Generating energy from fluid expansion

1. An apparatus comprising:

an electric generator having a stator and a rotor;

a first turbine having a first turbine wheel coupled to a first end of the rotor to rotate at the same speed as the rotor and configured to receive working fluid into an inlet side of the first turbine wheel and output working fluid from an outlet side of the first turbine wheel and rotate in response to expansion of working fluid flowing from the inlet side to the outlet side of the first turbine wheel, wherein the first turbine is in fluid communication with the electric generator to direct working fluid from the outlet side of the first turbine wheel in direct contact with the electric generator to cool the electric generator; and

a second turbine having a second turbine wheel coupled to a second end of the rotor, opposite the first end of the rotor, to rotate at the same speed as the rotor and configured to receive working fluid into an inlet side of the second turbine wheel and output working fluid from an outlet side of the second turbine wheel and rotate in response to expansion of working fluid flowing from the inlet side to the outlet side of the second turbine wheel, wherein the electric generator is arranged proximate the outlet side of the second turbine wheel.

2. The apparatus of claim 1 wherein the first turbine wheel is configured to receive working fluid radially into the inlet side of the first turbine wheel and output working fluid axially from the outlet side of the first turbine wheel.

3. The apparatus of claim 2 wherein the second turbine wheel is configured to receive working fluid radially into the inlet side of the second turbine wheel and output working fluid axially from the outlet side of the second turbine wheel.

4. The apparatus of claim 1 wherein the second turbine wheel is configured to direct working fluid from the outlet side of the second turbine wheel in direct contact with the electric generator.

5. The apparatus of claim 1 wherein the electric generator is arranged proximate the inlet side of the first turbine wheel.

6. The apparatus of claim 1 wherein the second turbine wheel is configured to receive working fluid into the inlet side of the second turbine wheel from the outlet side of the first turbine wheel.

7. The apparatus of claim 1 wherein the rotor is directly coupled to the first turbine wheel.

8. The apparatus of claim 1 wherein the rotor and the turbine wheel are coupled to rotate together without a gear box.

9. The apparatus of claim 1 wherein the apparatus further comprises at least one magnetic bearing supporting the rotor relative to the stator.

10. The apparatus of claim 1 wherein the apparatus is configured so that the first turbine wheel receives the same working fluid as the second turbine wheel.

11. The apparatus of claim 1 wherein the first turbine is configured to direct working fluid from the outlet side of the first turbine wheel through a gap between the stator and the rotor of the electric generator.

12. The apparatus of claim 1 wherein the first turbine is configured to direct working fluid from the outlet side of the first turbine wheel through the electric generator into the inlet side of the second turbine wheel.

13. A generator system for use in an organic Rankine cycle, comprising:

a liquid reservoir for a working fluid of the organic Rankine cycle;

a pump device coupled to the liquid reservoir to receive the working fluid from the liquid reservoir;

an evaporator heat exchanger coupled to the pump device to receive the working fluid from the pump and apply heat to the working fluid;

a turbine generator apparatus coupled to the evaporator heat exchanger to receive the working fluid from the evaporator heat exchanger and configured to generate electrical energy in response to expansion of the working fluid, the turbine generator apparatus comprising:

an electric generator having a stator and a rotor,

a first turbine having a first turbine wheel coupled to a first end of the rotor to rotate at the same speed as the rotor and configured to receive a working fluid into an inlet side of the first turbine wheel and output the working fluid from an outlet side of the first turbine wheel and rotate in response to expansion of the working fluid flowing from the inlet side to the outlet side of the first turbine wheel, wherein the first turbine is in fluid communication with the electric generator to direct at least part of the working fluid from the outlet side of the first turbine wheel in direct contact with the electric generator to cool the electric generator, and

a second turbine having a second turbine wheel coupled to a second end of the rotor, opposite the first end of the rotor, to rotate at the same speed as the rotor, wherein the second turbine wheel is in fluid communication with the electric generator to receive the at least part of the working fluid from an outlet of the electric generator to an inlet side of the second turbine wheel; and

a condenser heat exchanger coupled to the turbine generator apparatus to receive the working fluid from the turbine generator apparatus and extract heat from the working fluid.

14. The system of claim 13 wherein the first turbine wheel is configured to receive the working fluid radially into the inlet side of the first turbine wheel and output the working fluid axially from the outlet side of the first turbine wheel.

15. The system of claim 13 wherein the electric generator is arranged proximate the inlet side of the first turbine wheel.

16. The system of claim 13 wherein the rotor is directly coupled to the first turbine wheel.

17. The system of claim 13 wherein the second turbine wheel is configured to receive the working fluid into the inlet side of the second turbine wheel and output the working fluid from an outlet side of the second turbine wheel and rotate in response to expansion of the working fluid flowing from the inlet side to the outlet side of the second turbine wheel.

18. A method of circulating a working fluid through a working cycle, comprising:

vaporizing the working fluid;

receiving the vaporous working fluid into an inlet side of a first turbine wheel;

rotating the first turbine wheel in response to expansion of the working fluid through the first turbine wheel, and in turn rotating a rotor of an electric generator at the same speed as the first turbine wheel;

outputting the working fluid from an outlet side of the first turbine wheel;

receiving the working fluid from the outlet side of the first turbine wheel into an inlet side of a second turbine wheel disposed in a second turbine;

rotating the second turbine wheel in response to expansion of the working fluid through the second turbine wheel, and in turn rotating the rotor at the same speed as the second turbine wheel;

cooling the electric generator by directing at least part of the working fluid from an outlet side of the second turbine wheel in direct contact with the electric generator using the second turbine; and

condensing the working fluid to a liquid.

19. The method of claim 18 wherein receiving the vaporous working fluid into the inlet of the first turbine wheel comprises receiving the vaporous working fluid into a radial inlet of the first turbine wheel and outputting the working fluid from the outlet side of the first turbine wheel comprises outputting the working fluid axially from the outlet side of the first turbine wheel.

20. The method of claim 18 wherein rotating the rotor comprises rotating a shaft common to the first turbine wheel and the rotor.

21. The method of claim 20 wherein the shaft is connected to the second turbine wheel.

22. The method of claim 20 wherein the first and second turbine wheels are affixed directly to the rotor.

23. The method of claim 18 wherein the working cycle is an organic Rankine working cycle.

24. The method of claim 18 wherein the electric generator is arranged proximate the inlet side of the first turbine wheel and the electric generator is arranged proximate the outlet side of the second turbine wheel.