Download presentation

Presentation is loading. Please wait.

Published byBrenda Royston Modified about 1 year ago

1
Validity of Heat Transfer by Molecular Dynamics Thomas Prevenslik QED Radiations Discovery Bay, Hong Kong Tribochemistry - HAGI HAGI, October 26-28,

2
Molecular Dynamics (MD) is commonly used to simulate heat transfer at the nanoscale in the belief: Atomistic response using L-J potentials (ab initio) is more accurate than macroscopic finite element (FE) programs, e.g., ANSYS, COMSOL, etc. In this talk, I argue: FE gives equivalent heat transfer to MD, but both give meaningless results at the nanoscale. Moreover, both are invalid by Quantum Mechanics (QM) And Propose How to make MD and FE at least consistent with QM Introduction 2 Tribochemistry - HAGI HAGI, October 26-28, 2011

3
Restrictions MD and FE are restricted by Statistical Mechanics (SM) to atoms having thermal heat capacity Tribochemistry - HAGI HAGI, October 26-28,

4
Validity Historically, MD simulations of the bulk performed in submicron computation boxes under periodic boundary conditions (PBC) assume atoms have heat capacity In the macroscopic bulk being simulated, all atoms do indeed have heat capacity MD is therefore valid for bulk simulations Tribochemistry - HAGI HAGI, October 26-28,

5
Today, MD is not made for bulk simulations, but rather for the atomistic response of discrete nanostructures Problem is QM negates atoms in discrete nanostructures from having heat capacity Problem 5 Tribochemistry - HAGI HAGI, October 26-28, 2011

6
Heat Capacity of the Atom 6 Nanostructures kT eV SM, MD and FE (kT > 0) QM (kT = 0) Tribochemistry - HAGI HAGI, October 26-28, 2011 In nanostructures, the atom has no heat capacity by QM

7
MD and FE simulations of discrete nanostructures with atoms having heat capacity are a priori invalid Question What can be done to allow MD heat transfer of discrete nanostructures to be at least consistent with QM ? Argument Summary 7 Tribochemistry - HAGI HAGI, October 26-28, 2011

8
Conservation of Energy Lack of heat capacity by QM precludes EM energy conservation in discrete nanostructures by an increase in temperature, but how does conservation proceed? Conservation Proposal Absorbed EM energy is conserved by creating QED photons inside the nanostructure - by frequency up or down - conversion to the TIR resonance of the nanostructure. QED = Quantum Electrodynamics TIR = Total Internal Reflection Up-conversion produces high energy QED photons in tribochemistry, but down-conversion also occurs, e.g., redshift of galaxy photons in dust in the 2011 Nobel in physics on an expanding Universe 8

9
If the refractive index of nanostructure is greater than that of surroundings, the proposed QED photons are confined by TIR (Tyndall 1870) NPs have high surface to volume ratio. Propose EM energy is absorbed almost totally in the NP surface. Since the NP surface corresponds to the TIR wave function of the QED photons, QED photons are spontaneously created upon EM energy absorption in NPs. f = c/ = 2nD E = hf TIR Confinement 9 Tribochemistry - HAGI HAGI, October 26-28, 2011 For a spherical NP having diameter D, = 2D

10
Tribochemistry - HAGI HAGI, October 26-28, 2011 QED Heat Transfer 10 QED Photons Phonons Q QED is non-thermal radiation at TIR frequency Reduced conductivity in thin films explained by scattering of phonons, but slow to photons QED Radiation

11
Tribochemistry Source Tribochemistry - HAGI HAGI, October 26-28, 2011 At Kyoto, QED photons proposed as the source of tribochemistry Rubbing was shown to produce NPs - not electrons TIR converts frictional heating of NPs to QED photons QED photons have high Planck energy ( e.g., 10 nm NPs produce SXRs at 40 eV ) QED Photons are source of Triboplasma, the electrons and charged ions are produced by Einstein’s photoelectric effect SXRs → UV consistent with Nakayama and Hiratsuka 11

12
MD - Discrete and PBC Akimov, et al. “Molecular Dynamics of Surface- Moving Thermally Driven Nanocars,” J. Chem. Theory Comput. 4, 652 (2008). Sarkar et al., “Molecular dynamics simulation of effective thermal conductivity and study of enhance thermal transport in nanofluids,” J. Appl. Phys, 102, (2007). 12 Tribochemistry - HAGI HAGI, October 26-28, 2011 Pretty Picture v QM Correctness? MD for Discrete kT = 0, But MD assumes kT > 0 Car distorts but does not move Macroscopic analogy, Instead, QM forbids any increase in car temperature. Hence, QED radiation is produced that by Einstein’s photoelectric effect charges the cars that move by electrostatic interaction with each other. MD for kT > 0 is valid for PBC because atoms in macroscopic nanofluid have kT > 0

13
Thermal Gradients Tribochemistry - HAGI HAGI, October 26-28, Q-W Hou, B-Y Cao and Z-Y Guo,“Thermal gradient induced actuation of double-walled carbon nanotubes,”, Nanotechnology, Vol. 20, , 2009 MD of Concentric CNTs With MD, no CNT motion found. Motion by adding a thermophoretic spring, but then no need for MD By QM, more QED radiation is produced at hot than cold end Charge is produced Outer CNT moves under charge gradient to cold end. Classical physics does not produce charge

14
Sputtering Tribochemistry - HAGI HAGI, October 26-28, Vienna U. Technology, www. Research Group Surface & Plasma Technology -.mhtwww. Research Group Surface & Plasma Technology -.mht MD 5 keV Ar atoms Impacting Cu One answer to question: During MD solution, use Nose-Hoover thermostat to hold temperature constant as required by QM. The QED radiation emitted is the net thermostat heat. Input the QED radiation in FE programs to determine effect on the surroundings..

15
Car - Parrinello MD Tribochemistry - HAGI HAGI, October 26-28, 2011 [1] See The Car-Parrinello in computational chemistry [1] is a type of ab initio (first principles) molecular dynamics, usually employing periodic boundary conditions, planewave basis sets, and DFT. [2] R. Car and M. Parrinello, “Unified Approach for Molecular Dynamics and Density-Functional Theory,” Phys. Rev. Let., 55, 2471, CPMD formulated [2] for PBC Maybe the word usually is inserted to justify the many MD simulations that ignored QM 15

16
MD heat transfer based on SM assumes atoms have kT energy which is valid only for PBC Major problem for MD in Tribology and Tribochemistry because rubbing of surfaces cannot be simulated with PBC MD simulations of discrete nanostructures do not produce charge and are meaningless, except for pretty pictures. MD and FE provide equivalent heat transfer simulations of discrete nanostructures, but both are invalid by QM QM negates SM, thermal conduction, Fourier Theory, and heat current at the nanoscale. Recommendation Estimate the time-history of QED radiation and use in FE simulations to determine the effect on macroscopic surroundings. MD may not even be necessary Conclusions 16 Tribochemistry - HAGI HAGI, October 26-28, 2011

17
Expanding Unverse In 1929, Hubble measured the redshift of galaxy light that by the Doppler Effect showed the Universe is expanding. But cosmic dust of submicron NPs permeate space and redshift galaxy light without Universe expansion 17

18
Tribochemistry - HAGI HAGI, October 26-28, Redshift without Universe expansion Based on classical physics, astronomers assume absorbed galaxy photon increases temperature of dust NPs Redshift in Cosmic Dust

19
Tribochemistry - HAGI HAGI, October 26-28, 2011 Referring to his calculation showing acccelerated Universe expansion, Reiss is quoted as saying: "I remember thinking, I've made a terrible mistake and I have to find this mistake" Others said: “[Riess] did a lot after the initial result to show that there was no sneaky effect due to dust absorption“ Reiss did make a mistake - Redshift does occur in dust No Universe expansion, accelerated or otherwise 19 Nobel Mistake Astronomers Schmidt, Pearlmutter, and Reiss got the 2011 Nobel in Physics for an accelerated expanding Universe

Similar presentations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google