Internal heat exchanger

Abstract

The present invention provides a heat exchanger having an inner tube forming an inner flow path and having an inlet and an outlet; an outer tube radially surrounding at least a portion of the inner tube and spaced radially outwardly therefrom to form an annular space; and a thermally conductive spiral element wound around the inner cube and disposed in the space, wherein the spiral element forms, in conjunction with the inner tube and the outer tube, a helical flow path through the space, the helical flow path in fluid communication with an inlet and an outlet of the outer tube, and wherein the outer tube is thermally isolated from the spiral element. The invention further provides for collars connecting the outer tube to the inner tube.

What is claimed is: 
     
         1 . A heat exchanger comprising:
 an inner tube forming an inner flow path and having an inlet and an outlet;   an outer tube radially surrounding at least portion of the inner tube and spaced radially outwardly therefrom to form an annular space; and   a thermally conductive spiral element wound around the inner tube and disposed in the space,   wherein the spiral element forms, in conjunction with the inner tube and the outer tube, a helical flow path through the space, the helical flow path in fluid communication with an inlet and an outlet of the outer tube, and   wherein the outer tube is thermally isolated from the spiral element.   
     
     
         2 . The heat exchanger of  claim 1 , wherein the outer tube is thermally isolated from the spiral element by being spaced radially outwardly from the spiral element, forming an annular gap defining a bypass flow path. 
     
     
         3 . The heat exchanger of  claim 2 , wherein the bypass flow path accommodates less than about 5% of total flow through the bypass and helical flow paths. 
     
     
         4 . The heat exchanger of  claim 2 , wherein the bypass flow path accommodates less than about 1% of total flow through the bypass and helical flow paths. 
     
     
         5 . A heat exchanger comprising:
 an inner tube forming an inner flow path and having an inlet and an outlet;   an outer tube radially surrounding at least portion of the inner tube and spaced radially outwardly therefrom to form an annular space; and   a thermally conductive spiral element wound around the inner tube and disposed in the space,   wherein the spiral element surrounds the inner tube and forms, in conjunction with the inner tube and the outer tube, a helical flow path through the annular space, the helical flow path in fluid communication with an inlet and an outlet of the outer tube, and   wherein the spiral element continuously contacts the inner tube along a major length of the spiral element, and the spiral element is either integrally attached to the inner tube, as by welding or brazing, or resiliently biased against the inner tube such that the spiral element is tightly held against the inner tube.   
     
     
         6 . The heat exchanger of  claim 5 , wherein the inner tube has an outer diameter surface that is smooth. 
     
     
         7 . The heat exchanger of  claim 5 , wherein the outer diameter surface is of uniform diameter along the length thereof surrounded by the spiral element. 
     
     
         8 . The heat exchanger of  claim 5 , wherein the outer tube is thermally isolated from the spiral element by an insulation layer. 
     
     
         9 . The heat exchanger of  claim 8 , wherein the insulating layer extends along substantially the entire inside surface of the outer tube, extends along only the spiral element, or is intermittently disposed along the length of the inside surface of the outer tube so as to act as a spacer. 
     
     
         10 . The heat exchanger of  claim 9 , wherein the spiral element is not attached to at least one of the inner tube or outer tube. 
     
     
         11 . The heat exchanger of  claim 5 , wherein the turns of the spiral element are axially spaced apart. 
     
     
         12 . The heat exchanger of  claim 5 , wherein the spiral element is welded to the inner tube. 
     
     
         13 . The heat exchanger of  claim 8 , wherein the spiral element is in contact with the inner tube for substantially all of the length of the spiral element. 
     
     
         14 . The heat exchanger of  claim 5 , wherein axial ends of the outer tube are welded to the inner tube. 
     
     
         15 . The heat exchanger of  claim 5 , wherein the outer tube is connected to the inner tube by collars at respective axial ends of the outer tube. 
     
     
         16 . The heat exchanger of  claim 5 , further comprising a first collar configured to secure the outer tube to the inner tube at a first axial end of the outer tube, the first collar including a first radial hole and the helical flow path is in fluid communication with the first radial hole. 
     
     
         17 . The heat exchanger of  claim 16 , further comprising a second collar configured to secure the outer tube to the inner tube at a second axial end of the outer tube, the second collar including a second radial hole, wherein the helical flow path is in fluid communication with the second radial hole. 
     
     
         18 . The heat exchanger of  claim 17 , wherein the first collar includes a central bore having a diameter substantially equal to an outer diameter of the inner tube, a first counter bore with a diameter intermediate of the diameter of the central bore and a diameter of a second counter bore, the diameter of the second counter bore being substantially equal to outside diameter of the outer tube, and wherein the central bore receives the inner tube and the second counter bore receives the outer tube therein. 
     
     
         19 . The heat exchanger of  claim 18 , wherein the first radial hole is disposed in the first counter bore. 
     
     
         20 . A heat exchanger comprising:
 an inner tube forming an inner flow path and having an inlet and an outlet;   an outer tube spaced radially outwardly of the inner tube and radially surrounding at least portion of the inner tube at an overlap region forming a gap therein;   a thermally conductive spiral element wound around the inner tube and disposed in the gap of the overlap region; and   a first collar configured to secure the outer tube to the inner tube at a first axial end of the cuter tube, the first collar including a first radial hole;   wherein the spiral element forms, in conjunction with the inner tube and the outer tube, a helical flow path through the gap of the overlap region, and the helical flow path is in fluid communication with the first radial hole.   
     
     
         21 . The heat exchanger of  claim 20 , further comprising a second collar configured to secure the outer tube to the inner tube at a second axial end of the outer tube, the second collar including a second radial hole, wherein the helical flow path is in fluid communication with the second radial hole. 
     
     
         22 . The heat exchanger of either of  claim 21 , wherein the first collar includes a central bore having a diameter substantially equal to an outer diameter of the inner tube, a first counter bore with a diameter intermediate of the diameter of the central bore and a diameter of a second counter bore, the diameter of the second counter bore being substantially equal to outside diameter of the outer tube, and wherein the central bore receives the inner tube and the second counter bore receives the outer tube therein. 
     
     
         23 . The heat exchanger of  claim 22 , wherein the first radial hole is disposed in the first counter bore. 
     
     
         24 . The heat exchanger of  claim 23 , wherein the outer tube is thermally isolated from the spiral element.