Development and Evaluation of a CFD Model to Simulate Thermal Performance of Phase Change Material (PCM) Based Energy Storage Systems

Abstract: Waste heat can be recovered and used in different processes to increase energy efficiency and reduce CO2 emissions. It has become an attractive area of research for scientists and several techniques are being investigated and practiced to recover, store and use waste heat. Thermal Energy Storage is one of the modern techniques that is used to store and use waste heat. Energy can be stored in both sensible and latent forms of heat. Latent heat storage is the most efficient way of storing thermal energy as it provides higher storage density and lower temperature differential between storing and releasing heat. The materials that are used for latent energy storage are termed as Phase Change Materials (PCMs). This thesis work investigates the feasibility of a latent heat storage and heat exchanger performance based on phase change material to recover heat at elevated temperatures. The heat transfer study is done by using state of the art commercial CFD tool. Different model geometries of the Thermal Storage equipped with Shell and tube heat exchanger were built with different pipe configurations. The 1st type of model is a set of three 2D models built in COMSOL Multiphysics. These models constitute a cross section of a small portion of heat exchanger having four 10 mm outer diameter pipes immersed in PCM. Fins were mounted on the pipes to enhance the area for heat transfer and hence the heat transfer rate in modified models. Simulations were carried out for melting and solidification of PCM with these 2D models. After analyzing the results, a 3D model of the small block was created to get more realistic results and analyze the effect of pipe diameter on melting and solidification of PCM. The results of 2D models show the effect of fins on heat transfer rates. The model with eight fins on each pipe shows the best results as compared to other two models. The melting and solidification rates are nearly half for eight fin model as compared to the model without fins. The four fin model shows moderate results but better than the model without fins. The comparison of the results for different diameter pipes in 3D model shows that heat transfer rate increases for increasing diameters of the pipe with same flow rate in the case of melting.