Phase Change Materials for

Thermal Energy Storage

Jose Pereira da Cunha

Materials Review

Inorganic Eutectics Mass Ratio

Tmelt ΔHfusion Edensity

°C kJ/kg kWh/m3 AlCl3-ZnCl2 48-52 114 607 395

AlCl3-NaCl 80-20 106 285 156

AlCl3-LiCl 83-17 114 250 150

AlCl3-KCl 78-22 128 253 150

AlCl3-CaCl2 78-22 119 267 149

FeCl3-LiCl 57-43 150 353 257

AlCl3-KCl-LiCl 44-52-3 85 196 111

AlCl3-KCl-NaCl 58-26-15 88 191 102

LiNO3-KNO3 33-67 133 160 99

+18% NaNO3 30-18-52 120 135 78

KNO3-NaNO2 56-44 141 145 91

+ 7% NaNO3 58-7-35 142 266 144

KNO2-NaNO3 48-52 149 153 94

LiNO3-KCl 44-56 160 272 174

+5% NaNO3 53-5-42 160 266 173

LiNO3-NaNO3 48-52 190 280 175

+1% LiCl 48-1-51 180 267 169

KNO3-Mg(NO3)2 46-54 178 128 83

NaOH-KOH 37-63 170 207 127

LiOH-LiNO3 19-81 183 776 484

Organic - Inorganic Eutectics Mass Ratio

Tmelt ΔHfusion Edensity

°C kJ/kg kWh/m3

K2CO3-Urea 15-85 102 225 100

NaCl-Urea 20-80 103 254 108

KCl-Urea 18-82 115 243 105

Mass Ratio

Tmelt ΔHfusion Edensity °C kJ/kg kWh/m3

Salicylic acid - Malonic acid 57-43 87 217 98

Salicylic acid - Benzoic acid 33-67 107 164 66

Malonic acid - Benzoic acid 36-64 107 183 77

Benzoic acid - Oxalic acid 67-33 114 312 135

Succinic acid- Benzoic Acid 29-71 116 189 77

Malonic acid - Succinic acid 47-53 119 268 126

Organic Melts CAS Tmelt ΔHfusion Edensity °C kJ/kg kWh/m3

Oxalic acid dihydrate 6153-56-6 105 370 178

Maleic acid 110-16-7 131 235 109

Adipic acid 124-04-9 152 220 101

HDPE MI 12g/10min 9002-88-4

130 255 67

HDPE MI 2g/10min 135 260 69

Phthalic anhydride 85-44-9 131 160 68

2-Chlorobenzoic acid 118-91-2 142 164 75

d-Mannitol 69-65-8 165 300 140

Inorganic Melts CAS Tmelt ΔHfusion Edensity °C kJ/kg kWh/m3

Ba(OH)2-(H2O)8 12230-71-6 78 270 164

Mg(NO3)2-(H2O)6 13446-18-9 90 150 72

MgCl2-(H2O)6 7791-18-6 117 120 68

Organic TGA Analysis

• Organics sublime around their melting point;

• Oxalic Acid dihydrate has a initial dehydration stage;

• Adipic Acid seemed suitable, but thermal stage

indicated also sublimation in its melting point;

Inorganic TGA Analysis

• Salt Hydrates dehydrate in their melting point:

Barium Hydroxide lost 1 water molecule;

Magnesium Nitrate lost 4 water molecules;

Magnesium Chloride lost 5 water molecules;

Organic DSC Analysis

• Mannitol and HDPE are the most suitable for

thermal storage;

• Normal lid tests showed good cycling properties;

• Adipic Acid proved thermal stability in

closed container;

Normal lid

Hermetic lid

Organic DSC Analysis

• 2-Chlorobenzoic acid and Phthalic Anhydride were

thermally stable only in hermetic container;

• Oxalic acid dihydrate showed poor thermal cycling even in

closed lid;

• Maleic Acid was inconclusive (large sub cooling didn’t allow

full crystallization);

Inorganic DSC Analysis

• Salt Hydrates • Dehydration leads to evolution of melting point;

• In closed container, only Barium Hydroxide proved not suitable for thermal storage;

Inorganic DSC Analysis

• Eutectic Mixtures • Excellent

Thermal

Properties;

• Very

hygroscopic;

LiNO3 – KNO3

LiNO3 - KCl

Inorganic DSC Analysis

• Eutectic Mixtures

• Only Nitrite

mixtures were non

hygroscopic;

LiNO3 – NaNO3

NaNO2 – KNO3

Conclusions

• Organics tested need to be enclosed for thermal storage;

• Only Mannitol and HDPE are stable at their melting temperature;

• Salt hydrates dehydrate severely in their melting point, also requiring a enclosed system for thermal storage;

• All inorganic eutectics tested showed excellent thermal cycling properties;

Organic Melts CAS Lid Tmelt ΔHfusion Cps Cpl Edensity ΔTWater

°C kJ/kg J/kg.K kWh/m3 for 1m3

Oxalic acid dihydrate 6153-56-6 Hermetic 105 269 2108 2890 135 116

Maleic acid 110-16-7 Hermetic 138 305 1662 2335 144 124

Adipic acid 124-04-9 Normal 153 96 810 1330 40 35

Hermetic 155 219 1750 2140 90 78

HDPE MI 12g/10min 9002-88-4

Normal 128 109 2600 2150 35 30

HDPE MI 2g/10min Normal 130 119 2560 2090 38 33

Phthalic anhydride 85-44-9 Hermetic 133 207 1925 2320 97 83

2-Chlorobenzoic acid 118-91-2 Hermetic 142 127 1390 1670 61 53

d-Mannitol 69-65-8 Normal 169 269 1700 2400 120 103

Inorganic Melts CAS Lid Tmelt ΔHfusion Cps Cpl Edensity ΔTWater

°C kJ/kg J/kg.K kWh/m3 for 1m3

Ba(OH)2-(H2O)8 12230-71-6 Hermetic 82 241 1346 2445 151 130

Mg(NO3)2-(H2O)6 13446-18-9 Hermetic 93 100 2500 3100 56 48

MgCl2-(H2O)6 7791-18-6 Hermetic 120 142 2000 2400 69 59

Eutectic Melts m/m

Lid Tmelt ΔHfusion Cps Cpl Edensity ΔTWater

% °C kJ/kg J/kg.K kWh/m3 for 1m3

LiNO3-KNO3 33-63 Stitched 128 135 1070 1430 82 71

"+18% NaNO3" 30-18-52 Stitched 127 167 1450 2030 104 90

LiNO3-KCl 58-42 Stitched 169 141 1430 1780 88 76

"+ 5% NaNO3" 53-5-42 Stitched 167 152 1530 1970 95 82

"+ 24% NaNO3" 42-24-34 Stitched 155 54 2120 1442 40 35

LiNO3-NaNO3 48-52 Stitched 195 142 1780 3150 99 85

"+1% LiCl" 47-1-52 Stitched 193 118 1780 2810 85 73

"+6% LiCl" 45-6-49 Stitched 195 210 1450 2250 137 118

KNO3-NaNO2 56-44 Stitched 142 45 2030 2485 38 33

KNO3-NaNO3 -NaNO2 56-44 Stitched 144 76 2210 1550 54 46

Color Code

Discarded

Poor thermal Cycling

Less Promising

Promising

Most Promising

Future Work

• Thermal Cycling of promising organics near their melting point (+- 20C);

• Development of a small scale prototype for higher volume testing;

• Sell-and-tube;

• Tube in tank;

• Preparation of Chloride

eutectics and novel nitrite

eutectics;

• Continuous research on

nitrate eutectics: • Adition of other salts;

• Corrosion tests of proven

samples;