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Quantum Mechanics questions thermal waves at the nanoscale
Thermal waves thought to explain how oil droplets enhance the thermal conductivity of water is questionable as quantum mechanics denies the droplets the heat capacity necessary to change in temperature to excite thermal waves
By: QED Radiations
In 2009, significant enhancement(
DPL theory  based on thermal waves was proposed for small scale heat transfer over 20 years ago. DPL stands for dual-phase-lag. The DPL is thought to capture the microstructural interaction in fast heat transport, i.e., the finite time required for various microstructural interactions to take place, e.g., photon induced electron heating in metals. Experimental basis for the DPL based  on 50 - 300 nm thick gold samples showed laser heating of thin Au films induced photoemission of electrons that lagged the surface temperature by a few picoseconds. More recently, the DPL based on extending macroscopic theory to the nanoscale was proposed  for nanofluids, i.e., NPs in the base fluids. NPs stands for nanoparticles. Unverified claims are made of the consistency of nanofluids with DPL heat conduction.
The DPL [1-4] based on thermal waves is thought consistent with nanoscale observations. However, only qualitative confirmations of the DPL are made. TWM is used extensively at the macroscale to show the existence of thermal waves. TWM stands for thermal wave microscopy. But TWM to show thermal waves as assumed in the DPL exist are not reported. Further, the DPL assumes the atom always has heat capacity at the nanoscale when in fact QM requires the heat capacity to vanish. QM stands for quantum mechanics. Actually, QM precludes thermal waves at the nanocale as temperature changes necessary to initiate the thermal waves cannot occur. A QM mechanism is suggested.
Small scale heat transfer is proposed to be a consequence of QM that requires the heat capacity of the atoms in nanostructures to vanish in combination with QED. QED stands for quantum electrodynamics, but is a simple form of the complex QED theory advanced by Feynman and others. Briefly stated: Absent heat capacity, a QM box with submicron sides separated by distance d conserves heat by creating standing EM radiation having half-wavelength λ /2 = nd, where n and d are the refractive index and diameter of the NP. EM stands for electromagnetic.
But for the heat capacity to vanish, the Planck law requires high EM confinement of the atom which occurs naturally in nanostructures because of their high S/V ratios. S/V stands for surface-to-volume. Hence, absorbed heat is deposited in the surfaces of nanostructures. Since the distance d between surfaces is nanoscale, d < 100 nm, the atoms are placed under high EM confinement at nanoscale wavelengths, λ < 200n nm. Once the surface heat is expended in creating the standing EM radiation, the corresponding confinement vanishes allowing the EM radiation to charge the nanostructure by the photoelectric effect or escapes to the surroundings. See diverse QED applications at http://www.nanoqed.org, 2010 - 2016
QED applied to the thin Au films  is illustrated in the thumbnail. Heat Q from laser radiation is absorbed in the front and back surfaces of the film because of the high S/V ratio, but QM precludes any temperature increase. Conservation of heat Q creates EM radiation standing across the thickness d having wavelength λ = 2 nd that by the photoelectric effect creates hot electrons. Since the macroscopic substrate has heat capacity, the heat Q changes the substrate temperature but is delayed by a few picoseconds as the electrons produced by the QED induced EM radiation in the film are promoted into the conduction band of the film.
Summary and Conclusions
QM and not classical physics governs the nanoscale. Macroscopic heat transfer equations based on finite heat capacity are no longer valid - at the nanoscale the high S/V ratio places the atoms under high EM confinement that by the Planck law causes the heat capacity of the atom to vanish. Therefore, temperature changes cannot occur in oil NPs  to initiate thermal waves.
Consistent with QM, thermal waves do indeed exist at the macroscale, but not at the nanoscale. The DPL  based on thermal waves is therefore invalid at the nanoscale. But TWM at the nanoscale is not likely to be successful as temperatures are not expected to change by QM.
Like DPL, QED is a wave theory in that the EM standing waves carry heat Q between front and back surfaces of the film at the speed of light, but the film does not increase in temperature. Moreover, film temperatures inferred  from reflectance measurements are questionable as surface strain induced by temperature is based on the classical thermal response of a semi-infinite solid having heat capacity. Regardless, even without thermal changes, the film surface is still strained by QED induced charge. Although temperatures are questionable, the heat arrival times at the substrate should be reasonably accurate.
In nanofluids, enhanced thermal conductivity of base fluids  from thermal waves by NPs is not verified, but unlikely by QM as NPs cannot change in temperature to initiate thermal waves.
 X. Wei and L. Wang, "1+12:
 D.Y. Tsou, "Experimental Support for the Lagging Behavior, "J. Thermophysics Heat Transfer, 9, 1995.
 S. D. Brorson, et al., "Femtosecond Electronic Heat-Transport Dynamics in Thin Gold Films," PRL, 59, 1962-1965, 1987.
 L. Wang and J. Fan, "Nanofluids Research: Key Issues," Nanoscale Res Lett, 5, 1241-1252, 2010.
Page Updated Last on: Apr 26, 2016