A Phase Change Material (PCM) is a substance with a high heat of fusion which, melting and solidifying at certain temperatures, is capable of storing or releasing large amounts of energy. Heat of fusion is the amount of heat energy which must be absorbed or lost for 1 gram of a substance to change states from a solid to a liquid or vice versa. ...

The only phase change used for PCMs is the solid-liquid change. Liquid-gas PCMs are not yet practical for use as thermal storage. Although they have a high heat of transformation, the increase in volume during the phase change from liquid to gas makes their use impractical.

Initially, the solid-liquid PCMs perform like conventional storage materials; their temperature rises as they absorb solar heat. Unlike conventional storage materials, however, when PCMs reach the temperature at which they change phase (their melting point) they absorb large amounts of heat without getting hotter. When the ambient temperature in the space around the PCM material drops, the PCM solidifies, releasing its stored latent heat. PCMs therefore absorb and emit heat while maintaining a nearly constant temperature. Within the human comfort range of 20° to 30°C, latent thermal storage materials are very effective. They store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry, or rock.

Phase change materials are employed in different fields of thermal engineering:

• Energy storage
• Thermal conditioning of buildings
• Waste heat recovery
• Off peak power utilisation
• Heat pump systems
• Space applications
• Laptop computer cooling
• Coolsuits
• Telecom shelters

Technology

The most commonly used PCMs are salt hydrides, fatty acids and esters, and various paraffins (such as octadecane). In chemistry, especially biochemistry, a fatty acid is a carboxylic acid (or organic acid), often with a long aliphatic tail (long chains), either saturated or unsaturated. ... General formula of a carboxylate ester. ... Paraffin is a common name for a group of high molecular weight alkane hydrocarbons with the general formula CnH2n+2, where n is greater than about 20, discovered by Carl Reichenbach. ... Octadecane is an alkane hydrocarbon with the chemical formula CH3(CH2)16CH3. ...

Phase change materials perform best in small containers, which therefore are usually divided in cells. The cells are shallow to reduce static head - based on the principle of shallow container geometry. The packaging material should conduct heat well; and it should be durable enough to withstand frequent changes in the storage material's volume as phase changes occur. It should also restrict the passage of water through the walls, so the materials will not dry out (or water-out, if the material is hydroscopic). Packaging must also resist leakage and corrosion. Steel and polyethylene are common packaging materials. Polyethylene or polyethene is a thermoplastic commodity heavily used in consumer products (over 60M tons are produced worldwide every year). ...

Currently, phase change materials (PCMs) are very widely used in tropical regions in telecom shelters at telecom sites. They protect the high-value equipment in the shelter by keeping the shelter temperature below the maximum permissible by absorbing heat generated by power-hungry equipment such as a Base Station Subsystem in case of a power failure to cooling systems, thus minimizing use of Diesel generators, and translating into enormous savings across thousands of telecom sites in the tropical region. The Base Station Subsystem (BSS) is the section of a GSM network which is responsible for handling traffic and signalling between a mobile phone and the Network Switching Subsystem. ...

Micro-Encapsulated Phase Change Materials

Microencapsulated PCMs provide a portable heat storage system.

By coating a microscopic sized PCM with a protective coating, the particles can be suspended within a continuous phase such as water. This system can be considered a phase change slurry (PCS).

External links

• Phase Change Material based Telecom Shelters
• Phase Change Material Telecom Shelters
• Phase Change Cooling Vests
• Phase Change Material Manufacturer