Introduction
Increasing demand for energy saving and environment friendly technology
is driving the growth for the phase Change Materials market. Cold chain is the
most widely used application requiring critical temperature control; hence
there is a need for awareness about PCM in this segment to reduce several
challenges presently faced. The term “cold
chain” applies to temperature-controlled supply chain that requires the
maintenance of a specified temperature range in order to retain their quality.
In order to maintain this chain of uninterrupted movement of goods there is a
need for innovative technologies which are cost effective, efficient and easy
to use for the end consumer. We will see the What, Why and How of Phase Change Materials Technology – A
Material having ability to store high amount of thermal energy by virtue of
change in its phase and be able to release this energy at a constant
temperature.
Phase
Change Materials
Phase
Change Materials (PCM) fall under the sub category of energy exchanging smart
materials. Energy exchanging smart materials is defined as those materials that
are able to store latent and sensible energy in the form of light, heat,
electricity or hydrogen and exhibit reversibility. A PCM has the ability to store and release
large amounts of heat/energy while maintaining a constant temperature. PCM’s
have tremendous potential to fulfill the growing need of energy
for cooling and heating applications across various industries.
A generic term “eutectics” are also used for describing PCMs but there
is a subtle difference. Eutectic solution are mixture of chemical compounds or elements that have
a single chemical composition that solidifies at a lower temperature than any other
composition made up of the same ingredients. This composition is known as the
eutectic composition and the temperature at which it solidifies is known as the
eutectic temperature. A eutectic solution to be qualified as a phase change
material for the purpose of storage of thermal energy there are other important
factors which are desired. Without the consideration of these factors a
eutectic solution would find its application as an anti-freeze solution or to utilize
it as a sensible heat storage medium at various temperatures..
The
concept of PCM can be better explained by drawing an analogy with water which
is a natural form of Phase Change Material (PCM) and most temperature control
packaging use water by utilizing it high thermal energy storage capacity during
its change of phase from liquid to solid or vice versa. The properties that
make water an ideal material for storage & transport of materials for
applications requiring temperature maintenance in the range of -2°C to 4°C are
as follows,
·
Consistent, repeatable, reliable phase
change material temperature of 0° C.
·
High latent heat of fusion.
·
Non-Toxic.
·
Easily packaged into pouches or bottles.
·
Inexpensive and easily available.
A good phase Change
Material is a one which should mimic these properties and offer the most
important ability which is of customizability to different temperature needs. The
below figure 1 illustrates the behavior of phase change materials against
non-phase change materials such as coolants, glycol solution, water based gels
etc. used for the purpose temperature storage. The non-phase changing materials
rely on the specific heat stored in them. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. The relationship between
heat and temperature change is usually expressed in the form shown below where
c is the specific heat.
This relationship does not apply if a phase change is encountered, because
the heat added or removed during a phase change does not change the
temperature. This is because the heat supplied to the object is used to
overcome the forces of attraction that hold the particles together during
change in the state. Hence, the formula to calculate heat added in independent
of the temperature change which is Q = m L where L is specific latent heat. The
figure 1 below illustrates the difference in the behavior of phase change
materials against non-Phase changing materials such as water based gels, Glycol
solutions, coolants etc. In case of PCMs the temperature stabilizes at the
point where the phase starts changing liberating higher amount of energy.
Classification
of Phase Change Materials
Phase
Change Materials can be broadly classified as Organic and Inorganic type and
the major difference between both the types are as follows;
Customizability
One of most widely used
application of PCM is for requirement of storage and release of energy at 2 – 8
deg C. Water is the most affordable, easily available and widely adopted PCM to
offer this temperature range. For example in central air-conditioning in large
buildings which require water at 4 – 7 deg C, Pharmaceutical vaccines which
requires temperature maintenance at 2 -8 deg C range. The challenge is when the
application demands a very narrow or no deviation from the desired temperature
or different temperature all together.
For applications which
are very critical to temperatures such as pharmaceutical drugs, tissues,
vaccines, perishable commodities there is a need to use a PCM for reliability
& stability of the performance. Using water in such application can cause
achieving no thermal backup leading to failure of performance due to
super-cooling effect, which is undesirable leading to non-freezing of the water
at its freezing point. PCMs are formulated with nucleating agents which
suppress and prevent super cooling. Due to super cooling, water may not get
frozen completely or partially at its desired temperature resulting in not
contributing towards only specific heat. Secondly, for applications requiring
different temperature range for instance -23 deg C for ice-creams, -10 deg C
for tissues, 22 deg C for blood platelets, wine, 65 deg C for hot water storage
etc. PCMs come in different melting/freezing point and hence can offer tailor
made solution.
It is important to
understand the following to arrive at the right PCM,
1)
The desired temperature at which the
product/application needs to be maintained.
-
This will enable to select the right
temperature PCM considering convective and conductive loses.
2)
The temperature available to charge the
PCM
-
PCM require to be given energy(storage)
in order to extract energy(release) out of it. Charging implies storage of energy
in the PCM by changing its phase (Melt/freeze). If the desired charging
temperature is not available then the PCM would not offer the backup.
3)
The compatible encapsulation
-
Depending on the type of PCM the right
encapsulation needs to be designed considering the materials resistance to
corrosion, temperature and mechanical stresses. Various different encapsulations
are explained below,
i)
Spherical
/ cuboid encapsulations: These are largely used in applications requiring very large bulk storage of thermal energy and also allow flexibility of discharging
this energy in controlled manner. These are widely used solar, building
air-conditioning, process cooling and milk chilling application. These
encapsulations can be customized to various sizes and the material depending on
the temperature that these encapsulations would be subjected to. Eg: HDPE (
>70 deg C), PE (<70 deg C>90 deg C), SS (< 90 deg C).
ii)
Pouches:
These are largely used as an inner lining within insulated panels used in deep
freezers, refrigerators, coolers for beverages, transport boxes. Pouches
provide a larger surface area in application in applications in which PCMs are
lined beneath the surface requiring cooling. Pouches are customized in shapes
and the material used depending on the application and the easier integration.
There are various innovative
ways of encapsulating PCMs other than the above two methods to make the end
product integration more aesthetically appealing and for enhancement in the
performance. At this stage its is very critical for the original equipment
manufacturer of the product and PCM manufacturer to closely work together to
understand the limitations and advantages of the various possibilities.
Applications
PCM has its application across various industries where there is a need for temperature control and regulation. Example of its application in other industries is summarized below
1.
Cold
Chain Industry – PCMs have been proven to be very useful in cold chain
industry. The major applications are to maintain temperatures during power
failures. Major deep freezer manufacturers have started using phase change
materials in their freezer to avoid the spoilage of products during power
cut-offs, which is a major problem in India. Many FMCG companies in the dairy
industry have started fast adopting phase change materials for last mile
distribution into rural areas. The PCM
based eutectic plates offer solution to existing challenges in the cold supply
chain issues such as power outages, poor infrastructure, high fuel costs and
critical last mile etc. When compared with traditional reefer trucks this
technology offer up to 80% savings in operating cost in virtue of the reduction
in diesel consumption. In addition PCMs enables multi-temperature transport
improving the payload factor thereby improving feasibility of part load
transportation.
PCM integrated into the end product – Deep
freezers at the retail
2.
Building
HVAC - PCM based thermal energy storage systems help in reducing capital costs,
operating cost and increase efficiency by utilizing off peak electricity during
the night hours. PCMs help store this energy during the off peak hours in large
insulated tanks, which can be harnessed during the day time for serving the
cooling needs of the building. PCM are used in commercial, residential and
industrial buildings.
3.
Solar
Applications- PCMs are being used to store the solar energy in the form of
thermal energy which can be used in the absence of sunlight. This enables the
solar based systems to work at night without use of external sources of
heat/electricity. Solar applications in driers, water heater and even air-conditioners
can make use of PCMs in improving the utilization factor. The figure below
illustrates a solar domestic water heater connected to a insulated tank filled with
spherical encapsulations filled with high temperature PCM. The selected PCM
should ensure that temperature provided by the water melts the PCM thereby also
charging it. When the sun’s energy is not available, the water in the tank
would start to gradually lose the heat. As soon as the temperature of the water
lowers down below the point of phase change temperature, the PCM begins to
solidify releasing it energy and maintaining the temperature of the water hot.
PCM application to store Solar energy
4.
Healthcare manufacturers need to safeguard their products and
offer evidence of complying
to maintain a certain temperature range throughout
the movement of goods. Biopharmaceuticals and
vaccines contribute to a majority of shipments of temperature-sensitive
pharmaceuticals, which are typically high in monetary value and have low
product volume. With the surge in mail order shipments, increasing scrutiny by
regulatory agencies and the desire to lower costs , the need to develop an
effective and reliable cold chain management protocol has become a
necessity of utmost importance.
5.
Temperature-controlled
clothing- PCMs can be incorporated with fabrics in various ways and can be used
to provide comfortable temperature even in extreme temperature conditions.
Many more possibilities are yet to be exploited
with PCMs extending its application into retail products, home appliances,
automobiles etc.
About Pluss Polymers Pvt. Ltd.
Pluss is a venture funded organization with
equity stake being held by Tata Capitals premium innovation fund promoted by
the Tata. Pluss is engaged in R&D and manufacturing of Specialized polymers
and Phase change materials (PCMs). PCM technology finds its application
globally in diverse sectors like cold supply chain, Building HVAC,
refrigeration, automobiles, thermal wear, waste heat recovery, consumer goods
and more; wherever there is a need to store thermal energy. Pluss has pioneered
in the PCM technology in India and is presently the only company in India with
a wide range of indigenously manufactured PCMs with many patents. For
more information, please visit www.pluss.co.in.
This article was published in the Cold Chain
supplement of Air Conditioning and Refrigeration Journal,
Mar-Apr 2014. Copyright 2014 Air
Conditioning and Refrigeration Journal. Reprinted here by
permission from Air Conditioning and Refrigeration Journal. This
article may not be copied nor distributed in either paper or digital
form by other parties without permission from Air
Conditioning and Refrigeration Journal.
