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International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963

Basakayi J.K. 1; Storm C.P.2


Department of Mechanical Engineering, Vaal University of Technology,
School of Mechanical and Nuclear Engineering, North West University, Potchefstroom

The supply of fossil energy source such as coal is becoming less reliable. The CO2 has to be reduced. At the same
time energy consumption is increasing in South Africa.
One of the solutions is to make use of phase change materials in the thermal systems. Phase change materials
absorb and release thermal energy at a constant temperature. In addition, they have high density energy storage.
Integrating phase change materials in thermal systems can improve the efficiency and reliability of those systems.
Different potential applications of Phase change materials are provided in this paper that can be valuable in the
context of South Africa for storing energy and control temperature purpose.

KEYWORDS: Phase change material, thermal energy &latent heat storage.



Lack of reliable and cost effective energy is one of the major problems facing social and economic
development of each country. South Africa has an increasing population. The excessive demand of
energy consumption keeps on increasing with the growing of the population. Industries and production
companies also require abundant and reliable energy to run their activities.
In South Africa, electricity is essentially generated from coal [1]. The disadvantages associated with
this traditional type of energy are numerous: the pollution of the atmosphere, depletion of the Ozone
and limited amount of coal.
To deal with the high demand of energy and the problems linked to the use of energy produced by fossil
fuel, the two possible ways are: investigate other forms of energy such as solar energy and well manage
the existing energy.
Since the crisis of energy during the period of 1970s, other types of energy have been considered.
Renewable energy is one type of energy that is constantly and regularly replenished and will never
come to an end anytime soon. Among the types of renewable energy investigated there are: Bio-mass,
wind, solar energy, geothermal.
Solar energy is one of the most promising types of renewable energy that offers a better alternative to
the energy generated by the fossil fuel. It is available, clean and abundant [2].
The excessive solar energy can be also stored when it is available for later use. It is about well managing
the existing energy by making use of some form of storage when sun is shining and more solar radiation
is accessible.
Different techniques used for storing thermal energy are: Sensible energy, latent heat energy and
thermo-chemical reaction. Among those three methods considered for storing thermal energy, the latent
heat energy emerges as the best option thanks to the advantages of releasing and absorbing energy at
constant temperature for the storage material used and also to the possibility of having high energy


Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963
density storage compared to the sensible heat storage. Thermo-chemical storage system can provide
high density energy but it is still under development [3].
Latent heat storage systems make use of the material called Phase Change Material (PCM) due to the
change of phase that occurs during the discharge and the charge processes. In addition of storing and
releasing the latent thermal energy during the charging and discharging processes, PCM can be also
used for thermal control for different applications purposes.
Since solar energy is not available during night or cloudy day, the integration of a storage system in a
solar thermal energy as a latent heat can increase the reliability and the performance of thermal systems.
In applications for temperature control, the focus is on the temperature regulation and for storage of
heat or cold with high storage density; the emphasis is on the amount of heat supplied.
The applications found in literature for PCMs include solar hot water heating, solar cooking, solar
absorption, solar green house, thermal control of instruments, heating of building. Some applications
for thermal control are: spacecraft thermal control environment, integration of PCMs in delicate and
precise instrument thermal control.
Many investigations have been carried out elsewhere and successful applications are increasing in
different developed countries. No practical applications are found in the market here in South Africa
expect for few studies that are done in academic institutions for research purposes.
The immediate objective of this paper is to provide a basic understanding of the behaviour of PCM,
indicate how this material can be selected for a given application and finally provide different potential
applications of PCM with reference to thermal energy systems in South Africa, so that the integration
of the PCM can contribute in solving the problem of energy in this country.
This paper focuses on the potential applications of PCM in South Africa. The second section gives some
constructive ideas for using PCM. The basic concept of Latent heat storage systems is explain in the
third section. In the fourth section, the selection of PCM for different applications is presented. The
following section covers the potential applications of PCM here in South Africa. The last section
includes the future work which will be on the modelling of a latent heat storage.



More energy from sunlight strikes the Earth in one hour (4.3 × 1020 J) than all the energy consumed on
the planet in a year (4.1 × 1020 J) [1]. Most areas in South Africa average more than 2 500 hours of
sunshine per year, and average solar radiation levels range between 4.5 and 6.5 kWh/m2 in one day [4].
South Africa has therefore one of the highest solar radiations in the world.
Today, many solar energy systems able to convert solar radiation directly into thermal energy have been
developed for low, medium and high temperature heating applications in different developed countries.
Solar thermal power generation and solar space heating are examples of industrial applications;
domestic applications include solar water heating and solar absorption refrigeration. The previouslymentioned examples are only a sample of applications of solar energy to name but a few.
Although solar energy has its advantages, it remains, however, intermittent and unpredictable. Its total
available value is seasonal and often dependent on meteorological conditions of a location. Therefore,
solar energy cannot, for example, be trusted to produce cooling during periods of low solar energy
irradiation for a solar absorption machine. Some form of thermal energy storage is necessary for
effective utilisation of such an energy source, to meet demand on cloudy days and at night. Thermal
energy storage, therefore, plays an important role in conserving thermal energy, leading to an
improvement in the performance and reliability of a range of energy systems.
Thermal energy storage refers to a number of technologies which store energy in a thermal accumulator
for later re-use. Integrating thermal energy storage in a thermal system has a potential to increase
effective use of thermal energy equipment and it can facilitate large scale switching [5]. This energy
storage is used for correcting the mismatch between the supply and the demand of energy.
The use of PCM as an energy storage medium is now worldwide considered as an option with a number
of advantages. The combination of solar energy and the use of PCMs in any thermal energy system
may result on alleviating the problem of pollution due to the use of fossil sources energy, assisting the
management of energy with the high demand of energy increasing by storing when it is available and


Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963
use later or during cloudy and low solar radiation. It is also important to make use of PCM wherever
there is a need to control the temperature of space, equipment or human body.



Latent Heat Thermal Energy Storage (LHS) is based on the heat absorption or release when a storage
material undergoes a phase change from solid to liquid, solid to solid or liquid to gas or vice-versa.
Figure 1 summarises the classification of LHS materials.
Latent heat storage materials








Inorganic Inorganic




Fig.1 Classification of the LHS materials (modified after Shama et al., 2004)

Latent heat storage can be accomplished through solid-liquid, liquid-gas, solid-gas, and solid-solid
phase transformations. Only two are of practical interest, solid-liquid and solid-solid [6]. Solid-gas and
liquid-gas transition have a higher latent heat of fusion, but their large volume changes on phase
transition are associated with containment problems and rule out their potential utility in thermal storage
systems. Solid-liquid PCMs present the advantages of smaller volume change during the phase change
process and longer lifespan [6]:
The storage capacity of a LHS system with a PCM is given by:

Q  m[amH  Csp(Tm - Ti )  Clp (Tf - Tm )]
Where Q = quantity of heat stored;
m = mass of the PCM;
am = fraction melted;
H = latent heat of fusion;
Csp = average specific heat between temperatures Ti and Tm;
Clp = average specific heat between temperatures Tm and Tf;
Ti = Initial temperature;
Tf = Final temperature;
Tm = Melting point


Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963





Fig.2 Thermal energy stored in a PCM as a function of temperature (modified after Rubitherm, 2008)

Figure 2 illustrates the change in stored energy (internal energy) as a function of temperature. At the
beginning of the heating process the material is in a solid state. Before it reaches the melting point T m,
the heat absorbed is sensible heat. Starting at melting point, the material undergoes a change of state
from a solid to a liquid. During this process, the material absorbs heat known as enthalpy melting. The
temperature remains constant. If the material is heated up further after this process, there will be
sensible heat added on completion of melting.



A PCM is selected depending on the application. The following criteria are considered for the selection
of a PCM [7]:
1. The thermo-physical properties:- Melting temperature in the desired operating temperature range, High latent heat of fusion per unit volume, - High specific heat and high thermal conductivity (the low
thermal conductivity is one of major problems in use of PCM), -Small volume changes on phase
transformation and congruent melting for a constant storage capacity.
2. Kinetic properties: Among kinetic properties to be considered are: High nucleation rate and high rate
of crystal growth.
3. Chemical properties: Chemical stability, complete reversible freeze/melt cycle, no-degradation after
a larger number of freeze/melt cycles, non-corrosiveness to the construction materials, non-toxic, nonflammable and non-explosive for safety.
4. Economic: PCMs should be cost effective, abundant and be available on a large scale.
There are different ranges of PCMs. Table 1 presents some commercial PCMs available on the market.
Table 1: Some commercial PCMs available on the market (Zalba et al., 2003)
Commercial Name

Type of product

Melting point (oC)

Heat of fusion (kJ/kg)

Source (Producer)

RT 20
SP 22 A4
SP 25 A8
ClimSEL C22
ClimSEL C28

Salt hydrate
Salt hydrate




In Table 2, the advantages and disadvantages of organic and inorganic materials are presented. From
the behaviour of the PCM shown in Table 2, an appropriate PCM can be selected for a given application.
Table 2: Comparisons of organic and inorganic PCMs (Zalba et al., 2003)




great change enthalpy

Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963
little or no supercooling
chemically and thermally stable
lower phase change enthalpy
low thermal conductivity


good thermal conductivity
cheap and non-flammable

corrosion to most metals
phase separation
phase segregation
lack of thermal stability


In this section, some potential applications of PCM that can be useful in South Africa to address the
issue of energy are presented.

5.1. Solar water heating and Space heating
Water heating accounts for up to 40% of household energy consumption in South Africa [8]. Up to now,
solar water heating system use in South Africa makes use mostly of sensible heat technology in their
systems. It has been proved that the integration of PCM in a solar water heating system can improve
the efficiency of the system. By decreasing the volume of geyser and by providing thermal energy stored
at all most constant temperature for a long period compared to sensible heating system. 5 - 14 times
more energy can be stored by using latent heat than the sensible heat [9].
Using the latent heat storage with PCM like in hospital, restaurants and residential area will
tremendously improve the life of population with an efficient energy system [10].
In a latent heat storage solar water heating systems, water is heated up during the sunshine period. The
heat is transferred to the PCM. During cloudy or period of low solar radiation, the hot water is taken
out and is replaced by cold water, which absorbs energy from the PCM. The energy is released by the
PCM during the solidification process (changing from liquid to solid).
A study done by Mehling et al. [11] showed that a PCM module at the top of a stratified water tank
increased the energy storage and improved the performance of the tank. Paraffin wax, stearic acid, Na2
SO4. 10 H2O have been tested and good results were obtained for solar heating systems [12]. Hasan et
al. [13] recommended that myristic acid, palmitic acid and stearic, with melting temperature between
50o C – 70o C are the promising PCMs for water heating.
In South Africa, space heating is one of the largest energy loads on a typical house. Using a LTE system
can reduce the amount of energy consumed for these loads by storing excess thermal energy that is
either available during the day (diurnal storage) or available in the summer (seasonal storage).
Solar air heater integrated with PCM can be used for heating space. Strich et al. [14] used transparent
insulation material and translucent PCM in the wall for heating the air for the ventilation of the house.
Paraffin wax was used as PCM. The efficiency of solar energy absorbed into the PCM and transferred
to the ventilation air was 45% on average.

5.2 Solar cookers
The use of solar stoves can have great significance in South Africa if they are used in combination with
PCM. The utilization of PCM in the solar cooker would assist to conserve the environment by not using
fuel wood for cooking as it is currently used. According to CSIR, rural households in South Africa use
between 4.5 and 6.7 million tonnes of fuelwood per year [15].
Some box-type solar cooker with PCM has been tested and proved to be efficient to cook food even
during the evening (Buddhi and Sahoo [16] and Sharma et al. [17]). Commercial grade stearic acid,
acetamide, erythritol are some of PCMs that can be used for this application.

5.3 Solar cooling
Often during summertime, there is a need to cool the buildings and houses. Cooling TES systems can
be used to reduce the amount of energy consumed for space cooling. PCMs are used as a storage media
for space cooling. As examples of PCMs used for space cooling, there are: inorganic salt hydrates,
organic paraffin waxes and mixture of these, Rubitherm RT 5.


Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963
Typically building services that include lighting, electronic devices and appliances account for 57% of
the electricity consumption and thermal comfort systems (Heating, Ventilation and Air Conditioning HVAC) make up the remaining 43% [18].
Agyenim et al. [19] investigated the possibility of integrating latent thermal energy storage to the hot
side of a LiBr absorption cooling system to cover 100% of the peak cooling load for a three bedroom
house on the hottest summer day in Cardiff, Wales. A 100 l of Erythritol was required to provide about
4.4 hours of cooling at peak loads based on the optimum Coefficient Of Performance (COP) of 0.7
PCMs can be used to store coolness. In this application, the cold stored from ambient air during night
is relieved to the indoor ambient during the hottest hours of the day [7].

5.4 Intermittent Power Plants
Integrating PCM in a latent heat storage in a power plant for example to smooth out the supply of
electricity from intermittent power plants for the utility grid can be beneficial. This can result on
generating electricity more effectively during the distribution and to take control and manage the energy
more adequately. Electricity can be produced by solar energy that was stored several days earlier by
storing excess energy in large thermal reservoirs. Nitrate salt represents possible PCM for applications
beyond 100 °C [19].
In his investigation, Hunold et al. [20] proved that phase change storage is technical feasible and
proposed a storage design for a power plant. South Africa generates electricity from different power
plants. By incorporating PCM in the power plant, it is possible to improve the distribution of electricity
in South Africa.

5.5 Waste heat recovery systems
Air conditioning system ejects heat. The exhausting temperature of the compressor is relatively high
when using Freon as refrigerant. Therefore, it can be recovered using an accumulator and gets heat of
higher temperature.
Zu et al. [21] developed a heat recovery system using PCM to recover the ejected heat of air
conditioning system and producing low temperature hot water for washing and bathing. It was observed
that the efficiency ratio of the system is improved effectively when all the rejected heat from air
conditioning systems is recovered. Erythritol, stearic acid have been used and tested as PCMs for this

5.6 Greenhouse heating
Greenhouse requires control of temperature, humidity, solar irradiance and internal gas composition
with rational consumption of energy.
Some PCMs were used for this application: CaCl2.6H2O, Na2SO4.10H2O, paraffins. Nishina and
Takakura [22] compared conventional greenhouse with PCM storage type storage. Efficiency of the
greenhouse with PCM storage integrated with solar collector was 59% and able to maintain 8 oC inside
the greenhouse at night.

5.7 Electrical Power Devices
PCMs with high melt temperatures can be used in conjunction with electronic power-producing
systems. Radiators used to collect solar energy can be packed with PCM to store the energy via phase
change at the melt temperature.
This stored energy can then be converted into electrical power by using the large temperature difference
between the radiator and deep space in either thermionic or thermoelectric devices.
Preliminary analytical and experimental studies reported in [23] indicate the feasibility of PCM
application, and materials have been found with suitable properties for such PCM systems.
To maintain high photovoltaic (PV) efficiency and increasing operating PV life by maintaining them at
a lower temperature, PCMs are integrated into PV panels to absorb excess heat by latent heat absorption
mechanism and regulate PV temperature. The results show that such systems are financially viable in
higher temperature and high solar radiation environment [24].


Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963
5.8 Transport
Containers with PCMs can be used to transport film, food, waste products, biological samples, etc.
Such containers represent isothermal protection systems for perishable cargo.
Applications in transport and storage containers are in most cases basically an insulated environment
with heat capacity increased by PCM.
When food or medications are transported, they must be kept in a certain range of temperature. PCM
are very suitable in transportation of these products (food and medications).
Companies such as Rubitherm GmbH, Sofrigam, PCM thermal Solutions design transport boxes for
sensitive materials [7].

5.9 Delicate instrument thermal control
For delicate, highly temperature-sensitive instruments, PCM can be used to maintain these instruments
within extremely small temperature ranges.
Precise Thermal Control of Instruments Temperature - sensitive instruments required to deliver highly
accurate responses have been protected by PCM thermal control systems. Russian investigators have
studied the feasibility of using PCM to precisely control the temperature of gravity meters which require
a relative accuracy of 10-8[24].

5. 10.Applications for the human body
The common approach to use PCM to control and stabilize the temperature of the human body is to
integrate the PCM into clothes. Approaches are: macro encapsulation, microencapsulation, composite
Pocket heater (used to release heat when a person is freezing), Vests for different applications,
developed by Climator [25]. Those vests are developed to cool the body of people who work in hot
environments (such as mine), or with extreme physical exercise. Clothes and underwear are used to
reduce sweating. Other applications include: Kidney belt, plumeaus and sleeping bags and shoe inlets.
Another important application can be found in medical field: the use of ice for cooling as a treatment
of different sports injuries.
In Textile, PCMS make it possible to engineer fabrics that help regulate human body temperature.
Microencapsulation makes phase change materials light and portable enough to incorporate into
textiles, either as a top-coat or as an addition to the fabric fibers [26].



Make use of the PCM can be useful and relevant in South Africa if this material is used in conjunction
with solar energy and waste thermal energy system. It can significantly contribute to solve some
problems related to energy. Several problems may be resolved such as pollution of environment, load
shading, management of electrical power, deforestation and energy consumption.
There is a necessity to turn to the PCM with some of applications point out in this paper; life of millions
of South Africans can be alleviated. To attain this result, there is a need to do more research in the field
of energy, to inform people about other possible solutions to the problem of energy and apply those
solution such as the integration of PCM in different thermal systems.
In the next paper, the focus will be on modelling a latent heat storage system for solar refrigeration
system. A mathematical model will be proposed for a latent shell and tube heat exchanger in order to
understand the mechanics of a latent heat storage.



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Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963








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Vol. 7, Issue 3, pp. 692-700

International Journal of Advances in Engineering & Technology, July, 2014.
ISSN: 22311963

Basakayi, J.K graduated with a BEng degree from the Universite de Mbujimayi (U.M), The
Democratic Republic of Congo in 2001. He then completed a Master of Engineering degree
in 2012 from the University of Johannesburg in South Africa.
In 2007, Basakayi has worked at the University of Johannesburg as a Part Time Lecturer in
Mechanical Engineering before joining the Cape Peninsula University of Technology from
2008 until 2013. He is a currently lecturer at Vaal University of Technology (VUT) in
mechanical engineering Department. He is a member of South African Institute of
Mechanical Engineering (SaiMech).

Storm C.P. received the B.Eng degree from the University of Pretoria and M. Eng degree
from the North West University, South Africa, in 1982 and 1994 respectively, and the Phd.
Degree from the North-West University in 1998. He was Director of the School of
Mechanical and nuclear engineering from 2007 until 2013 at the
North West University. He is currently Professor of Engineering. Since 1997, he has been
actively involved as a researcher and lecturer in the area of thermodynamics and
Optimization of thermal systems. He did publish a number of papers in the field of
thermodynamics and power plant.
Prof Storm worked at Eskom from 1982 until 1999 as assistant Engineer, manager and Senior Engineer


Vol. 7, Issue 3, pp. 692-700

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