Thermal actuator including fluid with high temperature stability

1. A thermal actuator, comprising:

an enclosure comprising shoulder portions;

a movable element coupled to the enclosure and configured to occupy first and second positions relative to the enclosure, the movable element being biased toward the first position; and

an expansion material disposed within the enclosure such that, when the expansion material expands, the expansion material moves the movable element toward the second position,

the expansion material comprising an inorganic salt mixture, further comprising:

a diaphragm disposed between the movable element and the expansion material, the diaphragm being at least one of affixed, fastened or adhered to the shoulder portions of the enclosure to constrain movement of the diaphragm; and

a plug formed of compliant material disposed between the movable element and the diaphragm.

2. The thermal actuator according to claim 1 , wherein the expansion material is eutectic.

3. The thermal actuator according to claim 1 , wherein the expansion material has a melting point in the range from 50° C. to 600° C. and its volumetric coefficient of thermal expansion is above 180 10 −6 1/K and is thermally stable above 450 C.

4. The thermal actuator according to claim 1 , wherein the movable element is linearly movable.

5. A turbine assembly, comprising:

rotor and stator assemblies positioned adjacent to one another to define a wheel space cavity;

fixed and adjustable orifices respectively associated with the stator assembly to provide to the wheel space cavity a flow of purge air and an adjustable flow of cooling air, respectively; and

a flow control device comprising an expansion material configured to vary the adjustable flow of cooling air to the wheel space cavity by varying a size of the adjustable orifice in accordance with an expansion condition of the expansion material,

the expansion material comprising an inorganic salt mixture,

the thermal actuator further comprising:

a diaphragm disposed between the movable element and the expansion material;

an enclosure comprising shoulder portions, the diaphragm being at least one of affixed, fastened or adhered to the shoulder portions of the enclosure to constrain movement of the diaphragm; and

a plug formed of compliant material disposed between the movable element and the diaphragm.

6. The turbine assembly according to claim 5 , wherein the expansion material is eutectic.

7. The turbine assembly according to claim 5 , wherein the stator assembly comprises a stator wall formed to define a stator cavity communicable with a flow of compressor extraction air.

8. The turbine assembly according to claim 7 , wherein the fixed and adjustable orifices are each positioned in the stator wall and the flow control device is positioned in the stator cavity.

9. The turbine assembly according to claim 7 , wherein the flow of purge air and the adjustable flow of cooling air each comprise compressor extraction air.

10. The turbine assembly according to claim 5 , further comprising a temperature sensor associated with the wheel space cavity and in communication with the adjustable orifice.

11. The turbine assembly according to claim 5 , further comprising an inter-stage seal positioned between the rotor assembly and the stator assembly.

12. The turbine assembly according to claim 5 , wherein the expansion material comprises a eutectic salt mixture.

13. The turbine assembly according to claim 5 , wherein the expansion material has a melting point in the range from 50° C. to 600° C. and its volumetric coefficient of thermal expansion is above 180 10 −6 1/K and is thermally stable above 450 C.

14. The turbine assembly according to claim 5 , wherein the flow control device comprises a movable element that is linearly movable in accordance with the expansion condition of the expansion material.