3.014 Materials Laboratory

Thermal Energy Storage using Phase Change Materials
Nicole Ozminkowski
3.014 Materials Laboratory
Introduction
Thermal energy systems take advantage of material properties to
collect energy, store it, and make it available for retrieval. Phase
change materials can be used for a variety of thermal energy storage
applications. Some include building insulation, jackets and outerwear,
and blood test incubation systems in developing countries. In order
to determine which materials are good phase change materials,
properties such as specific heat capacity, latent heat of fusion, and
melting temperature must be studied.
Theoretical Background
Thermal energy systems use three types of heat storage: sensible
heat storage, thermochemical heat storage, and latent heat storage.
Sensible heat storage can be measured by specific heat capacity,
which is the amount of heat required to raise the temperature of a
material 1 degree Kelvin. Thermochemical heat storage is heat
stored through chemical reactions. Latent heat is the amount of heat
required or released through a phase change. In this experiment, we
focus on latent heat of fusion: how much heat is required to melt
the material. Successful phase change materials have high specific
heats and latent heats of fusion: they can store a larger amount of
energy without a large change in temperature. Another important
characteristic of phase change materials is melting temperature.
Since the material will stay at about a constant melting temperature
during the phase change, it is important that the temperature
required for the application is very close to the melting temperature.
This is one reason why even though water has a high specific heat
capacity, it is not good for keeping buildings at a comfortable
temperature: it’s melting point is too low.
Phase change materials can be pure materials or mixtures. However,
when two materials are mixed, their melting characteristics are not
just the average of the two mixtures. The mixture’s melting point
will be lower than that of the each of the pure substances. Melting
points of binary mixtures are modeled using a phase diagram. The
upper boundary, called the liquidus, is the temperature at which the
entirety of the mixture became liquid. The bottom boundary, called
the solidus, is the temperature at which the entirety of the mixture
became solid. At the eutectic point, the liquidus and solidus
intersect.
Materials and Methods
Melting and Freezing Points for All Materials4
1.  2-8 mg of the following materials were added into aluminum
pans, which were then crimped closed:
1.  Mixtures of Lauric and Stearic Acid of various
compositions were created by mixing the solids together
and heating at a temperature above 69C and allowing the
mixture to equilibrate for 10 minutes.
2.  PCM paraffin products:
n-Hexadecane: MPCM 18-D
n-Octadecane: MPCM 28-D
3. Tempertex continuous climate control interlinings:
NWH-38 – thermally enhanced nonwoven style.
4. Sapphire calibration standard for calculating specific heat.
Specific Heat of Lauric/Stearic Acid Mixtures3
2.  Differential Scanning Calorimetry (DSC) was used to
measure the heat flux involved in melting each of the
materials in comparison to a reference aluminum pan.
Thermal profiles were obtained for single and cyclical scans.
Binary Phase Diagram3
Results
1.  Thermal profiles for each material were obtained. From
each, the latent heat of melting and melting temperature
could be read directly.
Discussion
• As temperature rises, specific heats for all materials
also rises, due to the increased vibrations and
movements of atoms.
• Specific heat for all Lauric/Stearic Acid mixtures
remains about constant at between 1400 and 2600 J/
kgK. It mainly changes with temperature, not
composition.
• The binary mixture between Lauric Acid and Stearic
Acid shows a eutectic point at a Lauric Acid
composition of about .8. The eutectic composition is
ideal because the temperature remains completely
constant during the phase change.
• Tempertex has a much lower latent heat of melting
than any other substance, probably due to the fact that
it is not completely composed of PCM, so the mass
measured was larger than the actual PCM mass.
• The extent of supercooling was between 5-10C for all
materials, but was largest for MPCM-18D and 50% wt
Lauric Acid.
• Most runs showed good thermal stability after the first
cycle. The first cycle si probably different because of
inconsistincies in the packing of the material.
Conclusion
Tm
Phase change materials work best when their melting
temperatures are at the desired temperature and when
latent heat of fusion is high. Although materials like rocks
have high latent heats of fusion, their melting points are
too high for that to be valuable. Both n-Hexadecane and
n-Octadecane are good PCM candidates, and due to
melting point similarities, it is clear that n-Octadecane is
used in Tempertex. In the future, materials with different
melting points should be tested as phase change materials
for different applications.
Binary Phase Diagram2
Latent Heat of Melting for Various
Materials
250
ΔHfusion
200
Latent Heat of Melting (J/g)
2. Thermal profiles for sapphire were used to calculate specific
heat values for each material using the following equation:
3
150
References
1. 
Berera, Geetha “Entropy of Phase Change & Thermal Energy Balance,” 3.014 Materials
Laboratory (2014)
2. 
Armstrong, Kathleen. “Foothill College Chemistry.” (2014) http://www.foothill.edu/psme/armstrong/
meltingpoints.shtml
3. 
Created by Christopher Klingshirtn
4. 
Created by Jennie Glerum
100
50
0
Tempertex
100% Lauric 90% Lauric
75% Lauric
60% Lauric
40% Lauric
20% Lauric
0% Lauric
MPCM 28D
MPCM 18D
Acknowledgements
Thank you to Geetha Berera and Vivek Singh for meeting with me outside of class and furthering my
understanding of this topic. Thank you to my lab group members for helping with data analysis.
nicoleoz

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