ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Binary mixtures of
Fatty Acids with Sodium
Acetate Trihydrate as
PCMs
Muhsin MAZMAN, Yeliz KONUKLU
Hunay EVLİYA, Halime Ö. PAKSOY
Çukurova University, Adana,-TURKIYE
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Contents
1.
2.
3.
4.
5.
6.
7.
Introduction
Previous work
Purpose
PCMs used and their thermophysical
properties
Mixtures prepared
Results
Conclusions
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Phase Change Materials
(PCMs)
During their phase transition
| can absorb or release large quantities
of latent heat
| at fairly constant temperatures
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Challenges in PCM utilization
Finding the optimum combination of
| appropriate phase transition
temperature
| favorable thermal properties
| encapsulation technique
| cost of PCM
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Solid-Liquid phase change
|
Organics
Paraffins
z Fatty Acids
z Mixtures
z
|
Inorganics
Hydrated salts
z Mixtures
z
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Advantages - Disadvantages
|
Inorganic materials;
z
z
z
z
Subcooling,
Corrosion,
Phase separation
Lack of thermal
stability.
|
Organic materials;
z
z
Lower phase
change enthalpy
and thermal
conductivity,
flammability
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Designing PCM mixtures
|
Additives
overcome problems like supercooling,
phase separation
z increase thermal conductivity
z
|
Multi-component PCM mixtures
to adjust the melting range for a given
application
z to enhance storage capacity
z
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Previous work on mixtures
|
|
Several studies on paraffin-paraffin, fatty
acid-fatty acid and inorganic-inorganic
mixtures
Fatty Acids-Paraffins
z
z
|
Buddhi et al. (1988):
Fatty acids, naphthalene and paraffin wax in
a solar cooker
Dimaano and Watanabe (2002)
capric-lauric acid and pentadecane
Fatty Acids-Hydrated salts
z
No present work
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Purpose
|
|
|
prepare hydrated salt (sodium acetate
trihydrate) - fatty acid (capric and lauric
acid) mixtures
determine stability of mixtures to
melting/freezing cycles,
determine melting range and latent heat
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
PCMs used
|
Fatty acids
z
z
|
capric acid
lauric acid
Hydrated salt
z
Sodium acetate trihydrate
(CH3COONa.3H2O)
•
Na2HPO4·12H2O as nucleator
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Thermophysical properties of the PCMs
PCMs
Lauric Acid
Capric Acid
Sodium acetate
trihydrate
Chemical Formula
C12H24O2
C10 H20O2
CH3COONa·3H2O
Molecular Weight (g/mol)
200
172
136
Melting Point (°C)
43-45
29-32
58
Latent Heat (kJ/kg)
178
153
264
Thermal Conductivity
(W/m·K)
0.147(50 °C)
0.153 (38 °C)
-
Density
(kg/m3)
Liquid 862 (60°C)
Solid 1007 (24°C)
886 (84°C)
1004 (24°C)
1450
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Mixtures
|
|
Capric acid -CH3COONa.3H2O
z 10:90*
z 20:80
z 30:70
Lauric acid- CH3COONa.3H2O
z 10:90*
z 20:80
z 30:70
*% weight ratio of fatty acid to salt hydrate
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Results
Lauric Acid - CH3COONa·3H2O
|
100
90
80
70
60
50
40
30
20
10
0
Subcooling effect (3-4°C)
Temperature (°C)
90:10 lauric-NaAc
80:20 lauric-NaAc
70:30 lauric-NaAc
0
50
100
Time (min.)
150
200
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Results
|
|
(20:80, 30:70)
mixed
homogeneously
when the lauric
acid ratios were
increased (40:60),
in a few
melting/freezing
cycles observed
phase separation.
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Lauric acid - CH3COONa.3H2O (30:70)
at 10 °C/min scan rate with DSC
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Lauric acid - CH3COONa.3H2O (20:80)
at 5 °C/min scan rate with DSC
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Results
Capric Acid - CH3COONa·3H2O
(20:80, 30:70) mixed homogeneously
| when capric acid ratios were
increased (like, 40:60) the mixtures
showed phase separation
|
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Capric acid - CH3COONa.3H2O (30:70)
at 10 °C/min scan rate with DSC
ECOSTOCK 10th International Conference on Thermal Energy Storage, may 31-June 2, 2006, Stockton
Capric acid - CH3COONa.3H2O (20:80)
at 5 °C/min scan rate with DSC