Internally finned tube having enhanced nucleation centers, heat exchangers, and methods of manufacture

Abstract

Tubing having internal fins projecting inward from the tube wall, each fin having an external surface that includes multiple acute interior angles or crevices that may form nucleation boiling sites, heat exchangers comprising such tubing, and methods of making same. Acute angles, crevices, or elongated slits may be formed in the sides, center, or both, of the fins or between the fins and the tube wall, and convex rounded surfaces may be provided therebetween. Fins may be parallel to the tube centerline or helically wound. Tubing may be expanded with a bullet which may form an interference fit with external fins, may modify the fins to create more effective nucleate boiling cavities, or both.

1 . Enhanced tubing for conducting heat between a first fluid within the tubing and a second fluid exterior to the tubing, the tubing comprising:
 at least one tube wall defining an interior passageway; and   multiple internal fins projecting inward from the at least one tube wall, each internal fin having an external surface comprising multiple acute interior angles.   
   
   
       2 . The tubing of  claim 1  the internal fins having sides) wherein at least multiple of the acute interior angles are formed in the sides of the internal fins. 
   
   
       3 . The tubing of either  claim 1  wherein at least a portion of the acute interior angles are formed between the internal fins and the tube wall. 
   
   
       4 . The tubing of  claim 3  wherein each internal fin has a first side and a second side, and wherein for each of the internal fins, a first acute interior angle is formed between the first side of the internal fin and the tube wall, and a second acute interior angle is formed between the second side of the internal fin and the tube wall. 
   
   
       5 . The tubing of  claim 1 , each internal fin having a center, wherein each of the internal fins comprises one of the acute interior angles at the center of the internal fin. 
   
   
       6 . The tubing of  claim 1  wherein the tubing has a centerline and the multiple internal fins are parallel to the centerline. 
   
   
       7 . The tubing of  claim 1  wherein the tubing has a centerline and the acute interior angles are parallel to the centerline. 
   
   
       8 . The tubing of  claim 1  wherein the tubing has a centerline and the multiple internal fins are helically wound around the centerline. 
   
   
       9 . The tubing of  claim 1  wherein the tubing has a centerline and the acute interior angles are helically wound around the centerline. 
   
   
       10 . The tubing of  claim 1  wherein each internal fin further comprises an elongated slit therein. 
   
   
       11 . The tubing of  claim 10  each internal fin having a center, wherein the elongated slit is in the center of the internal fin. 
   
   
       12 . The tubing of  claim 1  wherein the multiple internal fins include at least four internal fins. 
   
   
       13 . The tubing of  claim 1  wherein multiple of the acute interior angles is between 20 and 85 degrees. 
   
   
       14 . The tubing of  claim 1  wherein each of the multiple internal fins comprises at least one convex rounded surface between at least two of the acute interior angles. 
   
   
       15 . The tubing of  claim 1  wherein each of the multiple internal fins comprises multiple convex rounded surfaces between the acute interior angles. 
   
   
       16 . The tubing of  claim 1  further comprising a first straight section of tubing, a second straight section of tubing, and a 180 degree bend between the first section and the second section. 
   
   
       17 . The tubing of  claim 1 , the tube wall having an exterior surface, the exterior surface comprising scalloped relief areas. 
   
   
       18 . The tubing of  claim 17  wherein there is one of the scalloped relief areas across the tube wall from each one of the internal fins. 
   
   
       19 . A method of making a heat exchanger that has enhanced heat transfer characteristics, the method comprising in any order at least the acts of:
 forming tubing having at least one tube wall defining an interior passageway, and multiple internal fins projecting inward from the at least one tube wall;   stacking multiple exterior fins, each exterior fin having multiple holes therethrough, wherein the act of stacking includes lining up the holes in the multiple exterior fins;   passing the tubing through the holes in the multiple exterior fins;   expanding the tubing to create an interference fit between the tubing and the holes; and   modifying the internal fins to create more effective nucleate boiling cavities.   
   
   
       20 . A heat exchanger for effectively transferring heat energy between a first fluid and a second fluid, the heat exchanger comprising:
 multiple sections of tubing;   each section of tubing having at least one tube wall defining an interior passageway;   each section of tubing further comprising multiple internal fins projecting into the passageway from the at least one tube wall, each internal fin having multiple crevices forming nucleation boiling sites;   multiple external fins having holes, wherein the multiple sections of tubing pass through the holes and form an interference fit with the holes; and   multiple 180 degree bends joining the multiple sections of tubing.