Material technology book pdf

When the sodium acetate solution crystallises, it becomes warm. The PCM continues to absorb heat without a significant rise in temperature until material technology book pdf the material is transformed to the liquid phase.

When the ambient temperature around a liquid material falls, the PCM solidifies, releasing its stored latent heat. C, some PCMs are very effective. They store 5 to 14 times more heat per unit volume than conventional storage materials such as water, masonry or rock. Low thermal conductivity in their solid state. Applied for passive temperature stabilization to result in building HVAC energy conservation. PCMs, they do not require nucleation to prevent supercooling.

As most of the organic solutions are water-free, they can be exposed to air, but all salt based PCM solutions must be encapsulated to prevent water evaporation or uptake. Both types offer certain advantages and disadvantages and if they are correctly applied some of the disadvantages becomes an advantage for certain applications. The temperature range offered by the PCM technology provides a new horizon for the building services and refrigeration engineers regarding medium and high temperature energy storage applications. The scope of this thermal energy application is wide-ranging of solar heating, hot water, heating rejection, i. PCMs tend to solidify at the edges of the containers preventing effective heat transfer. Micro-encapsulated PCMs also provide a portable heat storage system.

Molecular-encapsulation is another technology, developed by Dupont de Nemours that allows a very high concentration of PCM within a polymer compound. Molecular-encapsulation allows drilling and cutting through the material without any PCM leakage. As phase change materials perform best in small containers, therefore they are usually divided in cells. A simple example is a copper-mesh immersed in a paraffin-wax. The copper-mesh within parraffin-wax can be considered a composite material, dubbed a thermal-composite.