Division of Information Technology, Engineering and the Environment
School of Advanced Manufacturing and Mechanical Engineering
School of Advanced Manufacturing and Mechanical Engineering
Thesis Abstract
Cold storage is a practical energy storage method in applications where cooling can be generated more efficiently or for less cost outside of the period of cooling demand. Thermal storage also makes it possible to use smaller cooling equipment. This technique can be applied in applications where the refrigeration load is needed for a short period. Cold storage is also applicable when the electricity is more costly during the peak as compared to the non-peak hours and it can also serve as a backup in the event of refrigeration plant breakdown.
Significant research has been conducted on phase change thermal storage systems over the years. However, tube-in-tank phase change thermal energy storage systems have not been investigated in detail. This research endeavours to develop and optimise a tube-in-tank thermal energy storage system that can store latent energy for refrigeration applications. Experimental investigations had been performed for a thermal energy storage system with coils of tube inside a phase change material (PCM) filled cylindrical tank. Several works involving different configurations of Polyvinyl Chloride as well as copper tubes had been conducted with different types of PCMs. It was observed for all freezing and melting tests that the outlet temperature increases or decreases rapidly initially, achieves a constant temperature for a long period of time and then begins to increase or decrease at the end of the process towards the inlet temperature.
Thermal storage systems with PCMs are predominantly designed, analysed and optimised through numerical modelling. An alternative simplified method was being proposed for the characterisation of these systems. The method is based on the effectiveness-number of transfer units (ε-NTU) technique. A simplified mathematical representation has been analytically developed using the ε-NTU technique for a cylindrical tank filled with PCM, with HTF flowing through tubes inside the tank. A computational fluid dynamic (CFD) model for tubes in a phase change thermal energy storage system was also developed and validated with experimental results.
Experimental results compare well with those calculated from the ε-NTU as well as the CFD models. The results show that the models developed can readily be used as a design tool for sizing and optimising a thermal storage unit with phase change materials.
