PCMs suitable for applications in thermal storage, regulation and protection are highly crystalline, stable compounds that undergo sharp melting and freezing transitions with high heat capacity.
The most common types of PCM for many applications are speciality organic waxes, inorganic salt hydrate formulations and eutectic mixtures.
Along the value chain are microencapsulated PCMs that have the ability to be incorporated into composite products to provide high thermal mass.
Materials that in their solid form are crystalline waxes containing saturated aliphatic hydrocarbon units (-CH2)n-) within the molecular structure. The most common are the “paraffins” i.e. linear hydrocarbons also known as n-alkanes with chemical formula CnH2n+2. Recent developments have taken place in oleochemical PCMs. For example, fatty acid esters, fatty alcohols and even paraffins can be derived from plant lipids or animal fats. These types can be considered to be renewable and may be referred to as “bio-based PCMs”. The best commercially available organic wax PCMs offer the advantages of high latent heat capacity (usually between 170 – 220 kJ/kg), sharp thermal transitions, minimal supercooling, reliable thermal properties and long term stability. Another advantage is the range of phase change temperatures available, which can meet most applications excluding very high temperatures. Several suppliers offer materials varying in quality and price and Phase Energy can assist in sourcing the best product
Organic wax PCMs can be formulated into permanently solid or gelled forms and enclosed within robust containers to prevent leakage whilst allowing for the exchange of thermal energy between the transfer medium (usually air) and PCM. It is possible for the PCM to be either mouldable or rigid (shape-stable) and various containment options are potentially available including pouches, bags, blankets, moulded panels and other rigid containers in various sizes and geometries. Where flammability is a concern then solutions are available depending on the requirements of the application. If you are a PCM supplier or user then we can help you to quickly develop suitable forms of organic PCM, so do not hesitate to contact us to discuss your project.
Organic PCMs are also available in a microencapsulated form where the PCM is permanently enclosed within microscopically small particles – see microencapsulated PCMs
Salt hydrates are inorganic substances composed of ionic salts with crystal phase structures incorporating water molecules (“water of crystallisation”). Pure substances can have high heat capacity, relatively high density and therefore high volumetric heat storage capacity. Many commercial salt hydrate products, however, are carefully formulated to achieve a suitable operating temperature and to overcome shortcomings, notably a tendency to supercool and physical instability. The latter arises if the formulation melts incongruently i.e. where the crystalline solid phase melts to a mixture of solid and water (rather than a “clean” solid to liquid transition). The dense solid phase may be prone to sedimentation over time and additives such as inorganic or polymeric gelling or thickening agents can be used for stabilisation. This is essential as separation would lead to a gradual reduction in the concentration of the “active” PCM component and deterioration in the thermal transition properties.
That said salt hydrate PCMs can certainly be a good choice for some applications after carefully considering their attributes and limitations.
These are mixtures of often two substances exhibiting, at a particular composition (the eutectic composition), a single phase transition temperature that is lower that its constituents. Eutectics may be inorganic-inorganic, organic-organic or even inorganic-organic. Certain eutectic combinations can offer attractive properties such as high heat capacity at a targeted temperature, and, of course, Phase Energy is able to assist you in finding the right product for your purposes.
Please note that the category of “Eutectics” can include salt-water solutions which tend to have phase change temperatures below 0oC used for applications such as in refrigeration. As an example, 22.4% w/w aqueous solution of NaCl has a melting temperature of approximately -11oC.
Microencapsulated PCMs or mPCMs are a stable, particulate form of PCM provided as either a powder or water-based liquid that can be used to confer high heat capacity and temperature regulating capability to end-products into which they are added.
Microcapsules comprise microscopically small particles of organic wax PCM permanently enclosed by a thin shell of Perspex-like polymer. The particles are very durable conforming to the demanding PCM RAL quality standard for cycling stability: Category A (10,000 thermal cycles). The microcapsules are usually prepared from an emulsion comprised of tiny droplets of wax, dispersed in hot water, and the polymer shell is formed around each droplet. The finished product resembles white emulsion paint (see image above). The emulsion can be spray-dried to give an essentially dry powder (see image above).
Examples of where microencapsulated PCMs can be used to prepare end products with high thermal capacity:
Contact us for technical information, samples, product availability or if you require assistance in formulating with microencapsulated PCMs.