Posts
PHASE–CHANGE MATERIALS & THEIR USE IN CLOTHING
Bilal Rashid
Dept. of Garment Manufacturing
National Textile University, Faisalabad, Pakistan
Email: br.dmc.gcuf@gmail.com
INTRODUCTION:
PREAMBLE:
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.
PCMs & 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 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 & 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,
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.
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.
LIMITATIONS:
1. Initially, the solid–liquid PCMs behave like sensible heat storage (SHS) materials; their temperature rises as they absorb heat.
- 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.
1. 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.
2. 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.
3. The PCM continues to absorb heat without a significant rise in temperature until all the material is transformed to the liquid phase.
4. When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat.
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.
2. 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.
3. The PCM continues to absorb heat without a significant rise in temperature until all the material is transformed to the liquid phase.
4. When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat.
POINTS TO PONDER:
1. Organic PCMs:
Paraffin (CnH2n+2) and fatty acids (CH3(CH2)2nCOOH)
- Large number of PCMs are available in any required temperature range from −5 up to 190 oC.
- Within the human comfort range of 20° 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.
1. Organic PCMs:
Paraffin (CnH2n+2) and fatty acids (CH3(CH2)2nCOOH)
2- Inorganic PCMs:
Salt hydrates (MnH2O)
3- Eutectics:
Organic-organic, organic-inorganic, inorganic-inorganic compounds
4- Hygroscopic materials
Many natural building materials are hygroscopic.
SELECTION CRITERIA:
While selecting a Phase Change Material, following characteristics should be kept in mind:
Thermodynamic properties
- 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
- Availability
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,
SETBACK:
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.
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.
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 & USES IN CLOTHING:
1- Used In E- Textiles to provide auxillary system to the electronic components being installed by maintain temperature.
 |
| E-textile |
 |
| Electronic Gloves |
 |
| Army Uniforms |
.
No Responses to "Phase Change Material and Their Uses in Textile Clothing"