Double pipe for heat exchanger

Abstract

A double pipe for a heat exchanger includes an inner pipe having a plurality of spiral projections extending radially outward from an outer peripheral surface of the inner pipe. An outer pipe is disposed around the inner pipe. At least an inner peripheral surface of the outer pipe is at least substantially smooth and has an at least substantially circular cross section. The inner peripheral surface of the outer pipe contacts all of the projections of the inner pipe so as to define a plurality of peripherally-separated, outer flow paths between the inner pipe and the outer pipe. Fluid flowing within an inner flow path defined by the inner pipe exchanges heat with fluid flowing through the outer flow paths. Furthermore, an inscribed circle of the inner pipe has a first diameter (d 1 ), an inscribed circle of the outer pipe has a second diameter (d 2 ), and 0.6<d 1 /d 2.

1 . A double pipe for a heat exchanger comprising:
 an inner pipe having a plurality of spiral projections extending radially outward from an outer peripheral surface of the inner pipe, and   an outer pipe disposed around the inner pipe, at least an inner peripheral surface thereof being at least substantially smooth and having an at least substantially circular cross section,   wherein the inner peripheral surface of the outer pipe contacts all of the projections of the inner pipe so as to define a plurality of peripherally-separated, outer flow paths between the outer peripheral surface of the inner pipe and the inner peripheral surface of the outer pipe,   the double pipe is configured such that fluid flowing within an inner flow path defined by the inner pipe exchanges heat with fluid flowing through the outer flow paths, and   an inscribed circle of the inner pipe has a first diameter (d 1 ), an inscribed circle of the outer pipe has a second diameter (d 2 ), and the relationship 0.6<d 1 /d 2  is satisfied.   
     
     
         2 . The double pipe according to  claim 1 , wherein the inner pipe has 2-12 of the spiral projections. 
     
     
         3 . The double pipe according to  claim 2 , wherein the outer pipe has an outer diameter between 10-30 mm. 
     
     
         4 . The double pipe according to  claim 3 , wherein the inner pipe has a wall thickness of 0.5-2.0 mm. 
     
     
         5 . The double pipe according to  claim 4 , wherein the spiral projections each form an angle with a longitudinal axis of the inner pipe that is between 10°-70°. 
     
     
         6 . The double pipe according to  claim 5 , wherein both the inner pipe and the outer pipe are made of an aluminum alloy or a copper alloy. 
     
     
         7 . The double pipe according to  claim 6 , wherein the outer flow paths have a combined first cross sectional area (S 1 ), the inner flow path has a second cross sectional area (S 2 ) and the relationship S 2 /S 1 ≧1.5 is satisfied. 
     
     
         8 . The double pipe according to  claim 7 , wherein the spiral projections have a width as viewed in a direction orthogonal to a radial direction of the double pipe that extends through the tops of the projections, and the width gradually decreases towards the outside in the radial direction. 
     
     
         9 . The double pipe according to  claim 8 , wherein a plurality of longitudinally-extending grooves are defined in an outer peripheral surface of the outer pipe at spaced intervals around a circumferential direction of the outer pipe. 
     
     
         10 . The double pipe according to  claim 1 , wherein the outer pipe has an outer diameter between 10-30 mm. 
     
     
         11 . The double pipe according to  claim 1 , wherein the inner pipe has a wall thickness of 0.5-2.0 mm. 
     
     
         12 . The double pipe according to  claim 1 , wherein the spiral projections each form an angle with a longitudinal axis of the inner pipe that is between 10°-70°. 
     
     
         13 . The double pipe according to  claim 1 , wherein both the inner pipe and the outer pipe are made of an aluminum alloy or a copper alloy. 
     
     
         14 . The double pipe according to  claim 1 , wherein the outer flow paths have a combined first cross sectional area (S 1 ), the inner flow path has a second cross sectional area (S 2 ) and the relationship S 2 /S 1 ≧1.5 is satisfied. 
     
     
         15 . The double pipe according to  claim 1 , wherein the spiral projections have a width as viewed in a direction orthogonal to a radial direction of the double pipe that extends through the tops of the projections, and the width gradually decreases towards the outside in the radial direction. 
     
     
         16 . The double pipe according to  claim 1 , wherein a plurality of longitudinally-extending grooves are defined in an outer peripheral surface of the outer pipe at spaced intervals around a circumferential direction of the outer pipe. 
     
     
         17 . A double pipe for a heat exchanger having a double pipe structure formed by arranging an inner pipe inside of an outer pipe, the double pipe being configured such that fluid flowing within the inner pipe exchanges heat with fluid flowing between the inner pipe and the outer pipe;
 wherein the inner pipe has a profile formed by partly deforming its originally circular outer periphery in cross section so as to exhibit a plurality of longitudinally straight and narrow radially-outward-extending projections and then twisting the inner pipe having the plurality of longitudinally straight and narrow radially-outward-extending projections so as to form a plurality of spiral and narrow radially-outward-extending projections;   the outer pipe is formed of a smooth pipe, at least an inner peripheral surface thereof has a circular cross section;   the inner peripheral surface of the outer pipe contacts tops of the projections of the inner pipe so as to define a plurality of peripherally-separated, outer flow paths; and   a diameter (d 1 ) of an inscribed circle of the inner pipe and a diameter (d 2 ) of an inscribed circle of the outer pipe satisfy the relationship 0.6<d 1 /d 2 .   
     
     
         18 . The double pipe according to  claim 17 , wherein:
 the inner pipe has 2 to 12 of the spiral projections;   the outer pipe has an outer diameter of between 10-30 mm; and   the inner pipe has a wall thickness of between 0.5-2.0 mm.   
     
     
         19 . The double pipe according to  claim 17 , wherein:
 the spiral projections each form an angle with a longitudinal axis of the inner pipe that is between 10°-70°; and   the projections have a width, as viewed in a direction orthogonal to a radial direction extending through the tops of the projections, that gradually decreases toward the outside in the radial direction.   
     
     
         20 . The double pipe according to  claim 17 , wherein a cross sectional area (S 1 ) of the outer flow paths and a cross sectional area (S 2 ) of the inner flow path within the inner pipe satisfy the relationship S 2 /S 1 ≧1.5.