Double pipe heat exchanger and refrigeration cycle device

Abstract

A double pipe heat exchanger includes an inner pipe inside which a first fluid passes, an outer pipe that has a diameter larger than the diameter of the inner pipe and that covers the inner pipe, and second fluid passes through a space between the outer pipe and the inner pipe, and a heat transfer area enlargement pipe that is provided in the space and that has a projection-depression shape made to be larger than a length in the pipe-circumferential direction of outer contact portions to be contact areas with the inner wall of the outer pipe, and fin portions between the outer contact portion and the inner contact portion that traverse the space in a pipe cross section come into contact with the outer wall of the inner pipe and the inner wall of the outer pipe in oblique directions.

1 . A double pipe heat exchanger comprising:
 an inner pipe inside which a first fluid passes;   an outer pipe that has a diameter larger than a diameter of the inner pipe and that covers the inner pipe, the inner pipe and the outer pipe configured to allow a second fluid to pass through a space defined therebetween; and   a heat transfer area enlargement pipe that is provided in the space and in which, in a pipe cross section, an angle between the heat transfer area enlargement pipe and the outer wall of the inner pipe at each of inner contact portions to he contact areas between an outer wall of the inner pipe and the heat transfer area enlargement pipe is smaller than an angle between the heat transfer area enlargement pipe and the inner wall of the outer-pipe at each of outer contact portions to be contact areas between an inner wall of the outer pipe and the heat transfer area enlargement pipe the heat transfer area enlargement pipe having a projection-depression shape in the pipe cross section in which fin portions between the inner contact portions and the outer contact portions that traverse the space in the pipe cross section come into contact with the outer wall of the inner-pipe and the inner wall of the outer-pipe in oblique directions.   
     
     
         2 . The double pipe heat exchanger of  claim 1 , wherein the fin portions each have an arc shape in the pipe cross section. 
     
     
         3 . The double pipe heat exchanger of  claim 1 , wherein the fin portions each have a bent shape that projects toward the inner pipe side in the pipe cross section. 
     
     
         4 . The double pipe heat exchanger of  claim 1 , wherein, in the pipe cross section of the heat transfer area enlargement pipe, a length in a pipe-circumferential direction of each of the inner contact portions is made to be larger than a length in a pipe-circumferential direction of the outer contact portion. 
     
     
         5 . The double pipe heat exchanger of  claim 1 , wherein the contact portions are formed such that the outer contact portions are made to be point contacts in the pipe cross section, and the inner contact portions are made to be line contacts in the pipe cross section. 
     
     
         6 . The double pipe heat exchanger of  claim 1 , wherein the heat transfer area enlargement pipe is formed so as to satisfy
   θ1<(360 /n )×{doi/(dio+doi)}
   where θ 1  is an angle formed between both end portions of the outer contact portion and the center of the inner pipe and the outer pipe, dio is an outer diameter of the inner pipe, doi is an inner diameter of the outer pipe, n is a number of projecting shapes or depressed shapes of the heat transfer area enlargement pipe, and the projecting shapes and the depressed shapes all have an identical shape.   
     
     
         7 . The double pipe heat exchanger of  claim 1 , wherein the outer contact portions and the inner contact portions are each brazed. 
     
     
         8 . The double pipe heat exchanger of  claim 7 , wherein the heat transfer area enlargement e pipe is formed by a cladding material having a surface covered with a brazing material. 
     
     
         9 . A refrigeration cycle device that performs heat exchange between two kinds of refrigerants using the double pipe heat exchanger of  claim 1 . 
     
     
         10 . The refrigeration cycle device of  claim 9 , wherein at least one of the refrigerants is water or brine.