Double pipe for heat exchanger
A double pipe for a heat exchanger includes an inner pipe disposed in an outer pipe. In a straight-pipe portion of the double pipe, the inner pipe has a plurality of protruding parts extending in a helically offset manner along a longitudinal direction, an inner-circumferential surface of the outer pipe directly contacts the protruding parts, and outer-side channels are partitioned at a plurality of locations in a circumferential direction of the double pipe. The protruding parts are curved to protrude radially outward. In a cross section of the straight-pipe portion orthogonal to the longitudinal direction, the inner-circumferential surface of the outer pipe is circular, and an average value of D/L values of all the outer-side channels is 0.09-0.20, wherein D is defined as a maximum depth of each of the outer-side channels and L is defined as an arc length of each of the outer-side channels in the circumferential direction.
1. A double pipe for a heat exchanger having a double-pipe structure, in which an inner pipe is disposed in an interior of an outer pipe, to effect heat exchange between a fluid that flows in an interior of the inner pipe and a fluid that flows between the inner pipe and the outer pipe, wherein:
in a straight-pipe part of the double pipe, the inner pipe comprises a plurality of protruding parts extending in a longitudinal direction and curved to protrude toward an outer-circumference side and a plurality of helical recessed parts respectively provided between the protruding parts and curved so as to protrude toward an inner-circumference side;
the protruding parts are helically offset in the longitudinal direction;
the helical recessed parts are helically offset in the longitudinal direction;
boundary parts are respectively formed in an angular shape between the protruding parts and the helical recessed parts;
in a cross section of the straight-pipe part orthogonal to the longitudinal direction, an inner-circumferential surface of the outer pipe is circular;
in the straight-pipe part, the inner-circumferential surface of the outer pipe contacts the protruding parts of the inner pipe, and outer-side channels, which are partitioned at a plurality of locations in a circumferential direction of the double pipe, are formed between the outer pipe and the inner pipe; and
in the cross section of the straight-pipe part orthogonal to the longitudinal direction, D is defined as a maximum depth of each of the outer-side channels in millimeters, L is defined as an arc length of each of the outer-side channels in the circumferential direction in millimeters, and an average value of D/L values of all the outer-side channels is greater than 0.09 and less than 0.20.
2. The double pipe according to claim 1 , wherein the outer pipe contacts the protruding parts owing to the outer pipe being swaged toward the inner pipe.
3. The double pipe according to claim 1 , wherein, in the cross section of the straight-pipe part orthogonal to the longitudinal direction, a total of the arc lengths (L) of the outer-side channels has a length of 60% or more of a circumferential length (C) of a virtual circumscribed circle of the inner pipe.
4. The double pipe according to claim 1 , wherein, in the straight-pipe part, the number of the protruding parts provided on the inner pipe is four or more and six or fewer.
5. The double pipe according to claim 1 , wherein, in the straight-pipe part, a spiral angle of each of the protruding parts is 20° or more and 60° or less.
6. The double pipe according to claim 1 , wherein, in the cross section of the straight-pipe part orthogonal to the longitudinal direction, a total of the arc lengths (L) of the outer-side channels has a length of 90% or less of a circumferential length (C) of a virtual circumscribed circle of the inner pipe.
7. The double pipe according to claim 1 , wherein, in the cross section of the straight-pipe part orthogonal to the longitudinal direction, a total of channel cross-sectional areas of the outer-side channels is 5% or more and 30% or less of a channel cross-sectional area of the inner pipe.
8. The double pipe according to claim 2 , wherein, in the cross section of the straight-pipe part orthogonal to the longitudinal direction, a total length of the arc lengths (L) of the outer-side channels is 60% or more of circumferential length (C) of a virtual circumscribed circle of the inner pipe.
9. The double pipe according to claim 8 , wherein, in the straight-pipe part, four to six of the protruding parts are provided on the inner pipe.
10. The double pipe according to claim 9 , wherein, in the straight-pipe part, a spiral angle of each of the protruding parts is 20°-60°.
11. The double pipe according to claim 10 , wherein, in the cross section of the straight-pipe part orthogonal to the longitudinal direction, the total length of the arc lengths (L) of the outer-side channels is 90% or less of the circumferential length (C) of the virtual circumscribed circle of the inner pipe.
12. The double pipe according to claim 11 , wherein, in the cross section of the straight-pipe part orthogonal to the longitudinal direction, a total of channel cross-sectional areas of the outer-side channels is 5%-30% of a channel cross-sectional area of the inner pipe.
13. A double pipe for a heat exchanger, comprising:
a double-pipe structure having an inner pipe disposed in an interior of an outer pipe, the double-pipe structure being configured to effect heat exchange between a fluid that flows in an interior of the inner pipe and a fluid that flows in outer-side channels defined between the inner pipe and the outer pipe,
wherein:
in a straight-pipe portion of the double pipe, the inner pipe comprises a plurality of protruding parts extending in a helically offset manner along a longitudinal direction and a plurality of helical recessed parts respectively provided between the protruding parts, an inner-circumferential surface of the outer pipe directly contacts the protruding parts, and the outer-side channels are partitioned at a plurality of locations in a circumferential direction of the double pipe;
the protruding parts are curved to protrude radially outward;
the helical recessed parts are curved so as to protrude radially inward;
boundary parts are respectively formed in an angular shape between the protruding parts and the helical recessed parts; and
in a cross section of the straight-pipe portion orthogonal to the longitudinal direction, the inner-circumferential surface of the outer pipe is circular, and an average value of D/L values of all the outer-side channels is greater than 0.09 and less than 0.20, wherein D is defined as a maximum depth of each of the outer-side channels and L is defined as an arc length of each of the outer-side channels in the circumferential direction.
14. The double pipe according to claim 13 , wherein, in the cross section of the straight-pipe portion orthogonal to the longitudinal direction, a total length of the arc lengths (L) of the outer-side channels is 60%-90% of circumferential length (C) of a virtual circumscribed circle of the inner pipe.
15. The double pipe according to claim 14 , wherein, in the straight-pipe portion, four to six of the protruding parts are provided on the inner pipe.
16. The double pipe according to claim 15 , wherein, in the straight-pipe portion, a spiral angle of each of the protruding parts is 20°-60°.
17. The double pipe according to claim 16 , wherein, in the cross section of the straight-pipe portion orthogonal to the longitudinal direction, a total of channel cross-sectional areas of the outer-side channels is 5%-30% of a channel cross-sectional area of the inner pipe.