Heat transfer systems for superconductors

1. A cooling system for a superconducting electric machine, comprising:

a fluid reservoir;

a first fluid comprising a first mixture of hydrogen and helium configured to be stored in the fluid reservoir; and

a plurality of conduits fluidly coupled to the fluid reservoir and forming a closed loop between the fluid reservoir and the superconducting electric machine,

wherein the closed loop is configured to:

provide a first portion of the first fluid to a stator comprising a stator winding such that the first portion of the first fluid removes a first heat load from the stator winding, and

provide a second portion of the first fluid to a rotor comprising a rotor winding such that the second portion of the first fluid removes a second heat load from the rotor winding.

2. The cooling system of claim 1 , wherein the first mixture of hydrogen and helium comprises between about 2% and about 5% hydrogen and between about 98% and about 95% helium.

3. The cooling system of claim 2 , wherein the fluid reservoir comprises a cryogenic cooler.

4. The cooling system of claim 1 , wherein the first mixture of hydrogen and helium comprises between about 0.5% and about 10% hydrogen and between about 99.5% and about 90% helium.

5. The cooling system of claim 1 , wherein the fluid reservoir includes a heat exchanger comprising a working fluid configured to remove a heat load from the first fluid, and wherein the working fluid comprises a second mixture of hydrogen and helium, and wherein the second mixture of hydrogen and helium comprises between about 2% and about 5% hydrogen and between about 98% and about 95% helium.

6. The cooling system of claim 1 , wherein at least one of the stator winding or the rotor winding is formed of a superconducting material having a superconducting transition temperature between 0 Kelvin and 40 Kelvin.

7. The cooling system of claim 6 , wherein the least one of the stator winding or the rotor winding comprises magnesium diboride.

8. A superconducting electric machine, comprising:

a rotor configured to rotate about a central longitudinal axis;

a stator configured to be non-rotating relative to the central longitudinal axis;

a rotor winding coiled about the rotor and comprising a first superconducting material;

a stator winding coiled about the stator and comprising a second superconducting material; and

a cooling system configured to thermally couple a first fluid to the stator winding and the rotor winding, the first fluid comprising a non-flammable mixture of hydrogen and helium,

wherein the cooling system is configured to:

provide a first portion of the first fluid to the stator winding such that the first portion of the first fluid removes a first heat load from the stator winding, and

provide a second portion of the first fluid to the rotor winding such that the second portion of the first fluid removes a second heat load from a rotor winding.

9. The superconducting electric machine of claim 8 , wherein the non-flammable mixture of hydrogen and helium comprises between about 2% and about 5% hydrogen and between about 98% and about 95% helium.

10. The superconducting electric machine of claim 8 , wherein the cooling system further comprises:

a fluid reservoir configured to house the non-flammable mixture of hydrogen and helium; and

a plurality of conduits fluidly coupling to the fluid reservoir to the rotor and the stator.

11. The superconducting electric machine of claim 10 , wherein the fluid reservoir includes a heat exchanger comprising a working fluid configured to remove a heat load from the first fluid, and wherein the working fluid comprises the non-flammable mixture of hydrogen and helium.

12. The superconducting electric machine of claim 8 , wherein at least one of the stator winding or the rotor winding is formed of a superconducting material having a superconducting transition temperature of 40 Kelvin or less.

13. An aircraft engine, comprising:

a fan;

an exit guide vane located at an outlet of the fan;

an after-fan turbine located aft of the exit guide vane;

an electrical generator operably coupled to the after-fan turbine and configured to generate an electrical current in response to rotation of the after-fan turbine;

an electric motor electrically coupled to the electrical generator and rotationally coupled to the fan, the electric motor including a superconductor; and

a cooling system configured to thermally couple a supercooled fluid to the superconductor.

14. The aircraft engine of claim 13 , wherein the electric motor comprises

a rotor configured to rotate about a central longitudinal axis;

a stator configured to be non-rotating relative to the central longitudinal axis;

a rotor winding coiled about the rotor; and

a stator winding coiled about the stator, wherein at least one of the rotor winding or the stator winding comprises the superconductor.

15. The aircraft engine of claim 14 , wherein the cooling system is configured such that a first portion of the supercooled fluid removes a first heat load from the stator winding and a second portion of the supercooled fluid removes a second heat load from the rotor winding.

16. The aircraft engine of claim 15 , further comprising:

a compressor section aft of the after-fan turbine;

a combustor section configured to receive a compressed fluid from the compressor section; and

a turbine section aft of the combustor section.

17. The aircraft engine of claim 16 , further comprising a controller configured to control a current provided to the electric motor and a flow of fuel to the combustor section, wherein the controller is configured to determine whether to operate the aircraft engine as an electric engine or a gas combustion engine based on at least one of a rotations per minute of the after-fan turbine or a current output by the electrical generator.

18. The aircraft engine of claim 17 , wherein the supercooled fluid comprises between about 0.5% and about 10% hydrogen and between about 99.5% and about 90% helium.