Heat Transfer Interface And Method Of Improving Heat Transfer

Abstract

An embodiment of a heat transfer interface includes a solid material having first and second surfaces, and a nanotube forest covering at least a portion of the first surface, In operation in a heat exchanger, the heat transfer interface transmits heat from a first side to a second side of the heat transfer interface. An embodiment of a method of improving heat transfer in a heat exchanger includes applying a nanotube forest to a heat transfer surface of a heat transfer interface and installing the heat transfer interface in the heat exchanger.

Description

RELATED APPLICATIONS

This application is the national phase application of International application number PCT/US2010/026560, filed Mar. 8, 2010, which claims priority to and the benefit of U.S. Provisional Application No. 61/159,017, filed on Mar. 10, 2009, which is hereby incorporated by reference in its entirety.

STATEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to the field of heat exchange and, more particularly, to the field of heat exchange where a surface enhancement provides improved heat exchange.

BACKGROUND OF THE INVENTION

There is currently great interest in alternative energy sources including wind, geothermal, tidal, and solar. Solar energy has excellent long term potential. There are two major “direct” ways to extract energy from sunlight, which are to generate electricity in a photovoltaic cell or to generate heat that is then converted to electricity (e.g., the heat may be used to generate steam, which is used to drive a turbine that generates electricity). The latter is referred to as thermo-solar. Two key elements in thermo-solar are absorption of sunlight (i.e. radiant heat transfer or collection and heat transfer to a fluid (i.e. conduction and convection near an interface between a solid and a fluid).

SUMMARY OF THE INVENTION

According to an embodiment, the present invention is a heat transfer interface that includes a solid material having first and second surfaces, and a nanotube forest covering at least a portion of the first surface. In operation in a heat exchanger, the heat transfer interface transmits heat from a first side to a second side of the heat transfer interface.

According to another embodiment, the present invention is a method of improving heat transfer in a heat exchanger that includes applying a nanotube forest to a heat transfer surface of a heat transfer interface and installing the heat transfer interface in the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which:

FIG. 1 illustrates an embodiment of a heat transfer interface of the present invention;

FIG. 2 illustrates an embodiment of a heat transfer interface of the present invention;

FIG. 3 illustrates an embodiment of a heat transfer interface of the present invention;

FIG. 4 illustrates an embodiment of a heat transfer interface of the present invention;

FIG. 5 illustrates a cylindrically shaped solid material employed in and embodiment of a heat transfer interface of the present invention;

FIG. 6 illustrates an embodiment of a cylindrical heat transfer interface of present invention;

FIG. 7 illustrates an embodiment of a cylindrical heat transfer interface of the present invention;

FIG. 8 illustrates an embodiment of a heat exchanger of the present invention;

FIG. 9 is an SEM image of a nanotube forest in accordance with an embodiment of the present invention; and

FIGS. 10A and 10B illustrate a superhydrophilic surface treatment in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of a heat transfer interface of the present invention is illustrated in FIG. 1. The heat transfer interface 100 is a solid material 102 having first and second surface, 104 and 106. A nanotube forest 108 covers at least a portion of the first surface 104. The solid material 102 may be a metal or some other suitable material such as a dielectric. In an embodiment, the nanotube forest 108 includes carbon nanotubes. In other embodiments, the nanotube forest may include nanotubes of boron nitride (BN), hybrid nanotubes of boron, nitrogen, and carbon (B_xC_yN_z), or some other suitable nanotubes. In operation in a heat exchanger, the heat transfer interface 100 transfers heat from a first side 112 to a second side 114 of the interface 100.

Another embodiment of a heat transfer interface of the present invention is illustrated in FIG. 2. The heat transfer interface 200 is a solid material 102 having first and second surfaces, 104 and 106, and a nanotube forest 108 covers at least a portion of the first surface 104. In operation in a heat exchanger, radiant energy 210 (e.g., sunlight) on a first side 212 of the interface 200 illuminates at least a portion of the nanotube forest 108. Heat generated by the radiant energy conducts through the solid material 102 to a second side 214 of the interface 200.

It will be readily apparent to one skilled in the art that the radiation heat transfer for the heat transfer interface 200 may be away from the nanotube forest 108 to some radiation absorbing body that is at a temperature lower than a temperature of the nanotube forest 108.

Another embodiment of a heat transfer interface of the present invention is illustrated in FIG. 3. The heat transfer interface 300 is a solid material 102 having first and second surfaces, 104 and 106, and a nanotube forest 108 covers at least a portion of the first surface 104. In operation in a heat exchanger, heat is transferred from a first side 312 of the interface 300 to a second side 314 where a fluid 316 resides. In the vicinity of the first surface 104, the nanotube forest 108, and the fluid 316, the heat transfers by a combination of conduction within the solid material 102 and the nanotube forest 108, and convection in the fluid 316. In an embodiment, the fluid 316 is a liquid such as water. In an embodiment, the nanotube forest 108 includes a superhydrophilic surface treatment that acts to attract water and, thus, avoid cavitation in or near the nanotube forest 108.

It will be readily apparent to one skilled in the art that convection heat transfer of the heat transfer interface 300 may be from the fluid 316 to the nanotube forest 108 of the interface 200.

Another embodiment of a heat transfer interface of the present invention is illustrated in FIG. 4. The heat transfer interface 400 is a solid material 102 having first and second surfaces, 104 and 106, and nanotube forests, 108 and 409, cover at least portions of the first and second surfaces, 104 and 106, respectively. In operation in a heat exchanger, radiant energy 410 (e.g., sunlight) on a first side of the interface 400 illuminates at least a portion of the nanotube forest 108. Heat generated by the radiant energy conducts through the solid material 102 to the second nanotube forest 409, where convection transfers the heat to a fluid 416 on a second side 414 of the interface 400. In an embodiment, the second nanotube forest 409 includes a superhydrophilic surface treatment.

It will be readily apparent to one skilled in the art that that various modifications may be made to the heat transfer interface 400 such as including a superhydrophilic surface treatment for the nanotube forest 108.

An embodiment of a heat transfer interface of the present invention may include a cylinder that is illustrated in FIG. 5. The cylinder 500 is made of a solid material 502 having an outer surface 504 and an inner surface 506.

An embodiment of a cylindrical heat transfer interface of the present invention is illustrated in FIG. 6. The cylindrical heat transfer interface 600 is the solid material 502 having an outer surface 504 and an inner surface 506 and a nanotube forest 608 covers at least a portion of the outer surface 504. In operation in a heat exchanger, radiant energy 610 illuminates at least a portion of the nanotube forest 608. Heat generated by the radiant energy transfers to the inner surface 506.

Another embodiment of a cylindrical heat transfer interface of the present invention is illustrated in FIG. 7. The cylindrical heat transfer interface 700 includes the solid material 502 having outer and, inner surfaces, 504 and, 506, and a nanotube forest 708 covers at least a portion of the inner surface 506. In operation in a heat exchanger, heat is transferred to or from a fluid 712 by combination of convection within the fluid 712 as well as conduction within the solid material 502 and the nanotube forest 708. In an embodiment of the cylindrical heat transfer interface 700, the nanotube forest includes a superhydrophilic surface treatment.

It will be readily apparent to one skilled in the art that various modifications may be made to the cylindrical heat transfer interfaces, 600 (FIG. 6) and 700 (FIG. 7), such as covering at least in part both the outer and inner surfaces with nanotube forests or immersing the cylindrical heat transfer interface 600 or 700 in a fluid where heat is transferred to or from the outer surface 504 by convection.

An embodiment of a heat exchanger of the present invention is illustrated in FIG. 8. The heat exchanger includes a cylindrical heat transfer interface 801 and a mirror 803. The cylindrical heat transfer interface 801 is a solid material 802 having an outer surface 804 and an inner surface 806, and outer and inner nanotube forests (e.g., the nanotube forests, 608 and 708, of FIGS. 6 and 7) covering at least portions of the outer and inner surfaces, 804 and 806, respectively. The nanotube forest that covers at least a portion of the inner surface 806 may include a superhydrophilic surface treatment. The mirror 803 may be a parabolic shaped mirror. In operation of the heat exchanger 800, radiant energy 810 (e.g., sunlight) illuminates the outer nanotube forest 804 in part by reflection from the mirror 803. Heat generated by the radiant energy 810 conducts through the outer nanotube forest, the solid material 802, and the inner nanotube forest where it is transferred to a fluid 312 (e.g., liquid water).

A method of improving heat transfer within a heat exchanger in accordance with an embodiment of the present invention includes applying a nanotube forest to a heat transfer surface of a heat transfer interface and installing the heat transfer interface in the heat exchanger. The method may further comprise applying a superhydrophilic surface treatment to the nanotube forest.

Carbon nanotube forests have been applied to solid material substrates using a CVD technique (e.g., see Wang, K., et al., Proc. SPIE 2005, 5718, 22-29), which was modified as follows. To increase forest adhesion to a substrate, a 10 nm thick Fe catalyst film was applied to the substrate prior to applying the carbon nanotube forest to the substrate. Also, a high ethylene concentration was used during nanotube growth. Specifically, flowing pure ethylene at 200 sccm for 10 min. at a growth temperature of 750° C. resulted in forests with an average nanotube diameter of approximately 40 nm. The as-grown forests were resistant to deformation by strong solvent streams and significant mechanical pressure and scratching. It is believed that the observed durability stems form a cementing effect caused by amorphous carbon deposited on the nanotube surface during growth. FIG. 9 is an SEM photo of a nanotube forest that had been applied to a substrate using this technique.

Substrates having a carbon nanotube forest on at least a portion of a surface were subject to a superhydrophilic surface treatment using a perflouroazide as schematically illustrated in FIGS. 10A and 10B where the particular perflouroazide is shown in the figures. The substrates were dipped in a solution of the azide in acetone (10 mg/ml), allowed to dry, exposed to UV radiation (λ=254 nm) for 5 min., and then rinsed in an acetone stream. In FIG. 10A, a carbon nanotube 1000 in the presence of the perflouroazide is exposed to UV radiation 1002. FIG. 10B illustrates the nanotube 1000 after the surface treatment in which one possibility of bonding of the perflouroazide radicals to a surface of the nanotube 1000 is shown. Nanotube forests treated according to this technique exhibited a “sponge like” behavior with a water contact angle diminishing to near 0° after a few seconds. A contact angle near 0° verifies the superhydrophilic nature of a surface.

CONCLUSION

It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes.

Claims

1. A heat transfer interface comprising:

a solid material having first and second surfaces; and

a nanotube forest covering at least a portion of the first surface,

wherein in operation in a heat exchanger, the heat transfer interface transmits heat from a first side to a second side of the heat transfer interface.

2. The heat transfer interface of claim 1 wherein the nanotube forest comprises carbon nanotubes.

3. The heat transfer interface of claim 1 wherein in operation of the heat exchanger, the first surface receives radiant energy.

4. The heat transfer interface of claim 3 wherein the radiant energy comprises sunlight.

5. The heat transfer interface of claim 1 wherein in operation of the heat exchanger, the first surface transmits heat to a fluid.

6. The heat transfer interface of claim 5 wherein the fluid is a liquid.

7. The heat transfer interface of claim 6 wherein the nanotube forest further comprises a superhydrophilic surface treatment.

8. The heat transfer interface of claim 1 further comprising a second nanotube forest covering at least a portion of the second surface.

9. The heat transfer interface of claim 8 wherein in operation of the heat exchanger, the first surface receives radiant energy, thereby producing heat in the solid material, and the second surface transmits the heat to a fluid.

10. The heat transfer interface of claim 9 wherein the fluid is a liquid.

11. The heat transfer interface of claim 10 wherein the nanotube forest further comprises a superhydrophilic surface treatment.

12. A heat transfer interface comprising:

a solid material having first and second surfaces;

a first nanotube forest covering at least a portion of the first surface; and

a second nanotube forest covering at least a portion of the second surface, the second nanotube forest comprising a superhydrophilic surface treatment,

wherein in operation in a heat exchanger, the heat transfer interface transmits heat from a first side to a second side of the heat transfer interface.

13. The heat transfer interface of claim 12 wherein in operation of the heat exchanger, the first surface receives radiant energy that produces heat within the solid material and the second surface transfers the heat to a liquid.

14. The heat transfer interface of claim 13 wherein the liquid comprises water.

15. A method of improving heat transfer in a heat exchanger comprising:

applying a nanotube forest to a heat transfer surface of a heat transfer interface; and

installing the heat transfer interface in the heat exchanger.

16. The method of improving the heat transfer of claim 15 further comprising operating the heat exchanger.

17. The method of improving the heat transfer of claim 16 wherein the heat transfer surface receives radiant energy.

18. The method of improving the heat transfer of claim 16 wherein the heat transfer surface transfers heat to a fluid.

19. The method of improving the heat transfer of claim 18 wherein the fluid is a liquid.

20. The method of improving the heat transfer of claim 19 further comprising applying a superhydrophilic treatment to the nanotube forest.

21. The heat transfer interface of claim 1 wherein in operation of the heat exchanger, the first surface transmits radiant energy.

22. The heat transfer interface of claim 21 wherein the radiant energy comprises sunlight.

23. The heat transfer interface of claim 1 wherein in operation of the heat exchanger, the first surface transmits heat from a fluid.

24. The heat transfer interface of claim 23 wherein the fluid is a liquid.

25. The heat transfer interface of claim 24 wherein the nanotube forest further comprises a superhydrophilic surface treatment.

26. The method of improving the heat transfer of claim 16 wherein the heat transfer surface transmits radiant energy.

27. The method of improving the heat transfer of claim 16 wherein the heat transfer surface transfers heat from a fluid.

28. The method of improving the heat transfer of claim 27 wherein the fluid is a liquid.

29. The method of improving the heat transfer of claim 28 further comprising applying a superhydrophilic treatment to the nanotube forest.