Phase-change material

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A sodium acetate heating pad. When the sodium acetate solution crystallises, it becomes warm.

A phase-change material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa; thus, PCMs are classified as latent heat storage (LHS) units.

Characteristics and classification[edit]

PCMs latent heat storage can be achieved through solid–solid, solid–liquid, solid–gas and liquid–gas phase change. However, the only phase change used for PCMs is the solid–liquid change. Liquid-gas phase changes are not practical for use as thermal storage due to the large volumes or high pressures required to store the materials when in their gas phase. Liquid–gas transitions do have a higher heat of transformation than solid–liquid transitions. Solid–solid phase changes are typically very slow and have a rather low heat of transformation.

Initially, the solid–liquid PCMs behave like sensible heat storage (SHS) materials; their temperature rises as they absorb heat. Unlike conventional SHS, however, when PCMs reach the temperature at which they change phase (their melting temperature) they absorb large amounts of heat at an almost constant temperature. The PCM continues to absorb heat without a significant rise in temperature until all the material is transformed to the liquid phase. When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat. A large number of PCMs are available in any required temperature range from −5 up to 190 °C.[1] Within the human comfort range between 20–30 °C, some PCMs are very effective. They store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry or rock.[2]

Organic PCMs[edit]

Paraffin (CnH2n+2) and fatty acids (CH3(CH2)2nCOOH)[3]

Inorganic[edit]

Salt hydrates (MnH2O)[4]

Eutectics[edit]

Organic-organic, organic-inorganic, inorganic-inorganic compounds

Hygroscopic materials[edit]

Many natural building materials are hygroscopic, that is they can absorb (water condenses) and release water (water evaporates). The process is thus:

Whilst this process liberates a small quantity of energy, large surfaces area allows significant (1–2 °C) heating or cooling in buildings. The corresponding materials are wool insulation, earth/clay render finishes, etc.

Selection criteria[edit]

Thermophysical properties of common PCMs[edit]

Material
Organic
PCM
Melting
point

oC
Heat of
fusion

kJ·kg−1
Heat of
fusion

MJ·m−3
Specific heat, cp
solid
kJ·kg−1·K−1
Specific heat, cp
liquid
kJ·kg−1·K−1
Density, ρ
solid
kg·m−3
Density, ρ
liquid
kg·m−3
Thermal conductivity, k
solid
W·m−1·K−1
VHC
solid
kJ·m−3·K−1
VHC
liquid
kJ·m−3·K−1
Thermal effusivity, e
solid
J·m−2·K−1·s−1/2
Cost
USD·kg−1
WaterNo0333.6319.82.054.1869171,0001.6[6]-2.22[7]1,8804,1861,8900.003125[8]
Sodium sulfate (Na2SO4·10H2O)No32.42520.05 [9]
NaCl·Na2SO4·10H2ONo182860.05 [9]
Lauric acidYes[10][11]44.2[12]211.6197.71.762.271,0078621,7721,9571.6 [13][14]
TME(63%w/w)+H2O(37%w/w)Yes[10][11]29.8218.0240.92.753.581,1201,0903,0803,902
Mn(NO3)2·6H2O+MnCl2·4H2O(4%w/w)No[15][16]15–25125.9221.82.342.781,7951,7284,2004,804
Na2SiO3·5H2ONo[15][16]72.20267.0364.53.834.571,4501,2800.103−0.128[17]5,5545,8508018.04[18]
AluminiumNo660.32396.91,007.20.89692,7002,375237[19][20]2,422 ?23,9602.04626[21]
CopperNo1,084.62208.71,769.50.38468,9408,020401[22]3,438 ?37,1306.81256[23]
GoldNo1,064.1863.721,166.30.12919,30017,310318[24]2,49128,14034,297.8[23]
IronNo1,538247.31,836.60.44957,8746,98080.4[25]3,53916,8700.3248[26]
LeadNo327.4623.02253.20.128611,34010,66035.3[27]1,4597,1802.1151[23]
LithiumNo180.54432.2226.03.581653451284.8[28]1,91312,74062.2164[29]
SilverNo961.78104.61,035.80.23510,4909,320429[30]2,46532,520492.524[23]
TitaniumNo1,668295.61,273.50.52354,5064,11021.9[31]2,3597,1908.0469[32]
ZincNo419.53112.0767.50.38967,1406,570116[33]2,78217,9602.15735[23]
NaNO3No310174[34]
NaNO2No282212[34]
NaOHNo318158[34]
KNO3No337116[34]
KOHNo360167[34]
NaOH/ Na2CO3 (7.2%)No283340[34]
NaCl(26.8%)/NaOHNo370370[34]
NaCl/KCL(32.4%)/LiCl(32.8%)No346281[34]
NaCl(5.7%)/ NaNO3 (85.5%)/Na2SO4No287176[34]
NaCl/ NaNO3 (5.0%)No284171[34]
NaCl(5.0%)/ NaNO3No282212[34]
NaCl(42.5%)/KCl(20.5)/MgCl2No385-393410[34]
KNO3(10%)/NaNO3No290170[34]
KNO3/KCl(4,5%)No320150[34]
KNO3/KBr(4.7%)/KCl(7.3%)No342140[34]
Paraffin 14-Carbons [35]Yes5.5228
Paraffin 15-Carbons [35]Yes10205
Paraffin 16-Carbons [35]Yes16.7237.1
Paraffin 17-Carbons [35]Yes21.7213
Paraffin 18-Carbons [35]Yes28244
Paraffin 19-Carbons [35]Yes32222
Paraffin 20-Carbons [35]Yes36.7246
Paraffin 21-Carbons [35]Yes40.2200
Paraffin 22-Carbons [35]Yes44249
Paraffin 23-Carbons [35]Yes47.5232
Paraffin 24-Carbons [35]Yes50.6255
Paraffin 25-Carbons [35]Yes49.4238
Paraffin 26-Carbons [35]Yes56.3256
Paraffin 27-Carbons [35]Yes58.8236
Paraffin 28-Carbons [35]Yes61.6253
Paraffin 29-Carbons [35]Yes63.4240
Paraffin 30-Carbons [35]Yes65.4251
Paraffin 31-Carbons [35]Yes68242
Paraffin 32-Carbons [35]Yes69.5170
Paraffin 33-Carbons [35]Yes73.9268
Paraffin 34-Carbons [35]Yes75.9269
Formic acid [35]Yes7.8247
Caprilic acid [35]Yes16.3149
Glycerin [35]Yes17.9198.7
p-Lattic acid [35]Yes26184
Methyl palmitate [35]Yes29205
Camphenilone [35]Yes39205
Docasyl bromide [35]Yes40201
Caprylone [35]Yes40259
Phenol [35]Yes41120
Heptadecanone [35]Yes41201
1-Cyclohexylooctadecane [35]Yes41218
4-Heptadacanone [35]Yes41197
p-Joluidine [35]Yes43.3167
Cyanamide [35]Yes44209
Methyl eicosanate [35]Yes45230
3-Heptadecanone [35]Yes48218
2-Heptadecanone [35]Yes48218
Hydrocinnamic acid [35]Yes48118
Cetyl acid [35]Yes49.3141
α-Nepthylamine [35]Yes5993
Camphene [35]Yes50238
O-Nitroaniline [35]Yes5093
9-Heptadecanone [35]Yes51213
Thymol [35]Yes51.5115
Methyl behenate [35]Yes52234
Diphenyl amine [35]Yes52.9107
p-Dichlorobenzene [35]Yes53.1121
Oxolate [35]Yes54.3178
Hypophosphoric acid [35]Yes55213
O-Xylene dichloride [35]Yes55121
β-Chloroacetic acid [35]Yes56147
Chloroacetic acid [35]Yes56130
Nitro napthalene [35]Yes56.7103
Trimyristin [35]Yes33201
Heptaudecanoic acid [35]Yes60.6189
α-Chloroacetic acid [35]Yes61.2130
Bee wax [35]Yes61.8177
Bees wax [35]Yes61.8177
Glyolic acid [35]Yes63109
Glycolic acid [35]Yes63109
p-Bromophenol [35]Yes63.586
Azobenzene [35]Yes67.1121
Acrylic acid [35]Yes68115
Dinto toluent (2,4) [35]Yes70111
Phenylacetic acid [35]Yes76.7102
Thiosinamine [35]Yes77140
Bromcamphor [35]Yes77174
Durene [35]Yes79.3156
Benzylamine [35]Yes78174
Methly brombrenzoate [35]Yes81126
Alpha napthol [35]Yes96163
Glautaric acid [35]Yes97.5156
p-Xylene dichloride [35]Yes100138.7
Catechol [35]Yes104.3207
Quinone [35]Yes115171
Actanilide [35]Yes118.9222
Succinic anhydride [35]Yes119204
Benzoic acid [35]Yes121.7142.8
Stibene [35]Yes124167
Benzamide [35]Yes127.2169.4
Acetic acid [35]Yes16.7184
Polyethylene glycol 600 [35]Yes20146
Capric acid [35]Yes36152
Eladic acid [35]Yes47218
Pentadecanoic acid [35]Yes52.5178
Tristearin [35]Yes56191
Myristic acid [35]Yes58199
Palmatic acid [35]Yes55163
Stearic acid [35]Yes69.4199
Acetamide [35]Yes81241
Methyl fumarate [35]Yes102242

Volumetric heat capacity (VHC) J·m−3·K−1

VHC = \rho c_p

Thermal inertia (I) = Thermal effusivity (e) J·m−2·K−1·s−1/2

I = \sqrt{k\rho c_p} = e = {(k\rho c_p)}^{1/2}

Thermophysical properties of commercially available PCMs near room temperature[edit]

MaterialSupplierTypeFormMelting
temperature, Tm

oC
Melting
temperature, Tm

oF
Latent heat
of fusion, L

kJ/kg
Density, ρ
kg/m3
Thermal
conductivity, k

W/m·K
Specific
heat, cp

kJ/kg·K
PureTemp -37PureTemp [36]OrganicBulk-37-351478801.39
PureTemp -23PureTempOrganicBulk-23-91458602.11
PureTemp -21PureTempOrganicBulk-21-624010601.83
PureTemp -17PureTempOrganicBulk-1711458601.74
PureTemp -15PureTempOrganicBulk-15528610301.84
PureTemp -12PureTempOrganicBulk-12101688701.86
PureTemp -5PureTempOrganicBulk-5231508601.66
PureTemp 1PureTempOrganicBulk13430010002.32
PureTemp 4PureTempOrganicBulk4391958802.44
PureTemp 6PureTempOrganicBulk6431708601.56
PureTemp 8PureTempOrganicBulk8461808601.85
PureTemp 12PureTempOrganicBulk12541858601.76
PureTemp 15PureTempOrganicBulk15591658602.25
PureTemp 18PureTempOrganicBulk18641898601.47
PureTemp 20PureTempOrganicBulk20681808602.59
PureTemp 23PureTempOrganicBulk23732038301.84
PureTemp 24PureTempOrganicBulk24751858602.85
PureTemp 25PureTempOrganicBulk25771858601.99
PureTemp 27PureTempOrganicBulk27812008602.46
PureTemp 28PureTempOrganicBulk29842058602.34
PureTemp 29PureTempOrganicBulk29841898501.77
PureTemp 33PureTempOrganicBulk33911858502.34
PureTemp 35PureTempOrganicBulk35951808502.44
PureTemp 37PureTempOrganicBulk381002228402.21
PureTemp 48PureTempOrganicBulk521262458202.1
PureTemp 53PureTempOrganicBulk531272259902.36
PureTemp 58PureTempOrganicBulk581362378102.47
PureTemp 60PureTempOrganicBulk611422308702.04
PureTemp 63PureTempOrganicBulk631451998401.99
PureTemp 68PureTempOrganicBulk681541988701.85
PureTemp 103PureTempOrganicBulk10321715712202.09
PureTemp 151PureTempOrganicBulk15130417013602.06
Astorstat HA 17Honey well [37]OrganicBulk21.771
Astorstat HA 18Honey wellOrganicBulk27.281
RT26Rubitherm GmbH [38]OrganicBulk2475232
RT27Rubitherm GmbHOrganicBulk2882206
Climsel C -21Climator [39]InorganicBulk-21-628813000.63.6
Climsel C -18ClimatorInorganicBulk-18028813000.63.6
Climsel C 7ClimatorInorganicBulk74512614000.63.6
Climsel C 10ClimatorInorganicBulk10.55112614000.63.6
Climsel C 21ClimatorInorganicBulk217011213800.63.6
Climsel C24ClimatorInorganicBulk2475151.313800.63.6
Climsel C28ClimatorInorganicBulk2882162.314200.63.6
Climsel C32ClimatorInorganicBulk3290162.314200.63.6
Climsel C48ClimatorInorganicBulk4811818013600.63.6
Climsel C58ClimatorInorganicBulk58136288.514600.61.89
Climsel C70ClimatorInorganicBulk70158282.914000.63.6
STL27Mitsubishi Chemicals [40]InorganicBulk2781213
S27Cristopia [41]InorganicBulk2781207
TH 29TEAP [42]InorganicBulk2984188
RT 20Rubitherm GmbHOrganicBulk2272172
Climsel C23ClimatorInorganicBulk237314832
RT 26Rubitherm GmbHOrganicBulk2577131
STL 27Mitsubishi ChemicalsInorganicBulk2781213
RT 30Rubitherm GmbHOrganicBulk2882206
RT 32Rubitherm GmbHOrganicBulk2170130
DS 5000Micronal [43]Micro-encapsulated267945
DS 5007MicronalMicro-encapsulated237341
DS 5030MicronalMicro-encapsulated217037
DS 5001MicronalMicro-encapsulated2679110
DS 5008MicronalMicro-encapsulated2373100
DS 5029MicronalMicro-encapsulated217090
RT -9 HCRubitherm GmbHOrganicBulk-916260
RT -4Rubitherm GmbHOrganicBulk-425179
RT 0Rubitherm GmbHOrganicBulk032225
RT 2 HCRubitherm GmbHOrganicBulk236205
RT 3Rubitherm GmbHOrganicBulk337198
RT 3 HCRubitherm GmbHOrganicBulk337250
RT 4Rubitherm GmbHOrganicBulk439182
RT 5Rubitherm GmbHOrganicBulk541180
RT 5 HCRubitherm GmbHOrganicBulk541240
RT 6Rubitherm GmbHOrganicBulk643175
RT 8Rubitherm GmbHOrganicBulk846180
RT 9Rubitherm GmbHOrganicBulk948160
RT 10Rubitherm GmbHOrganicBulk1050150
RT 10 HCRubitherm GmbHOrganicBulk1050195
RT 11 HCRubitherm GmbHOrganicBulk1152190
RT 12Rubitherm GmbHOrganicBulk1254150
RT 15Rubitherm GmbHOrganicBulk1559140
RT 18 HCRubitherm GmbHOrganicBulk1864250
RT 21Rubitherm GmbHOrganicBulk2170160
RT 21 HCRubitherm GmbHOrganicBulk2170190
RT 22 HCRubitherm GmbHOrganicBulk2272200
RT 24Rubitherm GmbHOrganicBulk2475150
RT 25Rubitherm GmbHOrganicBulk2577148
RT 25 HCRubitherm GmbHOrganicBulk2577230
RT 27Rubitherm GmbHOrganicBulk2781179
RT 28 HCRubitherm GmbHOrganicBulk2882245
RT 31Rubitherm GmbHOrganicBulk3188170
RT 35Rubitherm GmbHOrganicBulk3595170
RT 35 HCRubitherm GmbHOrganicBulk3595240
RT 42Rubitherm GmbHOrganicBulk42108174
RT 44 HCRubitherm GmbHOrganicBulk44111255
RT 47Rubitherm GmbHOrganicBulk47117170
RT 50Rubitherm GmbHOrganicBulk50122168
RT 52Rubitherm GmbHOrganicBulk52126173
RT 55Rubitherm GmbHOrganicBulk55131172
RT 58Rubitherm GmbHOrganicBulk58136160
RT 60Rubitherm GmbHOrganicBulk60140144
RT 62Rubitherm GmbHOrganicBulk62144146
RT 65Rubitherm GmbHOrganicBulk65149152
RT 70 HCRubitherm GmbHOrganicBulk70158230
RT 80 HCRubitherm GmbHOrganicBulk79174240
RT 82Rubitherm GmbHOrganicBulk82180176
RT 90 HCRubitherm GmbHOrganicBulk90194200
S117PlusICE [44]InorganicBulk11724316014500.72.61
S89PlusICEInorganicBulk8919215115500.672.48
S83PlusICEInorganicBulk8318114116000.622.31
S72PlusICEInorganicBulk7216212716660.582.13
S70PlusICEInorganicBulk7015811016800.572.1
S58PlusICEInorganicBulk5813614515050.692.55
S50PlusICEInorganicBulk5012210016010.431.59
S46PlusICEInorganicBulk4611521015870.452.41
S44PlusICEInorganicBulk4411110015840.431.61
S34PlusICEInorganicBulk349311521000.522.1
S32PlusICEInorganicBulk329020014600.511.91
S30PlusICEInorganicBulk308619013040.481.9
S27PlusICEInorganicBulk278118315300.542.2
S25PlusICEInorganicBulk257718015300.542.2
S23PlusICEInorganicBulk237317515300.542.2
S21PlusICEInorganicBulk227217015300.542.2
S19PlusICEInorganicBulk196616015200.431.9
S17PlusICEInorganicBulk176316015250.431.9
S15PlusICEInorganicBulk155916015100.431.9
S13PlusICEInorganicBulk135516015150.431.9
S10PlusICEInorganicBulk105015514700.431.9
S8PlusICEInorganicBulk84615014750.441.9
S7PlusICEInorganicBulk74515017000.41.85
A164PlusICEOrganicBulk16432729015002.42
A155PlusICEOrganicBulk1553111009000.232.2
A144PlusICEOrganicBulk1442911158800.232.2
A133PlusICEOrganicBulk1332711268800.232.2
A118PlusICEOrganicBulk11824434014502.7
A95PlusICEOrganicBulk952032059000.222.2
A82PlusICEOrganicBulk821801558500.222.21
A70PlusICEOrganicBulk701581738900.232.2
A62PlusICEOrganicBulk621441459100.222.2
A60HPlusICEOrganicBulk601402128000.182.15
A60HPlusICEOrganicBulk601401459100.222.22
A58HPlusICEOrganicBulk581362438200.182.85
A58PlusICEOrganicBulk581361329100.222.22
A55PlusICEOrganicBulk551311359050.222.22
A53HPlusICEOrganicBulk531271668100.182.02
A53HPlusICEOrganicBulk531271309100.222.22
A52PlusICEOrganicBulk521262228100.182.15
A50PlusICEOrganicBulk501222188100.182.15
A48PlusICEOrganicBulk481182348100.182.85
A46PlusICEOrganicBulk461151559100.222.22
A44PlusICEOrganicBulk441112428050.182.15
A43PlusICEOrganicBulk431091657800.182.37
A42PlusICEOrganicBulk421081059050.212.22
A40PlusICEOrganicBulk401042308100.182.43
A39PlusICEOrganicBulk391021059000.222.22
A37PlusICEOrganicBulk37992358100.182.85
A36PlusICEOrganicBulk36972177900.182.37
A32PlusICEOrganicBulk32901308450.212.2
A29PlusICEOrganicBulk29842258100.182.15
A28PlusICEOrganicBulk28821557890.212.22
A26PlusICEOrganicBulk26791507900.212.22
A25HPlusICEOrganicBulk25772268100.182.15
A25PlusICEOrganicBulk25771507850.182.26
A24PlusICEOrganicBulk24751457900.182.22
A23PlusICEOrganicBulk23731457850.182.22
A22HPlusICEOrganicBulk22722168200.182.85
A22PlusICEOrganicBulk22721457850.182.22
A17PlusICEOrganicBulk17631507850.182.22
A16PlusICEOrganicBulk16612137600.182.37
A15PlusICEOrganicBulk15591307900.182.26
A9PlusICEOrganicBulk9481407750.212.16
A8PlusICEOrganicBulk8461507730.212.16
A6PlusICEOrganicBulk6431507700.212.17
A4PlusICEOrganicBulk4392007660.212.18
A3PlusICEOrganicBulk3372007650.212.2
A2PlusICEOrganicBulk2362007650.212.2
E0PlusICEEutecticBulk03233210000.584.19
E-2PlusICEEutecticBulk-22830610700.583.8
E-3PlusICEEutecticBulk-3.72531210600.63.84
E-6PlusICEEutecticBulk-62127511100.563.83
E-10PlusICEEutecticBulk-101428611400.563.33
E-11PlusICEEutecticBulk-11.61130110900.573.55
E-12PlusICEEutecticBulk-12.31025011100.563.47
E-14PlusICEEutecticBulk-14.8524312200.533.51
E-15PlusICEEutecticBulk-15530310600.533.87
E-19PlusICEEutecticBulk-18.7-228211250.583.29
E-21PlusICEEutecticBulk-20.6-526312400.513.13
E-22PlusICEEutecticBulk-22-823411800.573.34
E-26PlusICEEutecticBulk-26-1526012500.583.67
E-29PlusICEEutecticBulk-29-2022214200.643.69
E-32PlusICEEutecticBulk-32-2624312900.562.95
E-34PlusICEEutecticBulk-33.6-2824012050.543.05
E-37PlusICEEutecticBulk-36.5-3421315000.543.15
E-50PlusICEEutecticBulk-49.8-5821813250.563.28
E-75PlusICEEutecticBulk-75-1031029020.172.43
E-78PlusICEEutecticBulk-78-1081158800.141.96
E-90PlusICEEutecticBulk-90-130907860.142.56
E-114PlusICEEutecticBulk-114-1731077820.172.39
PCM-HS26NSAVENRG [45]InorganicBulk-26-152051200
PCM-HS23NSAVENRGInorganicBulk-23-92001180
PCM-HS10NSAVENRGInorganicBulk-10142201100
PCM-HS07NSAVENRGInorganicBulk-7192301120
PCM-HS01PSAVENRGInorganicBulk0322901010
PCM-OM05PSAVENRGOrganicBulk541198770
PCM-0M06PSAVENRGOrganicBulk5.542260735
PCM-0M08PSAVENRGOrganicBulk8461901050
PCM-0M11PSAVENRGOrganicBulk11522601060
PCM-0M21PSAVENRGOrganicBulk21701201050
PCM-H22PSAVENRGInorganicBulk22721851540
PCM-HS24PSAVENRGInorganicBulk24751851540
PCM-HS29PSAVENRGInorganicBulk29841901550
PCM-OM32PSAVENRGOrganicBulk3290235870
PCM-OM35PSAVENRGOrganicBulk3595197870
PCM-HS34PSAVENRGInorganicBulk34931501850
PCM-OM37PSAVENRGOrganicBulk3799218880
PCM-OM46PSAVENRGOrganicBulk46115245860
PCM-OM48PSAVENRGOrganicBulk48118255980
PCM-OM53PSAVENRGOrganicBulk53127192860
PCM-OM65PSAVENRGOrganicBulk65149210840
PCM-HS89PSAVENRGInorganicBulk891921801540
MPCM -30Microtek [46]OrganicMicro-encapsulated-30-22145
MPCM -30DMicrotekOrganicMicro-encapsulated-30-22145
MPCM -10MicrotekOrganicMicro-encapsulated-9.515155
MPCM -10DMicrotekOrganicMicro-encapsulated-9.515155
MPCM 6MicrotekOrganicMicro-encapsulated643162
MPCM 6DMicrotekOrganicMicro-encapsulated643162
MPCM 18MicrotekOrganicMicro-encapsulated1864168
MPCM 18DMicrotekOrganicMicro-encapsulated1864168
MPCM 28MicrotekOrganicMicro-encapsulated2882187.5
MPCM 28DMicrotekOrganicMicro-encapsulated2882187.5
MPCM28D-IRMicrotekOrganicMicro-encapsulated56133170
MPCM 37MicrotekOrganicMicro-encapsulated3799195
MPCM 37DMicrotekOrganicMicro-encapsulated3799195
MPCM 43DMicrotekOrganicMicro-encapsulated43109195
MPCM 56DMicrotekOrganicMicro-encapsulated56133170
Latest 29 TTEAPInorganicBulk2882175149012
Latest 25 TTEAPInorganicBulk2475175149012
Latest 20 TTEAPInorganicBulk1966175149012
Latest 18 TTEAPInorganicBulk1763175149012

The above dataset is also available as an Excel spreadsheet from UCLA Engineering

Technology, development and encapsulation[edit]

The most commonly used PCMs are salt hydrates, fatty acids and esters, and various paraffins (such as octadecane). Recently also ionic liquids were investigated as novel PCMs.

As most of the organic solutions are water-free, they can be exposed to air, but all salt based PCM solutions must be encapsulated to prevent water evaporation or uptake. Both types offer certain advantages and disadvantages and if they are correctly applied some of the disadvantages becomes an advantage for certain applications.

They have been used since the late 19th century as a medium for the thermal storage applications. They have been used in such diverse applications as refrigerated transportation[47] for rail[48] and road applications[49] and their physical properties are, therefore, well known.

Unlike the ice storage system, however, the PCM systems can be used with any conventional water chiller both for a new or alternatively retrofit application. The positive temperature phase change allows centrifugal and absorption chillers as well as the conventional reciprocating and screw chiller systems or even lower ambient conditions utilizing a cooling tower or dry cooler for charging the TES system.

The temperature range offered by the PCM technology provides a new horizon for the building services and refrigeration engineers regarding medium and high temperature energy storage applications. The scope of this thermal energy application is wide ranging of solar heating, hot water, heating rejection, i.e. cooling tower and dry cooler circuitry thermal energy storage applications.

Since PCMs transform between solid–liquid in thermal cycling, encapsulation[50] naturally become the obvious storage choice.

As phase change materials perform best in small containers, therefore they are usually divided in cells. The cells are shallow to reduce static head – based on the principle of shallow container geometry. The packaging material should conduct heat well; and it should be durable enough to withstand frequent changes in the storage material's volume as phase changes occur. It should also restrict the passage of water through the walls, so the materials will not dry out (or water-out, if the material is hygroscopic). Packaging must also resist leakage and corrosion. Common packaging materials showing chemical compatibility with room temperature PCMs include stainless steel, polypropylene and polyolefin.

Thermal composites[edit]

Thermal-composites is a term given to combinations of phase change materials (PCMs) and other (usually solid) structures. A simple example is a copper-mesh immersed in a paraffin-wax. The copper-mesh within parraffin-wax can be considered a composite material, dubbed a thermal-composite. Such hybrid materials are created to achieve specific overall or bulk properties.

Thermal conductivity is a common property which is targeted for maximisation by creating thermal composites. In this case the basic idea is to increase thermal conductivity by adding a highly conducting solid (such as the copper-mesh) into the relatively low conducting PCM thus increasing overall or bulk (thermal) conductivity. If the PCM is required to flow, the solid must be porous, such as a mesh.

Solid composites such as fibre-glass or kevlar-pre-preg for the aerospace industry usually refer to a fibre (the kevlar or the glass) and a matrix (the glue which solidifies to hold fibres and provide compressive strength). A thermal composite is not so clearly defined, but could similarly refer to a matrix (solid) and the PCM which is of course usually liquid and/or solid depending on conditions. They are also meant to discover minor elements in the earth.

Applications[edit]

Applications[1][51] of phase change materials include, but are not limited to:

Fire and safety issues[edit]

Some phase change materials are suspended in water, and are relatively nontoxic. Others are hydrocarbons or other flammable materials, or are toxic. As such, PCMs must be selected and applied very carefully, in accordance with fire and building codes and sound engineering practices. Because of the increased fire risk, flamespread, smoke, potential for explosion when held in containers, and liability, it may be wise not to use flammable PCMs within residential or other regularly occupied buildings. Phase change materials are also being used in thermal regulation of electronics.

See also[edit]

References[edit]

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Further reading[edit]