Experimental studies on the solidification behaviour of a phase change material in a vertical concentric cylinder

Abstract

In the eighties, researchers were interested in reducing the cost of newlineenergy and save the depleting fossil fuels. However, recently the importance newlinehas shifted from these goals towards the environmental perspective, with the newlineaim of reducing the pollutant emissions such as carbon dioxide, chloro fluro newlinecarbons etc. The dual challenge is how to meet the world s growing energy newlineneeds, while reducing the impact of energy use on the environment. This has newlineled to the utilization of sustainable energy sources and energy conservation newlinemethodologies. The building cooling is responsible approximately 40% of the newlinetotal world annual energy consumption. The concept of free cooling of newlinebuildings has gained a lot of attention among the researchers and engineers in newlinerecent years, as it reduces / eliminates the load on the conventional air newlineconditioning systems employed in building cooling, by avoiding the operation newlineof energy intensive air conditioning compressors. The Phase Change Material (PCM) based thermal energy storage systems, also known as latent heat newlinethermal energy storage systems (LHTES) have received greater research newlineattention in free cooling applications, to store the cool energy available in the newlineambient during the early morning hours, and to utilize the stored cool energy newlinefor the space cooling of buildings during the day time. newlineDuring the phase change in the LHTES units, the solid liquid newlineinterface moves away from the heat transfer surface. In this process, the newlinesurface heat flux decreases with respect to time, due to the increasing thermal newlineresistance of the growing layer of the molten/solidified medium, as the newlinethermal conductivity of the solidified PCM is very low. For most of the available PCMs, the Biot number (Bi= hR/k) becomes larger as the thermal newlineconductivity is very low, and the surface temperature of the PCM drops newlinewithin a short period after solidification is started, and this results in a very newlinelow heat flux thereafter. newline