Heat exchanger and heat exchanging system
A heat exchanging system ( 10 ) comprises a heat exchanger ( 1 ) including a tube ( 2 ) through which a first fluid flows and a plurality of fins ( 3 ) made from thin plates attached to the tube ( 2 ) and arranged parallel to each other in the direction along which the tube ( 2 ) extends, and a fan ( 4 ) for introducing a second fluid between the fins ( 3 ). The fin ( 3 ) includes concave parts ( 7 ) and convex parts ( 8 ) continuously and cyclically formed in a zigzag line. The concave parts ( 7 ) and the convex parts ( 8 ) are so arranged as to extend in the direction crossing the flow direction of the second fluid flowing between the fins ( 3 ), and the flow of the second fluid flowing between the fins ( 3 ) is made to be cyclically variable.
1. A heat exchanging system, comprising:
a heat exchanger including
a tube for a first fluid to flow therethrough and
a plurality of fins that are formed of thin plates, that are attached to the tube, and that are arranged side by side in an extending direction of the tube; and
a fan for introducing a second fluid between the fins,
wherein
the fins meander so as to have continuous concave and convex parts formed at a regular pitch,
the concave and convex parts are arranged so as to extend in a direction intersecting a passage direction of the second fluid passing between the fins, and
a flow rate of the second fluid passing between the fins is made variable at a regular cycle so as to bring about, at a regular cycle, a first state where a vortex stays in the concave part and becomes stagnant and a second state where a portion of the vortex extends out of the concave part due to a decrease in angular velocity of the vortex and heat exchange is performed between the portion of the vortex and a flow of the second fluid flowing between the fins.
2. The heat exchanging system according to claim 1 , wherein
a flow direction of the second fluid passing between the fins is inverted at a regular cycle so as to bring about, at a regular cycle, subsequently to the first and second states, a third state where the second fluid in the inverted flow direction flows into the concave part along the concave part and a fourth state where a vortex that rotates reversely to the vortex in the first state is generated in the concave part.
3. The heat exchanging system according to claim 2 , wherein
a flow direction of the second fluid being introduced to the fins is made variable at a regular cycle.
4. The heat exchanging system according to claim 1 , wherein
the concave and convex parts are arranged so as to extend in a direction orthogonal to the passage direction of the second fluid passing between the fins.
5. The heat exchanging system according to claim 1 , wherein
open sides of the concave parts of adjacent ones of the fins face each other.
6. The heat exchanging system according to claim 1 , wherein
the concave part of each of the fins faces the convex part of an adjacent one of the fins.
7. The heat exchanging system according to claim 1 , wherein
the convex part has a flat surface portion parallel to the passage direction of the second fluid passing between the fins, and the flat surface portion is continuous with a side wall of the concave part and forms a right angle or an acute angle with the side wall of the concave part.
8. The heat exchanging system according to claim 7 , wherein
the concave part has a rectangular shape in cross-section.
9. The heat exchanging system according to claim 1 , wherein
when the second fluid passes between the fins at a maximum flow velocity, a Reynolds number obtained with respect to a length of the concave part or the convex part in a passage direction as a representative length has a value larger than a critical Reynolds number.
10. The heat exchanging system according to claim 9 , wherein
when the second fluid passes between the fins at a minimum flow velocity, the Reynolds number obtained has a value smaller than the critical Reynolds number.
11. The heat exchanging system according to claim 2 , wherein
the fan is formed of an axial flow fan or a once-through fan, and a rotation direction of the fan is inverted at a regular cycle.
12. The heat exchanging system according to claim 2 , wherein
the fan is formed of an axial flow fan having a plurality of vane blades, and at least some of the vane blades are provided so as to have opposite angles of attack.
13. The heat exchanging system according to claim 2 , wherein
the fan is disposed on each of an upstream side and a downstream side of the heat exchanger, and the fan disposed on the upstream side and the fan disposed on the downstream side are driven alternately.
14. The heat exchanging system according to claim 13 , wherein
the fan is formed of a centrifugal fan.
15. The heat exchanging system according to claim 2 , wherein
a guide unit that guides the second fluid is provided on an upstream side or a downstream side of the fan, and by the guide unit, a flow direction of the second fluid is made variable at a regular cycle.
16. The heat exchanging system according to claim 2 , wherein
the fan is formed of a once-through fan or a centrifugal fan that is enclosed in a casing, on both ends of which a flow-in port and a flow-out port for the second fluid are provided, respectively, the heat exchanger is disposed so as to surround a periphery of the fan, and the casing is configured to be rotatable.