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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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Sol id-l iqu id-gas PCM Appl ic at ions 2
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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Sol id-l iqu id-gas PCM Appl ic at ions 3
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?