Investigation of Latent Heat Thermal Energy Storage System for Air- Conditioning Applications

Around 40% of the total energy in USA is consumed by buildings, and about $370 billion US dollar is spent each year to supply this energy and thus reduction in energy consumption is extremely important. One of the most effective and reliable ways to reduce energy consumption is the use of Phase Change Materials (PCMs) in Latent Heat Thermal Energy Storage (LHTES) systems. In this study an experimental setup was constructed to investigate the solidification process of PCM using two different types of heat exchangers: pipe heat exchanger and horizontal finned-pipe heat exchanger. The PCM used in this study is Rubitherm (RT-18) that has a melting point of 18°C, and the heat transfer fluid (HTF) is water. To investigate the performance of pipe heat exchanger versus finned-pipe heat exchanger, two experiments were performed under identical initial, thermal and boundary conditions. The PCM is cooled down from 20°C to 5°C in both heat exchangers. Result of the temperature distribution as a function of time during the solidification process inside the TES system is presented and investigated. Visualization of the solidification process inside the TES system is also presented. Generally, the PCM is solid when its temperature is lower than the melting point, and it is liquid when its temperature is higher. PCM stores thermal energy during melting and releases heat as it solidifies. Both visualization and periodic temperature distribution results showed that as time progresses, the amount of the solid PCM increases in both heat exchangers. At a certain time, finnedpipe heat exchanger has higher amount of the solid PCM than the pipe heat exchanger. Also, the solidification time is reduced significantly when fins are added to the TES system. After 75,000 seconds of solidification, the average PCM temperature of pipe heat exchanger reached to 8.5°C. Whereas, the average PCM temperature of the finned-pipe heat exchanger reached to 8.5°C after 19,000 seconds of solidification. Significant time reduction equivalent to 54,000 seconds is observed when the fins are added to the TES system. Employment of fin is preferred to improve heat transfer rate as the solidification process is enhanced due to the incorporation of fin.