Phase-change material
A phase-change material (PCM) is a substance which releases/absorbs sufficient energy at phase transition to provide useful heat or cooling.
Water/ice is therefore a very useful phase change material and has been used to store winter cold to cool buildings in summer since at least the time of the Achaemenid Empire.
By melting and solidifying at the phase-change temperature (PCT), a PCM is capable of storing and releasing large amounts of energy compared to sensible heat storage.
PCMs are used in many different commercial applications where energy storage and/or stable temperatures are required, including, among others, heating pads, cooling for telephone switching boxes, and clothing.
Solid-liquid phase-change materials are usually encapsulated for installation in the end application, to be contained in the liquid state.
Micro-encapsulation allows the material to remain solid, in the form of small bubbles, when the PCM core has melted.
When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat.
A specialized group of PCMs that undergo a solid/solid phase transition with the associated absorption and release of large amounts of heat.
These materials change their crystalline structure from one lattice configuration to another at a fixed and well-defined temperature, and the transformation can involve latent heats comparable to the most effective solid/liquid PCMs.
The positive temperature phase change allows centrifugal and absorption chillers as well as the conventional reciprocating and screw chiller systems or even lower ambient conditions utilizing a cooling tower or dry cooler for charging the TES system.
Common packaging materials showing chemical compatibility with room temperature PCMs include stainless steel, polypropylene, and polyolefin.
[23] Thermal composites is a term given to combinations of phase change materials (PCMs) and other (usually solid) structures.
Such hybrid materials are created to achieve specific overall or bulk properties (an example being the encapsulation of paraffin into distinct silicon dioxide nanospheres for increased surface area-to-volume ratio and, thus, higher heat transfer speeds [24]).
As such, PCMs must be selected and applied very carefully, in accordance with fire and building codes and sound engineering practices.
Because of the increased fire risk, flamespread, smoke, potential for explosion when held in containers, and liability, it may be wise not to use flammable PCMs within residential or other regularly occupied buildings.
