10. jata-rsa-thermal sciences

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THERMAL SCIENCES17 March 2011

KUMAR V. JATAProgram Manager

AFOSR/RSA

Air Force Office of Scientific Research

AFOSR

Distribution A: Approved for public release; distribution is unlimited 88ABW-2011-0792


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2011 AFOSR SPRING REVIEW2306A PORTFOLIO OVERVIEW

NAME: KUMAR V. JATABrief Description of Portfolio:

Understand thermal transport in materials to establish science-based approaches forinnovative thermal management of components and systems

Current Sub-areas in Portfolio:

1. Nano scale thermal transport far field and near field2. Heat extraction strategies for large scale heat flux situations

3. Thermal storage and conversion


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Rationale for Sub-area 1

. Sub-area 1: Nano scale thermal transport far

field and near field

Scientific Gaps

Interface effects are not accounted for

Strain, lattice mismatch, atom mixing areneglected

Discrepancy between predictions and experimentaldata remain

Phonon modes and polarization vectors are notconsidered

Contribution of long wavelength and smallwavelength phonon modes are not decoupled

Near field thermal transport phenomenon in general

is poorly understood

Discrepancy betweenexperiment and predictionJu and Goodson, 1999


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Rationale: Sub-area 2

Scientific Gaps:

Current heat sinks are not capable ofcarrying away heat densities >100 W/cm2

Physical mechanisms of convective heattransfer are unclear when surfaces are

modified by nano structured features

Plenty of room for novel phasetransformation concepts, but not beingexplored

PI: Andy Williams

Space Vehicles Directorate

Sub area 2: Heat removal for large scale heat flux situations


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Sub Area 3: Thermal storage and conversion Scientific Gaps

How do we tackle irregular and massive thermal transients

Science-base to develop materials for high rates of thermalenergy storage and release for thermal transients is lacking

Current thermal storage research is based on verytraditional materials not suitable for future Air Force

systems

Rationale: Sub-area 3


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Challenges and Opportunities

Thermal transport at nano-scale

Interface fabrication and probing of phonon transport Phonon physics for nano materials

Quantum mechanics based understanding and delineation ofphonon modes, frequency and polarization

Near field thermal radiative transport Novel ideas to better understand radiative heat transfer

Increasing heat extraction by several fold Unexplored Materials/Thermal Physics /Thermodynamics

concepts

Thermal energy storage and conversion Storing megawatt-per-second thermal energy that can be

highly irregular

Incorporating phonon properties at nano-scale to predict bulkthermal behavior

Enable bottom-up design of intelligent materials

200 mm

High-power pulsedpump beam

Low-powerpulsedprobe beam

Li3AlH6


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Transformational Opportunities

Thermal management for

Systems designed to remain airborne for long periods of time

High power electronic devices for active airbase and air vehicle -defense, andtactical strike

High altitude materials

Embedded propulsion systems

Efficient energy devices

Random access memory storage devices


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Other Organizations that FundRelated Work

NSF

Heat and mass transfer, biological and environment systems, large investment in thermoelectricmaterials for automobiles, broad engineering and societal impact

DARPA

Thermal management technologies

ONR

Nano lubricants, jet impingement, coolants, magnetic refrigeration, cooling power electronicmodules, ship level thermal management tool

ARO

Thermal management materials and novel thermal property characterization

ARPA-E

Industrial and consumer related large scale storage issues


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AFOSR Program Niche

Understanding phonon transport across tailored interfaces

Experiment and theory to understand thermal gradients acrosshard/soft interfaces, metal/insulator, hetero-structures and role of

multi-carriers Modeling and experiments of near field thermal transport

Extraordinarily transient and high flux heat storage and release

concepts for next-generation and on-demand systems Large scale heat extraction based on nano structured surfaces

coupled with external stimuli and novel phase transformations


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Thermal Transport at Weakly BoundHard/Soft Interfaces

AFOSR-MURI, U of Michigan, PI: Kevin Pipe

What is the role of interfacebond character and resonantphonon transfer on thermaltransport ?

CuPc film grown on Si Interfaces between Agand CuPc contribute tothermal resistance

Jin, Yadav, Sun, Sun, Pipe, Shtein, submitted to APL 2010

Pipe, U of Michigan, MURI-2010 Result


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11UIUC will be connecting theory to the experiment by fabricatingspecial cantilevers for atomic force microscopy experiments

Exponential suppression of thermalconductance as a function of channellength

Exponential Suppression ofThermal Conductance

Fan, Stanford, MURI-2010 Result

Photonic crystal heterostructureHow do heat transfer mechanisms change when number of non-identical layers increases?

As number of layers increases:

Photonic band structures form

Creates band gap over a very broad range of frequencies

Fundamentally new regime of thermal transport, different from bothincoherent thermal transport regime, and the previously consideredcoherent thermal transport regime has been discovered


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Measuring Radiative PropertiesUsing Scanning Probes

Sensitivities of bimaterial cantilevers to radiation aredetermined by their geometries, mechanical andspectral properties

Prof. King, UIUC, MURI-2010 Result

Doped Si cantilevers reaching 600C

Wave length, mm

Deflectionnm


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Thermal Transport Transfer

ab initio and experiments to understand near field thermal transport in CNT arrays

reflective back substrate

Emissivi ty Absorptivi ty Reflectivity Transmissivity

Complex refractive index

Maxwell Equations

Frequency-dependent

dielectric constantFirst-principle

calculations

Phonon

peak

Electronpeak

50 nm

E-beampre-pattern

Nano-imprintlithography mold

Ordered verticalSWCNTs in

dielectric pillarswithin PAA

Ruan and Fisher-- Purdue, 2010 Result

Multiscale modeling

nano scale effects: periodicity,

randomess, matrix materials

atomic scale effects:chirality, doping

Synthesis of patterned vertical CNT arrays


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Near Field Thermal Transport

Thermal rectification in near field radiation transport

Prior work (2006, 2007)

Potential Phononic Devices

Phonon is used to carry and process information

Thermal rectification plays the most central role in

phononics devices

Nano cone

CNT

Otey, et al., in print, PRL, 2011

Physical mechanismfor thermal diode isunderstood by thematch /mismatch

phonons DOS spectra

Cahill, UIUC, MURI 2010-Result

Th r l C d ti it fr Fir t


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Thermal Conductivity from FirstPrinciples

Alan McGaughey, YIP, CMU

Quantum-Mechanics Driven Prediction of Nanostructure Thermal Conductivity

Anharmonic term: Phonon

properties are obtained fromhere

Taylor expansion about the equilibrium energy E0 and N atoms

Harmonic force constant

Goes to zero

Describing the atomic interactions

Force constants can come from empirical potentials orquantum mechanics

Used in anharmonic lattice dynamics calculations to

predict phonon properties

Quantum effects are important

Atomic interactions

Occupation numbers

Bottom-up thermal conductivity

prediction Which modes dominate

transport?

How to control scattering?

Thermal transport innanostructures

Strategies for tailoring

properties

Multi-physics

challenges

Th l C d i i f Fi


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Thermal Conductivity from FirstPrinciples

Phonon occupation number

specific heat and scattering

Phononlinewidth

Contribution to thermal conductivity (Si)

Phonon properties from the spectral energy density (CNT)

Empty Water

filled

Acoustic 173 97

Optical (low) 196 190

Optical (high) 24 24

Total SED 393 311

Total NEMD 407 300


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Pam Norris- UVA

Beechem, Duda, Hopkins, and Norris, Applied Physics Letters, 97,061907, 2010.

Effect of Mixing on hBD

Thermal Boundary Conductance

Role of interface on TBD: MD Simulations and Experiments


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Phonon Modes Characterization

Phonon modes relevant to thermal properties can have

large Q Nanowire qzspans entire Brillouin zone, up to 1 -1

Phonon characterization

Zone boundary phonons require large momentumtransfer

Visible photons dont have enough momentum

Inelastic x-ray and neutron scattering require largevolumes

Thermal diffuse x-ray scattering offers the potential toprobe modest volumes with large momentum transfers

New low-frequency zone boundary modes

Paul Evans-- University of WisconsinMartin Holt-- Argonne


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Nano scale Enabled Thermal Transport

nanocomposite

bundles 2D/3D networks

Mesoscopic Modeling of Heat Transfer in Nanofibrous Materials

Atomistic MD simulations of energy dissipation and heat transferin individual CNTs are performed and are being extended to groupsof interacting CNTs

Scaling laws for thermal conductivity of straight bundles andisotropic networks of straight nanofibers are derived analyticallyand verified in Monte Carlo simulations

Develop a mesoscopic model capable of modeling structural self-organization and thermal transport in nanofibrous materials

Account for

Interfacial CNT-CNT and CNT-matrix heat transferparameterization of the mesoscopic model

Nanofibrous structures of increasing complexity

Monte Carlo calculation of statistical averages for quantities

entering the theoretical equations

Leonid Zhigilei, UVA

Molecular Junctions in


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Molecular Junctions inHeterostructured Materials

Jon Malen, CMU

Control thermal transport in interfaces and materials using hetero-structures assembled from

organic and inorganic building blocks 1-10 nm in size

Understand phonon transport behavior in 2-D molecular crystals (SAM) that form on inorganic surfaces 3-D arrays of semiconducting spheres spaced by organic molecules

Self assembled monolayer junctions

QDSLs spaced by organic molecules


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International Projects

Thermal conductivity of BBL/graphene systems, Kungpook National University,Park

Thermal transport in 1-D and 2-D nanostructures, Tata Institute of Fundamentalresearch, Deshmukh

Novel routes to thermal conductivity and thermoelectric properties of materials,National Institute for Materials Science, Mori

Heat transfer enhancement in small-scale devices, University of Briscia, Beretta

Determination of thermal properties in nano-structured solids and thermal

energy harvesting, Jawaharlal Nehru center for Advanced ScientificResearch(JNCASR), Waghmare

Thermal and electrical conductivities in nanowires for thermoelectric devices,Yonsei University, Lee

T bl th l ti ith


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Tunable thermal properties withgraphene like materials

C NGraphene X=0.0

X=0.5

B2N2C4(present study)

Questions: How does BN decorate the Carbon lattice?

How do properties depend on this ordering?

BN

B

X=0.25

Solution of h-BN and graphene on a

single lattice could lead to a rich variety

of 2-D structures with electric properties

ranging from metallic conductor tosemiconductor to insulator, with tunable

transport properties [electronic and

phonon structure behave similarly due to

formal similarity in their Hamiltonians]

Possible configurations and relative energy values


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DOS and Localization of States

States localized in domains or at interface

Energy band gap can be tuned with

chemical ordering of Boron, Carbon

and Nitrogen: band gap of B2N2C4changes from 0 eV to 2.36 eV

Energetics suggests possible

domains of BN in graphene:

interfaces will be very important to

transport properties

Phonon dispersion to have similar

tunability (in progress), particularly

the optical modes


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Thermal Storage and Conversion

RX LAB TASK

Objective: Develop understanding of metal hydrides for thermal energy storage and hydrogen desorptionApproach: Develop algorithms and tools to characterize particles sizes, packing and densification to account for

mesoscale thermal flow through porous media bed. Validate models through in situ XPS, Reaction rates

State of the art:

Metal hydrides typically possess high heats of reaction upon hydriding and de-hydriding, and this

characteristic will be exploited for high-density thermal storage exceeding 1 MJ/kg at the system level (the

material thermal density of MgH2 is 1.8 MJ/kg).

Reiser et al., International Journal of Hydrogen Energy 25, 425-430 (2000).

Temperature map in a metal hydride compact

obtained from a mesoscopic thermal model (BTE)

applied to the prediction of a particle compaction

algorithm (DEM). The temperature field includes boththe solid and gas phases.

Ajit Roy, RXBT


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Andrey Voevodin, Lab Task


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Recent Transitions

Several alumni of the AFOSR Thermal Sciences Program are nowworking in several of the AFRL TDs

Several PIs are collaborating with AFRL scientists

Prof. Xiulin Ruan, Purdue University, with Ajit Roy

Prof. Bill King, University of Michigan, with Andrey Voevodin Several others


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Program Trends

Far field and near field thermal transport

Heat removal for large scale heat flux situations

Thermal storage and conversion

Opportunities for new directions Scientific underpinnings of component and system level

thermal level management Non-linear thermal behavior and control Biomimetic-inspired thermal management Larger issues in thermal management


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