Phase Change Materials (PCM) are substances that consume and release thermal energy. This happens during a melting and freezing process. When a PCM freezes, it will actually release energy out in the form of a latent heat at a constant temperature. When the PCM melts, it will absorb the heat from the environment. When a temperature fluctuates, the PCM material is able to recharge. This makes the product perfect for applications that require temperature control. Water and ice are the most commonly used  PMC products. Ice is able to maintain a temperature of 0 degrees Celsius, which makes it an ideal PCM product. Water has a freezing point of 32 degrees Celsius, which makes it unsuitable for most of the thermal energy storage applications. There are many PCM products that are designed for a wide range of temperatures. They vary from negative 40 degrees Celsius to higher than 150 degrees Celsius. PCM products can store up to 14 times more heat per volume compared to water, rocks, or masonry. PCM’s are so appealing because they are able to offer storage options that range from high density energy to storing heat that falls in a narrow temperature range. Now that we have a basic breakdown of PCM, let’s go over a few of the aspects of what actually happens and how it works. First let’s discuss the two different types of heat energy.  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 will actually absorb the heat energy that is coming from the drink. When the ice cubes have melted it is because they have absorbed all of the latent energy that they are capable of. Another example of latent heat is hot wax. When wax is put onto skin, there is a burning sensation felt by the person. This is because the wax is releasing the internal latent heat energy that it is carrying. There is another type of heat energy that is called sensible. This type of heat energy is most commonly used with water heaters. This uses energy to alter the temperature of the substance without changing the phase of the substance. When sensible heat and latent heat work together, they are able to maintain the specific temperature that is needed for an extended period of time. Appliances now days are focusing on becoming more eco-friendly. Manufacturers want to sell products that are more energy efficient. As a result, the market for PCM products is in high demand. Some of the main products that are using PCM materials are refrigerators and freezers that will use less energy, shipping containers that will be able to maintain the temperature of goods for longer periods of time, construction materials that are used to make living spaces more comfortable and will in turn help reduce heating and cooling costs. There are many more uses for PCM materials that help provide consumers and manufacturers with lowering operating costs while being more energy efficient. There are four types of PCM’s. There are water based products, salt hydrates, paraffins and vegetable based products. The water based products are most commonly used for keeping products at 0 degrees Celsius. These types of products are non-toxic, environmentally friendly and have a low cost overhead. The salt hydrates are made up of salt and water. These type of products have a low overhead cost, they are able to maintain a high latent heat capacity, they have a high thermal conductivity and are inflammable, and they have a precise melting point of 15 degrees Celsius and 80 degrees Celsius. Paraffins are made from a petroleum. At room temperature they have a waxy consistency. They have a melting point range from -8 degrees Celsius and 40 degrees Celsius. They are able to freeze without supercooling. They are non-corrosive. Since they are composed from petroleum, their costs can fluctuate with the cost of petroleum, making it inconsistent. Vegetable based PCM products come from the fat of animals and plant oils. They have a melting point of -40 degrees Celsius and 151 degrees Celsius. The most common ones have a higher efficiency than salt and petroleum PCM’s. They are nontoxic, they are more stable and can last for decades, they are fire resistant and are able to product a high latent heat. There are a few key points to consider when determining the quality of PCM products. First it is important to remember that latent heat is measured in joules per gram. Latent heats are greater than 150 joules per gram and are ideal when they are greater than 180 joules per gram. When they have the higher latent of heat it means that less material was used to store the amount of energy that is required. You should be able to use the PCM product for many years. Over the course of the melting and freezing uses, the transition temperature and latent heat energy should remain the same. There are thermal tests that will be able to test the melting and freezing cycles to ensure that the changes in the hydration sphere of the PMC products isn’t changing. The material that ecompasses the PCM product is important to help prevent leakage, degradation and contamination. Plastic is the cheapest container that is typically used, but when the plastic is thick, it can reduce the level of thermal conductivity. When a metal container is used it can increase the thermal conductivity, but this is a more costly option. To make sure the that PCM products are safe to used, they should be nontoxic, nonflammable and environmentally friendly. Since many PCM products are used in products that are eco-friendly and energy saving, it is reassuring to know that once the products have fulfilled their shelf life, they are able to be disposed of in a landfill and will naturally degrade within six to twelve months.

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