Phase Change Materials (PCMs) are ideal products for thermal management solutions. This is beacuse they store and release thermal energy during the process of melting & freezing (changing from one phase to another). When such a material freezes, it releases large amounts of energy in the form of latent heat of fusion, or energy of crystallisation. Conversely, when the material is melted, an equal amount of energy is absorbed from the immediate environment as it changes from solid to liquid.
This property of PCMs can be used in a number of ways, such as thermal energy storage whereby heat or coolness can be stored from one process or period in time, and used at a later date or different location. PCMs are also very useful in providing thermal barriers or insulation, for example in temperature controlled transport.
The simplest, cheapest, and most effective phase change material is water/ice. Unfortunately, the freezing temperature of water is fixed at 0 °C (32°F), which makes it unsuitable for the majority of energy storage applications. Therefore a number of different materials have been identified and developed to offer products that freeze and melt like water/ice, but at temperatures from the cryogenic range to several hundred degrees centigrade.
PCMs can broadly be arranged into three categories: eutectics, salt hydrates, and organic materials.
- Eutectics tend to be solutions of salts in water that have a phase change temperature below 0 °C (32°F).
- Salt hydrates are specific salts that are able to incorporate water of crystallisation during their freezing process and tend to change phase above 0 °C (32 °F).
- Organic materials used as PCMs tend to be polymers with long chain molecules composed primarily of carbon and hydrogen. They tend to exhibit high orders of crystallinity when freezing and mostly change phase above 0 °C (32 °F). Examples of materials used as positive temperature organic PCMs include waxes, oils, fatty acids and polyglycols.