Adaptive trans-critical CO

1. A cooling system comprising:

a heat exchanger through which a refrigerant flows, and which rejects heat to a fluid;

an evaporator;

a recuperative heat exchanger;

a first circuit having an expansion device;

a second circuit having an expansion machine coupled to a first compressor, the second circuit split into two additional circuits after exiting the expansion machine, in which one split of the second circuit feeds the evaporator, and the other split of the second circuit bypasses the evaporator and flows in the recuperative heat exchanger opposite a flow direction of the first circuit to cool the refrigerant of the first circuit; and

a set of valves arranged to direct the refrigerant through the first circuit, the second circuit, or both the first and second circuits based on ambient conditions.

2. The cooling system of claim 1 , wherein the cooling system is for an aircraft, and the ambient conditions are defined by an operating condition of the aircraft.

3. The cooling system as claimed in claim 1 , further comprising:

the first compressor configured to compress the refrigerant to a first pressure; and

the evaporator configured to evaporate the refrigerant;

wherein the expansion machine is a first turbine that is rotationally coupled to the compressor through a shaft, and the expansion device is an expansion valve.

4. The cooling system as claimed in claim 3 , further comprising:

a second compressor configured to, prior to entering the first compressor, compress the refrigerant to a second pressure that is less than the first pressure; and

a second heat exchanger configured to cool the refrigerant prior to entering the first compressor but after exiting the second compressor.

5. The cooling system as claimed in claim 4 , further comprising:

an ejector positioned to:

receive the refrigerant from the recuperative heat exchanger as a first flowstream after having passed therethrough in a second direction;

receive the refrigerant from the evaporator as a second flowstream; and

combine the first and second flowstreams and pass a portion of the refrigerant to the recuperative heat exchanger in a first direction and as a gas from a liquid separator.

6. The cooling system as claimed in claim 5 , wherein the at least one component of the aircraft is a part of a gas turbine machine that is a primary mover for the aircraft, the part comprising one of a primary mover compressor, a combustor, and a primary mover turbine.

7. The cooling system as claimed in claim 1 , wherein the refrigerant is CO 2 .

8. The cooling system as claimed in claim 1 , wherein the refrigerant is in one of a sub-critical, a trans-critical state, and a super-critical state.

9. The cooling system of claim 1 , wherein the heat exchanger has refrigerant inlet conditions dependent on ambient conditions.

10. The cooling system of claim 1 , further comprising a third circuit having a heater coupled to the first and second circuits, the third circuit including a second expansion machine and the heater configured to receive waste heat from an aircraft, wherein the refrigerant is directed through the heater and the second expansion machine such that the second expansion machine is configured to extract energy from heated refrigerant that exits from the heater.

11. A method of operating a cooling system, the method comprising:

operating a set of valves that cause a refrigerant to:

pass the refrigerant through a heat exchanger;

pass the refrigerant through a recuperative heat exchanger and an evaporator;

direct the refrigerant through a first cooling circuit, a second cooling circuit, or both depending on ambient conditions;

wherein the first cooling circuit includes an expansion device and the second cooling circuit includes an expansion machine; and

split a flow of the refrigerant of the second cooling circuit exiting the expansion machine into two additional circuits, in which one split of the second circuit feeds the evaporator, and the other split of the second circuit bypasses the evaporator and flows in the recuperative heat exchanger opposite a flow direction of the first circuit to cool the refrigerant of the first circuit.

12. The method as claimed in claim 11 , further comprising:

compressing the refrigerant in the first compressor to a first pressure;

evaporating the refrigerant in the evaporator; and

cooling the refrigerant in a first fluid cooler;

wherein the expansion device is an expansion valve, and wherein the expansion machine is a first turbine.

13. The method as claimed in claim 12 , further comprising:

compressing the refrigerant in a second compressor to a second pressure that is less than the first pressure, prior to the refrigerant entering the first compressor; and

cooling the refrigerant in a second fluid cooler, prior to the refrigerant entering the first compressor but after exiting the second compressor.

14. The method as claimed in claim 13 , further comprising:

receiving the refrigerant from the recuperative heat exchanger as a first flow stream after having passed through the first fluid cooler;

receiving the refrigerant from the evaporator as a second flow stream;

combining the first and second flow streams in an ejector; and

passing a portion of the combined flow streams to the recuperative heat exchanger in a first direction and as a gas from a liquid separator.

15. The method as claimed in claim 11 , wherein the refrigerant comprises CO 2 in one of a sub-critical, a super-critical, and trans-critical state.

16. The method as claimed in claim 11 , wherein the heat exchanger is configured having a refrigerant inlet flow that is dependent on ambient conditions.

17. The method as claimed in claim 11 , wherein operating the valves further comprises passing the refrigerant through a third circuit having a heater coupled to the first and second circuits, the third circuit including a second expansion device and the heater configured to receive waste heat from an aircraft, wherein the refrigerant is directed through the heater and the second expansion machine such that the second expansion machine is configured to extract energy from heated refrigerant that exits from the heater.

18. An aircraft comprising:

a turbine engine; and

a cooling system for the aircraft comprising:

a heat exchanger through which a refrigerant flows, in which heat is rejected to a fluid;

a set of valves arranged to:

direct the refrigerant through a first circuit having a fluid expansion device; direct the refrigerant through a second circuit having a fluid expansion machine; or

direct the refrigerant through both circuits, based on ambient conditions; and

a third circuit having a heater coupled to the first and second circuits, the third circuit including a second expansion device and the heater configured to receive waste heat from the aircraft, wherein the refrigerant is directed through the heater and the second expansion machine such that the second expansion machine is configured to extract energy from heated refrigerant that exits from the heater.

19. The aircraft as claimed in claim 18 , the cooling system further comprising:

a first compressor configured to compress the refrigerant to a first pressure;

an evaporator configured to evaporate the refrigerant; and

a first gas cooler configured to cool the refrigerant.

20. The aircraft of claim 18 , wherein:

the fluid machine is a turbine that is rotationally coupled to the first compressor through a shaft; and

the fluid expansion device is an expansion valve.