Method and apparatus for operating an improved thermocline storage unit

• US 4,523,629 A
• Filed: 09/30/1982
• Issued: 06/18/1985
• Est. Priority Date: 09/30/1982
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Department of Energy (Government of the United States of America)
• Inventors: Copeland, Robert J.
• Primary Examiner(s): DAVIS JR, ALBERT
• Application Number:
  US06/429,740
• Time in Patent Office: 992 Days
• Field of Search: 165/104.19, 165/1, 126/437
• US Class Current: 165/104.19
• CPC Class Codes: F24D 11/002 water heating system
• CPC Class Codes: F28D 20/0039 with stratification of the heat storage material
• CPC Class Codes: F28D 2020/0047 using molten salts or liquid metals
• CPC Class Codes: F28D 2020/0095 movable or floating
• CPC Class Codes: Y02E 60/14 Thermal energy storage

Abstract

A method and apparatus for operating a thermocline storage unit in which an insulated barrier member is provided substantially at the interface region between the hot and cold liquids in the storage tank. The barrier member physically and thermally separates the hot and cold liquids substantially preventing any diffusing or mixing between them and substantially preventing any heat transfer therebetween. The barrier member follows the rise and fall of the interface region between the liquids as the tank is charged and discharged. Two methods of maintaining it in the interface region are disclosed. With the structure and operation of the present invention and in particular the significant reduction in diffusing or mixing between the hot and cold liquids as well as the significant reduction in the thermal heat transfer between them, the performance of the storage tank is improved. More specifically, the stability of the interface region or thermocline is enhanced and the thickness of the thermocline is reduced producing a corresponding increase in the steepness of the temperature gradient across the thermocline and a more efficiently operating thermocline storage unit.

Claims

1. An improved method for operating a thermocline storage unit, said method comprising the steps of:

(a) providing a tank containing a first fluid at a first density and a second fluid at a second density, said first density being less than said second density wherein said fluids stratify within said tank with said first fluid above the second fluid and forming a natural interface region therebetween extending substantially horizontally,

(b) maintaining said first fluid at a first temperature and maintaining said second fluid at a second temperature, said first temperature being higher than said second temperature,

(c) using a barrier member to substantially separate said first and second fluids from each other substantially at said horizontally extending interface region,

(d) selectively increasing and decreasing the respective volumes of the first and second fluids in said tank wherein said horizontally extending interface region therebetween moves substantially vertically relative to said tank,

(e) maintaining a difference in temperature between said first fluid of said first tank and said second fluid of said second tank, and maintaining such separation of said step (c) as said horizontally extending interface region moves vertically relative to said tank, and

(f) adapting said barrier member to float between said first and second fluids substantially at said interface region as said interface region moves relative to said tank to maintain such separation of step (c) and providing said barrier member with a plurality of nodules, said nodules being situate at said barrier member such that said barrier member is enabled to remain substantially centered relative to said tank while permitting relatively small portions of said fluids to freely pass by said barrier member.

2. The method of claim 1 wherein step (c) includes the further limitation of substantially thermally insulating said first and second fluids from each other substantially at said interface region and step (e) includes the further limitation of maintaining said thermal insulation between said first and second fluids as said interface region moves relative to said tank.

3. The method of claim 1 wherein step (e) includes the further limitations of maintaining said separation of step (c) by sensing the vertical movement of the interface region and mechanically moving said barrier member in response thereto to maintain said barrier member substantially at said interface region as said interface region moves relative to said tank.

4. The method of claim 3 further including the limitation of providing said barrier member with thermal insulation wherein said barrier member substantially thermally insulates said first and second fluids from each other.

5. The method of claim 1 further including the limitation of making the density of said barrier member to be greater than the density of the first fluid and less than the density of the second fluid.

6. The method of claim 5 further including the limitation of providing said barrier member with thermal insulation wherein said barrier member substantially thermally insulates said first and second fluids from each other.

7. The method of claim 5 further including the limitation of maintaining the density of the barrier member constant as said barrier member moves with said interface region relative to said tank.

8. The method of claim 1 further including the limitation of forming said barrier member by encapsulating thermal insulation within a fluid tight material.

9. The method of claim 1 further including the step of permitting a relatively small portion of said first and second fluids to freely flow past said barrier member.

10. The method of claim 1 further including the limitation of making said barrier member opaque to thermal radiation generated by said first and second fluids.

11. The method of claim 1 wherein said barrier member has a first height and said tank has a second height and said method includes the further limitation of making said first height to be about 5% of said second height.

12. The method of claim 1 further including the step of substantially equating the vertical thermal resistivity of the barrier member with the vertical thermal resistivity of the fluids in said tank.

13. The method of claim 1 wherein step (c) includes the further limitation of using a barrier member with a predetermined, rigid configuration to substantially separate said first and second fluids from each other at said interface region.

14. The method of claim 1 including the further limitation of using a common medium for said first and second fluids.

15. The method of claim 14 wherein said common medium is primarily water.

17. The method of claim 14 wherein said common medium is primarily oil.

16. The method of 14 wherein said common medium is primarily molten salt.

18. In a thermocline storage unit having a tank containing a first fluid at a first density and a second fluid at a second density, said first density being less than said second density wherein said fluids stratify within said tank with said first fluid above the second fluid and forming a natural interface region therebetween extending substantially horizontally, said unit further including means for selectively increasing and decreasing the respective volumes of the first and second fluids wherein said interface region therebetween moves substantially vertically relative to said tank, the improvement including:

(a) means for substantially separating said first and second fluids from each other substantially at said horizontally extending interface region, and

(b) means for maintaining said separating means substantially at said horizontally extending interface region as said interface region moves vertically relative to said tank, wherein said separating means includes a barrier member extending substantially between said first and second fluids at said interface region, said barrier member including a number of protruding members extending outwardly of said barrier member and spaced thereabout to maintain said barrier member substantially centered relative to said tank while permitting relatively small portion of fluids to freely pass by said barrier member.

19. The improvement of claim 18 wherein said separating means includes means for substantially thermally insulating said first and second fluids from each other substantially at said interface region as said interface region moves relative to said tank.

20. The improvement of claim 18 wherein said maintaining means includes means for sensing the vertical movement of the interface region and means for mechanically moving said barrier member in response thereto to maintain said barrier member substantially at said interface region as said interface region moves relative to said tank.

21. The improvement of claim 20 wherein said barrier member further includes means for substantially thermally insulating said first and second fluids from each other.

22. The improvement of claim 18 wherein said barrier member has a density greater than the density of said first fluid and less than the density of the second fluid wherein said barrier member floats between said first and second fluids substantially at said interface region as said interface region moves relative to said tank.

23. The improvement of claim 22 wherein said barrier member includes means for substantially thermally insulating said first and second fluids from each other.

24. The improvement of claim 22 further including means for maintaining the density of the barrier member constant as said barrier member moves with said interface region relative to said tank.

25. The improvement of claim 18 further including means for encapsulating said thermal insulation within a fluid tight material.

26. The improvement of claim 18 wherein said tank has an inner wall with a first cross-sectional shape and area and said barrier member has a second cross-sectional shape and area substantially corresponding thereto with said first area being greater than said second area whereby a relatively small portion of said first and second fluids can freely flow past said barrier member.

27. The improvement of claim 18 wherein said barrier member further includes means for reflecting thermal radiation wherein said barrier member is opaque to thermal radiation generated by said first and second fluids.

28. The improvement of claim 18 wherein said barrier member has a first height and said tank has a second height with said first height being about 5% of said second height.

29. The improvement of claim 18 wherein the fluids in said tank have a first thermal resistivity in a vertical direction and said barrier member has a second thermal resistivity in a vertical direction wherein said first and second thermal resistivities are substantially equal.

30. The improvement of claim 18, wherein said barrier member has a predetermined, rigid configuration.

31. The improvement of claim 18 wherein said first and second fluids are a common medium.

32. The improvement of claim 31 wherein said common medium is primarily water.

33. The improvement of claim 31 wherein said common medium is primarily molten salt.

34. The improvement of claim 31 wherein said common medium is primarily oil.

35. In a thermocline storage unit having a tank containing a first fluid at first density and a second fluid at a second density, said first density being less than said second density wherein said fluids stratify within said tank with said first fluid above the second fluid and forming a natural interface region therebetween extending substantially horizontally, said unit further including means for selectively increasing and decreasing the respective volume the respective volumes of the first and second fluids wherein said interface region therebetween moves substantially vertically relative to said tank, the improvement including:

(a) means for substantially separating said first and second fluids form each other substantially at said horizontally extending interface region, and

(b) means for maintaining said separating means substantially at said horizontally extending interface region as said interface region moves vertically relative to said tank, and wherein said separating means includes a barrier member extending substantially between said first and second fluids at said interface region, and wherein said tank has an inner wall with a first cross-sectional shape and area, and said barrier member has a second cross-sectional shape and area substantially corresponding thereto with said first area being greater than said second area whereby a relatively small portion of said first and second fluids can freely flow past said barrier member, and wherein said barrier member further includes a number of protruding members extending outwardly of said barrier member and spaced thereabout to maintain said barrier member substantially centered relative to said tank while permitting said relatively small portion of fluids to freely pass by said barrier member.