Counterflow helical heat exchanger

Abstract

A heat exchanger assembly comprising a tube with a thermally conductive tube insert sealed therein, the tube insert having a substantially similar cross-section to the cross-section of the tube, and a plurality of fluid ports for passage of fluid into and out of the tube, the fluid ports arranged for counterflow operation. The tube insert includes a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle. The tube insert is sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices.

Thus, having described the invention, what is claimed is:  
     
         1 . A helical heat exchanger assembly, comprising:
 a tube having first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter;   a thermally conductive tube insert having a length and a substantially similar cross-section to the cross-section of the tube, the tube insert having first and second ends and including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle, the tube insert sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices; and   a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube.   
     
     
         2 . The heat exchanger assembly of  claim 1  wherein the fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions. 
     
     
         3 . The heat exchanger assembly of  claim 2  wherein at least one of the inlet or outlet fluid ports in a set of fluid ports is positioned in an opening in a wall of the tube. 
     
     
         4 . The heat exchanger assembly of  claim 2  wherein at least one of the inlet or outlet fluid ports in a set of fluid ports is positioned on an end of the tube. 
     
     
         5 . The heat exchanger assembly of  claim 1  wherein each of the tube and tube insert has a substantially circular cross-section. 
     
     
         6 . The heat exchanger assembly of  claim 1  wherein the first ends of the helices are offset from each other by an angle of 180 degrees. 
     
     
         7 . The heat exchanger assembly of  claim 1  wherein each of the helices has a predetermined pitch which is less than the tube inner diameter. 
     
     
         8 . The heat exchanger assembly of  claim 1  wherein the tube insert does not extend substantially beyond the tube first or second ends. 
     
     
         9 . The heat exchanger assembly of  claim 1  wherein the assembly includes a first end cap sealed to the tube and tube insert first ends and a second end cap sealed to the tube and tube insert second ends. 
     
     
         10 . The heat exchanger assembly of  claim 9  wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube and tube insert to prevent fluid mixing inside the heat exchanger. 
     
     
         11 . The heat exchanger assembly of  claim 1  wherein the tube insert includes an inner expansion tube having first and second ends, a length and a diameter less than the tube insert outer diameter, the inner expansion tube capable of receiving an expansion mandrel inserted therein to expand the tube insert into a tight fit with an inner surface of the tube, the helices extending along the length of and winding around the inner expansion tube. 
     
     
         12 . The heat exchanger assembly of  claim 11  wherein the assembly includes a first end cap sealed to the tube, tube insert, and inner expansion tube first ends and a second end cap sealed to the tube, tube insert, and inner expansion tube second ends. 
     
     
         13 . The heat exchanger assembly of  claim 12  wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube, tube insert, and inner expansion tube to prevent fluid mixing inside the heat exchanger. 
     
     
         14 . The heat exchanger assembly of  claim 1  wherein at least one of the helices includes turbulating dimples or ridges. 
     
     
         15 . The heat exchanger assembly of  claim 1  wherein the tube and tube insert are comprised of braze-clad aluminum. 
     
     
         16 . The heat exchanger assembly of  claim 15  wherein the helices and tube are brazed together to create fluid-tight first and second fluid flow paths. 
     
     
         17 . The heat exchanger assembly of  claim 1  wherein the assembly includes a plurality of tubes with tube inserts sealed therein, the first fluid inlet ports of each tube arranged in parallel and the second fluid inlet ports of each tube arranged in parallel, and the first fluid outlet ports of each tube arranged in parallel and the second fluid outlet ports of each tube arranged in parallel, and further including:
 a first inlet manifold connecting each of the first fluid inlet ports, the first inlet manifold including a fluid inlet port for passage of a first fluid into the heat exchanger assembly; 
 a first outlet manifold connecting each of the first fluid outlet ports, the first outlet manifold including a fluid outlet port for passage of a first fluid out of the heat exchanger assembly; 
 a second inlet manifold connecting each of the second fluid inlet ports, the second inlet manifold including a fluid inlet port for passage of a second fluid into the heat exchanger assembly; and 
 a second outlet manifold connecting each of the second fluid outlet ports, the second outlet manifold including a fluid outlet port for passage of a second fluid out of the heat exchanger assembly, 
 wherein the inlet and outlet manifolds are each sealed to prevent fluid mixing inside the heat exchanger assembly. 
 
     
     
         18 . The heat exchanger assembly of  claim 17  wherein the first and second inlet and outlet manifold fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions. 
     
     
         19 . A method of assembling a heat exchanger, comprising the steps of:
 providing a tube having first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter;   providing a thermally conductive tube insert having first and second ends, a length and a substantially similar cross-section to the cross-section of the tube, the tube insert including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle;   inserting the tube insert within the tube and sealing the tube insert therein to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices; and   providing a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube.   
     
     
         20 . The method of  claim 19  wherein the fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions. 
     
     
         21 . The method of  claim 19  wherein the tube insert is inserted within the tube by automation. 
     
     
         22 . The method of  claim 19  wherein each of the tube and tube insert has a substantially circular cross-section. 
     
     
         23 . The method of  claim 19  wherein the first ends of the helices are offset from each other by an angle of 180 degrees. 
     
     
         24 . The method of  claim 19  wherein each of the helices has a predetermined pitch which is less than the tube inner diameter. 
     
     
         25 . The method of  claim 19  wherein the tube insert does not extend substantially beyond the tube first or second ends. 
     
     
         26 . The method of  claim 19  wherein at least one of the helices includes turbulating dimples or ridges. 
     
     
         27 . The method of  claim 19  further including the steps of:
 sealing a second end cap to the tube and tube insert second ends; and 
 sealing a first end cap to the tube and tube insert first ends. 
 
     
     
         28 . The method of  claim 27  wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube and tube insert to prevent fluid mixing inside the heat exchanger. 
     
     
         29 . The method of  claim 19  wherein the tube insert includes an inner expansion tube having first and second ends, a length and a diameter less than the tube insert outer diameter, the inner expansion tube capable of receiving an expansion mandrel inserted therein to expand the tube insert into a tight fit with an inner surface of the tube, the helices extending along the length of and winding around the inner expansion tube, and further including the step of:
 inserting the expansion mandrel into the inner expansion tube and expanding the tube insert until the tube insert is a tight fit against an inner surface of the tube. 
 
     
     
         30 . The method of  claim 29  further including the steps of:
 sealing a second end cap to the tube, tube insert, and inner expansion tube second ends; and 
 sealing a first end cap to the tube, tube insert, and inner expansion tube first ends. 
 
     
     
         31 . The method of  claim 30  wherein the first and second end caps are flat, circular plates and are sealed flush with the ends of the tube, tube insert, and inner expansion tube to prevent fluid mixing inside the heat exchanger. 
     
     
         32 . The method of  claim 19  wherein the tube and tube insert are comprised of braze-clad aluminum, and further including the step of:
 brazing the heat exchanger in a furnace to create fluid-tight first and second fluid flow paths. 
 
     
     
         33 . A method of operating a heat exchanger assembly, comprising:
 providing a heat exchanger having a tube with first and second ends, a length, an inner diameter and a cross-section incorporating the inner diameter; a thermally conductive tube insert having a length and a substantially similar cross-section to the cross-section of the tube, the tube insert including a pair of helices extending along the length of the tube insert, the helices having first and second sides offset from each other by a predetermined distance along the length of the tube insert and first and second ends, each of the first ends offset from the other by a predetermined angle and each of the second ends offset from the other by a predetermined angle, the tube insert sealed within the tube to form a first fluid flow path and a second fluid flow path, the first fluid flow path defined between the first sides of the helices and the second fluid path defined between the second sides of the helices; and a plurality of inlet and outlet fluid ports for passage of a first and second fluid into and out of the tube;   connecting inlet and outlet fluid lines for a first fluid to a first set of inlet and outlet ports;   connecting inlet and outlet fluid lines for a second fluid to a second set of inlet and outlet ports; and   flowing the first and second fluids through the first and second sets of inlet and outlet ports, respectively, to cool one of the fluids.   
     
     
         34 . The method of  claim 33  wherein the first and second sets of inlet and outlet fluid ports are arranged for counterflow operation whereby the first and second fluids flow in opposite directions through the first and second fluid paths between the helices.