate contact area.29. A method of providing a leak tight connection between a core tube and an accommodating header plate in a tube and shell type heat exchanger, including:a. providing a header plate with a core tube accommodating through bore therein; b. providing a braze foil with a core tube accommodating through bore therein; c. providing a core tube with an end having an outside diameter approximately the same as said header plate bore diameter; d. positioning said braze foil on top of said header plate so that said accommodating through bore in said braze foil is aligned with said accommodating through bore in said header plate; e. inserting said core tube end into the through bore in said header plate so that it is received therein and said tube end is substantially coplanar with said braze foil; f. installing a ferrule into said inserted core tube end, said ferrule having a cylindrical shank portion of a predetermined length having an outside diameter approximately the same as an inside diameter of said core tube and a head portion radially extending from one end of said cylindrical shank portion a distance greater than the wall thickness of said core tube; g. expanding said ferrule radially so that said cylindrical shank portion is pressed against said core tube, thus in turn deforming said core tube into an area of intimate contact with said accommodating through bore of the header plate; h. then deforming said ferrule head portion into an area of deformation contact with an adjacent portion of said braze foil at said intimate contact area of said header plate and core tube; and i. brazing said core tube and header plate in a brazing furnace at a temperature and for a time sufficient for said braze foil to melt and flow from said deformation contact area towards and into said intimate contact area of said header plate and core tube, via capillary action, thus forming a leak tight seal in said intimate contact area. 30. The method of claim 29, wherein in the deforming step, said ferrule head portion has a radial extent greater than said wall thickness of said core tube.31. The method of claim 29, further including:a. effecting the expansion of said ferrule by movement of a mandrel with an expander portion longitudinally through said ferrule from said cylindrical shank portion to and through said head portion, said expander portion having an outside diameter greater than an inside diameter of said ferrule; and b. simultaneously applying an opposing force to said ferrule in a direction opposite to said movement. 32. The method of claim 29, wherein said brazing step takes place in a vacuum furnace.33. The method of claim 31, wherein said expander portion is a tear-drop shaped portion, flexibly affixed to said mandrel.34. The method of claim 29, wherein the axial extent of said intimate contact area substantially corresponds to the length of said ferrule shank.35. The method of claim 29, wherein the axial extent of said seal substantially corresponds to the length of said ferrule shank.36. The method of claim 29, wherein the surface extent of the braze foil substantially corresponds to the bottom surface area of said ferrule head portion.37. The method of claim 29, wherein said deformed ferrule head portion directs said melted braze foil into said intimate contact area.38. A leak tight connection between a core tube and an accommodating header plate in a tube and shell type heat exchanger, which comprises in combination:a. a header plate of a deformable metallic material with a core tube-accommodating through bore therein; b. a metallic material braze foil with a core tube accommodating through bore therein positioned on top of said header plate so that said accommodating bore in said braze foil is aligned with said accommodating bore in said header plate; c. a core tube of a deformable metallic material with an end having an outside diameter approximately the same as said header plate bore diameter received within said accommodating through bores of said header plate and said braze foil; d. a ferrule installed inside said core tube end having a cylindrical shank portion with an outside diameter approximately the same as an inside diameter of said core tube and a head portion radially expanding from one end of said cylindrical shank portion a distance greater than the wall thickness of said core tube; e. means for deforming said ferrule such that deformation of said shank presses said core tube into intimate contact with said header plate and deformation of said head portion directs said braze foil into said intimate contact area; f. a fillet formed by heating said core tube and shell heat exchanger in a brazing furnace at a temperature and for a time sufficient for said braze foil to melt and flow from said deformation contact area towards and into said intimate contact area of said header plate and tube thus forming a seal, via capillary action, in said intimate contact area.