QED radiation cooling of electronics by coating circuit elements?

YOUNGWOOD, Pa. - Aug. 14, 2013 - PRLog -- Background
Heat exchange began with the Industrial Revolution. Pool-boiling rapidly emerged as the way to cool engines using water to transfer heat to the ambient air surroundings. Modern-day automobile engines use pool-boiling with water to dissipate heat to ambient air through finned radiators, but is difficult to implement in compact heat exchangers.
Recently, applying nanostructured 50-150 nm zinc oxide coatings to bare aluminum and copper surfaces was claimed [1] to remove heat 4-10 X faster than bare surfaces to make pool-boiling heat transfer at least as efficient as cooling fins. Coatings of zinc oxide are multi-textured having a flower-like structure, the petals of which thought to promote bubble formation and rapid, efficient replenishment of active pool-boiling sites.

Problem
The problem is the notion that porosity increases heat transfer finds basis in classical physics that excludes the size effect of QM. QM stands for quantum mechanics. QM requires [2] the heat capacity of the atom to vanish in nanoscale coatings, and therefore the temperature changes that take advantage of the increased area made available by porosity simply do not occur. What this means is increased heat transfer in pool-boiling has nothing to do with the porosity of the zinc oxide coating.

QED radiation cooling
Because of QM, the heat flow into the coating cannot be conserved by an increase in temperature. Provided the RI of the coating is greater than that of the surroundings, the heat is conserved by the QED induced creation of EM radiation inside the nanoscale coating. RI stands for refractive index, QED for quantum electrodynamics, and EM for electromagnetic.
Heat transfer enhancement in pool-boiling with zinc oxide coatings occurs because QED induced EM radiation created in the coating is absorbed in the water and substrate. Half of the heat is directly absorbed in the water, the other half absorbed in the substrate that absent another heat sink is eventually absorbed in the water. Porosity of the zinc oxide coating is inconsequential.

Cooling of electronics
In electronics cooling, pool-boiling heat transfer by QED radiation from nanoscale coatings of zinc oxide into the water avoids the complexity of finned surfaces but requires a source of water that may be difficult, if not impossible to implement in nanoelectronics. Avoiding pool-boiling altogether is desirable, but this leaves the zinc oxide coating alone to dissipate the Joule heat to the ambient air surroundings. Nevertheless, the notion is proposed that nanoelectronics may be cooled by simply applying a nanoscale zinc oxide coatings to the surfaces of circuit elements, the Joule heat directly dissipated by QED radiation cooling to the ambient air surroundings.  See http://www.nanoqed.org/ , “Electronic cooling by QED Radiation,” 2013.
QED radiation dissipates Joule heat at a wavelength depending on the thickness  d  of the coating. The thumbnail gives the wavelength of the QED emission for zinc oxide and silicon. For 50 < d < 150 nm zinc oxide coatings, the QED emission is in the UV-VIS. In water, all wavelengths except for the VIS are absorbed almost immediately while air is transparent for all wavelengths except for trace atmospheric gases. Absorption of QED radiation in electronics mediated by air alone therefore occurs at solid surfaces, the QED radiation successively emitted and absorbed by circuit elements throughout the electronic enclosure. Coating on the enclosure outer surface allows the QED radiation to be finally dissipated to the ambient environment

Discussion
Cooling by QED radiation is not new, having been misinterpreted over the past half century in nanoscale films as reduced thermal conductivity or ballistic heat transfer because measured heat flow is lower than that predicted by the Fourier equation, brief summaries of which are as follows.  

1 Thin Films Today, the BTE is primarily directed [3] to the steady state derivation of thickness dependent thermal conductivity of thin films. BTE stands for Boltzmann transport equation. Nevertheless, the BTE solutions are questionable because the heat balances assumed for the films do not include QED radiation loss, and therefore the thermal conductivity is concluded to be reduced from bulk. Indeed, the QED radiation actually cooled the films, but was mistakenly interpreted as a reduction in thermal conductivity.

2 Graphene Field-Effect Transistors Heat transfer analysis [4] of Joule heat in FETs is based on the Fourier diffusion equation. FET stands for Field-effect transistors. Classically, the graphene may lose heat by thermal BB radiation. However, BB radiation from the graphene at the peak temperature of 1000 K is negligible. Hence, the Joule heat is thought balanced solely by thermal conduction into the SiO2 substrate. The problem is the QED radiation loss required by QM is not included in the heat balance, the omission leading to the conclusion that Joule heat produces temperatures from 1000 K. By including QED radiation loss in the solution of Fourier’s equation, the FET temperatures remain near ambient.

3 Quasi-ballistic thermal transport Fourier theory of thermal transport is thought not valid at length scales smaller than the MFP of phonons in a material, which can be hundreds of nanometers in crystalline materials at room temperature. Instead, ballistic transfer is thought [5] to control heat transfer with the consequence that the heat flow away from a nanoscale hot spot is reduced by as much as 3X. Again, the exclusion of QED radiation loss from the hot spot explains why the Fourier equation over-predicts the heat flow. In effect, the beneficial cooling of the hot spot by QED radiation was sacrificed to justify ballistic transfer.

4 Non-diffusive Transport in Silicon Membrane. In silicon at room temperature, the majority of phonons have MFPs of about 43 nm, and therefore deviations from the classical Fourier equation are not expected at micron distances. However, laser experiments [6] with 400 nm silicon membranes again contrarily show reduced thermal conductivity. QED radiation emitted from the silicon membrane is in the NIR at 2.6 microns, the confirmation of which may be made with IR spectroscopy

Conclusions
The beneficial effect of QED radiation cooling should be considered in electronics packaging instead of justifying reduced thermal conductivity based on ballistic heat transfer or reduced heat flow from that predicted by the Fourier equation. 

References
[1] T. J. Hendricks, et al., International Journal Heat and Mass Transfer, vol. 53, pp. 3357–3365, 2010.
[2] T. Prevenslik, ASME InterPACK, Burlingame, CA, USA, July 16-18, 2013
[3] M. Aseghi and W. Liu, Electronics Cooling, February, 2007.
[4] M. Freitag, et al., Nano Lett., vol. 9, pp. 1883 – 1888, 2009.
[5] M. E. Siemens, et al., Nature Materials, vol. 9, pp. 26-30, 2010.
[6] J. A. Johnson, et al., PRL, vol. 110, 025901, 2013.