Hollow disc rotor for flywheel power storage device and method for manufacturing same
Provided are a hollow disk rotor for a flywheel energy storage system with a significantly improved circumferential velocity limit and stored energy limit, and a method for manufacturing the same. The rotor includes a plurality of circumferentially wound reinforcement fibers, a matrix material that fills gaps between the reinforcement fibers, and carbon nanotubes extending upward through the matrix material from surfaces of the reinforcement fibers as base points.
1. A hollow disk rotor of a flywheel for a flywheel energy storage system, comprising:
a plurality of circumferentially wound reinforcement fibers;
a matrix material that fills gaps between the reinforcement fibers; and
carbon nanotubes extending upward through the matrix material from surfaces of the reinforcement fibers as base points.
2. The hollow disk rotor according to claim 1 , wherein provided that a mean separation distance between monofilaments of a pair of nearest neighbor reinforcement fibers is represented by l, and a mean extension distance of the carbon nanotubes extending upward is represented by T, T and l, having the following relationship:
[
Math
2
]
T
≥
l
2
.
3. The hollow disk rotor according to claim 1 , wherein each of the base points on the surfaces of the reinforcement fibers has one of a graftage configuration that allows one end surface of each carbon nanotube to be fixed to a respective surface of the surfaces of the reinforcement fibers, or a point fixation configuration that allows a side surface of each carbon nanotube to be bonded to the surface at one point.
4. The hollow disk rotor according to claim 3 , wherein a relationship between a mean length dimension u and a mean extension distance T of the carbon nanotubes is as follows for the graftage configuration:
[
Math
3
]
u
≥
T
,
is as follows for the point fixation configuration:
[
Math
4
]
u
≥
2
T
.
5. The hollow disk rotor according to claim 1 , wherein a mean volume fraction V F of the reinforcement fibers is 0.5 (50%) or more.
6. The hollow disk rotor according to claim 5 , wherein the mean volume fraction V F of the reinforcement fibers is 0.6 (60%) or more.
7. The hollow disk rotor according to claim 1 , wherein the reinforcement fibers include one type of fiber selected from among carbon fibers, boron fibers, glass fibers, aramid fibers, alumina fibers, silicon carbide fibers, and various metal fibers, or composite fibers including two or more types of the foregoing fibers.
8. The hollow disk rotor according to claim 7 , wherein a mean value of diameters of the reinforcement fibers is in a range of 3 μm to 9 μm, and variation of the diameters is within the mean value ±1 μm.
9. The hollow disk rotor according to claim 8 , wherein the mean value of diameters of the reinforcement fibers is in a range of 5 μm to 7 μm, and the variation of the diameters is within the mean value ±0.5 μm.
10. The hollow disk rotor according to claim 1 , wherein the matrix material is one material selected from among thermoset resin, epoxy resin, unsaturated polyester resin, vinyl ester resin, and phenolic resin; or thermoplastic resin, polyolefin-based resin, polyamide-based resin, and polycarbonate-based resin.
11. The hollow disk rotor according to claim 1 , wherein the carbon nanotubes are single-layer carbon nanotubes with a diameter of 0.5 to 3 nm, multi-layer carbon nanotubes with a diameter of 5 to 30 nm, or carbon nanotubes including both the single-layer carbon nanotubes and the multi-layer carbon nanotubes in a mixed manner.
12. The hollow disk rotor according to claim 11 , wherein a concentration c, in weight %, of the carbon nanotubes in the matrix material is in a range of c=0.1 wt % to 8 wt %.
13. The hollow disk rotor according to claim 1 , wherein provided that a mean separation distance between monofilaments of a pair of nearest neighbor reinforcement fibers is represented by l, a mean diameter of the monofilaments is represented by D, and a mean extension distance of the carbon nanotubes extending upward is represented by T, T, l, and D having the following relationship:
[
Math
2
]
T
≥
1
2
(
(
2
-
1
)
D
+
2
l
)
.
14. A method for manufacturing the hollow disk rotor according to claim 1 , comprising:
a first step of fixing or bonding the carbon nanotubes to the reinforcement fibers;
a second step of gathering the reinforcement fibers attached with the carbon nanotubes formed in the first step into a bundle as a reinforcement fiber bundle; and
a third step of forming the hollow disk rotor with the reinforcement fiber bundle formed in the second step and the matrix material using a filament winding method.