Heat exchange surface

Abstract

A heating surface element with a zig zag arrangement of longitudinal undulations which serve to minimize the skew flow of the gas. The angle of the undulations is preferably 15° to 35° to the primary flow direction of the gas. When used in combination with a notched heat surface element, the undulation preferably crosses no more than one opposing notch before changing direction.

1 . A stack of heating surface elements with a primary direction, said stack comprising a first heating surface element having a herringbone structure, said herringbone structure having a plurality of regions, said plurality of regions being arranged such that the boundary of regions is along said primary direction, said plurality of regions comprising a first region having a plurality of undulations arranged laterally side by side, the longitudinal extent of said undulations in said first region being greater than 0° and less than 90° to said primary direction, said plurality of regions further comprising a second region, adjacent to said first region, said second region having a plurality of undulations arranged laterally side by side, the longitudinal extent of said undulations in said second region being less than 0° and more than −90° to said primary direction, said stack further comprising a second heating surface element, said second heating surface element comprising a notch extending along said primary direction, said notch being arranged such that it is not directly opposite the boundary between said first and second region. 
   
   
       2 . A stack according to  claim 1 , wherein said first heating surface element comprises a plurality of first regions, each having a plurality of undulations arranged laterally side by side, the longitudinal extent of said undulations being between +10° and +80° to said primary direction, said first heating surface further comprising a plurality of second regions, each having a plurality of undulations arranged laterally side by side, the longitudinal extent of said undulations being between −10° and −80° to said primary direction, each of said second regions being adjacent to at least one first region along a boundary arranged along said primary direction. 
   
   
       3 . A stack according to  claim 1 , wherein said second heating surface element comprises a plurality of notches extending along said primary direction, at least some of said plurality of notches being arranged such that they are not directly opposite a boundary between a first region and a second region on said first heating surface element. 
   
   
       4 . A stack according to  claim 1 , wherein said stack comprises a plurality of first heating surface elements and a plurality of second heating surface elements, each first heating surface element being adjacent to at least one of said second heating elements. 
   
   
       5 . A stack according to  claim 1 , wherein said first region directly borders said second region. 
   
   
       6 . A stack according to  claim 5 , wherein, at the boundary between said first and second region, the maximum of each peak of undulations in said first region substantially meets the maximum of a peak of an undulation in said second region. 
   
   
       7 . A stack according to  claim 1 , wherein the longitudinal extent of undulations in said first region are at an angle of between +15° to +35° to said primary direction and the longitudinal extent of the undulations in said second region are at an angle of between −15° to −35° to said primary direction. 
   
   
       8 . A stack according to  claim 1 , wherein said second heating surface element comprises a plurality of undulations arranged laterally side by side, the longitudinal extent of said undulations being either greater than 0° and less than 90° to said primary direction or being less than 0° and more than −90° to said primary direction. 
   
   
       9 . A stack according to  claim 1 , wherein the distance between the notches in the second heating surface element is greater than the distance between the boundary between the first and second regions in the first heating surface element. 
   
   
       10 . A rotary air heater comprising a stack of heating surface element according to  claim 1 .