US20120037337A1

US20120037337A1 - Heat transfer system, apparatus, and method therefor

Info

Publication number: US20120037337A1
Application number: US12/857,111
Authority: US
Inventors: Andrew J. Zillmer
Original assignee: Individual
Current assignee: Aerojet Rocketdyne of DE Inc
Priority date: 2010-08-16
Filing date: 2010-08-16
Publication date: 2012-02-16

Abstract

A heat transfer system includes a heat source, a heat sink, and a thermotransfer structure that is operable to transfer heat between the heat source and the heat sink. The thermotransfer structure includes a thermally conductive element and a thermal storage element adjacent the thermally conductive element.

Description

BACKGROUND

This disclosure relates to a system, device, and method for protecting components of a heat transfer system from thermal damage. Heat transfer structures, such as thermal shoes, transfer heat from a heat source to a heat sink. A conventional thermal shoe is formed from a thermally conductive body that includes a heat-receiving surface and a heat-emitting surface. The heat-receiving surface engages the heat source to accept heat, and the heat-emitting surface engages the heat sink to transfer the heat.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

FIG. 1 illustrates an example heat transfer system having a thermotransfer structure.

FIG. 2 illustrates a heat-affected zone generally surrounding the thermotransfer structure of FIG. 1.

FIG. 3 illustrates a cross-sectional view of the thermotransfer structure of FIG. 1.

FIG. 4 illustrates a cross-section of another example thermotransfer structure.

FIG. 5 illustrates another example thermotransfer structure.

FIG. 6 illustrates another example thermotransfer structure.

FIG. 7 illustrates another example thermal storage element.

FIG. 8 illustrates another example heat transfer system.

FIG. 9 illustrates a cross-sectional view of the thermotransfer structure of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates selected portions of an example heat transfer system 20 that includes a heat transfer apparatus 22 (hereafter “thermotransfer structure 22”). The heat transfer apparatus 22 may also be considered to be a hot shoe. The disclosed examples may be described with regard to use of the heat transfer system 20 within a solar power application. It is to be understood that the heat transfer system 20 and thermotransfer structure 22 may be used in other types of applications and is not limited to the examples disclosed herein. For instance, the heat transfer system 20 and/or thermotransfer structure 22 may alternatively be used in an application that would benefit from waste heat recovery, such as steel factories, concrete production, paper mills, or industrial batch processes that utilize high temperature processing.
In the illustrated example, the heat transfer system 20 includes a heat source 24. The type of heat source 24 may vary, depending on the type of system. In a solar power system, the heat source 24 is a vessel that is operable to contain a molten heat transfer fluid. The vessel may be a storage tank of the solar power system and may be adapted to handle high temperature, molten materials, such as molten salts, molten metallic materials, or other working fluids. In this regard, it is to be understood that the heat source 24 may include components that are not shown in the examples herein, such as but not limited to, piping, pumps, heat transfer structures, controls, or other structures/components that may be in contact with the working fluid.
The thermotransfer structure 22 is operable to transfer heat between the heat source 24 and a heat sink 26. In the example of the solar power system, the heat sink 26 may be a power conversion device, such as a Stirling power conversion device (e.g., a heat engine that operates by cyclic compression and expansion of air or other gas), thermoelectric power conversion device (e.g., a device that converts heat into electricity), or the like.
The thermotransfer structure 22 includes a first surface 22 a at one end and a second surface 22 b at the opposed end. The first surface 22 a is located adjacent the heat source 24 and therefore is a heat-receiving surface. The second surface 22 b is located adjacent the heat sink 26 and is therefore a heat-emitting surface. In the illustrated example, the thermotransfer structure 22 tapers such that the first surface 22 a has a first cross-sectional area (as represented by the horizontal dimension in the figure) and the second surface 22 b has a second cross-sectional area 22 b that is smaller than the first cross-sectional area, for efficient heat transfer.
The thermotransfer structure 22 includes a thermally conductive element 28 that extends continuously from the first surface 22 a to the second surface 22 b, and a thermal storage element 30 that is adjacent to the thermally conductive element 28. The thermally conductive element 28 may be a unitary, monolithic body for efficient heat transfer. In this example, the thermal storage element 30 is flush with the first surface 22 a and extends partially between the first surface 22 a and the second surface 22 b.
The thermally conductive element 28 has a first heat capacity and the thermal storage element 30 has a second heat capacity that is greater than the first heat capacity. That is, functionally, the thermally conductive element 28 operates to transfer heat between the heat source 24 and the heat sink 26, and the thermal storage element 30 operates to retain, or store, heat as will be described in further detail below.
The materials of the thermally conductive element 28 and the thermal storage element 30 influence the thermal conductivity and thermal storage properties. For instance, the thermally conductive element 28 may be made of a metallic material that has generally high thermal conductivity. In some examples, the metallic material may be a cobalt material, a nickel material, a tungsten material, a zirconium material, a molybdenum material, a copper material such as substantially pure copper or copper alloy, an iron material such as steel, an aluminum material such as substantially pure aluminum or aluminum alloy, or other type of metal or metal alloy having approximately equal or better thermal conductivity. Given this description, one of ordinary skill in the art will recognize other metallic materials or thermally conductive non-metallic material to meet their particular needs.
The thermal storage element 30 (i.e., thermal capacitor) may be made of a material that has generally high heat capacity (i.e., specific heat). For instance, the material may be a ceramic material or a phase change material that has a higher heat capacity than the material selected for the thermally conductive element 28. In some examples, the ceramic material may be an oxide, nitride, carbide or other type of ceramic material having a high heat capacity with regard to the material of the thermally conductive element 28. Alternatively, the material of the thermal storage element 30 may be a phase change material, such as a salt or metal that is liquid at the operating temperatures of the heat source 24.
In the example of a solar power system, the phase change material may have a melting temperature that is near the melting temperature of the working fluid contained within the vessel. For instance, the phase change material may have a composition that is based on the composition of the working fluid. In one particular example, the vessel of the solar power system contains sodium potassium nitrate salt that has a eutectic composition, and the phase change material selected as the thermal storage element 30 is a sodium potassium nitrate salt that has a hypoeutectic or hypereutectic composition such that the melting temperature of the phase change material is higher than the melting temperature of the working fluid within the vessel. Alternatively, the working fluid may be a eutectic metallic alloy and the phase change material may be a hypoeutectic or hypereutectic composition.
In a state of operation of the heat transfer system 20 (e.g., a first state), the thermotransfer structure 22 transfers heat from the heat source 24 to the heat sink 26. The state of operation depends on the type of application. In a solar power system application, the state of operation may be defined by the operation of the power conversion device and/or heat source 24. The heat transfer system 20 may be considered to be in operation or active when the power conversion device functions to generate electricity and/or the heat source 24 functions to generate heat. The heat transfer system 20 may be considered to be inoperative or inactive (e.g., a second state) when the power conversion device does not generate electricity and/or the heat source 24 does not generate heat. Thus, during operation, the thermal storage element 30 debits heat transfer efficiency of the thermotransfer structure 22 because of the high heat capacity and low thermal conductivity of the thermal storage element 30 relative to the thermally conductive element 28.
In an inoperative or inactive state, there is the potential that the working fluid or components in thermal communication with the thermotransfer structure 22 will cool. For instance, the working fluid may cool to a temperature below its melt temperature (i.e., freezing). The freezing of the working fluid may damage the vessel or other components in the vessel. Additionally, the power conversion device or components in the vessel may be sensitive to abrupt changes in temperature. In this regard, the thermal storage element 30 facilitates heating the working fluid and/or power conversion device and components to avoid thermal damage.
As shown in FIG. 2 when the heat transfer system 20 is inoperative or inactive, the thermal storage element 30 releases stored thermal energy to the surrounding environment and into the heat transfer fluid within the vessel. The released thermal energy heats the working fluid, as represented by a heat affected zone 32 surrounding the thermotransfer structure 22, and thereby prevents freezing or reduces the cooling rate of the working fluid. Similarly, the heat sink 26 may absorb some of the thermal energy and thereby reduce the cooling rate of the heat sink 26.
Depending upon the application of the thermotransfer structure 22, the ability of the thermal storage element 30 to store heat during use and later release the heat during inactivity can be used for different advantages and purposes. For instance, the thermal storage element 30 generally delays the time for the heat transfer fluid within the vessel to freeze in a solar power system. This allows for additional time before the material within the heat affected zone 32 will freeze and potentially damage nearby components. For a Stirling power converter, the thermal storage element 30 may also be used to “coast down” the temperature change between the vessel and the converter. Thus, the thermal storage element 30 provides a “thermal buffer” by storing and then later releasing thermal energy, some of which will be absorbed by the thermally conductive element 28 and transfer to the power conversion device to facilitate reduction in the temperature drop at the power conversion device. Thus, the thermal storage element 30 facilitates protection of the heat transfer system 20, which may allow for longer periods of shut down for maintenance and reduction in wear on the components of the system.
Referring also to the example of FIG. 3, the thermotransfer structure 22 generally has a frustoconical shape. The thermal storage element 30 may have a corresponding frustoconical shape. In this example, the thermally conductive element 28 includes a recessed cavity 40 and the thermal storage element 30 is located at least partially within the recessed cavity 40. As shown, the thermal storage element 30 is located completely within the recessed cavity 40. However, in other examples, the thermal storage element 30 may include portions which extend from the recessed cavity 40 past the first surface 22 a.
FIG. 4 illustrates a modified thermotransfer structure 122, which may be used within the heat transfer system 20 in place of the thermotransfer structure 22 of FIG. 1. In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits as the corresponding original elements. In this case, the geometry of the thermotransfer structure 122 differs from the prior example. The thermally conductive element 128 and the thermal storage element 130 have polygonal cross-sections, which in this case are square cross-sections that taper from end-to-end to form pyramidal shapes (not shown). Alternatively, the thermotransfer structure 22 may have a different geometric three-dimensional shape and need not necessarily taper from end-to-end (e.g., a cylinder).
FIG. 5 illustrates another example thermotransfer structure 222. In this case, the thermotransfer structure 222 includes a cover 242 that retains the thermal storage element 230 within the recessed cavity 40 of the thermally conductive element 228. The cover 242, which may also be considered to be a stop, forms the first surface 222 a of the thermotransfer structure 222. The cover 242 may completely close the mouth of the recessed cavity 40 such that the recessed cavity 40 is hermetically sealed from the exterior environment of the thermotransfer structure 222. Thus, the heat transfer fluid within the vessel cannot infiltrate the recessed cavity 40.
FIG. 6 illustrates an example thermotransfer structure 322 that is somewhat similar to the example thermotransfer structure 222 of FIG. 5. In this case, the thermotransfer structure 322 includes an open gap 344 between the thermal storage element 330 and the walls that form the recessed cavity 40 of the thermally conductive element 328. The open gap 344 allows relative movement between the thermal storage element 330 and the thermally conductive element 328. For instance, the open gap 344 may function as an expansion gap or bellows between the thermally conductive element 328 and the thermal storage element 330. If the material selected for each of the thermally conductive element 328 and the thermal storage element 330 are solid materials, the open gap 344 may be relatively small. Alternatively, if the thermal storage element 330 is a phase change material, the open gap 344 may be somewhat larger to accommodate the relatively larger difference in thermal expansion between the solid material of the thermally conductive element 328 and the phase change material of the thermal storage element 330.
FIG. 7 illustrates another example thermal storage element 430 that may be used in combination with any of the prior examples. In this case, the thermal storage element 430 includes a core 450 that is made of a first material and a protective cladding 452 made of a second material that encases the core 450. For instance, the protective cladding 452 completely encloses and seals the core 450 from the surrounding environment. In instances where the first material of the core 450 is incompatible with the heat transfer fluid, the protective cladding 452 may be used to limit or eliminate contact between the core 450 and the heat transfer fluid.
The first material of the core 450 has a first composition and the second material of the protective cladding 452 has a second composition that is different than the first composition. the first and second compositions may be metallic, ceramic, or combinations thereof. In one example, the first material is a metal or metal alloy and the second composition is different metal or metal alloy. In a further example, the protective cladding 452 may be a superalloy, such as a nickel-based, cobalt-based alloy, a steel alloy, or an aluminum alloy. In a further example, the core 450 is a ceramic material, such as an oxide, nitride, carbide, or the like.
FIG. 8 illustrates another example heat transfer system 520 that includes a thermotransfer structure 522. In this case, the thermotransfer structure 522 includes an open gap 544 between the walls that form the recessed cavity 540 of the thermally conductive element 528 and the thermal storage element 530. The open gap 544 substantially circumscribes the thermal storage element 530 such that there is reduced contact, or even no contact, between the thermal storage element 530 and the thermally conductive element 528.
The open gap 544 is fluidly connected with the surrounding environment such that, in a solar power system, the heat transfer fluid within the vessel can flow through the open gap 544. Thus, the open gap 544 provides access to additional surface area of the thermally conductive element 528 for contact with the heat transfer fluid while still allowing the thermal storage element 530 to absorb heat and, upon inactivity of the system as described above, release the thermal energy.
As illustrated in FIG. 9, the thermotransfer structure 522 includes multiple covers 542 that extend at least partially over the mouth of the recessed cavity 540 to retain the thermal storage element 530 within the recessed cavity 540. In this case, the covers 542 (e.g., stops) extend partially over the recessed cavity 540 and thereby permit flow of the working fluid into and out of the open gap 544. Optionally, the covers 542 may be bonded to the thermal storage element 530. However, in other examples, the thermal storage element 530 is free of any attachments or bonds to the thermally conductive element 528. That is, the thermal storage element 530 is suspended in the working fluid within the recessed cavity 540.
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.

Claims

What is claimed is:

1. An energy transfer apparatus comprising:

a vessel containing a fluid;

a hot shoe at least partially disposed in the fluid; and

a thermal capacitor integral with the hot shoe.

2. A heat transfer apparatus comprising:

a hot shoe; and

a thermal capacitor integral with the hot shoe.

3. An energy transfer apparatus comprising:

a vessel containing a fluid;

a hot shoe at least partially disposed in the fluid; and

a thermal capacitor attached to the hot shoe.

4. An energy transfer apparatus comprising:

a vessel containing a fluid;

a hot shoe at least partially disposed in the fluid; and

a thermal capacitor abutting the hot shoe.

5. A heat transfer system comprising:

a heat source;

a heat sink; and

a thermotransfer structure operable to transfer heat between the heat source and the heat sink, the thermotransfer structure including a thermally conductive element and a thermal storage element adjacent the thermally conductive element.

6. The heat transfer system as recited in claim 5, wherein the thermally conductive element is a metallic material selected from a group consisting of copper material, iron material, aluminum material, and combinations thereof, and the thermal storage element is selected from a group consisting of a molten salt, a molten metal, and a ceramic material.

7. The heat transfer system as recited in claim 5, wherein the thermally conductive element is a metallic material and the thermal storage element is selected from a group consisting of a phase change material and a ceramic material.

8. The heat transfer system as recited in claim 7, wherein the thermal storage element is the phase change material, and the phase change material selected from a group consisting of a molten salt and a molten metal.

9. The heat transfer system as recited in claim 5, wherein the thermally conductive element is selected from a group consisting of copper material, iron material, aluminum material, and combinations thereof.

10. The heat transfer system as recited in claim 5, wherein the thermal storage element includes a core comprising a first material and a protective cladding comprising a second, different material that encases the core.

11. The heat transfer system as recited in claim 10, wherein one of the first material or the second material is a ceramic material and the other of the first material or the second material is a metallic material.

12. The heat transfer system as recited in claim 10, wherein the first material is a first metallic material and the second material is a second metallic material having a different composition than the first metallic material.

13. The heat transfer system as recited in claim 5, wherein the heat source is a vessel having a molten heat transfer fluid therein, and the heat sink is a power conversion device.

14. The heat transfer system as recited in claim 13, wherein the power conversion device is selected from a group consisting of a Stirling power conversion device and a thermoelectric power conversion device.

15. The heat transfer system as recited in claim 5, wherein the thermally conductive element has a first heat capacity and the thermal storage element has a second heat capacity that is greater than the first heat capacity.

16. A heat transfer apparatus comprising:

a thermotransfer structure including a first surface for receiving heat and a second surface for emitting heat, the thermotransfer structure including a thermally conductive element extending from the first surface to the second surface and a thermal storage element adjacent the thermally conductive element.

17. The heat transfer apparatus as recited in claim 16, wherein the first surface of the thermotransfer structure has a first cross-sectional area and the second surface of the thermotransfer structure has a second cross-sectional area that is smaller than a first cross-sectional area.

18. The heat transfer apparatus as recited in claim 16, wherein the thermal storage element extends partially between the first surface and the second surface.

19. The heat transfer apparatus as recited in claim 16, wherein the thermally conductive element includes a recessed cavity and the thermal storage element is located at least partially within the recessed cavity.

20. The heat transfer apparatus as recited in claim 19, wherein the thermal transfer structure includes an open gap between walls that form the recessed cavity and the thermal storage element.

21. The heat transfer apparatus as recited in claim 19, wherein the thermal storage element is frustoconical, and the recessed cavity is frustoconical.

22. The heat transfer apparatus as recited in claim 19, wherein the thermal storage element is free of any attachments to the thermally conductive element.

23. The heat transfer apparatus as recited in claim 19, further including at least one cover over the recessed cavity to contain the thermal storage element therein.

24. A method for a heat transfer system including a heat source, a heat sink, and a thermotransfer structure operable to transfer heat between the heat source and the heat sink, the thermotransfer structure including a thermally conductive element and a thermal storage element adjacent the thermally conductive portion, the method comprising:

in a first state of the heat transfer system, storing thermal energy from the heat source in the thermal storage element of the thermotransfer structure; and

in a second state of the heat transfer system, upon cooling of the heat source, releasing the stored thermal energy from the thermal storage element to the heat source.

25. The method as recited in claim 24, wherein the heat source is a molten working fluid, and the releasing of the stored thermal energy limits freezing of the molten working fluid.