What are Phase Change Materials (PCM)?
A phase change material is a term used for any material that both absorbs and releases heat as it changes physical state, such as from a solid to a liquid, and vice-versa. As an output for this reaction, the material will typically become either warmer or cooler depending on the phase change temperature (PCT). For this reason, PCMs provide solutions for heat/cooling storage and retention, extreme weather protection and overall energy efficiency. They’re commonly found in applications such as high-efficiency appliances, clothing, and hardware materials.
Phase change materials are so useful in these applications because of a concept known as “latent” heat. This type of heat is the heat that not only changes the temperature of the material at hand but changes the physical state of that material. The most common example of a phase change material is water.
In its solid form, water (or ice) requires a (relatively) huge amount of energy to melt, whereas liquid water will change the temperature using much less energy. Heating and cooling gel packs are more examples of how this concept comes to life in modern applications: the gel will liquefy as it absorbs more heat, and it will re-solidify as it sits at room temperature, solidifying completely as the environment around it absorbs the gel’s “latent” heat.
Common Applications of Phase Change Materials
Society as a whole has gravitated toward energy-efficient solutions – especially in recent years. Phase change materials have been instrumental in the progress of energy-efficient solutions of all types. From building construction to frozen food, phase change materials enable modern energy solutions.
Even the fashion industry has tapped into the strategic use of phase change materials in the form of beads placed within textiles to increase the human body’s own energy efficiency.
There are four main types of phase change materials: water-based, salt hydrates, paraffins, and organics. Each of these materials is used for a different energy-saving application and each comes with their own unique considerations, advantages, and disadvantages.
Water-based PCMs are typically found in cooling applications, from refrigerators and freezers to gel packs. By adding an alcohol (such as glycol or ethanol) to water to prevent supercooling, the mixture’s freezing point is greatly reduced and it can therefore be an effective material in energy saving applications that reach up to -30ºC.
Water is typically only useful for its phase-changing properties when used for cooling applications (to keep surrounding materials around 0ºC.).
Salt Hydrate PCMs
Salt hydrates are some of the most cost-efficient PCM solutions, and the most readily available. Salt hydrate PCMs also have an impressive latent heat storage capacity, which makes them suitable for thermal energy saving applications like space heaters. However, salt hydrate PCMs also come with their fair share of adversities to look out for. Of all the phase change materials, salt hydrates can be among the most toxic after paraffin.
Salt hydrates also tend to be susceptible to supercooling, which may be preferable depending on the application. Finally, any application that utilizes salt hydrates should ensure that proper measures are taken to account for volume changes as the material changes phases – the volume of salt hydrates may change up to 10% during a phase transition.
Paraffin PCMs are other favorable material options depending on the application. Paraffins offer stability in their formulation over other competing organic compounds, which makes them more durable during heating and cooling processes. They are also non-corrosive, which is a huge asset when paired with metal materials that are exposed to moisture. However, paraffin comes with several disadvantages, too.
Derived from petrol, paraffin PCMs are typically hazardous to people. Similarly, their fossil fuel roots make paraffin a relatively unsustainable option. Cost-savings are also at risk when using paraffin, as their prices are closely tied to the volatile oil and gas industry.
Some of the most preferable phase change materials are plant-based. These organic compounds are free of toxicity, typically have high latent heat capacity, and are cheaper than most paraffin PCMs. Plant-based PCMs (and some made of animal fat) are found to be more efficient than salt hydrates and paraffin, and typically have a wide range of melting points depending on the raw materials involved.
Some manufacturers might find it difficult to rely solely on plant-based PCMs, however, due to their higher-than-average price point compared to the preceding options.
Important Factors when Choosing a PCM
No two phase change materials are alike, and each application warrants its own unique solution. When deciding on the type of PCM for your project, ensure you’ve taken the following measures into consideration:
- Latent heat (J/g)
- Temperatures involved
For direct consult on the right PCM solution for your next project, reach out to our team at KRA Fabrication today.