Heat-exchanger tube structured on both sides and a method for its manufacture

Abstract

The invention relates to a heat-exchanger tube structured on both sides with excellent heat transfer characteristics utilizing both outer and also inner fins and secondary grooves intersecting the inner fins. Two spaced-apart rolling tools are provided in the utilized device in order to form the outer fins of two adjacent rolling tools; the inner structure is formed by two differently profiled mandrels. The first mandrel forms in a first forming area the inner fins. The second mandrel forms in a second forming area the inventive secondary grooves into the earlier created inner fins.

What is claimed is:  
     
         1 . A heat exchanger tube comprising optionally plain ends, at least one structured area on the outside of the tube and inside of the tube and optionally plain center lands, which has the following characteristics: 
 a) integral outer fins extend helically over the outside of the tube;    b) integral inner fins extend axis-parallel or helically at a helix angle α=0 to 70°, measured against the tube axis, while forming primary grooves on the inside of the tube, wherein;    c) the inner fins are intersected by secondary grooves extending at a helix angle β measured against the tube axis;    d) the secondary grooves extend with respect to the inner fins at an angle of intersection γ of at least 10°; and    e) the depth T of the secondary grooves is at least 20% of the fin height H of the inner fins.    
     
     
         2 . The heat-exchanger tube according to  claim 1 , wherein the angle of intersection γ is in the range of 30° to 100°.  
     
     
         3 . The heat-exchanger tube according to  claim 2 , wherein the angle of intersection γ is in the range of 60° to 85°.  
     
     
         4 . The heat-exchanger tube according to  claim 1 , wherein in the case of oppositely extending inner fins and secondary grooves, the angle of intersection γ results as the sum of the helix angles α and β (γ=α+β).  
     
     
         5 . The heat-exchanger tube according to  claim 1 , wherein in the case of inner fins and secondary grooves, which extend in the same direction, the angle of intersection γ results as the difference of the helix angles α and β (γ=α−β).  
     
     
         6 . The heat-exchanger tube according to  claim 1 , wherein the depth T of the secondary grooves is at least 40% of the fin height H.  
     
     
         7 . The heat-exchanger tube according to  claim 1 , wherein the fin height H is in the range of 0.15 mm to 0.40 mm.  
     
     
         8 . The heat-exchanger tube according to  claim 1 , wherein the density of the intersecting points of inner fins and secondary grooves is in the range of 90 to 250 intersecting points/cm 2 .  
     
     
         9 . The heat-exchanger tube according to  claim 1 , wherein the depth T of the secondary grooves corresponds with the fin height H.  
     
     
         10 . The heat-exchanger tube according to  claim 9 , wherein the inside of the tube has a frustum-like structure.  
     
     
         11 . The heat-exchanger tube according to  claim 1 , wherein the share of the weight of the inner structure, which share refers to the outer envelope surface of the heat-exchanger tube, is 500 to 1000 g/m 2 , preferably 600 to 900 g/m 2 , and wherein the density of the material which is being used is 7.5 to 9.5 g/cm 3 .  
     
     
         12 . The heat-exchanger tube according to  claim 1 , wherein the share of the weight of the inner structure, which share refers to the outer envelope surface of the heat-exchanger tube, is 150 to 300 g/m 2 , preferably 180 to 270 g/m 2 , and wherein the density of the material which is being used is 2.5 to 3.0 g/cm 3 .  
     
     
         13 . The heat-exchanger tube according to  claim 1 , wherein it is designed as a seamless tube.  
     
     
         14 . A method for the manufacture of a heat-exchanger tube, comprising integral outer fins and inner fins worked out of the tube wall which extend helically on the outside of the tube and extend axially parallel or helically on the inside of the tube, and which inner fins are intersected by secondary grooves in which the following method steps are carried out; 
 helically extending outer fins are formed in a first forming area on the outside of a plain tube by the fin material being obtained by displacing material from the tube wall by means of a first finning step, and the finned tube which is being created is rotated by the rolling forces and moved corresponding with the helical fins which are being created, whereby the outer fins are formed with an increasing height out of the otherwise nonformed plain tube;    the tube wall is supported in a first forming area by a first mandrel lying in the tube, which mandrel is rotatable and profiled;    the outer fins are shaped with a further increasing height during a second finning step in a second forming area which is spaced from the first forming area, and the inner fins are provided with secondary grooves; whereby    the tube wall is supported in a second forming area by a second mandrel lying in the tube, which mandrel is also constructed rotatably and profiled, the profiling of which, however, differs from the profiling of the first mandrel with respect to the amount or the orientation of the helix angle.    
     
     
         15 . The method according to  claim 14 , wherein the spacing between the forming areas is chosen essentially as an integral multiple of the fin pitch p.  
     
     
         16 . The method according to  claim 14 , wherein the outside diameter of the second mandrel is chosen to be smaller than the outside diameter of the first mandrel.  
     
     
         17 . The method according to  claim 14  for the manufacture of a heat-exchanger tube with oppositely inner fins and secondary grooves, the angle of intersection γ resulting in the sum of the helix angles α and β (γ=α+β), wherein mandrels with oppositely oriented grooves are used.  
     
     
         18 . The method according to  claim 14  for the manufacture of a heat-exchanger tube with inner fins and secondary grooves which extend in the same direction, the angle of intersection γ resulting in the difference of the helix angles α and β (γ=α−β), wherein mandrels with grooves oriented in the same direction are used.  
     
     
         19 . The method according to  claim 14 , wherein the depth T of the secondary grooves is adjusted by selecting the diameters of the mandrels and by selecting the diameters of the respectively largest rolling disks of the two rolling tools.