Patent Publication Number: US-9891009-B2

Title: Tube for heat transfer

Description:
TECHNICAL FIELD 
     The present invention relates to a tube for heat transfer, in particular, to an inner-grooved tube for heat transfer with two types of fins in the inner surface thereof. 
     BACKGROUND 
     Seamless tubes, especially those made of materials of high heat-conductivity such as copper and aluminum, are used in heat exchangers to circulate heat-carrying fluid to transfer heat. Such tubes are internally grooved to increase the area of the inner surface for improve heat exchange area between the heat-carrying fluid and the inner surface of the tube and to generate turbulence, which improves heat exchange efficiency. 
     Employing an inner-grooved tube instead of one with a smooth inner surface in a heat exchanger significantly improves heat exchange efficiency and thus saves energy for environment protection. Notwithstanding the improved efficiency, previous inner-grooved tubes, due to the limitation of maximum hear transfer capacity, cannot satisfy the heat dissipation requirements for some large power equipment. 
     SUMMARY OF THE INVENTION 
     It is an object of the present disclosure to provide an inner-grooved tube with improved heat exchange efficiency. 
     The present disclosure is directed to a tube for heat transfer, the inner surface of the tube is grooved into a pattern, the pattern including a first fin and a second fin which have different shapes, wherein the first fin comprising a shaft and a head integrally formed, the shaft extending from the inner surface in a direction away from the inner surface, the head extending from the shaft in a direction away from the inner surface, in a transverse cross section of the tube, the circumferential width of the head is larger than that of the shaft. 
     The present inner-grooved tube for heat transfer, increases the heat transfer area and the capillary driving force, and thus improves the heat transfer capacity and heat transfer efficiency. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention. 
         FIG. 1  shows a longitudinal cross-sectional view of an inner-grooved tube according to one embodiment of the present disclosure; 
         FIG. 2  shows a transverse cross-sectional view of an inner-grooved tube according to one embodiment of the present disclosure; 
         FIG. 3  shows a transverse cross-sectional view of an inner-grooved tube according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a longitudinal cross-sectional view of an inner-grooved tube  1  according to one embodiment of the present disclosure. The tube is seamless as it is made through drawing a solid billet over a piercing rod to create a hollow shell (in contrast, a welded tube is made by rolling a plate and welding two edges of the plate); the tube, however, may also be a welded one. The inner surface of the tube is grooved into a pattern. Although the tube shown in  FIG. 1  is internally threaded, i.e., its inner surface is grooved into a helical thread, one skilled in the art knows that the inner surface can be grooved into any suitable pattern, e.g. a plurality of ribs extending along the longitudinal axis of the tube, or a helix on the inner surface of the tube. 
       FIG. 2  shows a transverse cross-sectional view of an inner-grooved tube  1  according to one embodiment of the present disclosure. The tube  1  shown in  FIG. 2  has a round cross section. The cross section of the tube, as understood by one skilled in the art, could be a plate shape, a rectangular shape or any other shape appropriate for a particular application. The tube  1  shown in  FIG. 2  has an outer diameter Do, an inner diameter Di and a wall thickness t. 
     The inner surface of the tube  1  is grooved into a pattern, the pattern including a first fin  10  and a second fin  20 . The first fin  10  and the second fin  20  each extend at an angle with respect to the longitudinal direction of the tube so as to form inner threads on the inner surface of the tube. The angle between the internal threads and the longitudinal axis of the tube is 0° to 60°, preferably 2° to 45°. The first fin  10  and the second fin  20  each have a constant transversal cross section along the longitudinal direction of the tube. 
     The first fin  10  and the second fin  20  have different shapes, wherein the first fin  10  comprises a shaft  102  (i.e., a ridge) and a head  101  integrally formed with the shaft  102 . The shaft  102  extends from the inner surface in a direction away from the inner surface, and the head  101  extends from the shaft  102  in a direction away from the inner surface. In a transverse cross section of the tube, the circumferential width W 1  of the head  101  is larger than that W 2  of the shaft  102 . The fin height in a radial direction of the first fin  10  is H 1 , wherein the height the head  101  is less than or equal to that of the shaft  102 . Preferably, the width W 1  in a circumferential direction of the head  101  either increases with the head extending away from the inner surface, or first increases with the head extending away from the inner surface and then decreases toward the tip of the head. The width W 2  in a circumferential direction of the shaft  102  may be constant with the shaft extending away from the inner surface. 
     As shown in  FIG. 2 , the addendum angle of the first fin  10  is α1. The dedendum of the first fin  10  is smoothly connected, at the first corner  11 , to the inner surface of the tube  1  with a curve transition. The curvature of the first corner  11  is R 1 . For instance, H 1  may be 0.05 mm to 0.30 mm and R 1  may be 0 to 0.15 mm. 
     The height in a radial direction of the second fin  20  is H 2  which is lower than the height H 1  of the first fin  10 . Preferably, the height H 2  of the second fin  20  is ⅓ to ½ of the height H 1  of the first fin  10 . The width at the top of the second fin  20 , i.e. the addendum width, is narrower than the width at the bottom the second fin  20 , i.e. the dedendum width. Preferably, the width in a circumferential direction of the second fin  20  decreases with the second fin  20  extending away from the inner surface. As shown in  FIG. 2 , the addendum angle of the second fin  20  is α2 which is 5° to 60°. The dedendum of the second fin  20  is smoothly connected, at the second corner  21 , to the inner surface of the tube  1  with a curve transition. The curvature of the second corner  21  is R 2 . For instance, H 2  may be 0.005 mm to H 1  and R 2  may be 0 to 0.15 mm. 
     In the embodiment shown in  FIG. 2 , the circumferential fin number N 1  of the first fin  10  is identical to the circumferential fin number N 2  of the second fin  20 . The first fin  10  and the second fin  20  are alternately arranged. The fin height H 1  of the first fin  10  is larger than the fin height H 2  of the second fin  20 . For instance, the fin height H 2  is between 0.005 mm and the fin height H 1 . 
     The alternately arranged first fin  10  and second fin  20  can increase the area of the inner surface of the tube, increase the heat transfer area between heat carrying fluid and the inner surface of the tube, and provide higher heat transfer efficiency. In addition, the cavity forms between the first fin  10  and the second fin  20  improve the capillary effects of the tube, provide strong capillary driving force and thus improve the heat transfer performance 
       FIG. 3  shows the transverse cross-sectional view of an inner grooved tube  1 ′ according to another embodiment of the present disclosure. Identical to the previous embodiment, the internal threads on the inner surface of the tube  1 ′ also includes a first fin  10 ′ and a second fin  20 ′. The present embodiment differs from the previous embodiment only in that, the circumferential fin number N 1  of the first fin  10 ′ is twice of the circumferential fin number N 2  of the second fin  20 ′. Every two first fins  10 ′ and one second fin  20 ′ are alternately arranged. However, one skilled in the art understands that, the circumferential fin number N 1  of the first fin  10 ′ can be any other integral times of the circumferential fin number N 2  of the second fin  20 ′, and the second fin is spaced by the first fins. Alternatively, as long as the first fin and the second fin are alternately arranged, the circumferential fin number N 1  of the first fin  10 ′ does not have to be integral times of the circumferential fin number N 2  of the second fin  20 ′. 
     Moreover, provided that the addendum width is larger than the width at the half of the height of the first fin, the first fin  10  is not limited to the shape as shown in  FIGS. 2 and 3 . For instance, the first fin  10  could be approximately inversed trapezoid. Provided that the addendum width is smaller than the dedendum width, the second fin  20  is not limited to the shape as shown in  FIGS. 2 and 3 . For instance, the second fin  20  could be approximately trapezoid. In these situations, the height of the second fin  20  shall be lower than that of the first fin  10 . 
     In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various other modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense. 
     Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.