Jung Yen Chou - Phase Change Materials

7/31/2019 Jung Yen Chou - Phase Change Materials

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Phase Change Mat er ia l sHous ing App l ic a t ions

MSE 395

Kevin, Jung Yen Chou


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Overview

Introduction and Background Exam les of hase chan e materials PCMs

Solid-liquid-gas phase change materials arac er s cs Classification and development Applications and examples

Thermochromic phase change materials Optical properties

Applications and examples


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Int roduc t ion and bac k ground

Any material goes through a phase change Temperature (thermo-)

Electric charge (electro-)

-

,

Pressure (piezo-) Phase changecauses changes in:

Two Classifications Mechanical

Magnetic- -

Crystal structural phase change Electrical

Thermo

Optical


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PCMs ex am ple Rew r i t ab le DVDs

Ge-Sb-Te (GST) chalcogenide alloy

High intensity / short pulse : Amorphous

Low intensity / long pulse : Crystalline


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Sol id-l iqu id-gas PCM

Solid-liquid, solid-solid, liquid-gas, solid-gas

Latent heat stora e LHS

Heat is absorbed melt liquid

Heat is released solidify solid

Heat of fusion (Hfusion)

eren rom sens e ea s orage Heat is stored by raising the temperature of material

p v


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Sol id-l iqu id-gas PCM - Charac t er is t ic s

Thermodynamic (i) Melting temperature in desired temperature range

Selection criteria

(iii) High specific heat, high density and thermal conductivity(iv) Small volume change on phase transformation(v) Congruent melting

KineticProperties

(i) High nucleation rate to avoid super cooling(ii) High rate of crystal growth to meet demand of heat recovery

Chemical

Properties

(i) Complete reversible freeze/melt cycle

(ii) No degradation after a large number of freeze/melt cycle(iii) No corrosiveness to the construction materials(iv) Non-toxic, non-flammable and non-explosive material

Properties

(ii) Large-scale availabilities


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Sol id -l iqu id-gas PCM Classi f ic at ion

Large numbers of PCMs available -5 to 190 oC

Classification

Organic Inorganic Eutectics

or anic-or anic

Thermally and chemically stable

No super cooling, segregation

Highest LHS / unit volume

Low cost, largely available

High LHS / unit volume

Sharp melting point

organic-inorganic

Paraffin

CnH2n+2 Low LHS / unit volume

Costl and flammable

Large super cooling effects

Deh dration and instabilit

Limited data is available

Stron odor

inorganic-inorganic

Salt hydrates

MnH2O

Fatty acids

CH3(CH2)2nCOOH


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Sol id -l iqu id-gas PCM Ex am ples

Materials Melting point Heat of fusion Specific Heat Density(oC) solid liquid

(kJ / kg)

solid/liquid(kJ / kg oC)

solid / liquid(kg / m3)

Water 0 333.6 2.05 / 4.18 999 / 1000

Lauric acid

CH3(CH2)10COOH

41 43 211.6 1.76 / 2.27 1007 / 862

Mn(NO3)2 6H2O +MnCl2 4H2O (4 wt%)

15 25 125.9 2.34 / 2.78 1795 / 1728

Capric acid (65 mol%) +Lauric acid (35 mol%)

18 20 140.8 1.97 / 2.24 - / -

E23 - EPS Ltd 23 155.0 0.69 / - 1475 / -

RT27 - Rubitherm 28 146.0 1.80 / 2.40 870 / 750


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Sol id-l iqu id-gas PCM Appl ic at ions 1

Macro-encapsulation

Tend to solidify at the edges

Micro-enca sulation

Easily incorporated into construction materials

Steel, polypropylene

Usually embedded with

high conductivity materials with

high conductive structure


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Passive storage systems Wallboards

Ceiling boards

Movable curtain (shutter)

PCM wallboards,

Saves up to 15% annual energy (3GJ)

O timal ~1 to 3 oC above RT


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Active storage systems Floor heating and cooling

Air-based heating and cooling Uni. South Australia in 1997

. Collect solar heat

Circulate indoor hot air to

Night time or Low Temp. Vent and circulate to warm

indoor air


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Sol id -l iquid-gas PCM Conc erns

Many manufacturers data not verified Discrepancy with independent research

No commonly accepted quantitative criteria

Lack knowledge on other properties

Chemical storage and safety concerns


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Therm oc hrom ic PCM

Optical properties vary in response to temperature, , , , 2

Idea: intelli ent thin film coatin on windows

Darken (hot) state: Reflect IR radiation while transmitting visible Transparent (cold) state: Allow IR for maximum solar heat gain

ncrease ermo an v sua com or

- o Band gap ~0.7eV

Low temperature semiconducting phase

High temperature metallic phase


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Thermoc hrom ic PCM opt i c a l p ropert y 1

Optical transmittance temperature dependency ransm ance ecrease rom o as ncrease

Visible transmittance relatively constant

Reversible TemperatureIncrease

Independent ofT rate


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Thermoc hrom ic PCM opt i c a l p ropert y 2

W- F- doped VO2 decreases transition temperature

Anti-reflection coatin

Better thermochromic transition


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Therm oc hrom ic PCM Conc erns

Atmospheric pressure CVD produced thin film

- , Delamination occurs in repeated thermal cycle

Oxidize easily to form other VOx High cost

RT thin film is yellow, undesirable for commercial use


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Conclus ions

PCMs are promising advanced materials forenergy e c en ous ng app ca ons

o - qu s Latent Heat storage units to maintain constant temperature e a e now e ge on proper es o se ec op mum s

Windows coating to provide thermo/visual comfort


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Questions and comments?

Jung Yen Chou - Phase Change Materials

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