Cryocooler containing additively-manufactured heat exchanger

1. An apparatus comprising:

a heat exchanger configured to transfer heat to a fluid and to absorb heat from the fluid as the fluid flows in a fluid flow direction between a warm end and a cold end of a cryocooler;

wherein the heat exchanger includes at least one section comprising:

a substrate comprising at least one allotropic form of carbon, the substrate configured to substantially block transfer of heat within the substrate substantially parallel to the fluid flow direction such that the substrate allows heat transfer within the substrate substantially perpendicular to the fluid flow direction more easily than heat transfer within the substrate substantially parallel to the fluid flow direction; and

a layer of nanoparticles on or over the substrate.

2. The apparatus of claim 1 , wherein:

the at least one section of the heat exchanger comprises multiple sections; and

the multiple sections collectively comprise multiple substrates and multiple layers of nanoparticles.

3. The apparatus of claim 2 , wherein the heat exchanger further comprises pores through the multiple sections of the heat exchanger, the pores configured to allow the fluid to flow through the heat exchanger and to contact the substrates and the layers of nanoparticles.

4. The apparatus of claim 2 , wherein the multiple sections are stacked to form the heat exchanger.

5. The apparatus of claim 1 , wherein the nanoparticles are arranged in a grid pattern on or over the substrate.

6. The apparatus of claim 1 , wherein:

the nanoparticles comprise at least one lanthanide element or alloy; and

the substrate comprises carbon nanotubes or graphene.

7. The apparatus of claim 1 , further comprising:

an ink forming part of the layer of nanoparticles.

8. The apparatus of claim 1 , wherein:

the substrate has a substantially planar surface that is oriented substantially perpendicular to the fluid flow direction;

the layer of nanoparticles is on or over the substantially planar surface of the substrate; and

the nanoparticles are arranged substantially parallel to the substantially planar surface of the substrate.

9. A method comprising:

forming a heat exchanger for a cryocooler, the heat exchanger configured to contain a fluid that flows in a fluid flow direction;

wherein forming the heat exchanger comprises forming multiple sections of the heat exchanger, each section of the heat exchanger comprising:

a substrate comprising at least one allotropic form of carbon, the substrate configured to substantially block transfer of heat within the substrate substantially parallel to the fluid flow direction such that the substrate allows heat transfer within the substrate substantially perpendicular to the fluid flow direction more easily than heat transfer within the substrate substantially parallel to the fluid flow direction; and

a layer of nanoparticles on or over the substrate.

10. The method of claim 9 , wherein forming the heat exchanger comprises forming alternating substrates and layers of nanoparticles.

11. The method of claim 9 , wherein forming the heat exchanger comprises:

depositing the layer of nanoparticles on or over the substrate;

cutting the substrate and the layer of nanoparticles into sections; and

stacking the sections to form the heat exchanger.

12. The method of claim 9 , wherein forming each section of the heat exchanger comprises:

forming the substrate for that section; and

depositing the layer of nanoparticles for that section on or over the substrate for that section.

13. The method of claim 9 , further comprising:

for each section, fusing the nanoparticles in the layer of nanoparticles.

14. The method of claim 9 , further comprising:

forming pores through the sections of the heat exchanger, the pores configured to allow a fluid to flow through the heat exchanger and to contact the substrates and the layers of nanoparticle.

15. The method of claim 9 , wherein forming the heat exchanger comprises:

for each section, printing an ink containing the nanoparticles on or over the substrate to form the layer of nanoparticles.

16. A method comprising:

forming a heat exchanger for a cryocooler, the heat exchanger configured to contain a fluid that flows in a fluid flow direction;

wherein forming the heat exchanger comprises forming multiple sections of the heat exchanger, each section of the heat exchanger comprising a substrate and a layer of metal on or over the substrate such that the heat exchanger comprises alternating substrates and layers of metal; and

wherein the substrate of each section is configured to substantially block transfer of heat within the substrate substantially parallel to the fluid flow direction such that the substrate allows heat transfer within the substrate substantially perpendicular to the fluid flow direction more easily than heat transfer within the substrate substantially parallel to the fluid flow direction.

17. The method of claim 16 , wherein:

the layer of metal in each section comprises a layer of nanoparticles; and

each layer of metal is formed by depositing an ink containing the nanoparticles.

18. The method of claim 17 , wherein the nanoparticles comprise at least one lanthanide element or alloy.

19. The method of claim 17 , wherein the layer of metal in each section is formed by heating spheres or pellets of metal under vacuum to directly deposit the layer of metal.

20. The method of claim 17 , wherein the layer of metal in each section is formed by depositing multiple layers of metal to form a stack and heating the multiple layers of metal to form an alloy.

21. A method comprising:

forming a heat exchanger for a cryocooler, wherein forming the heat exchanger comprises forming multiple sections of the heat exchanger, each section of the heat exchanger comprising a substrate and a layer of metal on or over the substrate such that the heat exchanger comprises alternating substrates and layers of metal;

wherein the layer of metal in each section comprises a layer of nanoparticles;

wherein each layer of metal is formed by depositing an ink containing the nanoparticles;

wherein the nanoparticles comprise at least one lanthanide element or alloy; and

wherein the method further comprises fabricating the nanoparticles by dissolving a metallic salt in a non-aqueous liquid to form a first solution, mixing the first solution with a second solution comprising a photo-initiator in a non-aqueous liquid, and exposing a resulting mixture to ultraviolet illumination.