Thermal energy storage (TES) is becoming increasingly important due to its significance in energy conservation alongside with its excellent use in heating or cooling applications thereby increasing the energy efficiency of a system. TES is achieved in three distinctive ways such as latent, thermochemical and sensible heat storage. Thermal storage units that use latent heat of phase change materials (PCMs) have received a considerable interest by researchers in recent years due to its large heat storage capacity. It provides energy density, which is greater than that achievable with sensible heat storage over the same temperature range. In addition, volumetric expansion during the melting process is negligible compared to the total energy capacity. LHTES using PCMs has the advantage of higher energy storage density resulting in smaller storage size and higher efficiency due to the nearly constant operational temperature. Hence, there are numerous applications need latent energy storage system such as energy conservation in buildings, solar energy equipment, refrigeration, desalination transport and storage containers, etc. There are a large number of organic and inorganic PCM materials but there is no single material can have all the required properties for an ideal thermal storage media for various applications. This lead to a significant amount of research published in this area to develop an adequate system design to overcome the poor physical property used in each application.  

In this speech, I will address the melting process of polyethylene glycol 1500 (PEG 1500) adjacent to a hot vertical wall in a rectangular enclosure. The study cover experimental investigation of the properties measurement and the melting process of Polyethylene glycol 1500. This materials was chosen because of its moderate melting temperature of 440C which make it a suitable candidate for energy storage-reuse and energy storage-insulation applications. Computational fluid dynamics (CFD) was also used to model the melting process. The change of melt percentage with time was predicted for different geometries to identify the optimum aspect ratio for melting/solidification process. The model was based upon a rectangular enclosure filled with PCM that was isothermally heated from one side with the opposite side maintained at a constant cold temperature. The study was conducted in two phases: i) The volume of the enclosure was held constant and the aspect ratio changed by varying the height and width; ii) The heating wall area was held constant and the width of the enclosure changed for constant breadth and depth to give the desired change in aspect ratio. 

The initial results show a qualitative agreement between the predicted contours of melting from simulation and the photos from experimental. The dimensions of the rectangular enclose has an effect on the heat transfer mechanism which lead to peak melting percentage at aspect ratio of 2.3. The results indicate that the best aspect ratio for energy storage-reuse is around 2.3 and for energy storage-insulation should be more than 5. 

Keywords: phase change materials, convection current, aspect ratio, thermal energy storage, CFD simulation