Uses of Phase Change Materials (PCMs) in Clothing
Dept. of Garment Manufacturing
National Textile University, Faisalabad, Pakistan
Whenever a material changes from solid to liquid it absorbs heat, and whenever a liquid changes to solid it releases heat. A material that is capable of absorbing heat energy or releasing heat energy, at a large-scale, is called Phase Change Material (PCM).
Phase change materials (PCMs) are thermal storage materials that are used to regulate temperature fluctuations. The thermal energy transfer occurs when a material changes from a solid to a liquid or from a liquid to a solid. This is called a change in state, or phase.
Incorporating microcapsules of PCM into textile structures improves the thermal performance of the textiles. Phase change materials store energy when they change from solid to liquid and dissipate it when they change back from liquid to solid. It would be most ideal, if the excess heat a person produces could be stored intermediately somewhere in the clothing system and then, according to the requirement, activated again when it starts to get chilly.
PCMs used in textiles are combinations of different types of paraffins – each with different melting and crystallization (i.e., freezing) points.
PCMs and Latent Heat:
PCMs are also known as latent heat storage units. By latent heat we mean the amount of heat energy absorbed or released by a body, without any change in temperature, as a whole.
For instance, phase change from solid to liquid absorbs energy, whereas liquid to solid requires release of energy.
PCMs and Enthalpy of Fusion:
PCMs are known for their high enthalpy of fusion or heat of fusion. By segregating the two parts of enthalpy of fusion, we can get a general idea of what is meant by this phrase,
Enthalpy means the measure of the total energy of a thermodynamic system or body. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.
Fusion which is also known as melting, is a physical process that results in the phase change of a substance from a solid to a liquid. The internal energy of a substance is increased, typically by the application of heat or pressure, resulting in a rise of its temperature to the melting point, at which the rigid ordering of molecular entities in the solid breaks down to a less-ordered state and the solid liquefies. An object that has melted completely is molten.
PCMs latent heat storage can be achieved through solid–solid, solid–liquid, solid–gas and liquid–gas phase change. However, the only phase change used for PCMs is the solid–liquid change.
Liquid-gas phase changes are not practical for use as thermal storage due to the large volumes or high pressures required to store the materials when in their gas phase.
Liquid–gas transitions do have a higher heat of transformation than solid–liquid transitions.
Solid–solid phase changes are typically very slow and have a rather low heat of transformation.
Working of PCMs:
Initially, the solid–liquid PCMs behave like sensible heat storage (SHS) materials; their temperature rises as they absorb heat.
Note: What is an SHS?
An SHS or Sensible Heat Storage material is a system that works on the principle of SENSIBLE HEAT, whereas sensible heat is a term that is used in contrast to the LATENT HEAT. Because in case of LATENT HEAT the system e. g, ice keeps on absorbing heat constantly and the temperature around it remains the same till it has changed its phase to liquid. However, in case of Sensible Heat the body with the absorption or release of heat also causes consistent change in temperature in the surrounding.
Unlike conventional SHS, however, when PCMs reach the temperature at which they change phase (their melting temperature) they absorb large amounts of heat at an almost constant temperature.
The PCM continues to absorb heat without a significant rise in temperature until all the material is transformed to the liquid phase.
When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat.
Points to Ponder:
- Large number of PCMs are available in any required temperature range from −5 up to 190°C.
- Within the human comfort range of 20°C to 30°C, some PCMs are very effective.
- They store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry or rock.
Major Types of PCMs:
1. Organic PCMs:
Paraffin (CnH2n+2) and fatty acids (CH3(CH2)2nCOOH)
2. Inorganic PCMs:
Salt hydrates (MnH2O)
Organic-organic, organic-inorganic, inorganic-inorganic compounds
4. Hygroscopic materials:
Many natural building materials are hygroscopic.
While selecting a Phase Change Material, following characteristics should be kept in mind:
- Melting temperature in the desired operating temperature range
- High latent heat of fusion per unit volume
- High specific heat, high density and high thermal conductivity
- Small volume changes on phase transformation and small vapor pressure at operating temperatures to reduce the containment problem
- Congruent melting
- High nucleation rate to avoid supercooling of the liquid phase
- High rate of crystal growth, so that the system can meet demands of heat recovery from the storage system
- Chemical properties
- Chemical stability
- Complete reversible freeze/melt cycle
- No degradation after a large number of freeze/melt cycle
- Non-corrosiveness, non-toxic, non-flammable and non-explosive materials
- Low cost
PCMs in Textile Clothing:
These are smart fabrics. Put a warm hand on PCM fabric swatches and you can feel it for yourself, as the fabric actively draws the heat from your hand. Alternatively, put a cold hand on there and you’ll feel it begin to get warmer.
Phase change materials (PCM’s) can keep you cool when it’s hot and warm you up when you get too cold. Well, that’s to say they can is you select the right. They can be used alone or in combination with other technologies to create passive cooling systems.
Currently, phase change materials are being used in a variety of outdoor apparel items (e.g., gloves, boots, jackets, earmuffs, etc.) under the trade names Outlast™ and ComforTempR. The addition of PCMs to fibers, foams, and fabrics substantially increases the price of the textile. The price increase varies based on the volume being produced and the percent by weight of PCM that is added. Considering product safety, performance, and cost issues, the effect of PCMs in types of garments worn in cold environments on thermal comfort should be investigated prior to their use. Therefore, the purpose of this project was to quantify the effect of PCMs in fabric-backed foams on selected fabric characteristics (Phase I), on heat loss from a thermal manikin’s surface to the environment during environmental temperature transients (Phase II), and on human subjects’ physiological responses and comfort perceptions during environmental temperature transients and changes in activity (Phase III). Identical fabrics and garments – with and without the PCMs – were compared.
PCM’s have, unfortunately, previously been victims of their own hype: they promised a lot but early users were often disappointed with the performance level they actually delivered.
Since then, however, new application methods mean that it’s now possible to achieve significant and permanent heat regulation effects even under very demanding conditions.
How PCMs Working in Clothing:
- As we know PCMs are latent heat storage units, so the garments or apparel units made up of these are also HEAT STORAGE UNITS.
- When a PCM garment is facing rise in temperature due to external or internal conditions, its solid phase encapsulations starts absorbing heat energy under a constant temperature and change to liquid phase, thus providing cooling effect to the user.
- In case of freezing temperature or cold conditions, the liquid phase encapsulated apparel releases the stored energy under constant temperature, thus providing heat and soothing effect to the body.
Scholastic Point of View:
1. Professor Doug Hittle, Ph. D of Colorado State University:
“As phase-change materials absorb body heat, they reduce the distractions of heat and cold fluctuations, providing a new superior level of comfort in clothing”
2. American Society for Testing and Materials (ASTM), is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services. To measure the dynamic thermal performance of fabrics containing phase change materials, a new standard is being developed by ASTM Committee D13 on Textiles.
Advantages and Uses of PCMs in Clothing:
Used in E-Textiles to provide auxiliary system to the electronic components being installed by maintain temperature.
Gloves (electronic or manual), for indoor and outdoor uses:
Used in Fire Brigade and Army Uniforms:
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.