Phase change materials (PCMs) are substances that absorb and release thermal energy during the process of melting and solidifying. When a PCM melts, it absorbs a large amount of heat (energy) from the environment. Conversely, when a PCM solidifies it releases a large amount of energy in the form of latent heat. PCMs continuously cycle through this process, making them ideal for a variety of everyday applications that require temperature management. PCMs reduce temperature swings and have the ability to maintain a specific temperature for extended periods of time.
PCMs are used in many industries including building/construction, refrigeration, HVAC, thermal energy storage, textiles, and electronics. PCMs are used in these applications because they are eco-friendly and energy-saving. Some PCM applications include:
- High-performance textiles and foams that provide relief from hot and cold conditions.
- Refrigerators and freezers that use less energy.
- Shipping containers that maintain goods at the desired temperature for longer periods.
- Construction material that keeps living spaces comfortable and reduces heating and cooling costs.
There are many PCM products that are designed for a wide range of temperatures. They vary from negative 50 degrees Celsius to higher than 150 degrees Celsius. PCM products can store up to 15 times more heat per volume compared to water and rocks.
A PCM works because of two different forms of heat energy: latent and sensible heat. Latent heat is the amount of energy that is needed to change matter from one state to another. For example, a liquid to a solid. The most common example of this type of heat energy is an ice cube. An ice cube will use the latent heat capacity and absorb the heat energy that is coming from the drink. When the ice cube has melted it is because it absorbed all of the latent energy that it is capable of. On the other hand, sensible heat is the amount of energy needed to alter the temperature of a substance without changing the phase of the substance. An example of this is a water heater. When latent and sensible heat work together, they are able to maintain the specific temperature that is needed for an extended period of time.
There are four types of PCMs: water-based, salt hydrates, paraffin, and vegetable-based products. The water-based products are most commonly used for keeping products at 0 degrees Celsius. The water-based products are non-toxic, environmentally friendly, and have a low overhead cost. The salt hydrates are made up of salt and water. These type of products have a low overhead cost, are able to maintain a high latent heat capacity, have a high thermal conductivity, and are nonflammable, and they have a precise melting and freezing point. Paraffin is derived from petroleum. They have a waxy consistency and can have various melting/freezing points depending on the design. Vegetable based PCM products come from the fat of animals and plant oils. The most common ones have a higher efficiency than salt and petroleum PCMs, are nontoxic, can last for decades, are fire resistant, and have high latent heat energy.
Lastly, PCM products last for many years and usually for the lifetime of the product they are used in or applied to depending on quality. Over the course of the melting and freezing uses, the transition temperature and latent heat energy should remain the same. Additionally, the PCM product is encapsulated by a shell to prevent leakage, degradation, and contamination.
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