The addition of latent heat storage systems in solar thermal applications has several benefits including volume reduction in storage tanks and maintaining the temperature range of the thermal storage. A phase change material (PCM) provides high energy storage density at a constant temperature corresponding to its phase transition temperature. In this paper, a high temperature PCM (melting temperature of 80°C) made of a composite of paraffin and graphite was tested to determine its thermal properties. Tests were conducted with a differential scanning calorimeter and allowed the determination of the melting and solidification characteristics, latent heat, specific heat at melting and solidification, and thermal conductivity of the composite. The results of the study showed an increase in thermal conductivity by a factor of 4 when the mass fraction of the graphite in the composite was increased to 16.5%. The specific heat of the composite PCM (CPCM) decreased as the thermal conductivity increased, while the latent heat remained the same as the PCM component. In addition, the phase transition temperature was not influenced by the addition of expanded graphite. To explore the feasibility of the CPCM for practical applications, a numerical solution of the phase change transition of a small cylinder was derived. Finally, a numerical simulation and the experimental results for a known volume of CPCM indicated a reduction in solidification time by a factor of 6. The numerical analysis was further explored to indicate the optimum operating Biot number for maximum efficiency of the composite PCM thermal energy storage.

1.
Sharma
,
S. D.
, 2005, “
Latent Heat Storage Materials and Systems: A Review
,”
Int. J. of Green Energy
,
2
, pp.
1
56
.
2.
Py
,
X.
,
Olives
,
R.
, and
Mauran
,
S.
, 2001, “
Paraffin/Porous-Graphite-Matrix Composite as a High and Constant Power Thermal Storage Material
,”
Int. J. Heat Mass Transfer
0017-9310,
44
, pp.
2727
2737
.
3.
Barba
,
A.
, and
Spiga
,
V.
, 2003, “
Discharge Mode for Encapsulated PCMs in Storage Tanks
,”
Sol. Energy
0038-092X,
74
, pp.
141
148
.
4.
Zalba
,
B.
,
Marin
,
J. M.
,
Cabeza
,
L. F.
, and
Mehling
,
H.
, 2003, “
Review on Thermal Energy Storage With Phase Change: Material, Heat Transfer Analysis and Applications
,”
Appl. Therm. Eng.
1359-4311,
23
, pp.
251
283
.
5.
Alva
,
L. H.
,
González
,
J. E.
, and
Dukham
,
N.
, 2006, “
Solar Air Conditioning Systems With PCM Solar Collectors
,”
ASME J. Sol. Energy Eng.
0199-6231,
128
, pp.
173
177
.
6.
Schawe
,
J. E.
,
Hutter
,
T.
,
Heitz
,
C.
,
Alig
,
I.
, and
Lellinger
,
D.
, 2006, “
Stochastic Temperature Modulation: A New Technique in Temperature-Modulated DSC
,”
Thermochim. Acta
0040-6031,
446
, pp.
147
155
.
7.
Incopera
,
P. F.
, and
DeWitt
,
D. P.
, 1996,
Fundamentals of Heat and Mass Transfer
,
4th ed.
,
Wiley
,
New York
.
9.
Hakvoort
,
G.
,
van Reijen
,
L. L.
, and
Aartsen
,
A. J.
, 1985, “
Measurement of the Thermal Conductivity of Solid Substances by DSC
,”
Thermochim. Acta
0040-6031,
93
, pp.
317
320
.
10.
Bonnissel
,
M.
,
Luo
,
L.
, and
Tondeur
,
D.
, 2001, “
Compacted Exfoliated Natural Graphite as Heat Conduction Medium
,”
Carbon
0008-6223,
39
, pp.
2151
2161
.
11.
Han
,
J. H.
,
Cho
,
K. W.
,
Lee
,
K. H.
, and
Kim
,
H.
, 1998, “
Porous Graphite Matrix for Chemical Heat Pump
,”
Carbon
0008-6223,
36
, pp.
1801
1810
.
12.
Lane
,
G. A.
, 1983,
Solar Heat Storage: Latent Heat Material
, Vol.
1
: Background and Scientific Principles,
CRC Press
,
Boca Raton, FL
.
13.
Özisik
,
M. N.
, 1993,
Heat Conduction
,
2nd ed.
,
Wiley
,
New York
.
14.
Gupta
,
R. S.
, and
Kumar
,
D.
, 1981, “
Variable Time Step Methods for One-Dimensional Stefan Problem With Mixed Boundary Condition
,”
Int. J. Heat Mass Transfer
0017-9310,
24
, pp.
251
259
.
15.
Arpaci
V. S.
, 1966,
Conduction Heat Transfer
,
Addison-Wesley
,
New York
.
16.
Rolle
,
K. C.
, 2000,
Heat and Mass Transfer
,
Prentice-Hall
,
Englewood Cliffs, NJ
.
17.
John
,
T. R.
, 1996,
An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements
,
University Science Book
,
2nd ed.
,
Maple-Vail Book Manufacturing Group
.
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