Heat transfer tube with ribbed inner surface

Abstract

A heat transfer tube ( 1 ) having a ribbed inner surface which is divided into at least two zones (Z 1 , Z 2 , . . . , Z n ) in circumferential direction, which zones are classified into at least two zone classes (K 1 , K 2 , . . . , K j+1 , . . . , K m ). Ribs ( 1 ) having a rib height h 1 extend at a helix angle α 1 with respect to the longitudinal direction of the tube in the zones of at least one zone class (K 1 , K 2 , . . . , K j ). Ribs ( 2 ) having a rib height h 2 extend at a helix angle α 2 in the zones of at least one further zone class (K j+1 , K j+2 , . . . , K m ), which ribs ( 2 ) are intersected by ribs ( 3 ) having a rib height h 3 extending at a helix angle α 3 (α 3 ≠α 2 ). Preferably are h 2 , h 3 ≦h 1 .

What is claimed is:  
     
         1 . In a heat transfer tube ( 4 ), the inner surface of which is divided in circumferential direction into at least two zones (Z 1 , Z 2 , . . . , Z n ) extending parallel to the longitudinal axis of the tube, and 
 wherein the zones are classified into at least two zone classes (K 1 , K 2 , . . . , K j , K j+1 , . . . , K m ), and    wherein zones of a different zone class alternate at any desired sequence in circumferential direction,    whereby in zones of at least one zone class (K 1 , K 2 , . . . , K j ) there extend ribs ( 1 ) having a rib height h 1  and at a helix angle α 1  with respect to the longitudinal direction of the tube so that, when several of these zone classes (K 1 , K 2 , . . . , K j ) exist, they differ in at least one of the characteristics of rib height and helix angle of inclination,    the improvement wherein: 
 in zones of at least one further zone class (K j+1 , K j+2 , . . . , K m ) there exist ribs ( 2 ) having a helix angle α 2  with respect to the longitudinal direction of the tube and a rib height h 2 , and which ribs ( 2 ) are intersected by ribs ( 3 ) having a rib height h 3 , which ribs ( 3 ) extend at a helix angle α 3  with respect to the longitudinal direction of the tube (α 3 ≠α 2 ), whereby the rib heights h 2  and h 3  of the intersecting ribs ( 2 ) and ( 3 ) in the zones of the zone classes (K j+1 , K j+2 , . . . , K m ) are the same or preferably smaller than the rib heights h 1  of the ribs ( 1 ) in the zones of the zone classes (K 1 , K 2 , . . . , K j ), which zones are the closest in circumferential direction.  
   
     
     
         2 . The heat transfer tube according to  claim 1 , wherein the interesting ribs ( 2 ) and ( 3 ) form an intersection angle of 30° to 90° in the zones of the zone classes (K j+1 , K j+2 , . . . , K m ).  
     
     
         3 . The heat transfer tube according to  claim 1 , wherein the rib density of the ribs ( 3 ), measured as number of ribs per unit of length in direction of the ribs ( 2 ), is 0.5-4 per millimeter, preferably 1-3 per millimeter, in the zones of the zone classes (K j+1 , K j+2 , . . . , K m ).  
     
     
         4 . The heat transfer tube according to  claim 1 , wherein the intersecting ribs ( 2 ) and ( 3 ) produce a lattice-like pattern in the zones of the zone classes (K j+1 , K j+2 , . . . , K m ), in which pattern the ribs ( 2 ) and ( 3 ) of one zone enclose at least one cavity ( 5 ) in one closed rib pattern.  
     
     
         5 . The heat transfer tube according to  claim 1 , wherein the zones are classified into two zone classes (K 1 , K 2 ), and the zones of the zone classes K 1  and K 2  alternate in circumferential direction, whereby ribs ( 1 ) with a rib height h 1  and a helix angle α 1  extend in longitudinal direction of the tube in zones of the zone class K 1 , and ribs ( 2 ) extend in alignment with the ribs ( 1 ) at the same helix angle of inclination α 2  (α 2 =α 1 ) with respect to the longitudinal direction of the tube with the rib height h 2  in zones of the zone class K 2 , and are intersected by ribs ( 3 ) having a rib height h 3 , which ribs ( 3 ) extend at a helix angle α 3  with respect to the longitudinal direction of the tube (α 3 ≠α 2 ).  
     
     
         6 . The heat transfer tube according to  claim 5 , wherein the width B of the zones of one zone class, measured in circumferential direction, is the same in each case, and the width of the zones of the zone class K 2  is less than the width of the zones of the zone class K 1 .  
     
     
         7 . The heat transfer tube according to  claim 6 , wherein the width of the zones of the zone class K 2 , measured in circumferential direction, is 3% to 70% of the width of the zones of the zone class K 1 .  
     
     
         8 . The heat transfer tube according to  claim 5 , wherein the rib height h 1  of the ribs ( 1 ) is 0.15-0.40 mm.  
     
     
         9 . The heat transfer tube according to  claim 1 , wherein the core-wall thickness of the heat transfer tube, measured at the base of a groove ( 9 ) between the ribs ( 1 ) in the zones of the zone classes (K 1 , K 2 , . . . , K j ) or in the cavities ( 5 ) between the ribs ( 2 ,  3 ) in the zones of the zone classes (K j+1 , K j+2 , . . . , K m ) outside of a welding-seam section ( 7 ), is uniform in circumferential direction of the tube.  
     
     
         10 . The heat transfer tube according to  claim 1 , wherein the ribs ( 1 ) have notches ( 8 ) in individual or several zones of the zone classes (K 1 , K 2 , . . . , K j ) whereby the notches ( 8 ) extend aligned at an angle α 4 , which is different from the helix angle α 1  of the ribs ( 1 ) of the respective zone, with respect to the longitudinal direction of the tube, and the notch depth k is at least 20% of the rib height h 1  of the ribs ( 1 ) of the respective zone.