8.3 Applications of phase change materials for sustainable energy  (Page 7/26)

Summary

There is a great interest in saving energy and in the use of renewable energies. PCMs provide an underused option for developing new energy storage devices in order to minimize greenhouse effects. They operate at constant temperature; as heat is added to the material, the temperature remains stable, but the heat drives the change to a higher energy phase. A PCM stores heat in the form of latent heat of fusion which is about 100 times more than the sensible heat. Hydrated salts, paraffin waxes, fatty acids and eutectics of organic and non-organic compounds are the major types of PCMs that melt at a wide range of temperatures. The specific melting point of the PCM determines the design of thermal storage system.

In this module, applications of PCM in solar energy, buildings, and vehicles were reviewed. Solar heaters have been popular since 1960s and PCMs have been used to store the precious energy from sun since 1980s. They have been used extensively in solar cookers, especially in the third world countries in order to decrease the thermal related costs. The cookers do not use fuel and hence reduce air pollution.

PCM can be used for temperature regulation in order to minimize the heat loss or gain through building walls. They have been used to capture solar heat and decrease the temperature fluctuations in buildings. Moreover, since a small amount of PCM is sufficient in order to store solar energy, thermal comfort is achieved without substantial increase in the weight of the construction materials.

Application of PCMs in transportation is growing widely. Today, refrigerated trucks are regulated by refrigeration units, but the use of PCMs is a viable option to prevent the denaturation of food during transportation. The transfer rate of heat can be reduced significantly with PCMs. Moreover, PCM makes Li-ion batteries, which have high energy density, viable for high-power applications. The generated energy during discharge or drive mode can be transferred from the body of the battery to environment with the help of PCMs. Battery packs can be maintained at an optimum temperature with proper thermal management and the PCM has been shown to be capable of removing large quantities of heat due to its high latent heat of fusion.

Even though there is a lot of on-going research on effective and efficient applications of PCMs in a variety of areas (e.g. solar cookers, buildings, vehicles), PCMs have yet to become a widely used technology for sustainable energy. The advantages of PCMs are hardly known by many people and, therefore, the applications of PCMs and their benefits should be offered to consumers. The sun is out there, continuously transferring its energy for free, but we need to do more to harness that sustainable energy for our own needs.

Review questions

References

Ahmed, M., Meade, O.,&Medina, M. A. (2010, March). Reducing heat transfer across the insulated walls of refrigerated truck trailers by the application of phase change materials. Energy Conversion and Management, 51 , 383-392. doi: 10.1016/j.enconman.2009.09.003

Buddhi, D.&Sahoo, L. K. (1997, March). Solar cooker with latent heat storage: Design and experimental testing. Energy Conversion and Management, 38 , 493-498. doi: 10.1016/S0196-8904(96)00066-0

Sveum, P., Kizilel, R., Khader, M.,&Al-Hallaj, S. (2007, September). IIT Plug-in Conversion Project with the City of Chicago. Paper presented at the Vehicle Power and Propulsion Conference, Arlington, TX. doi: 10.1109/VPPC.2007.4544174