DEVELOPMENT OF FORM STABLE PHASE
CHANGE MATERIAL FOR SOLAR WATER
HEATER
YU GEN QIAN
UNIVERSITI TUNKU ABDUL RAHMAN
DEVELOPMENT OF FORM STABLE PHASE CHANGE MATERIAL FOR
SOLAR WATER HEATER
YU GEN QIAN
A project report submitted in partial fulfillment of the
requirements for the award of the degree of
Bachelor of Engineering (Hons) Petrochemical Engineering
Faculty of Engineering and Green Technology
Universiti Tunku Abdul Rahman
May 2018
ii
DECLARATION
I hereby declare that this project report is based on my original work except for
citations and quotations which have been duly acknowledged. I also declare that it
has not been previously and concurrently submitted for any other degree or award at
UTAR or other institutions.
Signature : ___________________________
Name : Yu Gen Qian
ID No. : 13AGB05459
Date : 2 May 2018
iii
APPROVAL FOR SUBMISSION
I certify that this project report entitled “DEVELOPMENT OF FORM STABLE
PHASE CHANGE MATERIAL FOR SOLAR WATER HEATER” was
prepared by YU GEN QIAN has met the required standard for submission in partial
fulfilment of the requirements for the award of Bachelor of Engineering (Hons)
Petrochemical Engineering at Universiti Tunku Abdul Rahman.
Approved by,
Signature : _________________________
Supervisor : Associate Professor Dr. Yamuna a/p Munusamy
Date : _________________________
Signature : _________________________
Co-Supervisor : Dr. Lai Koon Chun
Date : _________________________
iv
The copyright of this report belongs to the author under the terms of the
copyright Act 1987 as qualified by Intellectual Property Policy of Universiti Tunku
Abdul Rahman. Due acknowledgement shall always be made of the use of any
material contained in, or derived from, this report.
© 2018, Yu Gen Qian. All right reserved.
v
Specially dedicated this thesis to my parents, David Yu Sing Ong and Teong Chooi
Hua who have always loved me unconditionally and whose good examples have
taught me to work hard for the things that I aspire to achieve. This work is also
dedicated to my brothers: Gen Cheng, Gen Jin, Gen Xin, my girlfriend Sharon Teh
and best friends who have always been a constant source of support and
encouragement during the challenges of my whole university life.
vi
ACKNOWLEDGEMENTS
Jesus said to him, "I am the way, the truth, and the life. No one comes to the
Father except through me”. John 14:6
For God so loved the world that he gave his one and only Son, that whoever
believes in him shall not perish but have eternal life. John 3:16
Thank you Almighty God for the blessings and graciously allowing me to complete
this research paper. I would like to express my outmost gratitude to my research
supervisor, Associate Professor Dr. Yamuna Munusamy for her guidance throughout
the development of the research. I would also like to thank the lecturers, staffs of
UTAR and postgraduate especially Ms. Kee Shin Yiing who had given me a lot of
assistance and advices during the course of the project. Nonetheless, I would like to
thank my parents for supporting me spiritually throughout writing this thesis and my
life in general.
Last but not least, I would also like to express my gratitude to my friends for
their support.
vii
DEVELOPMENT OF FORM STABLE PHASE CHANGE MATERIAL FOR
SOLAR WATER HEATER
ABSTRACT
Demand for solar water heater is increasing due to their low cost, easy fabrication
and maintenance. It can also reduce the emission of carbon dioxide in the atmosphere.
Phase change material (PCM) is the most popular and widely used thermal energy
storage material in solar water heater. PCM is able to absorb and release large
amount of latent heat energy during the phase transition process over a narrow
temperature range. In this work, form stable PCM was prepared by blending the
myristic acid with PMMA and then coating with nitrile butadiene rubber (NBR) and
polyarylic (PA). The purpose of adding PMMA into the myristic acid is to increase
the thermal stability of the PCM during phase change process. Leakage test results
showed that addition of 20 wt% PMMA to the myristic acid while reduce the weight
percentage of myristic acid together with coating layers could eliminate leakage.
Tensile test results showed that combination of PA and NBR coating material
provide sufficient strength and elasticity to contain the PCM during the phase change
process, while Fourier transform infrared spectroscopy (FTIR) analysis results
proves that a compact and uniform coating without cracks were formed on the
surface of PCM. Differential scanning calorimetry (DSC) results show that the latent
heat of melting and freezing of the form stable PCM80 is 107.56 J/g and 102.26 J/g
which is comparable with others results in literature.
Keywords: Phase change material; PMMA; myristic acid; coating
viii
TABLE OF CONTENTS
DECLARATION ii
APPROVAL FOR SUBMISSION iii
ACKNOWLEDGEMENTS vi
ABSTRACT vii
TABLE OF CONTENTS viii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF SYMBOLS / ABBREVIATIONS xiii
LIST OF APPENDICES xv
CHAPTER
1 INTRODUCTION 1
1.1 Background of Study 1
1.2 Problem Statement 5
1.3 Research Objectives 6
2 LITERATURE REVIEW 7
2.1 Classification of Phase Change Material (PCM) 7
2.1.1 Inorganic materials 8
2.1.2 Organic materials 9
2.1.3 Polymeric PCM 10
2.2 Differentiation of Various Types of PCMs 12
2.3 Criteria of Selecting PCMs 12
2.4 Solar Renewable Energy 15
2.5 Thermal Energy Storage 16
2.6 Form stable PCM 18
2.6.1 Encapsulation Method 19
2.6.2 Shape-stabilized Encapsulation Method 20
2.6.3 Microencapsulation Method 23
2.6.4 Crosslinked Polymer Coating Method 24
2.7 Coating 25
ix
2.7.1 Coating Application Methods 25
2.7.2 Coating of Phase Change Material 26
2.8 Stability of Non-paraffin Organic PCMs 28
2.9 Challenges to Produce Good Coating 29
2.10 Applications of PCMs 30
3 METHODOLOGY 33
3.1 Materials 33
3.1.1 Experiment Flow Chart 33
3.2 Preparation of PCM 34
3.2.1 Preparation of PCM Blending 34
3.2.2 Pelletizing of PCM 37
3.3 Coating of Polyacrylic and Nitrile Butadiene Rubber on PCM
through Dip Coating Method 38
3.4 Characterization 40
3.4.1 Fourier Transform Infrared Spectroscopy (FTIR-ATR) 40
3.4.2 Differential Scanning Calorimetry (DSC) 40
3.4.3 Leakage test 41
3.4.4 Tensile Test 42
4 RESULTS AND DISCUSSIONS 44
4.1 Characterization of Form Stable PCM 44
4.1.1 Tensile Test 44
4.1.2 Leakage Test 45
4.1.3 Differential Scanning Calorimetry (DSC) 48
4.1.4 Fourier Transform Infrared Spectroscopy (FTIR-ATR) 54
5 CONCLUSION AND RECOMMENDATIONS 60
5.1 Conclusion 60
5.2 Recommendation 61
REFERENCES 62
APPENDICES 78
x
LIST OF TABLES
TABLE TITLE PAGE
2.1 Comparison of Different Types of PCMs 12
2.2 PCM Selection Criteria 13
2.3 Thermal Properties of Fatty Acids, Eudragit
S/Fatty Acid Blends (30/70 wt%) as Form-stable
PCMs 20
2.4 Thermal Properties of Some Fatty Acids and
Form-stable Compositions 21
2.5 Thermal Properties of Fatty Acids and 30%
Eudragit E/70% Fatty Acid (w/w) Blends as Form-
stable PCM 22
3.1 Formulation of PCM samples 35
4.1 Tensile properties of polymer coating film 45
4.2 Leakage area of non-coated PCMs 47
4.3 Leakage area of coated PCMs 47
4.4 Latent Heat Absorbed and Released by PCM 48
4.5 Examples of Form Stable Solid-Liquid Organic
PCMs and Some of Their Thermal Properties 51
4.6 Absorption Frequency Obtained for PA 55
4.7 Absorption Frequency Obtained for Myristic Acid 56
4.8 Absorption Frequency Regions and Functional
Groups for coated PCMs. 59
xi
LIST OF FIGURES
FIGURE TITLE PAGE
1.1 Features of a Latent Heat Storage Material 2
1.2 Schematic Experimental Setup of Solar Water
Heater Integrated with PCMs 4
2.1 Classification of PCM 8
2.2 Melting Temperature and Phase Change Enthalpy
of Currently Applicable PCMs 13
2.3 Schematic Representation of a Phase Change
Process 14
2.4 The storage capacity of various composites 18
3.1 Overall Flow of Methodology 34
3.2 The process of stirring the PMMA and MA in
chloroform 35
3.3 Setup of the mixing process 36
3.4 The drying process of the mixture solution 36
3.5 The formation of phase change material blending
composition 36
3.6 FTIR presser 38
3.7 The die 38
3.8 The NBR coating solution (left) and PA coating
solution (right) 39
3.9 The PCM sample preparation on a Teflon sheet. 39
3.10 The set up for leakage test 41
xii
3.11 Specimen for Tensile Test 42
3.12 Teflon mold 42
4.1 Leakage of coated PCM after 30 thermal cyclic
process 46
4.2 Leakage of PCM without coating after 30 thermal
cyclic process 46
4.3 DSC graph combination for different weight
percentage of PMMA in PCM of heat absorption
peaks 49
4.4 DSC graph combination for different weight
percentage of PMMA in PCM of heat release
peaks 49
4.5 FTIR spectrum of pure myristic acid 54
4.6 Combination of FTIR spectrum of PCMs without
coating 57
4.7 Combination of FTIR spectrum of PCMs with
coating 58
xiii
LIST OF SYMBOLS / ABBREVIATIONS
∆H enthalpy
Al aluminium
Al2O3 aluminium oxide
CA capric acid
Cr chromium
Cr2O chromium oxide
Cu copper
DSC Differential Scanning Calorimetry
EG expanded graphite
EP expanded perlite
EVA ethylene-vinyl acetate
FTIR Fourier Transform Infrared Spectroscopy
HDPE high density poly(ethylene)
LDPE low density poly(ethylene)
IR infrared
LA lauric acid
LCOE levelized cost of electricity
LHTES latent heat thermal energy storage
MA myristic acid
MPCM microencapsulated PCMs
NaNO3 sodium nitrate
NBR nitrile butadiene rubber
Ni nickel
PA polyacrylic
PA palmitic acid
PAOs polyalphaolefins
PCM phase change material
xiv
PE poly (ethylene)
PEG polyethylene glycol
PEN poly (ethylene-2, 6-naphthalate)
PEX crosslinked high density polyethylene
PMMA polymethyl methacrylate
PP polypropylene
PS polystyrene
PVC polyvinyl chloride
RGO reduced graphene oxide
SA stearic acid
SBS styrene butadiene styrene copolymer
SS304L stainless steel
Steel C20 carbon steel
TCS thermo-chemical heat storage
TES thermal energy storage
Tom melting temperature
λ wavelength
xv
LIST OF APPENDICES
APPENDIX TITLE PAGE
A Fourier Transform Infrared Spectroscopy 78
B Differential Scanning Calorimetry 82
C Conference Proceeding 88
D Novel Research and Innovation Competition
2017 (NRIC) 90
1
CHAPTER 1
INTRODUCTION
1.1 Background of Study
Technology for storage of heat energy has emerged as a highly rated feature in rising
of global energy demand as well as energy saving circumstances. The shrinkage of
fossil fuel production and boost of renewable energy usage in recent years shift the
balance from conventional fossil fuels to environmental friendly renewable energy.
There are several methods to store heat energy, the most common methods are;
chemical energy, sensible heat energy and latent heat energy storage
(Extension.purdue.edu, 2017; Diaz, 2016). Among all these three ways of heat
storage alternatives, the most preferable method to store heat energy is latent heat
storage (Murali, Mayilsamy and Ali, 2015), because of their variety, capacity and
performance in thermal usages.
Phase change material (PCM) is a material that can store and release energy.
Application of PCM is the most general and prospective technique being used to
store latent heat energy. This is because of its storing and releasing capability of very
large amount of energy for each unit mass at nearly a constant temperature (Nayak et
al., 2011). Absorption of a huge amount of heat from the surroundings will melt the
PCM. Then, the freezing of PCM will discharges a great amount of energy, which is
latent heat at a rather constant temperature. The oscillation of temperature enables
PCM to recharge, showing that PCM is an ideal material for temperature monitoring
applications (Asyraf et al., 2016). PCMs have been developed for use across a broad
range of temperatures. They typically store 5 to 14 times more heat per unit volume
2
than materials such as water (Khan et al., 2017). Building applications integrated
with PCMs as a system to store latent heat energy are gaining much attention and
demand. The technological and market readiness of such systems are largely affected
by the heat transfer processes, and current cost of implementations of the system
(Kapsalis and Karamanis, 2016; Eames et al., 2014). Figure 1.1 shows the favourable
features of a latent heat storage material.
Figure 1.1: Features of a latent heat storage material (Khan et al., 2017).
Solar based water heaters are getting acknowledgment because of its sensible
value, ease of fabrication and maintenance. Application of sun based water radiator
reduces hazardous greenhouse emission associated with power generation (Energy
Saving Trust, 2015). Hot water is needed for showering, drinking, domestic and
business use (Marken, 2005). For the duration of 20 years of using only one sunlight
based water heater, 50 tons of carbon dioxide discharged can be eliminated (Shukla
et al., 2009). The hot water demand can be satisfied by taking into consideration the
temperature in the atmosphere and a rightfully designed sun oriented water heater.
Even though the system can operate at any weather, the performance of the system is
highly reliable on availability of solar energy at that respective place and the
temperature of water coming into the framework (Khan et al., 2015). The sunlight
based hot water frameworks in the year 2007 was around 154 GW. China is the
3
world pioneer in their utilization with 70 GW introduced starting from 2006 and a
long haul objective of 210 GW by 2020 (Moore, 2015).
In order to fulfil the requirement of energy storage at night, significant
amount of solar energy should be stored during daytime. The reason is because solar
radiation supply is inconsistent in daytime and at night. Solar radiation integrated
energy storage system are in high demand, because it improves the system utility and
operability by adjusting temporal mismatches between the storage load and the
variation of solar energy intensity (Kumar, 2014). Sun based radiation cannot be
easily stored, so as a matter of first importance an energy transformation must be
achieved and, dependent upon this process, a storage device is required. For this
reason, heat storage using PCM is of huge significance due to its high storage density
and its isothermal nature of the storage (Sharma and Chen, 2009).
Storage and collector units are two main parts of functional solar energy
system. The collector’s function is to collect the radiation that hits on it and change a
fraction of it to other forms of energy. The solar energy that received by the collector
is not constant. Only an average of 250-300 W/m2 of solar energy is received by the
best locations on Earth, if averaged over the entire day-night cycles and over the
whole summer-winter a year (Alternative Energy Tutorials, 2014). In order to
increase the thermal storage efficiency, a storage unit is required to store the energy.
Storing thermal energy in the form of latent heat of fusion has more perks compared
to sensible heat. This is due to its isothermal nature of storage process at melting
temperature and high storage density (Shahare et al., 2017).
Energy collectors can be categorized into two types on operation mode and
condition basis which are active and passive system (Ogueke et al., 2009). A
significant difference between an active system and a passive system is that a passive
system has no pump while an active system has an electric pump. The function of
this pump is to regulate the heat transfer fluid. According to Sharma and Chen,
(2009), PCM can be efficiently used in a passive solar water heating system. This is
because PCM does not require any additional energy. Figure 1.2 shows the schematic
diagram for the setup of the solar water heater integrated with phase change material.
4
Figure 1.2: Schematic Experimental Setup of Solar Water Heater Integrated with
PCMs ((1) solar flat plate collector (varying heat source); (2) constant temperature
bath; (3) electric heater; (4) stirrer; (5) pump; (6 and 7) flow control valves; (8) flow
meter; (9) TES tank; (10) PCM capsules; (11) temperature indicator) (Zhou et al.,
2012).
An extensive range of inorganic, organic and mixtures of PCMs are available.
In this project, the main aim is to find out the best coating and blending composition
of myristic acid and PMMA to produce form stable PCM. Myristic acids have no
supercooling effects with reproducible freezing and melting behaviour, exhibit
suitable solid-liquid phase change temperature, good thermal properties, high latent
heat storage capacity and good thermal reliability (Sari and Kaygusuz, 2001; Fauzi et
al., 2014). However, throughout the phase change heat transfer process, the fatty acid
tends to melt and corrode the wall of the solar water heater heat storage tank (S.
Wahile et al., 2015; Sharma et al., 2004). Thus, myristic acid based PCMs must be
well confined to avoid them from leaking during the phase change process when
melting. This measure must be taken into deliberation in order to use them
practically.
5
1.2 Problem Statement
Application of PCMs in thermal energy storage improves thermal inertia, increases
thermal comfort, reduce internal temperature variations, and decreases heating and
cooling conditions (Pons et al., 2014). Nonetheless, they must be properly enclosed
to stop them from leaking in order to be usable in reality. In previous research, the
form-stable composite PCM was prepared by mixing PMMA and myristic acid in
different weight ratios. PMMA’s role was a supporting material while myristic acid
was used as PCM. Nevertheless, during the phase change process, volume change
induced leakage of a tiny amount of liquid PCMs from supporting material. Leakage
can be detected by measuring the weight of the PCM before and after the thermal
cyclic test or by using litmus paper. The acid that leaks out during the phase change
process is unwanted in PCM integrated thermal energy storage system because acid
has corrosive potential to corrode the internal area of the equipment (Whiffen and
Riffat, 2012; Cui and Riffat, 2011).
Encapsulation of PCM is a method to enhance the heat transfer surface area,
increase thermal conductivity, improve in operating temperature, diminish the risk of
phase segregation, and most importantly controls the PCM volume change to avoid
leakage during phase transition (Khan et al., 2017). According to several studies,
there are some common methods used to prevent leakage of PCM. Kumar et al.
(2015) stated that fusion of nanofillers with size less than 100 nm in PMMA will
enhance the mechanical, physical and thermal properties of the coating, but the short
coming of this method is the nanoscale dispersion of fillers and choice of
compatilizer to increase the interfacial adhesion between nanofiller and polymer
matrix. G. Serale et al., (2014) selected microencapsulated PCM filled with n-
eicosane paraffin wax, with phase transition temperature around 35 - 39 °C. The
disadvantage of this method is the like hood of subcooling issue to happen in
microencapsulated PCM due to greater heat transfer rate and greater contact surface.
Subcooling can be reduced by altering the encapsulation size, apply nucleating
agents or metal additives, improving the composition and shell structure, and by
varying the fill volume in the encapsulation (Khan et al., 2017). On the other hand,
Li et al., (2014) stated that form-stable PCM composites are produced by entrapment
6
of PCM into porous particles with absence of shielding coat on the surface. The short
coming is leakage of PCM will occur when the temperature is greater than the
melting temperature of PCM, thus the heat storage capacity will decrease.
In order to overcome these shortcomings, a form-stable composite PCM with
polymethyl methacrylate (PMMA) blending was developed in this work. Different
weight percentage of myristic acid and PMMA were tested to get a PCM with good
stability and latent heat storage. The ratio of myristic acid to PMMA are 20:80, 40:60,
60:40, 80:20, and 100:0. Based on reviewing some journals on usage of coating
together with blending method may yield better results in leakage prevention. It has
been decided to use nitrile butadiene rubber (NBR) and polyacrylic (PA) coating
layers to increase the physical and mechanical properties of coating to contain the
PCMs better.
1.3 Research Objectives
To overcome the problems encountered in producing form stable PCM, several
objectives are established. First of all, the objective is to produce form stable PCM
blended with PMMA and coated with NBR and PA. The next objective is to
characterize form stable PCM. Furthermore, the effect of PMMA blending and
coating on the performance of PCMs are evaluated by leakage test, thermal cyclic
and latent heat, with the aim to produce long lasting form stable PCMs. The
summaries of objectives of this study are:
1) To produce form stable PCM blended with PMMA and coated with NBR/PA.
2) To characterize the PCM blended with PMMA and coated with NBR/PA.
3) To evaluate the performance of the PCMs by leakage test, thermal cyclic and
latent heat.
7
CHAPTER 2
LITERATURE REVIEW
2.1 Classification of Phase Change Material (PCM)
In the light of phase change state, PCMs can be divided into three main categories
which are liquid-gas PCMs, solid-liquid PCMs and solid-solid PCMs. Among these
three categories, solid-liquid PCMs are the most suitable to be applied onto thermal
energy storage due to their light weight, has stable amount of latent heat, minimal
volume change compared to gas phase change materials and no considerations of
pressure involved (Cui and Riffat, 2011). The various form of solid-liquid PCMs are
inorganic PCMs, organic PCMs and eutectics (Zhou, Zhao and Tian, 2012). Several
reviews have been conducted with full classification of the most recent PCMs with
their thermos-physical properties provided in Figure 2.1 (Vadhera et al., 2018; Iten,
and Liu, 2014; Kapsalis and Karamanis, 2016).
8
Figure 2.1: Classification of PCM (Vadhera et al., 2018; Iten, and Liu, 2014;
Kapsalis and Karamanis, 2016).
2.1.1 Inorganic materials
Few examples of commercially used inorganic PCMs are alloys, eutectics, salt
hydrides, hydroxides and salts. Due to high solidification and melting range of
metallic PCMs, they are not being used widely for building application (Farid et al.,
2004).
The most famous inorganic PCMs are salt hydrates. They are applied
preferably because of their high latent heat storage, high thermal conductivity, and
tendency to lower the specific heats and compared to paraffin PCMs, salt hydrates
are more effective in volumetric density and thermal conductivity (Farid et al., 2004).
At first, the salt hydrate undergo dehydration process followed by the solid to liquid
phase change process which is analogous to freezing or melting process. Incongruent
or semi-congruent fusion often occurs with high rate of hydration. However, the
level of hydration increases if their fusion heat get higher. Salt hydrates also
demonstrate low crystallization rate, sub cooling effect, corrosive nature due to
leakage, incongruent melting and phase segregation during transition (Mehling and
Cabeza, 2008; PCM Price challenge, 2009; Hasan et al., 2016). To overcome the
shortcomings of phase segregation, the utilization of Bentonite clay and Glauber’s
9
salt, have been suggested by Wei Chiu et al., (2010). None the less, the rate of heat
exchange and crystallization will be reduced by using this combination. To achieve
the purpose to reduce the sub cooling effect, nucleating agent like Borax has been
proposed, but this involves some thickening agent to anticipate settling of the high
density Borax. Most of the other salt hydrates encounter the same problems.
Moreover, the volume change with the transition by an order of 10% is another
drawback of salt hydrates (Farid et al., 2004).
Some of the benefits of inorganic phase change materials are that they have
high and sharp phase change enthalpy, their latent heat of fusion is high, excellent in
terms of conductivity, minimal volume change during phase transition, inflammable,
low cost, compatible with plastic container and low environmental impact (Memon,
2014; Soares et al., 2013).
2.1.2 Organic materials
Paraffin wax is a type of organic material which has lower thermal conductivity than
hydrates of salt and their specific heats are high in both liquid and solid phase. This
is due to the fact that paraffin wax is made of saturated hydrocarbons. Paraffin PCMs
have no super cooling because of the fast rate of crystallization compared to salt
hydrates (Fortuniak et al., 2012).
Besides, there are plenty of non-paraffinic organic PCM classes, for instances,
esters, glycol, alcohols and unsaturated fats. Some of these PCMs have good latent
heat storage properties in building applications. Fatty acids have no super cooling
effects and the melting and freezing point of fatty acids are suitable for a solar based
applications. The general chemical form of fatty acids is CH3(CH2)2n-COOH. The
most suitable and noteworthy fatty acids for solar based applications are capric acid
(CA), lauric acid (LA), myristic acid (MA), palmitic acid (PA) and stearic acid (SA).
The main weakness of these materials is their low heat conductivity (Zhang et al.,
2014).
10
The employment of MA, PA and SA in domestic water heating system were
investigated by Hasan and Sayigh (2004). Those acids with purity of 95% have
transition temperatures in the range of 50-54⁰C, 58-62⁰C, and 65-69⁰C respectively.
When heated from 25⁰C to 80⁰C, those fatty acids show a volumetric expansion
more than 10%. The stated fatty acids release up to 10% heat of fusion after 450
thermal cycles which is approximately a year (Rathod and Banerjee, 2013). Farid et
al., (2004) have investigated the CA, LA, PA, and SA fatty acids binary mixtures and
thermal properties. These fatty acids have melting temperature of 30-65⁰C, and latent
heat of transition of 153-182 kJ/kg, which are crucial factor in designing the latent
heat thermal energy storage system. Evaluation of CA and LA mixture for low
temperature energy retention was done to determine the melting point of the mixture
of 14 ⁰C and latent heat of transition of 113-133 kJ/kg (Farid et al., 2004).
Fatty acids have some superior properties over other PCMs such as melting
congruency, good chemical stability, non-toxicity and suitable melting temperature
range for solar passive heating instruments (Teke et al., 2016). They also have high
latent heat and specific heat around 1.9-2.1 J/g⁰C and volume changes during phase
change process is low around 0.1-0.2ml/g (Rozanna et al., 2005). Besides, they do
not have any supercooling effects during phase transfer process. Fatty acids are
chemically stable, heat and colour stable, show low corrosion activity and nontoxic
due to the presence of carbonyl group (Feldman et al., 1995).
2.1.3 Polymeric PCM
Polymeric PCMs remain solid during the phase change process, hence it do not
involve any liquid or gas release. The issues of needing a sealed container are
irrelevant. Polyurethane and polybutadiene are used widely as polymeric PCM due to
their high thermal energy storage efficiency (Jamekhorshid et al., 2014).
According to Yanshan et al (2014), the usage of polyethylene glycol (PEG)
based cross-linked copolymer mixed with formaldehyde and melamine had shown
very good performance at various temperature ranges, good thermal stability, no
11
leakage, and fire proof. These features are vital to promote their practical application
as a PCM for thermal storage applications.
The study on Low Density Polyethylene (LDPE), glycerine and paraffin wax
as alternative material to be used as PCM has done by Robaidi (2013). In this blend,
small molecular weight species were dispersed in high molecular weight materials to
generate latent heat storage materials. Addition of paraffin wax; PEG and ethylene
glycol to LDPE reduces the melting temperature and increases melt flow index of the
material. The addition of glycerin to the polymer resin increases the enthalpy and
also acts as a crosslinking agent.
Pielichowska and Pielichowski (2014) examined polyethylene glycol (PEG),
an imperative semi-crystalline polymer which comprises of repeating unit of
dimethyl ether chains with hydroxyl-ended gatherings, OHCH2(CH2OCH2)nCH2OH
as PCM. It has the double feature of water dissolvability and organic solvency. The
substantial heat of fusion (117-170 kJ/kg) is corresponding to the molecular weight
and is ascribed to a high level of crystallinity. The melting point shifts from 4-70 ⁰C.
With all these features, it is appropriate to be applied in sun oriented thermal energy
storage (TES) frameworks with wide temperature range. PEG is used alone or in
blends with various compositions.
Polymeric PCMs act as suitable functional materials for latent heat thermal
energy storage due to their excellent features such as suitable melting and
crystallizing temperature range, congruent melting and solidifying behavior,
relatively high phase change enthalpy of fusion and solidification during its melting
or freezing temperature range and environmental friendly (Alkan et al., 2012;
Pielichowski and Flejtuch, 2003). Mochane and Luyt (2015) have studied on PCMs
based on polyolefins (Ethylene-vinyl acetate (EVA) and Polypropylene (PP))
blended with wax and mixed with expanded graphite (EG). The main aim of this
project is to enhance both the thermal conductivity and flame resistance of the shape-
stabilized PCMs. Sari and Karaipekli, (2007) investigated the correlation between
thermal conductivities of the PCMs with 2%, 4%, 7%, and 10% EG in paraffin wax
and increase of thermal conductivity of paraffin (0.22 W/m K) to 81.2%, 136.3%,
209.1%, and 272.7%.
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2.2 Differentiation of Various Types of PCMs
The advantages and disadvantages of various PCMs are listed in Table 2.1.
Table 2.1: Comparison of Different Types of PCMs (Cui and Riffat, 2011;
Kenfack and Bauer, 2014).
Classification Advantages Disadvantages
Organic PCMs 1. High heat of fusion
2. Chemically stable
3. Recyclable
4. Great compatibility with other
materials
5. No supercooling
6. Availability in a large temperature
range
1. Relatively large
volume change
2. Flammability
3. Low thermal
conductivity
Inorganic PCMs 1. High thermal conductivity
2. High heat of fusion
3. Low change in volume
4. Availability in low cost
1. Corrosion
2. Supercooling
Eutectics 1. High volumetric thermal storage
density
2. Sharp melting temperature
Lack of currently
available data of
thermos-physical
properties
2.3 Criteria of Selecting PCMs
Fatty acids, paraffin, eutectic mixtures and salt hydrates are the commonly used
PCMs as latent heat storage material for building and solar applications as a result of
their melting temperature (Madessa, 2014; Rozanna et al., 2015). Figure 2.2 indicates
the melting temperature and enthalpy of currently applicable PCMs (Diekmann,
2006).
13
Figure 2.2: Melting Temperature and Phase Change Enthalpy of Currently
Applicable PCMs (Diekmann, 2006).
Features such as kinetic, thermodynamics, chemical and economic properties
need to be taken into account in order to select the appropriate material in latent heat
storage system which is stated in Table 2.2. Figure 2.3 shows the schematic
representation of a phase change process.
Table 2.2: PCM Selection Criteria (Sharma and Kar, 2015; Sharma et al., 2009;
Cabeza et al., 2011).
Properties Criteria
Thermodynamics 1. High thermal conductivity
2. High latent heat of fusion per unit volume
3. High specific heat and high density
4. Desired range of melting temperature
5. Small volume changes during phase transformation and small
vapour pressure at operating temperatures to reduce
containment problems
6. Congruent melting
14
Kinetic 1. High nucleation rate to avoid super cooling
2. High rate of crystal growth to meet demands of heat recovery
from the storage system
Chemical 1. Chemical stability
2. No corrosiveness
3. No degradation after numerous number of freezing/melting
cycle
4. No toxic, no flammable and no explosive material
5. Completely reversible freezing/melting cycle
Economic 1. Large scale availabilities
2. Cost effective
Figure 2.3: Schematic Representation of a Phase Change Process (Mochane, 2011).
15
2.4 Solar Renewable Energy
Renewable energy is originated from the nature, example, sunlight, wind, geothermal
heat, and rain, which they are naturally replenish. The technologies that are invented
to harvest the renewable energy are hydroelectric generation, solar power, wind
power, biomass and biofuels for transportation.
In recent years, the terms ―renewable energy‖ and ―alternative energy‖
become more significant because the global energy demand surge indicates faster
rate of depletion of conventional energy resources. Renewable energy can be defined
as energy generated from natural processes that are endlessly replenished. This
energy impossible to use up and is continuously renewed. On the other hand,
alternative energy is defined as alternative energy source compared to fossil fuels. It
usually used to categorize energies that are unconventional and have minimal
environmental effect. As comparison, alternative energy may not have significant
environmental impact, whereas renewable energy may or may not harm the
environment (Ciolkosz, 2017).
The sun is the major source of renewable energy nowadays. Researchers are
finding ways to make use of solar radiation by transforming it into valuable heat or
electrical energy. The common types of solar energy systems are photovoltaics, and
thermal systems (Kabir, 2018). Photovoltaic produces energy by conversion of solar
radiation using silicon panels, which produces electricity when light energy is
absorbed. Thermal systems is used to keep heat from the sun to be used for various
functions, by application of active systems, such as solar hot water heaters with
pump, and passive systems, for example auto temperature regulating building that
retain and utilizes solar energy. Glass house is suitable for passive system, where it
can gather solar heat on bright days during winter and use it to warm up the house at
night (Gupta and Tiwari, 2016).
The core benefits of solar energy are it is renewable, clean energy, and
independent operation or integration with conventional energy sources. The key
drawbacks are it is more costly than conventional energy, and the inconsistency of
availability of solar radiation daily and in seasons (Mohtasham, 2015).
16
2.5 Thermal Energy Storage
Thermal energy storage (TES) is a process where a medium stores heat energy when
the heat is available, and discharges it when the heat is scarce. This application is
useful in solar facilities. Heat can be kept in constituents in the form of sensible,
latent and thermo-chemical where alteration of temperature, phase or chemical
composition occurs. Sensible heat storage has been extensively studied but it has
drawbacks in its application. According to Alva et al., (2018), the main disadvantage
of sensible TES materials is the stability of temperature when releasing energy.
When the thermal discharge is ongoing, the outlet temperature of the heat transfer
fluid decrease with time. This is also due to sensible TES requires a large volume of
100 L per day to 1000 L per day of storage tank needed. As for latent heat storage,
the drawback is poor thermal conductivity. The thermal conductivity of salt PCMs
are between 0.5 W/m.K and 1 W/m.K, whereas organic PCMs are between 0.1
W/m.K and 0.3 W/m.K. The utilization of phase change materials (PCMs) allow
storage of latent heat, in which the phase switch from solid to liquid to collect latent
heat. This enables a compact, effective and low cost operating system. For thermo-
chemical heat storage (TCS) method, it is at the infant period of research although it
caught the attention of the society for its long term energy storage application (Zhang
et al., 2016).
TES system is able to decrease the levelized cost of electricity (LCOE) of
renewable energy systems, where the storage medium temperature is the parameter
that influences the most. Sensible TES is practically used at large scale (Badenhorst,
2018). Inorganic PCMs latent heat storage is normally applied in high temperature
applications. PCM and TCS storage media require encapsulation of suitable materials,
possible containment constituents are studied.
The sensible TES used hot water buffer storage tank of large volume, which
functions to save energy in water heater by utilizing on solar energy and in co-
generation energy supply systems. Hauer, (2013) revealed that water tank storage is
an economical selection, due to the increase of effectiveness by ideal water
stratification inside the tank and decent thermal insulation, such as an evacuated
super-insulation with a thermal loss of λ = 0.01 W/mK at 90°C and 0.1 mbar
17
improved system integration. This technology is suitable to apply in countries with
different seasons to provide heat domestically. The district system and heating
installations are connected to the living area to avoid temperature drop at heat
exchangers and escalates the temperature distribution. The heat exchanger has hot
stream of 60°C with a cold stream of 30°C. The seasonal storage has a broad
operating temperature spectrum between 10-90°C (Pawar, 2015).
Next, the underground TES is a long term seasonal storage because of its
great thermal inertia. It exists in several forms, such as borehole, aquifer, cavern and
pit. The application of underground TES is subject to the geological circumstances. It
is an active energy storage system. Underground TES is able to provide 13-15% of
the overall space heating demand in Sweden, but the possible damages to the
environment are leakage of thermal energy carriers, biological and chemical harm on
the water source, ecological impact and contamination (Lim, 2013).
Subsequently, the Phase Change Material (PCM) based TES has high energy
storage capacities and target oriented discharging temperatures (Sarbu and
Sebarchievici, 2018). PCMs are suitable for short-term and long term energy storage.
PCMs can capture extra energy at the peak of sun irradiation, and kept for use during
absence of solar irradiation. Application of PCM in the building wall can store heat
during morning and discharges heat to the room at night, which improves the thermal
comfort for a low temperature region (Guo and Pang, 2016). The trend of PCM cost
is expected to decline PCM development matures, nevertheless PCMs that are not
used up throughout the operation will not affect the heat capacity even it faced
extended charging-discharging cycle (Wani and Loharkar, 2017).
Thermo-chemical storage (TCS) has high energy density and huge storage
capacity. It applies the concept of reversible reactions that require discharge and
charging of energy for TES. The example of TCS is adsorption for heat storage and
moisture control. For instance, adsorption of water vapour to micro-porous
crystalline alumino-silicates silica-gel or zeolites, and lithium-chloride open sorption
methods to decrease water temperature and utilizes zeolites to adjust humidity
(Hauer, 2013). The different TES technologies: sensible heat; latent heat; and
thermo-chemical shown in Figure 2.4.
18
Figure 2.4: The storage capacity of various composites (Sarbu and Sebarchievici,
2018).
2.6 Form stable PCM
A form-stable PCM is a composite structure comprises of solid-liquid PCMs which
act as latent heat thermal storage material and encapsulated with a supporting
material (Silakhori et al, 2015). During the event of increase in surrounding
temperature where the PCM undergoes transformation from solid state to liquid state,
the inorganic or polymer coating will act as supporting material to inhibit leakage or
changes in shape, Besides that, a good form-stable PCM must have a lesser amount
of leakage whereby, the mass before and after the thermal cycle process of the form-
stable PCM must not have great differences. The efficiency of the thermal storage
highly depends on the total mass leakage percentage, as the latent heat of the form-
stable PCM can be verified from the total mass leakage percentage. Therefore, the
total leakage is considered to be the most significant feature to decide the type of the
coating and appropriate coating technique (Huang et al., 2013).
19
2.6.1 Encapsulation Method
Fatty acids such as stearic acid (SA), palmitic acid (PA), myristic acid (MA), and
lauric acid (LA) are promising PCMs for latent heat thermal energy storage (LHTES)
applications but the major drawback of utilizing fatty acid is their leakage which
causes corrosion in LHTES applications (Kosny, 2015; Sari and Kaygusuz, 2003;
Murali et al., 2015). The use of fatty acids as form-stable PCM will increase their
feasibilities in practical LHTES applications due to reduced corrosion in the energy
storage system.
Alkan and Sari, (2008) had prepared new kinds of form-stable PCMs of fatty
acid/polymethyl methacrylate (PMMA) for LHTES systems by encapsulation of the
fatty acids (SA, PA, MA, and LA) in PMMA. It was concluded that the form-stable
fatty acid/PMMA can be considered as candidate PCMs for LHTES applications
such as under floor space heating of buildings and solar energy storage using
wallboard and plasterboard impregnated with form-stable PCM due to having good
thermal properties which is shown in Table 2.3. The compatibility of fatty acids with
the Eudragit S (a brand name for PMMA) is proved by microscopic investigation and
infrared Fourier Transform Infrared Spectroscopy (FTIR). The thermal properties
measured by Differential Scanning Calorimetry (DSC) method of the form stable
PCMs are as shown in Table 2.3. The maximum mass percentage of all fatty acids in
the form-stable PCMs is 70%, and no leakage of fatty acid is observed at the
temperature range of 50—70⁰C from 0 to 1000 heating cycles (Alkan , 2008; Kant,
Shukla and Sharma, 2016; Sari et al., 2006). Eudragit is the brand name for a diverse
range of polymethacrylate-based copolymers, which includes anionic, cationic, and
neutral copolymers based on methacrylic acid and methacrylic/acrylic esters or their
derivatives (Thakral et al., 2012).
20
Table 2.3: Thermal Properties of Fatty Acids, Eudragit S/Fatty Acid Blends
(30/70 wt%) as Form-stable PCMs (Alkan, 2008).
Phase Change
Material
Melting
point (oC)
Heat of fusion
(J/g)
Freezing
point (oC)
Heat of freezing
(J/g)
Myristic acid
(MA)
51.80 198.14 51.4 181.83
Palmitic acid
(PA)
60.42 233.24 59.88 237.11
Stearic acid
(SA)
66.82 258.98 66.36 262.32
Eudragit
S/MA
51.82 132.47 50.47 133.01
Eudragit S/PA 59.60 170.64 59.26 170.92
Eudragit S/SA 66.70 184.22 65.43 184.88
2.6.2 Shape-stabilized Encapsulation Method
In order to prepare novel shape-stabilized PCMs, Sari and Kaygusuz (2003) have
investigated the compositions of such fatty acids as LA, MA, PA and SA as PCM
and poly(vinyl chloride) (PVC) as supporting material. Table 2.4 shows that the
maximum composition ratio of all fatty acids in the shape stabilized PCMs was 50 wt%
in which no leakage of fatty acid was observed over their melting temperatures for
several heating cycles. The miscibility of fatty acids with the PVC and the interaction
between the blend components which are responsible for the miscibility has been
proved by microscopic investigation and Infrared (IR) spectroscopy. The melting
temperature and the latent heat of fusion of the shape stabilized PCMs are measured
by DSC analysis method. The melting temperatures and latent heats of the shape-
stabilized PVC/LA, PVC/MA, PVC/PA and PVC/SA (50/50 wt%) PCMs
are determined as 38.8⁰C, 49.2⁰C, 54.4⁰C and 64.7⁰C, and 97.8 J/g, 103.2 J/g, 120.3
J/g and 129.3 J/g, respectively. The results indicate that the PVC/fatty acids blends as
shape-stabilized PCMs have great potential for passive solar thermal energy
21
applications in terms of their reasonable thermal properties and advantages of easy
preparation with desirable dimensions and direct application in LHTES applications
(Sari and Kaygusuz, 2003).
Table 2.4: Thermal Properties of Some Fatty Acids and Form-stable
Compositions (Sari and Kaygusuz, 2003).
Phase Change Material Melting point (oC) Heat of fusion (J/g)
Lauric acid (LA) 42.6 183.2
Myristic acid (MA) 52.8 198.4
Palmitic acid (PA) 62.4 224.8
Stearic acid (SA) 69.8 238.6
PVC: LA (50 wt.%: 50 wt.%) 38.8 91.6
PVC: MA (50 wt.%: 50 wt.%) 49.2 99.2
PVC: PA (50 wt.%: 50 wt.%) 54.4 112.4
PVC: SA (50 wt.%: 50 wt.%) 64.7 119.3
Kaygusuz et al., (2008) prepared and investigated novel shape PCMs by
introducing fatty acids; SA, PA and MA in an acrylic resin (Eudragit E) as
supporting material. The blends of Eudragit E with fatty acids were prepared by the
solution casting method. Eudragit E and one of the fatty acids in chloroform were
dissolved in separate beakers, and fatty acid solution was added to Eudragit E
solution dropwise. Then, the blend was casted at room temperature for 15 days. The
blends were prepared at 40, 50, 60, 70, and 80% w/w fatty acid compositions to
obtain the maximum encapsulation ratio without leakage of the fatty acid from the
blends when the blend was heated above the melting points of MA, PA, and SA. The
maximum percentage of all fatty acids in the shape-stabilized PCMs was found to be
70 wt.% in which no fatty acid leakage was observed as the blends were heated
above the melting points of the fatty acids. The melting and freezing temperatures
and latent heats of the shape-stabilized PCMs were measured by the DSC method
and the results were presented in Table 2.5 (Kaygusuz et al., 2008).
22
Table 2.5: Thermal Properties of Fatty Acids and 30% Eudragit E/70%
Fatty Acid (w/w) Blends as Form-stable PCM (Kaygusuz et al., 2008).
Phase Change
Material
Melting point
(oC)
Heat of fusion
(J/g)
Freezing point
(oC)
Heat of freezing
(J/g)
Myristic acid
(MA)
51.80 178.13 51.74 181.63
Palmitic acid
(PA)
60.42 233.24 59.88 237.11
Stearic acid
(SA)
66.82 258.98 66.36 263.32
30% Eudragit
E/ 70% MA
51.44 135.62 51.11 134.02
30% Eudragit
E/ 70% PA
58.74 172.43 58.22 172.86
30% Eudragit
E/ 70% SA
65.41 185.64 65.08 185.83
PCMs require special LHTES devices in different shapes or elements
such as shell and tube PCM heat exchanger or a lot of containers to encapsulate
them since they change from solid to liquid during the energy storage period
(Kuboth et al., 2017). Although the use of such materials solved the problem of
PCM leakage during solid-liquid phase change, it increases the heat resistance
and the cost of the LHTES system. However, these problems can be overcome
using form stable PCM which can be prepared by encapsulation of PCM into a
polymeric structure (Agarwal and Sarviya, 2016). Thus, the main advantages of
using shape stabilized encapsulated PCMs are no leakage of melted PCM during
phase transition process, no additional storage container for encapsulation, and
thus reducing the cost of LHTES system, eliminating the thermal resistance
caused by capsule shell, reducing the reactivity of PCM with the outside
environment, controlling the volume change of the PCMs during the solid-liquid
phase change and ease of preparing it in desired dimension (Khudhair and Farid,
2004; Farid et al., 2004).
23
Xing et al, (2006) had analyzed the thermal and hydrophilic-lipophilic
properties of form-stable high density polyethylene (HDPE)/paraffin PCM
encapsulated in silica gel. The authors proposed this PCM for use in the building
field because of its good thermal properties and better hydrophilicity and fire-
proofing properties.
On the other hand, PMMA is a group of commercially available acrylic resin
and is fully polymerized methyl methacrylate. It has high impact strength and
chemical resistance in addition to optical clarity. These properties make it a
potential encapsulation material for PCMs (Ramrakhiani, Parashar and Datt, 2005).
2.6.3 Microencapsulation Method
Giro-Paloma et al (2016) have researched about the different types of PCM, the
different shell materials used, the methods of encapsulation, the most used
techniques for their characterization, and the main applications
of microencapsulated PCM (MP CM). Both natural and synthetic polymers can be
used as shell material depending on the requirements and considerations of the
PCM applications. The authors also stated that the combination of core/shell is
one of the most important parameters in microencapsulation. The morphology of
the microcapsules in MPCM can be very diverse (irregular shape, simple, multi-
wall, multi-core, or matrix particle), and there are four types of MPCM
(mononuclear, poly nuclear, matrix encapsulation, and multi-film).
The most common microencapsulate shell materials for PCM
reinforcement are melamine and urea formaldehydes, polyurethane, HDPE,
styrene butadiene styrene copolymer and PMMA. PMMA is a transparent
thermoplastic which is easily available. It has modest
properties, simple processing, good impact strength, relatively high chemical
resistance and cheap. Thus, PMMA is a promising polymer as shell material
containing PCM for TES applications (Wang et al., 2011). The authors also
created a sequence of PMMA microcapsules containing capric acid/lauric
24
acid, capric acid/myristic acid, capric acid/stearic acid and lauric
acid/myristic acid eutectics work as the heat-absorbing materials using the
technique of self-polymerization (Wang and Meng, 2010).
2.6.4 Crosslinked Polymer Coating Method
Mochane (2011) had investigated the morphology and properties of polypropylene
(PP) containing crosslinked polystyrene (PS) encapsulated paraffin wax. The
research shows that the thermal properties such as melting points (Tm), onset
temperatures of melting (Tom), and melting enthalpies (∆H) were strongly affected
by the use of crosslinking agents (Mochane, 2011).
Oliveira and Costa, (2010) focused on optimization of process conditions,
characterization and mechanical properties of silane crosslinked HDPE. The
crosslinking process resulted in the formation of PEX (crosslinked high density
polyethylene) from HDPE. In addition, the crosslinking can extend the use of PE by
raising its operating limit to high temperatures such as 2000C and improving its
mechanical properties, due to formation of three dimension chain network structure.
It was stated that this structure ensures higher tensile strength and improves hardness
and chemical resistance, as well as dimensional and thermal stability of the polymer
(Oliveira and Costa, 2010).
Zhang et al., (2006) developed form-stable PCMs for building applications.
Paraffin with the melting point of 200C and 60
0C was chosen as PCM. As for
supporting material, HDPE/ styrene butadiene styrene copolymer (SBS)/graphite
composite were used. In the latter, each component played a different role: powder-
like HDPE endowed PCM rigidity; SBS absorbed the paraffin strongly while it was
in liquid condition and graphite acted as a thermal conductive component. The
paraffin and the supporting material were mixed evenly and coextruded at about
140⁰C in a two-screw extruder. The shape of the product-plate, rod, pellet, etc.
varied according to the different application manner. In order to prevent the possible
leakage of paraffin, the surface of composite material was grafted and crosslinked.
25
Despite of paraffin’s condition (liquid or solid), the polymer network stands still to
support the shape (Zhang et al., 2006).
2.7 Coating
The purpose of coating is to cover the surface of a product or substance. The most
general method of coating using polymers is known as conformal coating. Conformal
coating enhance in operational integrity of a product, safeguard the product from heat,
moisture, corrosion, contamination and lengthen the product life (Flitney, 2009).
Leakage prevention of fatty acid and corrosion prevention of the internal system of
the solar water heater are the key reasons to coat PCM (Kong et al., 2016). Silicon
coating, acrylic coating, epoxy coating, parylene coating and polyurethane coating
are the five main categories of conformal coating. Selection of coating method is
fully dependent on the operational requirements and product applications. Acrylic
coating is chosen because of its chemical resistant property, cost effective, high
melting point and vast availability (Inc., 2017).
2.7.1 Coating Application Methods
There are six coating methods for acrylic coating in general, which are automated
spraying, manual spraying, selective coating, brushing, vapour deposition and
dipping.
In automated spraying, a modified spray system that moves the object on a
conveyor under a responding spray head used to apply coating. Coating application is
normally trailed by an oven that quickens the curing so it can be done rapidly
(Koleske, 2012).
Secondly, for manual spray coating, coating can be applied by an aerosol can
or hand held spray gun. It is largely utilized for low volume production when costly
26
hardware is not accessible. This technique can be tedious on the grounds that regions
not requiring coating should be masked. It is likewise operator dependent, so
variations are common (Aziz and Ismail, 2015).
Subsequently, in selective coating method, an automated procedure that
utilizes programmable mechanical spray nozzles is used to apply the coating to each
particular part of the object. Usually this process is chosen for large production
(Barriga et al., 2014).
Whereas in brushing, it is a basic application method utilized fundamentally
in repair. The conformal covering is applied with a brush to particular zones on the
object. It is cost effective, but labour intensive and highly variable technique, and it
is most appropriate for little production runs (Wang et al., 2003).
2.7.2 Coating of Phase Change Material
A recent study of coating of melamine formaldehyde PCM microcapsules with silver
layer was done by Cao et al (2015). This coated material is dispersed into
polyalphaolefins (PAOs) to produce a high thermal conductivity fluid. Xu et al (2014)
had carried out a study on coating PCM microcapsules with silver in an ammonia
aqueous solution. The thermal conductivity of PCM microcapsules was increased
from 0.152 to only 0.251W/m.K. Furthermore, the latent heat reduced from 42.6 to
32 J/g. It is obvious that there is a need to enhance the thermal conductivity of PCM
microcapsules further without reducing its latent heat. Besides, it has been reported
that silver coating cannot be achieved successfully without activation and
sensitization (Gao and Zhan, 2009).
Coating of PCM microcapsules with a metal using dopamine surface
activation followed by electrolyte plating was studied by Al-Shannaq et al (2016).
This method is done to overcome the low thermal conductivity of the microcapsules
shell. It was stated that the silver coating was used to enhance the thermal
conductivity of the PCM microcapsules. The apparent thermal conductivity was
27
decreased with decreasing the size of the microcapsules. The measured apparent
thermal conductivity of the PCM microcapsules increased significantly by metal
coating from 0.189 to 2.41 W/m K.
A novel composite for heat sink application was done by Stappers et al
(2005), where rapid heat dissipation application were prepared by integration of
PCM in electrodeposited of copper metals. In this research, copper coating with 35
vol% of integrated PCM have heat absorption capacity of 10.9 J/g. For other PCMs
such as hydrated salts, microencapsulation might be used to prevent contact between
the PCM and the metal in composite coatings, because this would lead to corrosion
of the metal coating. This coating method of microencapsulated PCM is always
feasible due to the difficulties of producing pure PCM particles or due to chemical
incompatibilities between the PCM particles and the metal coating.
According to Kee et al., (2017), solution blending nanocomposites displayed
improved overall properties than in situ polymerized nanocomposites because of the
better dispersion of reduced graphene oxide (RGO) in solution blending.
RGO/polymethyl methacrylate (PMMA) nanocomposites with 0.5 wt% loading
increased the Young’s modulus from 330.47 MPa to 463.02 MPa and tensile strength
from 35.89 MPa to 36.64 MPa, but decreased the elongation at break from 15.10% to
10.02%. This is due to the good dispersion of RGO in the nanocomposites.
A novel composite PCM particle with a coating film, through paraffin
integrated with expanded perlite (EP) by vacuum adsorption to prevent leakage
problem. It is stated that the best proportion of paraffin in PCM were determined to
be 47.5 wt% because this proportion does not have any leakages when the PCM
melts (Kong et al., 2016). Moreover, the phase change temperature and latent heat of
coated PCM were measured to be 21.6 ⁰C and 56.3 J/g. The latent heat released by
the pure paraffin wax is 171.4 J/g (Sun et al., 2017). The latent heat released by the
coated composite PCM is very low compared to the latent heat of pure paraffin wax.
Kee et al., (2017) have studied the use of two coatings, which are polyacrylic
coating and conformal coating to overcome the leakage problem of composite PCM
comprising of polymethyl methacrylsate (PMMA) and myristic acid (MA) in
28
different weight percentage. There are no leakages occurred to the composite PCMs
with coatings compared to those without coating under the same ratio of PMMA/MA.
The two coatings improved the thermal stability, thermal reliability of composite
PCM after 1000 times thermal cycles, as well as the latent heat only decreased 0.16%
and 1.02% for the PCMs coated with conformal coating and polyacrylic coating
correspondingly.
2.8 Stability of Non-paraffin Organic PCMs
The most common and abundant non-paraffin organic PCMs are fatty acids. They are
being commercially used because of their proper phase change temperature and high
range of heat of fusion. They are easily available because they can be derived from
various sources of vegetable and animal oils. Thus, the supply is continuous unlike
the shortage of other fuel sources (Chuah et al., 2015). The thermal stability and
thermal cycle tests of various types of fatty acids had been investigated by many
researchers.
Thermal reliability test on a mixture of industrial grade MA, LA, PA and SA
were carried out by Sari, (2003). The melting points of those fatty acids are 53⁰C,
61.31⁰C, 54.7⁰C, and 42.46⁰C respectively. The fatty acids were subjected to 1200
melt/freeze cycles to determine the latent heat thermal energy storage (LHTES)
characteristics. It was reported that the examined fatty acids had shown convincingly
good thermal stability in terms of melting temperature and latent heat. The melting
temperature of the mixture was nearly the same in the range of 40.78-42⁰C and the
latent heat also had shown nearly the same trend in the range of 174.47-175.34 J/g
from 0 number of thermal cycle to 1200 times.
Furthermore, study of thermal stabilities of industrial grade MA, PA and SA
with 95% purity were conducted by Sari and Kaygusuz (2003). Differential Scanning
Calorimetry (DSC) was used to evaluate the phase transition temperature and latent
heat storage capacity of those PCMs by running continuous thermal cycles of 40, 410,
700 and 910 times. The findings showed that appropriate fatty acid PCMs which can
29
be used for long term basis in solar based systems are MA and PA because of their
low melting and freezing temperature which are 52.5⁰C and 61.2⁰C respectively and
high latent heat of fusion around 182-200 J/g (Sari, 2003; Sari and Kaygusuz, 2001;
Sari and Kaygusuz, 2002). Furthermore, the corrosion resistant of some containment
materials such as stainless steel (SS304L), carbon steel (Steel C20), aluminium (Al)
and copper (Cu) towards fatty acids over a long period of time in contact was also
tested. In this study, it was revealed that stainless steel (SS304L) with chromium
oxide (Cr2O) surface layer and aluminium (Al) metals with aluminium oxide (Al2O3)
surface layers have good resistance towards fatty acids.
2.9 Challenges to Produce Good Coating
The advantages of a good coating are adequate surface area for heat transfer, capsule
walls protect against destructive environmental reactions, and ease of handling. The
challenges to fabricate a rigid coating are high chemical corrosion when in contact
with metal shell, and expand in volume when transition of phase from solid to liquid
occur (Nomura et al., 2015).
Zhang et al., (2014) suggested to use chromium periodic-barrel electroplate
and nickel barrel-plating to encapsulate chromium-nickel (Cr-Ni) bi-layer on Cu-
based PCM. The outcome displayed that the capsule is able to withstand thermal
cycles without leakage, and demonstrated stability between the core and Cr-Ni shell.
The disadvantage is the shell has large thickness and storage density (50 J/g) was as
low as 20 wt% of its pure form.
Mathur et al., (2013) stated that leaving a void in the shell to permit volume
expansion of PCM. The sodium nitrate (NaNO3) PCM pill produced with voids by
integrating a sacrificial polymer at the middle layer between the PCM capsules and
the shell.
30
Thus, in order to get rid of the leakage problem, an elastic coating with
sufficient tensile strength and adequate thickness that the latent heat will not be much
affected will be studied in this work.
2.10 Applications of PCMs
An effective usage of PCMs does not only concentrate on high energy storage.
However, it is very crucial in charging and discharging the energy storage with a
thermal power which is pertinent for desired application. The low thermal
conductivity of the materials used as PCMs is one of the main disadvantages of latent
thermal energy storage. This disadvantage restricts the power which can be extracted
from thermal energy storage. The ability of PCM to absorb and release energy during
the essential time makes it to be useful in many fields. Currently, the researches
about those materials keep increasing due to their benefits in energy systems (Giro-
Paloma et al., 2016).
Over the years PCMs has been used in many industries such as packaging,
food, buildings, textiles, medical therapies and many more. Ever since 1980, PCM
have been deliberated in TES. Climatization is considered as one of those
applications for PCM (Oro et al., 2012). According to Gil et al., (2014) PCMs has
large potential usage in solar cooling. Oro et al (2013) carried out research on the
effect of PCM introduction in freezer states that it enhances the quality of ice cream.
Those types of materials can be included in the container drinks to store energy.
Besides, the energy was released when the systems require energy. The research
conducted by Oro et al., (2013) focuses on thermal performance of PCMs and the
compatibility of PCM with metallic materials used to store food stuffs.
The effect of temperature storage conditions using PCM has been studied for
a number of food products such as vegetables (Cruz et al., 2009), frozen dough
(Phimolsiripol et al., 2008), ice cream, and meat (Duun et al., 2008; Yanniotis et al.,
2008). It has been stated that it is important to maintain stable temperatures in the
storage and transportation of frozen foods. This is to maintain the quality and
31
lifetime of the product. In general, frozen foods must be kept below 18⁰C. This
temperature should be maintained right in freezers and it can be achieved with the
aid of PCM integrated refrigerator systems. Nevertheless, during storage and
transportation, frozen foods may undergo temperature fluctuations due to heat loads
imposed on the system. In order to overcome this issue, Gin and Farid, (2010) had
studied the effect of PCM panels placed against the internal walls of a freezer. They
stated that the comparisons of the freezer air temperature and product temperature in
a freezer containing PCM panels showed lower temperature fluctuations than in a
freezer without PCM.
PCMs had also been used in automobiles. Diesel is used as a source of energy
due to the extremely costly operation of refrigerated trucks. The price of diesel-
generated energy is 6 times higher compared to conservative electricity price
(Materials PCM, 2016). PCM is already used today in a latent heat battery offered by
BMW as optional equipment in its 5 series. When the motor runs at the operational
temperature, the storage material will be connected to the radiator and keeps
excessive heat. To achieve interior driving comfort, the heat which is available at the
next cold start will heat up the motor rapidly. The latent heat battery has an
exceptional insulation where it could preserve the energy at 200⁰C for 2 days.
Moreover, PCM can also be utilized in tail pipes like exhaust of vehicles as an
addition to this application. Excessive hydrocarbon emission during vehicle start-up
will be reduced by keeping the catalytic converter at its design temperature
(Pielichowski and Flejtuch, 2003).
During the course of the day, the atmosphere in a room is found comfortable
by its occupants if it differs a little compared to the environment outside the room.
Due to this factor, the thick walls in homes are very comfortable in all types of
weathers. It is suggested to implement materials made up of PCM as wall which is
able to mimic the purpose of thick walls from traditional building materials. This will
ensure the realization of comfort with less massive constructions (Zalba et al., 2003).
PCMs are also used in greenhouses. In order for plants cultivate in a greenhouse to
flourish, it is essential to keep the temperatures in the greenhouse in small range.
Many of the greenhouses need air-conditioning or heating because of large
temperature swings in daytime and night time temperatures. The dependence on air-
32
conditioning or heating is reduced or removed when the PCM is fixed in floor of
such greenhouses (Bentz and Turpin, 2007).
33
CHAPTER 3
METHODOLOGY
3.1 Materials
Polymethyl methacrylate, PMMA (120, 000 molecular weight) was purchased from
Sigma Aldrich, Subang Jaya, Malaysia. Myristic acid (purity ≥ 98%), and chloroform
(stabilized with 0.6-1.0% ethanol) were purchased from R&M Chemicals, Semenyih,
Malaysia. Nitrile butadiene rubber (NBR) coating (Total solid content of 44.70%)
was purchased from Synthomer, Kluang, Malaysia. Polyacrylic (PA) coating (Total
solid content of 36.35%) was provided by Dr. Chee Swee Yong from Faculty of
Science, UTAR.
3.1.1 Experiment Flow Chart
The experimental flow chart for this research work is shown in Figure 3.1.
34
Figure 3.1: Overall Flow of Methodology.
3.2 Preparation of PCM
3.2.1 Preparation of PCM Blending
The phase change material (PCM) was prepared by solution blending method.
PMMA was dissolved in a fixed amount of chloroform with a ratio of 100ml of
chloroform to 1g of PMMA powder in a beaker. The solution was stirred using the
aid of hot plate magnetic stirrer (Model: Stuart SB 162-3) at room temperature about
25⁰C until all the PMMA powder are completely dissolved. Myristic acid was
dissolved in a fixed amount of chloroform with a ratio of 5ml of chloroform to 1g of
myristic acid powder in a beaker. The solution was stirred using the aid of hot plate
magnetic stirrer (Model: Stuart SB 162-3) at room temperature about 25⁰C until all
the myristic acid powder are completely dissolved, shown in Figure 3.2. Then, the
PMMA solution is poured into a separating funnel fixed on a retort stand. The
Preparation of PCM Blending with
PMMA
Pelletizing of PCM
Coating of Polyacrylic and Nitrile Butadiene Rubber on PCM through Dip Coating Method
Characterization and Performance
Fourier Transform Infrared
Spectroscopy
(FTIR-ATR)
Differential Scanning
Calorimetry (DSC)
Tensile Test Leakage Test
35
myristic acid solution is poured into a Teflon folded container and placed on the hot
plate magnetic stirrer. The hot plate magnetic stirrer speed is set at 4, and at the same
time the PMMA solution in the separating funnel is dripped dropwise to ensure even
mixing, shown in Figure 3.3. After all the PMMA in the funnel is consumed, the
mixture was continuously stirred for 30 minutes to ensure well mixing. The surface
of the container inside the fumehood was completely covered using aluminum foil
sheets to prevent contamination, shown in Figure 3.4. Formulations of PCMs are
shown in Table 3.1.
Table 3.1 Formulation of PCM samples.
Sample Percentage (%) Coating
Myristic acid PMMA
PCM20 20 80 NBR layered with PA
PCM40 40 60
PCM60 60 40
PCM80 80 20
PCM100 100 0
Figure 3.2: The process of stirring the PMMA and MA in chloroform.
36
Figure 3.3: Setup of the mixing process.
Figure 3.4: The drying process of the mixture solution.
Figure 3.5: The formation of phase change material blending composition.
37
The controlled variables of this process are the stirring speed, volume of
chloroform, temperature of the solution, and stirring time. All these factors must be
taken into consideration and fixed in a minimum amount while preparing the solution
to prevent under or over mixing. In this study, the volume of chloroform has fixed to
be 100ml for 1g of PMMA, stirring speed of 4, process temperature at 25⁰C, 30
minutes of stirring time and the surface of beaker was closed with aluminium foil.
The volume of chloroform has fixed to be 5ml for 1g of myristic acid, stirring speed
of 4, process temperature at 25⁰C, 30 minutes of stirring time and the surface of
beaker was closed with aluminium foil.
The duration of drying is 24 hours, until it completely dried to form powder
as shown in Figure 3.5. The dried sample is scrap out of the Teflon container and
crush into smaller size using spatula to form the powder. The PMMA solution was
blended with different weight percentage of myristic acid solution (20%, 40%, 60%
and 80%) and dissolved completely in the chloroform solution.
3.2.2 Pelletizing of PCM
The PCM was originally in powder form. In order to cast it into a disc shape, the
Fourier Transform Infrared Spectroscopy (FTIR) presser was used. At first, the dry
powder of PCM was measured using a weighing machine, with the model number
Sartorius AX224. The weight range was from 0.2750 to 0.2800 g for each sample.
Then, parts of the presser were cleaned with absolute ethanol to remove impurities to
reduce contamination of PCM. After that, the dry powder sample was poured into the
die and pressed to 4000 kPa. When the pressure dropped to 3800 kPa, the die was
removed from the presser. The pellet was removed from the die, weighed and
recorded. The FTIR presser and die are shown in Figure 3.6 and 3.7.
38
Figure 3.6: FTIR presser.
Figure 3.7: The die.
3.3 Coating of Polyacrylic and Nitrile Butadiene Rubber on PCM through Dip
Coating Method
The PCMs were coated using dip coating method. Nitrile butadiene rubber (NBR)
coating solution has total solid content of 44.70%, and the total solid content of
polyacrylic (PA) coating solution is 36.35%, shown in Figure 3.8. A small pellet of
myristic acid was dipped into NBR coating solution at fixed immersion time of 5
seconds with the aid of forceps. The coated samples were placed on Teflon sheet and
dried in fumehood at room temperature with the blower switched on for 3 days. Then,
39
the dried sample was flipped to the other side and dipped into NBR coating solution
at fixed immersion time of 5 seconds with the aid of forceps, and placed on Teflon
sheet to dry in fumehood at room temperature with the blower switched on for
another 3 days. After the NBR layer was dried, the sample was dipped into PA
coating solution at fixed immersion time of 5 seconds with the aid of forceps. The
coated samples were placed on Teflon sheet and dried in fumehood at room
temperature with the blower switched on for 3 days. After the first layer of PA
coating was dried, the sample was flipped to the other side and dipped into PA
coating solution at fixed immersion time of 5 seconds with the aid of forceps, and
placed on Teflon sheet to dry in fumehood at room temperature with the blower
switched on for 3 days. These steps were done to ensure the front and back of the
pellet was well coated. The mass and the thickness of the pellet was recorded after
each of the step was done. Figure 3.9 shows the sample preparation of dip coated
PCM on Teflon sheet.
Figure 3.8: The NBR coating solution (left) and PA coating solution (right).
Figure 3.9: The PCM sample preparation on a Teflon sheet.
40
A grid was drawn in a Teflon sheet to place the form-stable PCM. This is
because the coating of NBR layer on PCM will stick on the other materials such as
glassware. In order to produce a smooth surface of polymer layer which can be taken
out easily without any damages, the polymer coated material should be placed on a
Teflon sheet. The grids on the Teflon sheet labelled with the details and weights of
coated material and sample numbers. Pure myristic acid pellets were also prepared as
reference samples.
3.4 Characterization
3.4.1 Fourier Transform Infrared Spectroscopy (FTIR-ATR)
Infrared spectra were used to study the interaction between PMMA and myristic
acids. The infrared spectra of PCMs with coating and without coating were recorded
using PerkinElmer Spectrum Two FTIR Spectrometer. Attenuated Total Reflectance
(ATR) was used for this analysis because it can analyze the composite PCMs with
coating in their natural states without grinding and destroying the coating. Analysis
was conducted in the wavelength range of 4000 to 400 cm-1
with 32 scans.
3.4.2 Differential Scanning Calorimetry (DSC)
Thermal properties of composite PCMs were measured by using Mettler Toledo
TOPEM differential scanning calorimetry (DSC). The analysis of latent heat were
carried out at the temperature of 25-120 ⁰C and 5 ⁰C/min heating rate under a
constant stream of nitrogen gas at the flow rate of 10mL/min. DSC was used to
analyze the melting point and freezing point. A PCM pellet was dissolved in 150 mL
chloroform by stirring with hot plate magnetic stirrer (Model: Stuart SB 162-3) with
41
speed of 4 for 1 hour, then the dried sample was placed in a 40µL crucible. The
weight of the sample was recorded. Then, the crucible was encapsulated with lid.
3.4.3 Leakage test
Few strips of blue litmus paper were stick on a paper. A grid was drawn as shown in
Figure 3.10 below.
Figure 3.10: The set up for leakage test.
The form stable PCM samples with different blending compositions of
PMMA (0%, 20%, 40%, 60%, and 80%) with rubber and PA coatings were placed
on the blue litmus paper. The leakage of PCM can be observed through the colour
change of litmus paper from blue to pink. The leakage test method was modified
from the selection of proper mass percentage of different form stable PCMs by
Huang et al., (2013).
42
Subsequently, samples with different weight percentage of PMMA (0%, 20%,
40%, 60%, and 80%) composition with coating and without coating are tested for 30
thermal cycles, which is 1 hour for 1 thermal cycle at temperature of 65⁰C using
drying oven (Model: Memmert UN 110). After the testing, the leakage area of PCMs
were measured and recorded by using GIMP 2 and Image J software. The dimension
of the test area is 4.6 cm × 6.6 cm.
3.4.4 Tensile Test
The PA, NBR and combination of NBR layered with PA were casted into films of
3.5g – 3.8g using Teflon mold in Figure 3.12. The samples were cut into dumbbell
shape using a dumbbell cutter, shown in Figure 3.11. After that, the samples were
measured the thickness using a digital Vernier calliper (Model: Mitutoyo CD-12‖C).
The thickness were measured at the neck and both ends of the samples, then the
average thickness were calculated from the readings recorded.
Figure 3.11: Specimen for Tensile Test.
Figure 3.12: Teflon mold.
43
Subsequently, the sample was placed on the holder, and tightens before the
tensile test started. Next, the average thickness, width of the neck, and gage length
for the sample were inserted into the software. Once finished, the tensile test was
started until the sample broke. The data such as Young’s modulus, Ultimate Tensile
Strength and Elongation at break were recorded. The settings of the tensile test are:
force is 500N, gage length is 30mm, and width is 26 mm. The model of tensile
machine is Tinius Olsen H10KS-0748 with a load cell of 500N, at a crosshead speed
of 500 mm/min.
44
CHAPTER 4
RESULTS AND DISCUSSIONS
4.1 Characterization of Form Stable PCM
4.1.1 Tensile Test
The phase change material produced in this research was coated with NBR layered
with PA coating. This formulation was chosen as coating material based on its tensile
properties.
NBR coating, PA coating and NBR layered with PA coating are casted into
thin sheet of film with weight average of 3.5-3.8 g, then cut into test samples using a
dumbbell cutter. The tensile test results are summarized in Table 4.1. From the
results, the PA samples display the highest tensile strength, followed by NBR layered
with PA coating (NBR-PA), and NBR coating. NBR shows the highest percentage of
elongation at break, followed by NBR-PA and PA.
The NBR layered with PA coating was selected as coating for the PCM. This
is because it has elasticity to withstand the volume change of PCM inside the core,
and at the same time PA can provide good tensile strength to hold the structure of the
PCM from deforming. These attributes are crucial to prevent the leakage of PCM
when exposed to heat.
45
Table 4.1 Tensile properties of polymer coating film.
Polymer
coating
Young’s modulus
(MPa)
Tensile Strength
(MPa)
Elongation at
break (%)
NBR 9.22x10-2
± 3.94x10-3
2.32 ± 2.88x10-1
1250.22 ± 10.01
PA 130.84 ± 9.88 12.19 ± 1.34 167.86 ± 11.76
NBR-PA 76.10 ± 5.43 8.21 ± 3.14x10-1
193.92 ± 2.88
4.1.2 Leakage Test
Leakage of dip coated PCM after the thermal cycle process can be seen in Figure 4.1.
Leakage of PCM without coating after the thermal cycle process can be seen in
Figure 4.2. The change of colour in litmus paper from blue to red confirms that there
is acid leakage from PCM. This is because of the volume expansion of PCM during
phase change process. The PMMA in the PCM blending acts as a stabilizer to control
the leakage problem. As the weight percentage of the PMMA increases, and at the
same time the weight percentage of myristic acid decreases, the leakage area of the
PCM is decrease for both coated and non-coated samples. The other problem is
during the dipping process, the presence of bubble in the coating solution will cause
bubble to trap on the surface of coating. In addition, the uneven surface of the Teflon
during drying process will also produce coating with uneven thickness. These factors
will be the weak points for leakage to occur. The leaked percentage influences the
latent heat of form stable PCM which determines the thermal storage effect. Thus,
the total leakage percentage is considered as a crucial factor (Huang et al., 2013).
46
Time
(h)
PCM20 PCM40 PCM60 PCM80 PCM100
0
30
Figure 4.1: Leakage of coated PCM after 30 thermal cyclic process.
Time
(h)
PCM20 PCM40 PCM60 PCM80 PCM100
0
30
Figure 4.2: Leakage of PCM without coating after 30 thermal cyclic process.
47
Table 4.2 Leakage area of non-coated PCMs.
PCM 20 40 60 80 100
Duration (hour) Area (cm2)
5 1.952 3.650 6.651 25.680 28.006
10 2.200 4.066 7.614 26.141 28.403
15 2.307 4.066 7.709 26.141 28.403
20 3.070 4.066 7.881 26.141 28.403
25 3.070 4.066 8.772 26.141 28.403
30 3.070 4.066 9.099 26.141 28.403
Leakage area
percentage (%)
10.112 13.393 29.970 86.103 93.554
Table 4.3 Leakage area of coated PCMs.
PCM 20 40 60 80 100
Duration (hour) Area (cm2)
5 0 0 0 0 0
10 0 0 0 0 2.284
15 0 0 0 0 8.141
20 0 0 0 0 9.298
25 0 0 0 0 10.104
30 0 0 0 0 12.351
Leakage area
percentage (%)
0 0 0 0 40.682
As the percentage of PMMA increases and percentage of MA decreases, the
leakage area will also possess a decreasing trend. The presence of PMMA as
stabilizer is crucial to increase the thermal stability of the PCM to prevent leakage to
occur as shown in PCM20, PCM40, PCM60 and PCM80 in Table 4.3.
48
4.1.3 Differential Scanning Calorimetry (DSC)
4.1.3.1 Latent Heat
The result obtained from DSC is to evaluate the latent heat absorbed and released by
myristic acid (PCM) with different PMMA loading. The endothermic peak indicates
the heat absorbed by the PCM while the exothermic peak indicates the heat released
by the PCMs. The peaks were obtained at the melting and freezing temperature of
myristic acid which is around 50-55⁰C. The latent heat of melting of pure myristic
acid with more than 98% purity is 221.04 J/g. Meanwhile, the latent heat of melting
of PCMs coated with NBR and PA with 0 wt%, 20 wt%, 40 wt%, 60wt%, and 80wt%
PMMA loading are 135.79 J/g, 107.56 J/g, 82.95 J/g, 53.21 J/g, and 25.79 J/g. The
latent heat of freezing of pure myristic acid is 224.14 J/g, whereas the latent heat of
freezing of PCMs coated with NBR and PA with 0 wt%, 20 wt%, 40 wt%, 60wt%,
and 80wt% PMMA loading are 134.77 J/g, 102.26 J/g, 82.85 J/g, 54.17 J/g, and
25.51 J/g. The latent heat shows a decreasing trend as the weight percentage of the
PMMA in PCMs increase and the weight percentage of MA decrease, and the lowest
latent heat is obtained from PCM20 with 80wt% PMMA. This is due to the content
of phase change material, which is myristic acid has decreased. The latent heat
released and absorbed by the PCMs during thermal phase change process is tabulated
in Table 4.4.
Table 4.4 Latent Heat Absorbed and Released by PCM.
Samples Weight Percentage of
PMMA in PCM (%)
Amount of Heat
Absorbed
(Endothermic), J/g
Amount of Heat
Released
(Exothermic), J/g
PCM20 80 25.79 25.51
PCM40 60 53.21 54.17
PCM60 40 82.95 82.85
PCM80 20 107.56 102.26
PCM100 0 135.79 134.77
Pure MA Pure MA 221.04 224.14
49
Figure 4.3 and 4.4 indicate the combination of heat absorption peaks and heat
release peaks by PCMs with different weight percentage of myristic acid (MA) and
polymethyl methacrylate (PMMA) blending.
Figure 4.3: DSC graph combination for different weight percentage of PMMA in
PCM of heat absorption peaks.
Figure 4.4: DSC graph combination for different weight percentage of PMMA in
PCM of heat release peaks.
-30
-25
-20
-15
-10
-5
0
25 32.5 40 47.5 55 62.5 70 77.5 85 92.5
mW
Tr (⁰C)
PCM20
PCM40
PCM60
PCM80
PCM100
PURE MA
0
10
20
30
40
50
60
100 87.5 75 62.5 50 37.5 25
mW
Tr (⁰C)
PCM20
PCM40
PCM60
PCM80
PCM100
PURE MA
50
The reduction of latent heat is due to replacement of MA which has high
latent heat with PMMA which has low latent heat. Moreover, the thickness of the
coating layer also influences the heat transfer rate of the PCM. The latent heat will
reduce if the thickness of the coating layer increases. The leakage is due to the phase
change during the melting process. Hence, with addition of PMMA, the melting will
happen but the PCM will remain solid.
The results of DSC from this work are comparable with other results done by
other researchers from their previous works. Table 4.5 summarized the form stable
solid-liquid organic PCMs and some of their thermal properties as comparison to the
current study.
51
Table 4.5 Examples of form stable solid-liquid organic PCMs and some of their thermal properties (Kee et al., 2018)
No. Material and method Pure PCM FSCPCM Findings References
Melting
point (⁰C)
Latent heat of
melting (J/g)
Optimum
PCM mass
percentage
Melting
point
(⁰C)
Latent heat of
melting (J/g)
1 PCM: myristic acid
Porous material:
polymethylmethacrylate
(PMMA)
Method: solution blending of
PMMA and MA, coated with
NBR-PA
50-55 221.04 80wt% 52-56 107.56 - Thermally reliable: After 30
thermal cycling test
- FTIR spectrum shows that the
PCM is well coated with PA
Current
study
2 PCM: stearic acid
Polymeric matrix:
polymethylmethacrylate
Method: dispersion
polymerization through UV
photoinitiated method
59.90 177.80 51.8 wt% 60.4 92.1
(Reduced by
48.20%)
- Thermally and chemically reliable:
After 500 thermal cycling tests,
the reduction of latent heat is
1.2% and no much changes of
shape and frequency value of all
FTIR peaks
- The core/shell structure of
microcapsules was formed well as
shown in scanning electron
microscope (SEM) image which
improve the thermal stability
Wang et al.,
2011
52
3 PCM: caprylic acid
Polymeric matrices:
ureaformaldehyde resin
Method: microencapsulation via
simple coacervation method
19.31 158.44 59 wt% 13.90 93.9
(Reduced by
40.74%)
- SEM images showed that
microcapsules have spherical
structure and well encapsulated
- No leakage test
Konuklu et
al., 2014
4 PCM: composite paraffin
Porous material: calcined
diatomite
Method: fusion adsorption
method
29.94 145.90 61% 33.04 89.5
(Reduced by
38.66%)
- Thermally reliable: After 200
thermal cycling tests, the
reduction in latent heat is less than
5%
- Composite paraffin was
impregnated and confined into the
pores of calcine diatomite because
diatomite has high porosity, high
permeability and large specific
surface area
Sun et al.,
2013
5 PCM: PEG
Porous material: activated
carbon
Method: direct blending and an
impregnating method.
N/A N/A 70% 45–65 81–86 - Thermal stability is assessed by
TGA and no decomposition was
found below 250 ⁰C
- It is thermally stable because
activated carbon has extensive
pore structures with high specific
surface area and absorption
capacity for PEG
Feng et al.,
2011
53
6 PCM: Polyethylene glycol
(PEG)
Porous material: diatomite
Method: vacuum impregnation
method
33.32 143.16 50 wt% 27.70 87.09
(Reduced by
39.17%)
- Thermally reliable: After 1000
thermal cycling test, the reduction
of latent heat of melting is 1.1%
- PEG was impregnated and
confined into the pores of
diatomite because diatomite has
high porosity and absorptive
Karaman et
al., 2011
7 PCM: PEG
Porous material: expanded
graphite
Method: direct blending and an
impregnating method
N/A N/A 90 wt% 60–65 150–160 - Expanded graphite with
macroporous structures can
effectively stabilize the melted
PEG through both the capillary
force of the pores and the
hydrogen bonding resulting from
the surface functional groups
Wang et al.,
2012
54
4.1.4 Fourier Transform Infrared Spectroscopy (FTIR-ATR)
FTIR analysis was conducted on samples with different weight percentages of
PMMA (80 wt%, 60 wt%, 40wt%, 20wt%, and 0 wt%) with and without NBR-PA
coating in order to determine the functional group present. Figure 4.5 shows the IR
spectrum of pure myristic acid as reference.
Figure 4.5: FTIR spectrum of pure myristic acid.
PA coating is the outer coating of the PCM. PA molecules have high
presence of C-O bonds. Therefore, majority of the vibration peaks are subjected to
the C-O bonds. The stretching of C-H, C=O, deformation of CH3 and CH2 single
bond stretching of C-O-C and single bond deformation of C-O-C occurs at a range of
3050-2990 cm-1
, 1730 cm-1
, 1450-1395 cm-1
, 1260-1040 cm-1
and 960-880 cm-1
respectively (Sites.google.com, 2015). Furthermore, the bending around 3437 cm-1
indicates OH group stretching due to physisorbed moisture according to Duan et al.,
(2008). Besides, Gayosso et al., (2015) also states that the stretching of C=O occurs
around 1730 cm-1
and 1250 cm-1
and the stretching occurs around 3000-2800 cm-1
indicates the vibration for CH3 and CH2. Abdelrazek et al., (2016), Rajendran and
Uma, (2000) and Pan et al., (2012) have reported that C=O stretching, CH2 bending,
CH2 stretching, C-O-C stretching, C-O stretching and C-C stretching for PA occur at
55
1726 cm-1
, 1473 cm-1
, 2942-2862 cm-1
, 1233-1042 cm-1
, 1160 cm-1
, and 1290 cm-1
respectively. On the other hand, the FTIR spectrum for myristic acid have C=O
stretching at 1701 cm-1
, asymmetrical stretching of -CH2 at 2916 cm-1
and 2848 cm-1
,
OH stretching peaks at 686 cm-1
, 721 cm-1
, and 939 cm-1
, C-H bending at 1286 cm-1
and C-C bending at 1261 cm-1
(Sharma et al., 2009; Trivedi et al., 2015). Table 4.6
and Table 4.7 shows the absorption frequencies obtained for PA and MA with
functional groups corresponding to the peaks respectively.
Table 4.6 Absorption Frequency Obtained for PA.
PA Functional Groups Corresponding peaks References
OH group stretching 3447 cm-1
(Duan et al., 2008)
The stretching of C-H 2999-2953cm-1
(Sites.google.com, 2015)
The stretching of C=O 1735 cm-1
(Gayosso et al., 2015)
Deformation of CH3 and
CH2
1463 cm-1
(Abdelrazek et al., 2016)
Single bond stretching of
C-O-C
1147 cm-1
(Rajendran and Uma,
2000)
C-C stretching vibration 989 cm-1
and 749 cm-1
(Ramesh et al., 2007;
Gunasekaran, 2016)
Single bond deformation
of C-O-C
960-880 cm-1
(Pan et al., 2012)
C-H deformation 483 cm-1
(Uthayakumar et al., 2013)
56
Table 4.7 Absorption Frequency Obtained for Myristic Acid.
Myristic Acid Functional
Groups
Corresponding peaks References
C=O stretching 1697 cm-1
(Sharma et al., 2009;
Trivedi et al., 2015) Asymmetrical stretching
of –CH2
2917 cm-1
OH stretching peaks 3300-2500 cm-1
, 939 and
720 cm-1
C-H bending 1286 cm-1
C-C bending 1261 cm-1
Figure 4.6 shows the IR spectrum of PCM100 (0 wt% PMMA), PCM80 (20
wt% PMMA), PCM60 (40 wt% PMMA), PCM40 (60 wt% PMMA), and PCM20
(80 wt% PMMA) without NBR-PA coating, and Figure 4.7 shows the IR spectrum of
PCM100 (0 wt% PMMA), PCM80 (20 wt% PMMA), PCM60 (40 wt% PMMA),
PCM40 (60 wt% PMMA), and PCM20 (80 wt% PMMA) with NBR-PA coating.
The spectrum of PCM pellets show peaks at 2962-2956 cm-1
, 1733-1728 cm-1
, 1464-
1452 cm-1
, 1152-1146 cm-1
, 949-942 cm-1
, 994-988 cm-1
, 759-749 cm-1
, and 489-483
cm-1
which are assigned to CH stretching, C=O stretching, CH3 stretching, single
bond stretching of C-O-C, single bond deformation of C-O-C, C-C stretching
vibration, and C-H deformation respectively. The FTIR spectrum shows that the
PCM is well coated with PA because only PA coating peak was detected after
coating. The frequency obtained for each spectrums of each samples are tabulated in
Table 4.8.
57
Figure 4.6: Combination of FTIR spectrum of PCMs without coating.
58
Figure 4.7: Combination of FTIR spectrum of PCMs with coating.
59
Table 4.8 Absorption Frequency Regions and Functional Groups for coated
PCMs.
Absorption
Frequency
Range (cm-1
)
Absorption Frequency (cm-1
)
Functional Groups PCM
20
PCM
40
PCM
60
PCM
80
PCM
100
2962-2956
2958 2961 2962 2961 2956 Stretching of C-H
1733-1728
1728 1729 1732 1733 1728 Stretching of C=O
1464-1452
1452 1464 1454 1455 1451 Deformation of CH3
and CH2
1152-1146
1146 1147 1151 1152 1146 Single bond stretching
of C-O-C
949-942
942 944 948 949 940 Single bond
deformation of C-O-C
994-988,
759-749
990,
756
988,
753
994,
759
991,
760
989,
757
C-C stretching
vibration
489-483
484 484 486 489 483 C-H deformation
60
CHAPTER 5
CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion
The phase change material (PCM) used in this research is myristic acid since the
melting point (55⁰C) of this fatty acid is suitable and low to be used as latent heat
transfer material in solar water heaters. The major drawback of using myristic acid in
solar water heater is, the acid tend to corrode the wall of the solar water heater during
the phase change process. Therefore, the method of blending myristic acid with
PMMA and coat with nitrile butadiene rubber (NBR) and polyacrylic (PA) was
carried out. The tensile properties for the combination of NBR and PA coating is the
most suitable due to its sufficient elasticity contributed by the NBR, and good tensile
strength contributed by the PA to withstand volume expansion of PCM during phase
transition process. Only the amount of leakage could be reduced by just coating with
NBR and PA but the leakage still persist. In order to overcome this drawback, the
method of blending the PCM with different weight percentage of PMMA was
studied in this research.
The leakage results show that the leakage percentage decrease and eliminated
when the weight percentage of PMMA increase while the weight percentage of MA
decrease. Moreover, the latent heat of melting and freezing of form stable PCM80
with 20 wt% PMMA is 107.56 J/g and 102.26 J/g respectively. This concludes that
the form stable PCM80 has great thermal stability, which withstand 30 thermal
cycles without leakage. The FTIR of the coated PCMs show that the coating is
completely covered the PCMs.
61
5.2 Recommendation
In this study, form stable PCM without leakage is successfully produced, but the
latent heat of melting and freezing of the form stable PCM is quite low, which is
around 107.56 J/g and 102.26 J/g while pure myristic acid can absorb and release
heat up to 221.04 J/g and 224.14 J/g. This drawback can be corrected by choosing an
appropriate stabilizer as blending composite. The stabilizer should have good thermal
conductivity, good thermal stability, good latent heat and compatible with myristic
acid.
The next recommendation is to produce a thinner coat, which is more
compact and strong, as the thickness of the coat also influences the latent heat of
PCMs. This can be done by incorporating the filler such as reduced graphene oxide
to strengthen the properties of the coating.
62
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APPENDICES
APPENDIX A: Fourier Transform Infrared Spectroscopy
(a) PCM20 COATED
(b) PCM40 COATED
4000 4003500 3000 2500 2000 1500 1000 500
101
47
50
55
60
65
70
75
80
85
90
95
100
cm-1
%T
1727.30cm-11145.70cm-1
1236.89cm-1
1449.63cm-1
2956.09cm-1
1065.90cm-1
988.95cm-1
963.17cm-1
4000 4003500 3000 2500 2000 1500 1000 500
102
35
40
45
50
55
60
65
70
75
80
85
90
95
100
cm-1
%T
1727.11cm-11145.59cm-1
1236.84cm-1
1449.53cm-1
2955.94cm-1
1065.64cm-1
988.84cm-1
962.87cm-1
79
(c) PCM60 COATED
(d) PCM80 COATED
(e) PCM100 COATED
4000 4003500 3000 2500 2000 1500 1000 500
102
34
40
45
50
55
60
65
70
75
80
85
90
95
100
cm-1
%T
1727.08cm-1 1145.60cm-1
1236.80cm-1
1449.52cm-1
2956.00cm-1
1065.77cm-1
988.92cm-1
962.99cm-1
80
(f) PCM20 NON COATED
(g) PCM40 NON COATED
(h) PCM60 NON COATED
4000 4003500 3000 2500 2000 1500 1000 500
99.8
93.2
93.5
94.0
94.5
95.0
95.5
96.0
96.5
97.0
97.5
98.0
98.5
99.0
99.5
cm-1
%T
1696.80cm-1
2912.02cm-1 2847.77cm-1
1471.12cm-1 1145.94cm-1
1236.93cm-1
7 1 6 . 6 9 c m - 1
1190.26cm-1
1260.55cm-1
1433.07cm-1
916.43cm-1
750.88cm-1
81
(i) PCM80 NON COATED
(j) PCM100 NON COATED
4000 4003500 3000 2500 2000 1500 1000 500
100
88
89
90
91
92
93
94
95
96
97
98
99
cm-1
%T
1698.74cm -1 1146 .00cm -1
1723.01cm-12913.66cm-11190.42cm-12848.50cm-1
1237.20cm -1
1471.35cm-1
1261.00cm-1
1434.47cm-1
717.07cm-1
9 1 5 . 0 5 c m - 1
82
APPENDIX B: Differential Scanning Calorimetry
(a) PCM20 COATED
83
(b) PCM40 COATED
84
(c) PCM60 COATED
85
(d) PCM80 COATED
86
(e) PCM100 COATED
87
(f) Pure myristic acid
88
APPENDIX C: Conference Proceeding
Conference Proceeding Title: DEVELOPMENT OF FORM STABLE COMPOSITE
PHASE CHANGE MATERIAL WITH POLYMER COATING FOR THERMAL
ENERGY STORAGE
By: Shin Yiing Kee, Yamuna Munusamy, Kok Seng Ong, Swee Yong Chee, and Yu
Gen Qian
Citation: Proceeding – 3rd
Putrajaya International Built Environment, Technology
and Engineering Conference, (2017); ISBN: 978-967-2072-10-2
Published by the Proceeding – 3rd
Putrajaya International Built Environment,
Technology and Engineering Conference (PIBEC3)
89
90
APPENDIX D: Novel Research and Innovation Competition 2017 (NRIC)
(a) Poster of “FOSTPCM For Photovoltaic Cooling”
91
(b) Participants (From left: Yu Gen Qian, Nagarathanam, Ariff)
92
(c) Certificate of Bronze Medal of NRIC