Structures for radiative cooling

1. An apparatus for cooling fluids, the apparatus comprising:

a radiative cooling device including a solar spectrum reflector and a thermal emitter configured and arranged to prohibit coupling of incoming electromagnetic radiation to a portion of the radiative cooling device and facilitate thermally-generated electromagnetic emissions from the radiative cooling device; and

a heat exchanger configured and arranged to exchange heat between the radiative cooling device and a fluid passing beneath it, wherein the fluid is to be cooled below an ambient temperature under solar irradiance.

2. The apparatus of claim 1 , further including a heat pump configured and arranged with the heat exchanger to exchange heat between the radiative cooling device and the fluid passing beneath it.

3. The apparatus of claim 2 , further including fluidic channels configured and arranged with the heat pump to cycle the fluid through the fluidic channels.

4. The apparatus of claim 1 , wherein the solar spectrum reflector includes a plurality of material layers.

5. The apparatus of claim 1 , wherein the solar spectrum reflector includes a plurality of layers of alternating materials configured and arranged to suppress light modes of at least some wavelengths in the solar spectrum, thereby inhibiting coupling of incoming electromagnetic radiation.

6. The apparatus of claim 1 , wherein the thermal emitter includes material configured and arranged to facilitate the thermally-generated electromagnetic emissions from the radiative cooling device in mid-infrared (IR) wavelengths.

7. The apparatus of claim 1 , wherein the heat exchanger is a first heat exchanger, wherein the fluid is a first fluid, further comprising a second heat exchanger configured to cool a second fluid, wherein the first heat exchanger and the second heat exchanger are arranged to circulate the first fluid to cool the second fluid.

8. The apparatus of claim 7 , wherein the second fluid comprises a refrigerant.

9. The apparatus of claim 8 , wherein the second heat exchanger is configured and arranged to subcool the refrigerant.

10. The apparatus of claim 8 , wherein the refrigerant is provided by a vapor compression system.

11. The apparatus of claim 1 , wherein the thermal emitter comprises at least one layer of a material configured to couple surface phonon-polaritons to free-space light modes between 8-13 microns.

12. The apparatus of claim 1 , wherein the solar spectrum reflector comprises a multi-layer stack comprising alternating layers of TiO 2 and MgF 2 .

13. The apparatus of claim 12 , wherein the multi-layer stack comprises:

fifteen layers in total comprising three sets of five bilayers, wherein:

a first set of the three sets comprises layers of TiO 2 having a thickness of 25 nm and layers of MgF 2 having a thickness of 35 nm;

a second set of the three sets comprises layers of TiO 2 having a thickness of 50 nm and layers of MgF 2 having a thickness of 70 nm; and

a third set of the three sets comprises layers of TiO 2 having a thickness of 75 nm and layers of MgF 2 having a thickness of 105 nm.

14. The apparatus of claim 1 , wherein the solar spectrum reflector comprises:

a metallic reflector; and

at least one dielectric layer arranged on top of the metallic reflector.

15. The apparatus of claim 14 , wherein the at least one dielectric layer comprises at least one of TiO 2 , MgF 2 , or SiO 2 .

16. The apparatus of claim 1 , wherein the radiative cooling device is configured to cause the fluid to be cooled below an ambient temperature under solar irradiance.

17. The apparatus of claim 1 , wherein the solar spectrum reflector comprises a metallic layer and at least one dielectric layer.

18. The apparatus of claim 1 , wherein the solar spectrum reflector comprises a plurality of material layers.