WE CLAIM:
1. A compressed air heat exchanger, the heat exchanger comprising:
a cylindrical flow path pipe that includes a first end at one end in an axial direction and a second end at the other end in the axial direction and that causes heat exchange to be performed between a heat source and compressed air in a main heat transfer flow path inside thereof; and
a heat exchange flow path portion that includes an inlet flow path for introducing compressed air from an outside into the main heat transfer flow path and an outlet flow path for discharging compressed air after heat exchange to the outside from the main heat transfer flow path and that causes heat exchange to be performed between compressed air that flows in the inlet flow path and compressed air that flows in the outlet flow path,
wherein the heat exchange flow path portion includes a first heat transfer wall and a second heat transfer wall each of which has a spiral shape, an inner end of each of the first heat transfer wall and the second heat transfer wall is hermetically fixed to an outer periphery of the flow path pipe, the first heat transfer wall and the second heat transfer wall are alternately wound around the outer periphery of the flow path pipe in a state in which a predetermined gap is interposed therebetween, and the inlet flow path and the outlet flow path are alternately formed from the gap between the first heat transfer wall and the second heat transfer wall,
wherein, in an outer peripheral part of the heat exchange flow path portion, an inlet opening for allowing compressed air from the outside to flow into the inlet flow path and an outlet opening for allowing compressed air to flow out from the outlet flow path are formed, and
wherein an inflow opening through which the inlet flow path and the main heat transfer flow path communicate with each other is formed on the first end side of the flow path pipe, and an outflow opening through which the

main heat transfer flow path and the outlet flow path communicate with each other is formed on the second end side of the flow path pipe.
2. The heat exchanger according to Claim 1,
wherein each of the first heat transfer wall and the second heat transfer wall includes a plurality of convex fins each of which is made by forming a recess in one of inner and outer surfaces thereof and forming a projection on the other surface thereof.
3. The heat exchanger according to Claim 2,
wherein an opening edge of the recess of each of the convex fins is chamfered in a substantially circular shape, and an angle between an inner surface of the recess and the one surface of the heat transfer wall at the opening edge is larger than 90 degrees, and a depth of the recess is smaller than a radius of the opening edge.
4. The heat exchanger according to Claim 1,
wherein the inner ends of the first heat transfer wall and the second heat transfer wall are fixed to the outer periphery of the flow path pipe so as to be separated from each other by 180 degrees, and outer ends of the first heat transfer wall and the second heat transfer wall are disposed in an outer peripheral part of the heat exchange flow path portion so as to be separated from each other by 180 degrees.
5. The heat exchanger according to Claim 4,
wherein the inner ends and the outer ends of the first heat transfer wall and the second heat transfer wall are disposed on a same plane that includes an axis of the flow path pipe, and the inflow opening and the outflow opening are respectively formed in one angular range and the other angular range in the flow path pipe that are located with the plane interposed therebetween.
6. A dehumidification unit for dehumidifying compressed air,
the dehumidification unit comprising: a cooling heat source! a heat

exchanger for reheating compressed air, cooled and dehumidified by the cooling heat source, by heat exchange with compressed air before dehumidification; and a hollow case in which the heat exchanger and the cooling heat source are contained,
wherein the heat exchanger includes
a cylindrical flow path pipe that includes a first end at one end in an axial direction and a second end at the other end in the axial direction and in which the cooling heat source is disposed in a main heat transfer flow path inside thereof, and
a heat exchange flow path portion that includes an inlet flow path for introducing compressed air from an outside into the main heat transfer flow path and an outlet flow path for discharging compressed air after dehumidification, cooled in the main heat transfer flow path, to the outside and that causes heat exchange to be performed between compressed air that flows in the inlet flow path and compressed air that flows in the outlet flow path,
wherein the heat exchange flow path portion includes a first heat transfer wall and a second heat transfer wall each of which has a spiral shape, an inner end of each of the first heat transfer wall and the second heat transfer wall is hermetically fixed to an outer periphery of the flow path pipe, the first heat transfer wall and the second heat transfer wall are alternately wound around the outer periphery of the flow path pipe in a state in which a predetermined gap is interposed therebetween, and the inlet flow path and the outlet flow path are alternately formed from the gap between the first heat transfer wall and the second heat transfer wall,
wherein, in an outer peripheral part of the heat exchange flow path portion, an inlet opening for allowing compressed air to be dehumidified to flow into the inlet flow path and an outlet opening for allowing compressed air after dehumidification to flow out from the outlet flow path are formed,

wherein an inflow opening through which the inlet flow path and the main heat transfer flow path communicate with each other is formed on the first end side of the flow path pipe, and an outflow opening through which the main heat transfer flow path and the outlet flow path communicate with each other is formed on the second end side of the flow path pipe, and
wherein, in the case, an input port that communicates with the inlet opening of the heat exchanger, an output port that communicates with the outlet opening of the heat exchanger, and a drain discharge port that communicates with the second end side of the main heat transfer flow path and through which drain water generated in the heat exchanger is discharged to the outside are formed.
7. The dehumidification unit according to Claim 6,
wherein a hollow space is formed between a periphery of the heat exchanger and the case, and the hollow space is divided by a first separation wall and a second separation wall into three spaces, which are a first space on the first end side, a second space on the second end side, and a third space interposed between the first space and the second space, and
wherein one of connection between the input port and the inlet opening and connection between the output port and the outlet opening is made via the first space and the other of the connections is made via the third space, and the second end side of the main heat transfer flow path is connected to the drain discharge port via the second space.
8. The dehumidification unit according to Claim 7,
wherein the input port and the output port are disposed at positions higher than the drain discharge port.
9. The dehumidification unit according to Claim 7,
wherein the input port and the inlet opening are connected via the first space, and the output port and the outlet opening are connected via the third

space,
wherein an outer end of the first heat transfer wall is hermetically fixed to the second heat transfer wall adjacent to an inside of the first heat transfer wall, and the inlet opening is formed in an outermost wall portion of the first heat transfer wall disposed on an outermost side, and
wherein the outlet opening is formed from a gap formed between an outer end of the second heat transfer wall and the first heat transfer wall adjacent to an inside of the outer end.
10. The dehumidification unit according to Claim 6,
wherein the inner end of the first heat transfer wall and the inner end of the second heat transfer wall are fixed to the outer periphery of the flow path pipe so as to be separated from each other by 180 degrees, and an outer end of the first heat transfer wall and an outer end of the second heat transfer wall are disposed in an outer peripheral part of the heat exchange flow path portion so as to be separated from each other by 180 degrees.
11. The dehumidification unit according to Claim 10,
wherein the inner end and the outer end of the first heat transfer wall and the inner end and the outer end of the second heat transfer wall are disposed on a single plane that includes an axis of the flow path pipe, and the inflow opening and the outflow opening are respectively formed in one angular range and the other angular range in the flow path pipe that are located with the plane interposed therebetween.
12. The dehumidification unit according to Claim 11,
wherein the outflow opening is formed in an angular range of the flow path pipe that is located on an opposite side from the drain discharge port with the plane interposed therebetween.
13. The dehumidification unit according to Claim 6,
wherein the cooling heat source is a refrigerant pipe that is inserted into

the main heat transfer flow path from the first end of the flow path pipe and through which a refrigerant flows.
14. A dehumidification system provided with the dehumidification unit according to Claim 13, the dehumidification system comprising:
a refrigeration circuit that causes a refrigerant decompressed by a decompressor to flow to the refrigerant pipe, and that circulates a refrigerant that has performed heat exchange with compressed air in the main heat transfer flow path by causing the refrigerant to flow to the decompressor again through a compressor and a condenser,
wherein an auto-drain is connected to the drain discharge port of the dehumidification unit.