Phase Change Material (PCM) | Characteristics of Phase Change Materials (PCMs) | Applications of Phase Change Materials (PCMs)

Phase Change Materials (PCMs):
Phase change materials (PCMs) materials have high heats of fusion so they can absorb a lot of energy before melting or solidifying. A PCM temperature remains constant during the phase change, which is useful for keeping the subject at a uniform temperature. It is one of the application of technical textile.
Building Insulation
PCM have been studied for use in direct thermal energy storage , solar energy applications and more recently, in response to growing international concern to climate change, building temperature regulation .

PCM can undergo solid-solid, liquid-gas and solid-liquid transformations. Solid-solid PCMs generally have high transition temperatures which are beyond the scope of practical use. Liquid-gas PCMs are not considered usable for most applications due to the large volume change that occurs at phase change. Solid-liquid PCMs have seen the most use in research and applications as they have high latent heat capacities and good thermal conductivity, making them practical for use. There are however several difficulties that can arise when using certain solid-liquid PCMs such as, subcooling, phase segregation and corrosiveness.

Energy and environment are the two major issues facing human beings nowadays. Industrial developments and population boom in the past few centuries have resulted in an enormous increase in energy demand with an annual increasing rate at about 2.3%. The increasing demand for energy-saving and environment-friendly technology is driving the growth of the global phase change material (PCM) market. The global PCM market is expected to grow from $300.8 million in 2009 to $1,488.1 million in 2015, at an estimated CAGR of 31.7% from 2010 to 2015. The paraffin-based PCM market commands the largest share of the overall PCM market in terms of value, while salt hydrate-based PCMs lead the market in terms of volume.

Building and construction currently forms the largest application market due to the globally increasing demand for cooling buildings, which in turn has arisen due to the shift from heavy thermal mass design to lightweight architecture. While this application contributed 22% to the global PCM market revenues in 2009, textile applications are expected to have the highest CAGR of 38.5% from 2010 to 2015.On this occasion, scientists had begun to research in renewable energy technologies in order to turn the tide of climate change and achieve a sustainable development for human beings. Phase Change Materials (PCMs) provides a high heat storage density and has the capability of storing a large amount of heat during the phase change process with a small variation of PCM volume and temperature.

PCM Materials and Their Characteristics:
Different kinds of materials were used as PCM. In principal materials should fulfill different criteria in order to be suitable to serve as a PCM.
  1. Suitable melting temperature
  2. High melting enthalpy per volume unit [kJ/m³]
  3. High specific heat [kJ/(kg.K)]
  4. Low volume change due to the phase change
  5. High thermal conductivity
  6. Cycling stability
  7. Not flammable, not poisonous
  8. Not corrosive
As one of the goals of latent energy storage is to achieve a high storage density in a relatively small volume, PCMs should have a high melting enthalpy [kJ/kg] and a high density [kg/m³], i.e. a high volumetric melting enthalpy [kJ/m³].

Classification of PCM:
Based on phase change state, PCMs fall into three groups: solid– solid PCMs, solid–liquid PCMs and liquid–gas PCMs. Among them the solid–liquid PCMs are most suitable for thermal energy storage. The solid–liquid PCMs comprise organic PCMs, inorganic PCMs and eutectics.

Comparison of different kinds of PCMs:

1. Availability in a large
temperature range
2. High heat of fusion
3. No supercooling
4. Chemically stable and
5. Good compatibility
with other materials
1. Low thermal conductivity
(around 0.2 W/m K)
2. Relative large volume change
1.High heat of fusion
2. High thermal
conductivity (around 0.5 W/m K)
3. Low volume change
4. Availability in low cost
     1.   Super cooling
     2.   Corrosion
1. Sharp melting Temperature
2. High volumetric thermal storage density
Lack of currently available test data of thermo-physical properties

Applications of PCM:
1.Cooling Packs
2. Thermasorb Capsules
3. Body Cooler
4. Bridge Warmer
5. NASA Dive Suit
6. Building Insulation
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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