Phase change materials (PCMs) are environmentally benign salts or organic compounds with variable environmental credentials, which store and release latent heat by changing chemical bonds through a phase transformation, unlike sensible heat storage materials such as water or masonry, which change structure mechanically.
Initially, solid-liquid PCMs perform like conventional storage materials; their temperature rises as they absorb heat. However, when PCMs reach melting point (phase change temperature) they absorb large amounts of heat without getting hotter. When the ambient temperature drops, the PCM solidifies, releasing its stored latent heat. PCMs absorb and emit heat while maintaining a nearly constant temperature.
Within the human comfort range of 20-30C, PCMs store 5 to 14 times more heat per unit volume than sensible storage materials. PCMs can be used for any heating and cooling requirement in buildings, vehicles or fabrics, including insulation and engine cooling, refrigeration, process cooling or contributing to process heat, and combined heat and power systems.
The challenge to greater use of PCMs is their packaging, cost and knowledge, both technical and among potential customer and user communities.
Protection from extreme environment has always been a critical requirement of textile industries. Clothing that protects from water, extreme winter intensive heat, open fire, high voltage, propelled bullets, toxic chemicals, nuclear radiations and biological toxins, etc. are some of the examples.
These clothing finds application as a sportswear, fire fighting wear, defence wear, bulletproof jackets and other professional wear. Textile products can be made more comfortable when the properties of textile material adapt to the environment.
One of such important intelligent material at the present is Phase Change Material (PCM), which absorb, stores or release heat according to the change of temperature during Phase Change Process are most frequently used in the manufacturing of smart textiles.
What are PCMS?
Phase change is the process of going from one physical state to another i.e. from solid to liquid. Substances that undergo the process of phase change are better known as Phase Change Materials (PCM). These material stores, release or absorb heat as they oscillate between solid and liquid form. They give off heat as they change to a solid state and absorb as they return to liquid state. The three fundamentals Phases of a matter solid, liquid and gas are known, but other are consider to exist, including the crystalline, colloid, glassy, amorphous and plasma phase.
The fundamental phenomena of a science was initially cultivated and employed for building space suits for astronauts for space programs. These suits kept astronaut warm in a black void of space and cool in a solar glare. Phase Change Materials are compounds, which melts and solidify at certain temperature and in doing so are capable of storing or releasing large amount of energy. The storage of thermal energy by changing the phase of material at a constant temperature is called latent heat, that is, changing from a liquid state to solid state. When a PCM undergoes a phase change a large amount of energy is required. The most important characteristic of latent heat is that it involves the transfer of much larger packets of energy than sensible heat transfer.
Some of these PCMs change phase within a temperature range just above and below human skin temperature. This property of certain substance is used for making protective all season outfits, and for abruptly changing climatic conditions. Fibre, fabric and foam with built-in PCMs store the warmth of body and then release it back to the body, as it needs it. Since the process of phase change is dynamic, the material are constantly changing from a solid to liquid and back depending upon level of physical activity of the body and outside temperature. Moreover, phase change material are used, but never get used up.