What is PCM?

When materials change from one phase to anther phase, there is heat release or absorb. Materials has three different phases, solid, liquid and gaseous. The volume changes too much when material changes from liquid to gaseous. It is too hard to use it. So normally for Phase Change Materials (PCMs), It means materials which changes between solid and liquid. For example, water is a good 0 deg C phase change material (PCM0C). It will absorb lots of heat when it changes from solid to liquid, while keep temperature almost unchanged. And it will release lots of heat when it changes from Liquid to Solid, while keep temperature almost no change. For the heat it released or absorbed when water changes between solid and liquid, it is called latent heat. When liquid water being heated, the temperature will increase, it will also absorb heat. The heat it is called sensible heat.
Phase Change Materials, when they are changed from solid to liquid, they will absorb heat from environment, to make refrigeration effect. And when they are changed from liquid to solid, they will release heat into environment to make heating effect. Using this character, using phase change material can make refrigeration, heating or Constant temperature effect.
There are three different kinds of phase change materials, inorganic PCMs, Organic PCMs, Composite PCMs, For Inorganic PCMs, there are Crystalline hydrated salts, molten salts, metals or alloys, etc. For Organic PCMs, there are Paraffin, acetic acid and other organic matter. For Composite PCMs, they will overcome the disadvantages of Single phase change material, improve the effect and expand the usage of PCMS. The development of composite phase change materials has become a hot research topic in the field of PCMs.