WO2011007224A2

WO2011007224A2 - Low cost, high thermal conductivity heat flux transporter

Info

Publication number: WO2011007224A2
Application number: PCT/IB2010/001563
Authority: WO
Inventors: Mark Garfinkel
Original assignee: Clipper Windpower, Inc.
Priority date: 2009-07-13
Filing date: 2010-06-28
Publication date: 2011-01-20
Also published as: WO2011007224A3

Abstract

A thermal transport cooling apparatus including a metal tower, a heat source (a transformer) within the tower and a heat sink inner surface of the tower, and a hollow duct, the interior of which is filled with crushable compressed aluminium foil. A first end of the duct is close to the heat source, and a second end of the duct is close to the beat sink, such that the duct guides the heat generated by the heat source to the heat sink. Both ends of the thermal transport comprise a greaseless thermal interface flexible pad.

Description

LOW COST, HIGH THERMAL CONDUCTIVITY HEAT FLUX TRANSPORTER

BACKGROUND OF THE INVENTON

1. Field of the Invention

This invention relates to wind turbines and more

particularly to an apparatus for cooling of a heat-generating device located within a wind turbine tower. Furthermore, this invention relates to a method of creating a thermal bridge between a heart-generating device and a heat sink.

2. Description of the Prior Art

Prior methods of cooling heat-generating devices, e.g. a transformer, located within a wind turbine tower use forced air cooling with fans and a heat exchanger, liquid cooling, or a heat pipe. Forced air cooling has the disadvantage of requiring elaborate cooling ducts, fans and an opening in the tower wall. Liquid cooling has the disadvantage of requiring plumbing, a recirculation pump and the additional heat load on the liquid cooled system.

A heat pipe is a heat transfer mechanism that can transport large quantities of heat with a very small difference in

temperature between the hotter and colder interfaces of the heat pipe. Inside a heat pipe, at the hot interface, a fluid turns to vapor and the gas flows and condenses on the colder interface.

The liquid falls by gravity or is moved by capillary action back to the hot interface to evaporate again and repeat the cycle. Heat pipes generally include a hermetically sealed hollow vessel, a working fluid, and a closed-loop capillary

recirculation system. Heat pipes have the disadvantage that they are an expensive system requiring hermetically sealed hollow vessel and expensive working fluids. Furthermore, when heat pipes are heated above a certain temperature, all of the working fluid in the heat pipe will vaporize and the condensation process will cease to occur; in such conditions, the heat pipe's thermal conductivity is effectively reduced to the heat conduction properties of its solid metal casing alone. In addition, below a certain temperature, the working fluid will not undergo phase change, and the thermal conductivity will, once again, be reduced to that of the solid metal casing.

Therefore, one of the key criteria for the selection of a working fluid is the desired operational temperature range of the application.

It is therefore an object of the present invention to provide a low cost, high thermal transport cooling apparatus, which does not exhibit these unsatisfactory characteristics, and to provide to method for such cooling apparatus.

SUMMARY OF THE INVENTION

The object of the present is solved by a thermal transport cooling apparatus comprising a wind turbine tower, a heat- generating device within said wind turbine tower, a heat sink and a hollow duct. The hollow duct comprises a first end and a second end and the interior of the hollow duct is filled with a thermally conductive material. The first end of said duct is in thermal contact with the heat-generating device and the second end of said duct is in thermal contact with said heat sink, such that the duct and the thermally conductive material within guide the heat generated by the heat-generating device to the heat sink.

The apparatus in accordance with the present invention is very cost-effective with regard to the used parts and the installation within the wind turbine tower since all used parts are popular and no special tools are required for the

installation. The choice of material used for the hollow duct is not essential, although it is preferred to use a material with a good thermal conductivity.

The hollow duct can simply be arranged between the heat- generating device and the heat sink so that the ends of the hollow duct, and the thermally conductive material, are in direct contact with the surfaces of the device and the heat sink. To facilitate installation of the hollow tube between the heat-generating device and the heat sink the heat-generating device may be laterally moveable, i.e. the distance between the surfaces of the heat sink and the heat-generating device is adjustable .

To enhance heat transfer between the hollow duct, the heat- generating device and/or the heat sink it is possible to use a thermal grease at the interface (s) . However, handling of thermal grease is unpleasantly, and it is likely that the thermal grease is pushed out of space between the hollow duct, the heat- generating device and/or the heat sink and it is therefore preferred that one or both ends of the hollow duct comprise a thermal interface pad, said at least one pad being arranged between the hollow duct and the heat-generating device and/or the heat sink. As such pad is solid, it is less likely that it is pushed out of space and so the heat transfer does not decline over time. Furthermore, the thermal interface pads can be handled more easily than thermal grease. To further enhance heat transfer the end of the pad(s) facing the heat-generating device and/or the heat sink may be flange-like.

The hollow duct and/or the pads can be mounted to the heat- generating device and the heat sink, although such mounting is not essential as long as a good heat transfer to and from the hollow duct (via the pad(s) if used) is ensured. For example, it is also possible to clamp the hollow duct (with or without pads) between the heat-sink and the heat-generating device.

Regarding the material of the thermal interface pads it is preferred that the material used has a good thermal

conductivity. It is also preferred that the at least one thermal interface pad has a temperature-dependent deformability, i.e. the material used for the thermal pads has the ability to change its physical characteristics. At the temperature of the interior of the wind turbine tower (hereinafter referred to as room temperature) , the pad material is firm / solid and easy to handle. This allows more control when applying the solid pads to the heat sink and the heat-generating device. The thermal material softens as it reaches the operating temperature of the heat-generating device. With the heat from the heat-generating device and a light clamping pressure, the pad material readily conforms to both device and heat sink surfaces, and to the thermally conductive material. This ability to completely fill the air gaps and surface voids allows performance comparable to thermal grease without the handling disadvantages mentioned above.

A thermal compound can be distributed in a uniform manner on the thermal interface pads . The pads should contain the

appropriate amount of thermal compound needed to achieve optimal heat dissipation to the heat sink. Such an optimal level of dissipation is proportional to the temperature rise of the heat generating device according to generally accepted principles of thermal management .

The apparatus in accordance with the invention comprises a heat sink, and it is preferred that the heat sink is provided by the inner surface of the wind turbine tower. By using the inner surface of the wind turbine tower as the heat sink an easy way of dissipating the heat is provided since the wind turbine tower is constantly cooled by the environment. To enhance the heat dissipation capacity of the wind turbine tower at least the area being in thermal contact with the hollow duct can be made of metal .

With regard to the thermally conductive material it is important that it has a good thermal conductivity. For example, a thermally deformable material can be used. When the heat- generating device produces heat the material softens and

enhanced the contact area between the thermally conductive material and the heat-generating material and the heat sink.

It is preferred that the thermally conductive material is solid at the temperature of the interior of the wind turbine tower, and it may comprise air gaps to accommodate thermal expansion, wherein such air gaps are not within the material as such but are formed by the material when it is inserted or arranged within the hollow duct. In other words, the thermally conductive material may comprises a pore structure when arranged within the hollow duct. In particularly, it is preferred that the thermally conductive material is a crushable metal foil. Such crushable metal foil is low-priced, provides a high reliability and no maintenance is necessary. Furthermore, the crushable metal foil can be insert and removed easily and can be recycled after removing. When using a crushable metal foil as thermally

conductive material, i.e. a non- fluent material, all the

disadvantages of a liquid thermally conductive material can be avoided. There is no need to install and maintain a pumping system and no additional wear parts are added. A further big advantage of the crushable metal foil is the fact that it is very lightweight in comparison with liquid or a fully solid thermally conductive material (a duct filled with solid copper) and therefore mounting, installation, support and transport of the hollow duct / the thermally conductive material is less complex and time-consuming as well as more cost-effective.

In case a crushable metal foil is used as the thermally conductive material within the hollow duct, it is preferred to provide at least one access opening in the hollow duct. Such access opening facilitates the access to the crushable metal foil within the hollow duct as well as inserting and removing the foil. Furthermore, it facilitates contacting the crushable metal foil with heat-generating device and the heat sink.

With regard to the metal used it is preferred that the thermally conductive material is crushable compressed aluminium foil. An aluminium foil is cost-effective, commercially

available and low in weight.

The object is further solved by a method of creating a thermal bridge between a heat-generating device within a wind turbine tower and a heat sink, wherein the method comprises the steps of

providing a heat-generating device and a heat sink within a wind turbine tower,

arranging a hollow duct comprising a first end and a second end between the heat-generating device and the heat sink,

enabling a heat transfer between the ends of the hollow duct and the heat-generating device and the heat sink by contacting the hollow duct and a thermally conductive material within the hollow duct with the heat-generating device and the heat sink.

The thermally conductive material is inserted into the hollow duct before and/or during the installation of the hollow duct .

In case a thermally deformable conductive material is used, contacting the thermally conductive material with the heat- generating device and the heat sink can be achieved by heating the thermally conductive material within the hollow duct.

In case a crushable metal foil is used as the thermally conductive material contacting the metal foil with the heat- generating device and the heat sink can be achieved by pulling some of the crushable foil at the ends of the hollow duct out of the duct. It is also possible to provide a hollow duct filled with thermally conductive material, wherein this material comprises plugs at both ends of the hollow duct protruding from the ends of the hollow duct. When installing the hollow duct, which is slightly shorter than the distance between the heat- generating device and the heat sink, the pug material comes into contact with the surfaces of the device and the heat sink.

The invention also pertains the use of a hollow duct filled with a compressed metal foil as a heat bridge between a heat- generating device within a wind turbine tower and a heat sink, wherein it is preferred that the heat sink is provided by the inner surface of the wind turbine tower.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a view of a wind turbine tower supported on a concrete base in which this invention is embodied; and

FIGURES 2a-2c are perspective views of various forms of the hollow duct filled with thermally conductive material shown in FIGURE 1.

DETAILED DESCRIPTION

Ducts are used in heating, ventilation, and air conditioning to deliver and remove air. In this specification the duct may or may not deliver and remove air. Refer to FIGURE 1. FIGURE 1 shows one embodiment of the thermal transport cooling apparatus in accordance with the invention, wherein this embodiment uses the inner wall surface 16 of a wind turbine tower 10 as heat sink. The circular wind turbine tower 10 rests upon and is bolted to a concrete slab 12. A heat-generating device 14, e.g. an electrical transformer within the confines of the wind turbine tower 10 rests upon and is bolted to the concrete slab 12 by bolts 17, 19. The heat- generating device 14 is arranged close to the inner wall surface 16 of the wind turbine tower 10, i.e. close to the heat sink. In practice the distance between the heat-generating device 14 and the inner wall surface 16 may be six inches. The inner wall surface 16 of the wind turbine tower 10 acts as a heat sink. The embodiment shown further comprises a thermal transport device which includes a hollow duct 18, the interior of which is filled with thermally conductive material 20 (such as crushable

compressed aluminium foil) , and is placed between the heat- generating device 14 and the inner wall surface 16 of the wind turbine tower 10. The heat-generating device 14 is preferably moveable laterally at the bolts 17, 19 so as to adjust the distance to the inner wall surface 16 to accommodate the hollow duct 18. A first end 22 of the hollow duct 18 is arranged close (in thermal contact) to the heat source, i.e. the heat- generating device 14, and a second end 24 of the hollow duct 18 is arranged close (in thermal contact) to the heat sink, i.e. inner wall surface 16, such that the hollow duct 14 and/or the thermally conductive material 22 within the duct guides the heat generated by the heat-generating device 14 to the heat sink, i.e. the inner wall surface 16 of the wind turbine tower 10. In case of the shown embodiment (to enhance thermal conduction) the thermal transport device comprises at both ends 22, 24 of the hollow duct 18 a greaseless thermal interface flexible pad 22a, 24b. The greaseless thermal interface flexible pads 22a, 24b arranged on both ends of the duct 18 can be mounted to the duct by gluing, taping, press fitting, etc. The pads 22a, 24a do not need to be soldered or welded to the duct and the duct may or may not be hermetically sealed. The greaseless thermal interface flexible pads 22a, 24a can comprise or consist of a material with a good thermal conductivity. Furthermore, they have a temperature-dependent deformability, i.e. the material used for the thermal pads 22a, 24a has the ability to change its physical characteristics. At room temperature the pad material is firm and easy to handle. This allows more control when applying the solid pads to the heat sink and the heat-generating device 14. The thermal material softens as it reaches the operating

temperature of the heat-generating device 14. With the heat from the heat-generating device 14 and a light clamping pressure, the pad material readily conforms to both heat-generating device 14 and heat sink surfaces, and to the thermally conductive

material. This ability to completely fill the air gaps and surface voids allows performance comparable to thermal grease. A thermal compound can be distributed in a uniform manner on the thermal interface pads, wherein the pads should contain the appropriate amount of thermal compound needed to achieve optimal heat dissipation to the heat sink.

It is preferred to use aluminium foil as thermally

conductive material, and the aluminium foil is bought in rolls, and is crushed and inserted before and/or during installation of the hollow duct 14. Copper foil can be used as well . It would make for a smaller but more expensive heat transport device. Brass foil, steel wool, or other metal foil could also be used, but with a higher thermal drop, and most likely lower overall cost .

In the following an embodiment of the method in accordance with the invention is disclosed. The thermal transport device in accordance with this embodiment includes the hollow duct 18, thermally conductive material 20 and the thermal pads 22a, 24b. Within the wind turbine tower 10 a heat-generating device 14, e.g. an electrical transformer, and a heat sink 16 are provided. A hollow duct 18 comprising a first end 22 and a second end 24 is arranged between the heat-generating device 14 and the heat sink, and finally a heat transfer between the ends 22, 24 of the hollow duct and the heat-generating device and the heat sink is provided by contacting a thermally conductive material 22 within the hollow tube 18 with the heat-generating device 14 and the heat sink 16.

Depending on the thermally conductive material used the hollow duct may comprise two initial conductive material plugs, for example initial foil plugs. To facilitate installation the thermal transport device may be slightly shorter than the distance from the heat-generating device 14 outside wall contact surface 21 to the curved inner wall contact surface 16 (the heat sink) . The thermal transport device is manually put in place. Afterwards, the initial foil plugs can pushed out further to enhance the heat transfer between the thermally conductive material, the heat-generating device 14 and the heat sink 16, i.e. the inner wall surface. To facilitate this, the middle of the hollow duct 14 may comprise an access door 25 by which the two initial plugs of foil are manually pushed against the heat- generating device 14 surface and the inner wall surface 16, respectively. In case any air space remains in the hollow duct 18 it is tightly filled with additional compressed foil until there is no additional air space remaining.

To hold the thermal transport device in place it can be clamped between the heat-generating device 14 and the inner wall surface 16. Due to the low weight of the device such clamping may be sufficient; otherwise the thermal transport device may be supported by (not shown) holding means. The hollow duct 18 can be filled with the thermally conductive material 20 before and/or during installation.

Refer to FIGURES 2a-2c which show perspective views of various forms of the hollow duct 18 filled with crushable metal foil 20.

Crushable Compressed Aluminium foil in a low cost hollow duct becomes a "modular fluid-less heat pipe", which provides low cost, high heat flux transport with flexibility, high reliability and high performance. In experiments conducted with a 50 Hz. transformer as the heat-generating device, a hollow duct filled with crushable compressed aluminium foil reduced a 50 Hz. transformer thermal drop to the inside skin of a turbine tower wall by a factor of more than 7600% over air, with modularity, low cost fabrication and installation. There is no maintenance, and there are no moving parts. All parts can be recycled if necessary.

Not counting indirect cooling, preliminary calculations show that at least half the 50 Hz. transformer loss (12.5 kw) can be transported from the side of the transformer a 6 -inch distance to the inside tower wall with a thermal resistance drop of only 4 to 6 degrees. This is much simpler and reliable than the use of forced air cooling with fans and a heat exchanger, or liquid cooling with the additional complication of more plumbing, and the additional heat load on the liquid-cooled system.

Claims

C l a i m s

1. A thermal transport cooling apparatus, comprising:

a wind turbine tower 10;

a heat-generating device 14 within said wind turbine tower 10;

a heat sink 16, and

a hollow duct 18 comprising a first end 22 and a second end 24, the interior of which is filled with thermally

conductive material 20,

wherein the first end 22 of said duct being in thermal contact with the heat-generating device 14, and the second end 24 of said duct being in thermal contact with said heat sink 16, such that the duct 18 and the thermally conductive

material 20 guide the heat generated by the heat-generating device 14 to the heat sink 16.

2. The cooling apparatus of claim 1, wherein one or both ends 22, 24 of the hollow duct 18 comprise a thermal interface pad 22a, 22b, said at least one pad being arranged between the hollow duct 18 and the heat-generating device 14 and/or the heat sink 16.

3. The cooling apparatus of claim 2, wherein the at least one thermal interface pad 22a, 22b has a temperature-dependent deformability .

4. The cooling apparatus of any of the claims 1 - 3, wherein the heat sink 16 is provided by the inner surface of the wind turbine tower 10.

5. The cooling apparatus of any of the claims 1 - 4, wherein the thermally conductive material 20 is solid at the temperature of the interior of the wind turbine tower, and may contain air gaps to accommodate thermal expansion.

6. The cooling apparatus of any of the claims 1 - 5, wherein the thermally conductive material 20 is crushable metal foil .

7. The cooling apparatus of any of the claims 1 - 6, wherein the thermally conductive material 20 is crushable compressed aluminium foil .

8. A method of creating a thermal bridge between a heat- generating device within a wind turbine tower and a heat sink, comprising the steps of

providing a heat-generating device 14 and a heat sink 16 within a wind turbine tower 10,

arranging a hollow duct 18 comprising a first end 22 and a second end 24 between the heat-generating device 14 and the heat sink 16,

enabling a heat transfer between the ends 22, 24 of the hollow duct and the heat-generating device 14 and the heat sink 16 by contacting a thermally conductive material 22 within the hollow tube 18 with the heat-generating device 14 and the heat sink 16.

9. The method of claim 8, wherein the thermally conductive material 20 is inserted into the hollow duct 18 before and/or during the installation of the hollow tube.

10. The method of claims 8 or 9, wherein contacting the thermally conductive material 20 with the heat-generating device 14 and the heat sink is achieved by heating the

thermally conductive material 20 within the tube.

11. The use of a hollow duct 18 filled with compressed metal foil as a heat bridge between a heat-generating device 14 within a wind turbine tower 10 and a heat sink 16.

12. The use of claim 10, wherein the heat sink 16 is provided by the inner surface of the wind turbine tower 10.