On thermal logic: Why? What? How? Who? logic.pdfHeat ﬂuxes are abundant in nature and technology T...

On thermal logic:Why? What? How? Who?

Ishwar K. PuriN. Waldo Harrison Professor of Engineering Science & Mechanics

Heat fluxes are abundant in nature and technology

Th

Tc

q

High temperature reservoir

Low temperature reservoir


Th

Tc

q



w

Nature and humans utilize heat fluxes for work, e.g., atmospheric currents, power generation


Th

Tc

q



w

Nature and humans utilize heat fluxes for work, e.g., atmospheric currents, power generation

qNature controls heat transfer, e.g., in mammals, why not human logic devices?

Can we utilize heat fluxes in innovative ways?

Logic devices

• Electronic devices have transformed us

• Electrons and information flow through diode, transistor, and OR, AND, NOT, NAND gates

• Can heat fluxes be similarly controlled?

Problem

• Heat does not flow in discrete quantities

• It changes material properties

• It also readily dissipates

• Besides, phonons are diffuse energy carriers with changeable properties

If this were overcome, it would lead to novel and

transformative technologies

Opportunities exist at the nanoscale

First step: Diode

Current on

Anode Cathode

Current off

Threshold Voltage

Thermal diode: rectification

• A sufficient condition for rectification is that thermal conductivity k, a function of position and temperature, is not functionally separable

• k(x,T) ≠ f(x) g(T)

• This inequality is satisfied for inhomogeneous or asymmetric materials

Manipulating k(x,T) in solids

Balasubramanian, G., I.K. Puri, M.C. Bohm, and F. Leroy, Thermal conductivity reduction through isotope substitution in nanomaterials: predictions from an analytical classical model and nonequilibrium molecular dynamics simulations.

Nanoscale, 2011. 3(9): p. 3714-3720.

Homogeneous material

k

x

Doping

k

x

Differential stress

k

x

Liangruksa, M., and Puri, I. K., “Lattice thermal conductivity of a silicon nanowire under surface stress,” Journal of Applied Physics, 2011. 109:113501.

Use solid-fluid interfaces

• Solids have fixed structures that can be tuned, e.g., by applying mechanical stress or doping

• However, structural manipulations of solid lattices are typically much more energy intensive than efforts involving solid-liquid interfaces that are more easily manipulated

A necessary digression: About nanoscale transport

What we know

• The same physical laws that govern flows at the micro- and macroscales describe

• Nanoscale flows in the absence of strong interfacial forces

• Thermal phonon transport through long nonmetallic one-dimensional structures

• And so on…

What we find

What we find

• A number as small as ≈102 molecules in a control volume is adequate for continuum relations to hold

What we find

• A number as small as ≈102 molecules in a control volume is adequate for continuum relations to hold

• But interfacial effects become very important

So how is the nanoscale different?

Colliding nanojets

How thenanoscale is

different

S. Murad and I. K. Puri, Nanoscale Jet Collision and Mixing Dynamics. Nano Letters, 2007. 7 (3), p. 707–712.

The mixing physicsS. Murad and I. K. Puri, Nanoscale Jet Collision and Mixing Dynamics. Nano Letters, 2007. 7 (3), p. 707–712.

A hydrophilic orifice

hydrophilichydrophobic

S. Murad and I. K. Puri, Dynamics of nanoscale jet formation and impingement on flat surfaces. Physics of Fluids, 2007. 19(12), p. 128102.

Wall vibrationsS. Murad and I. K. Puri, Anomalous flow behavior in closed and open thin walled nanochannels. Physics Letters A, 2010.

374(41), p. 4242–4246.

Interfacial vibrations

• Fluid flow at nanoscale influenced by the vibrational characteristics of hydrophilic bounding surface molecules

• Free cantilever end (x = L) has larger vibration amplitude, since d2y/dx2 = d3y/dx3 = 0, than one attached to stiff spring, which mimics pinned end with y ≈ d2y/dx2 ≈ 0

BehaviorsS. Murad and I. K. Puri, Anomalous flow behavior in closed and open thin walled nanochannels. Physics Letters A, 2010.

374(41), p. 4242–4246.

Interfacial temperatureG. Balasubramanian, S. Banerjee, and I. K. Puri, Unsteady nanoscale thermal transport across a solid-fluid interface.

Journal of Applied Physics, 2008. 104(6), p. 064306.

Kapitza Resistance

• Thermal energy transport through a solid-fluid interface faces an interfacial resistance

• Causes a temperature discontinuity across the boundary

• Kapitza resistance (1941), Rk

Hypothesis: decrease Rk

• For better phonon transport, increase fluid pressure to facilitate better acoustic matching

• Make interface more solid-like by adsorbing and ordering additional fluid molecule layers

• e.g., hydrophilic interface

Fluid-solid interfacesS. Murad and I. K. Puri, Thermal transport across nanoscale solid-fluid interfaces. Applied Physics Letters, 2008. 92(13),

p. 133105.

LayeringG. Balasubramanian, S. Banerjee, and I. K. Puri, Unsteady nanoscale thermal transport across a solid-fluid interface.

Journal of Applied Physics, 2008. 104(6), p. 064306.

Implications for qS. Murad and I. K. Puri, Thermal transport across nanoscale solid-fluid interfaces. Applied Physics Letters, 2008. 92(13),

p. 133105.

Now back to the core talk

Manipulating interfacial resistance

Murad, S. and I.K. Puri, Communication: Thermal rectification in liquids by manipulating the solid-liquid interface. The Journal of Chemical Physics, 2012. 137(8): p. 081101-081101-4.



Th

Tc

High temperature solid reservoir

Low temperature solid reservoir

q



Alter dT/dx, hence fluxTh

Tc

High temperature solid reservoir

Low temperature solid reservoir

q

Surface wetting, body force?




Alter dT/dx, hence flux

A simple application



When Ta<Ti



When Ta>Ti


Possible device

Th

Tc

High temperature fluid reservoir

Low temperature fluid reservoir

q

Possible device

Device behavior

Inert wallsLinear behavior

Device behavior


Hydrophilic wallsNonlinear behavior

Device behavior

This is a transistor


Emitter

Collector

Base(Input)

(Output)

This is a transistor


EmitterCollector

Base

Th

Tc

Ti(Input)

(Output)

qh

qc

qi

Base Junction Transistor

• Current flowing through the base IB (or input heat flux qi) controls the current through the collector IC (or cold side flux qc)

• Transport factor α = IC/IE (or qc/qh)

• Current gain β = IC/IB (or qc/qi) = α/(1-α)

Three terminal transistor

α = qc/qh, β = qc/qi


Emitter thresholdswitch


α>1α<1


Transport factor


α>1α<1


Collectorswitch

Transport factor


α>1α<1

β>1β<1


Collectorswitch

Transport factor

Current gain

Game changer?

Such research requires significant interdisciplinary breadth and disciplinary

depth

Teams

Thermal logic devices

Electronics

Transport Phenomena

Surfa

ce

Engin

eerin

g

Nanofab

ricati

on

Computational Science

Materials

Teams

Thermal logic devices

Electronics

Transport Phenomena

Surfa

ce

Engin

eerin

g

Nanofab

ricati

on

Computational Science

Materials

Bioinspiration?

???

Bioinspiration?

Bioinspiration?

Thermal regulation in bluefin tuna

Thermal rectification

Needs

• Energy

• Electronic-type devices that use waste or ambient heat

• Healthcare

• Disaster recovery

• National security

• Infrastructure

Big idea: Rectify solid-fluid interfacial

heat transfer to develop thermal logic devices

EFRI Community Panel Presentation, January 2013

NSF panel: Strengths• High novelty.

• Requires multidisciplinary approach. Case has been made for strongly interdisciplinary teams: thermal physics, nanofab, bioinspiration. Is interdisciplinary with engineers as leaders of teams.

• Heat transfer is an important problem.

• The nano-thermal community is starving for new opportunities beyond materials research; this could provide an important new direction.

• The proposed work is on building logic circuits using thermal rectification on liquid-solid interfaces. While thermal rectification has been studied in liquids in the past, and liquid transistors in similar forms has been proposed, detailed logic circuit elements proposed by this proposal have not been studied.

• Building thermal logic circuits requires interdisciplinary expertise and contributions from basic sciences and non-engineering fields.National need for conserving energy and providing power in certain scenarios (personalized medical devices, natural disasters, defense, infrastructure)

NSF Panel: Opportunities• The topic shouldn’t restrict focus to digital logic; there may well be

more valuable functionality coming from use of the phenomenon in other thermal control functions (heating, cooling, switching, sensing, etc.).

• There may be potential huge opportunities for enhanced thermal properties with transformative impacts on waste energy recovery technologies, but these should be sought after and identified.

• A major opportunity of this topic is to identify heat transfer and control concepts that would affect fields like building engineering, etc., rather than developing a replacement technology for the existing electronic logic circuits.

NSF panel: Weaknesses• Direct applications are not clear. Potential competitiveness with conventional electronics for logical functions

seems highly questionable. Is there, in fact, an advantage of using thermal logic (vs. electron logic)? But there’s no need to restrict the application scope to logic.

• Are the sizes of the available nonlinearities (and potentially reasonably) large enough to enable competitive applications?

• Effect size is controlled to some degree by confinement of phonons, which is much weaker than confinement of electrons in electron devices.

• There is no national need or grand challenge that is met by the topic.

• This is very early research. Is there a large enough community to sustain (or even to fill out 4-5 awards of several researchers each)? It might be more suitable for single-investigator grants for now.

• Needs to be benchmarked against thermoelectric conversion to sustain electronic devices.

• Even though many ideas are nicely explained, [panelist] does not think this proposal is transformative enough to create a new research area. [Panelist] also does not think there is a potential for making significant progress on a current national need.

• Proposed work needs a strong experimental component.

Very novel but early research. What are the

applications? National need?

What do you think?

On thermal logic:Why? What? How? Who?

Ishwar K. PuriN. Waldo Harrison Professor of Engineering Science & Mechanics

On thermal logic: Why? What? How? Who? logic.pdfHeat ﬂuxes are abundant in nature and technology T...

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